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The Federal Agency of Health Protection and Social Development
The Stavropol State Medical Academy
Microbiology, Virology, Immunology Department
I.A. Bazikov, Е.V. Lysogora,
I.V. Klimanovich, I.S. Selivanova
The Manual
for the Students of General Medicine
of the English-speaking Medium
Stavropol 2010
ГОСУДАРСТВЕННОЕ ОБРАЗОВАТЕЛЬНОЕ УЧРЕЖДЕНИЕ ВЫСШЕГО
ПРОФЕССИОНАЛЬНОГО ОБРАЗОВАНИЯ
Ставропольская государственная медицинская академия Федерального
агентства по здравоохранению и социальному развитию
Кафедра микробиологии, вирусологии и иммунологии
The Federal Agency of Health Protection and Social Development
The Stavropol State Medical Academy
Microbiology, Virology, Immunology Department
Базиков И.А., Лысогора Е.В.,
Климанович И.В., Селиванова И.С.
I.A. Bazikov, E.V.Lysogora, I.V. Klimanovich, I.S. Selivanova
Общая микробиология.
Морфология и ультраструктура микроорганизмов
Учебно-методическое пособие
для студентов лечебного факультета англоязычного отделения
General Microbiology.
Morphology and ultrastructure of microorganisms.
The Manual
for the Students of General Medicine
of the English-speaking Medium
Ставрополь 2010
Stavropol 2010
2
УДК 535.317.68 (07.07)
ББК 52.64 я 73
G 36
Общая микробиология. Морфология и ультраструктура микроорганизмов.
Учебное пособие для студентов лечебного факультета англоязычного
отделения (на английском языке). – Ставрополь: Изд-во СтГМА. – 2010. – 35 с.
Авторы:
Базиков Игорь Александрович доктор медицинских наук, профессор,
завудующий кафедрой микробиологии, вирусологии и иммунологии СтГМА.
Лысогора Елизавета Вильевна, кандидат медицинских наук, доцент
кафедры микробиологии, вирусологии и иммунологии.
Климанович Инна Викторовна, ассистент кафедры микробиологии
вирусологии и иммунологии.
Селиванова Ирина Сергеевна, ассистент кафедры микробиологии
вирусологии и иммунологии.
Учебно-методическое пособие включает в себя основные темы курса
«Общая
микробиология.
Морфология
и
ультраструктура
микроорганизмов» для иностранных студентов англоязычного отделения:
«Классификация микроорганизмов», «Морфология микроорганизмов»,
«Строение бактерий», «Морфология и ультраструктура спирохет»,
«Морфология и ультраструктура риккетсий», «Морфология и
ультраструктура микоплазм», «Морфология и ультраструктура грибов»,
«Морфология и ультраструктура актиномицет».
Рецензенты:
Ходжаян Анна Борисовна, доктор медицинских наук, профессор, зав.
кафедрой биологии с экологией СтГМА.
Знаменская Стояна Васильевна, кандидат педагогических наук, доцент,
декан факультета иностранных студентов СтГМА, заведующая кафедрой
иностранных языков с курсом латинского языка.
УДК 535.317.68 (07.07)
ББК 52.64 я 73
G 36
Рекомендовано
к
печати
редакционно-издательским
советом
Ставропольской государственной медицинской академии по англоязычному
обучению иностранных студентов.
© Ставропольская государственная медицинская академия, 2010
3
УДК 535.317.68 (07.07)
ББК 52.64 я 73
G 36
General Microbiology. Morphology and Ultrastructure of Microorganisms.
Manual for the Students of the English-speaking Medium (on English). – Stavropol. –
Publisher: Stavropol State Medical Academy. – 2010. – 35 p.
Authors:
Basikov I.A., Professor, D. M. S, Head of Microbiology, Virology,
Immunology Department of Stavropol State Medical Academy.
Lysogora L.V., Senior Lecturers of Microbiology, Virology, Immunology
Department of Stavropol State Medical Academy.
Klimanovich I.V., assistant of Microbiology, Virology, Immunology
Department of Stavropol State Medical Academy.
Selivanova I.S., assistant of Microbiology, Virology, Immunology Department
of Stavropol State Medical Academy.
The manual includes the basic themes of course «General Microbiology.
Morphology and Ultrastructure of Microorganisms» for the foreign students of
the English-speaking Medium: «Classification of Microorganisms», «Morphology
of Bacteria», «Bacterial Anatomy», «Morphology and Ultrastructure of
Spirochaetes», «Morphology and Ultrastructure of Rickettsiae», «Morphology
and Ultrastructure of Mycoplasmas», «Morphology and Ultrastructure of
Fungi», «Morphology and Ultrastructure of Actinomycetes».
Reviewers:
Hodzhayan Anna Boriusovna, D. M. S.Professor, the Head of Biology with
Ecology Department of Stavropol State Medical Academy.
Znamenskaya Stoyana Vasilievna, C. P.S., Associate Professor, Dean of the
foreign students’ faculty of Stavropol State Medical Academy, the Head of Latin and
foreign languages department.
УДК 535.317.68 (07.07)
ББК 52.64 я 73
G 36
© Stavropol State Medical Academy, 2010
4
ВВЕДЕНИЕ
Учебно-методическое пособие по микробиологии на английском языке
предназначено для иностранных студентов англоязычного отделения. Оно
включает основные темы из курса «Общая микробиология. Морфология и
ультраструктура микроорганизмов».
Цель методического пособия – это знакомство студентов второго курса с
морфологией
и
ультраструктурой
микроорганизмов,
современной
классификацией бактерий, принципами микроскопического исследования.
Данные знания являются ключевыми в изучении курса микробиологии и
направлены на облегчение восприятия материалов предмета в дальнейшем.
Изучение основ микробиологии необходимо врачу любой специальности для
осуществления правильных и своевременных лечебно-диагностических и
профилактических мероприятий.
«Морфология и ультраструктура микроорганизмов» вызывает затруднения
у второкурсников. Поэтому в пособии кратко и в доступной форме изложены
теоретические аспекты данной темы. Кроме того, представлен обширный
наглядный материал в виде таблиц, схем и фотографий, которые облегчают
восприятие данной темы.
5
INTRODUCTION
The manual in microbiology in English is for the foreign students of the Englishspeaking Medium. It includes the basic themes of a course «General Microbiology.
Morphology and Ultrastructure of Microorganisms».
The purpose of the manual is to acquaint the second-year students with
morphology and ultrastructure of microorganisms, modern classification of bacteria,
and principles of the microscopic study. The study of bases of microbiology is
necessary for the doctor of any speciality in diagnostics, prevention and treatment of
infection diseases.
«Morphology and Ultrastructure of Microorganisms» causes some difficulties in
mastering this theme by the second-year students. Therefore, theoretical aspects of
the given theme are stated briefly and accessibly in the manual. Besides, there is the
additional evident material as tables, schemes, and photos in the manual.
6
Theme 1. Microbiological laboratory. Safety regulations at work with gas
and microorganisms
Rules of work in a laboratory:
1. Don't be indoors without your special practical clothes (a gown and kb-cap).
2. Don't bring foreign things in a laboratory.
3. Don't leave a laboratory in your special wear.
4. Don't smoke, eat or keep food substances in a laboratory.
5. It is necessary to be careful while unpacking infectious material: jars, testtubes should be rubbed dry and put on a tray.
6. If any utensils (jars, test-tubes) containing infectious material break, carry out
the procedure for disinfection immediately.
7. Infectious material and needless cultures of bacteria are liable to destruction.
Disinfect the instruments used during practice and the table surface after the
practicals are completed.
8. After the practicals sponge your hands with soap.
9. Infectious material and cultures of bacteria are put into a safe or a refrigerator
after the practicals are completed.
Disinfection and sterilization of materials
Disinfection means the destruction of all pathogenic organisms or organisms
causing infection by using antiseptics. Antiseptics are chemical disinfectants which
can be safely applied to skin or mucous membrane surfaces and are used to prevent
infection by inhibiting the growth of bacteria. Pathological materials (excrement,
urine, phlegm, spinal fluid and blood) are disinfected with 5% Phenol or 3% Lysol
before they elimination in sewage system.
Pipettes, glass spatulas and metallic instruments, contaminated by pathological
material or cultures of microorganisms, are soaked into jars with disinfectant
solutions (3% solution of chloramine).
Object-plates or cover-glasses are disinfected with 3% solution of chloramine
because viable microorganisms can preserve in fixed and stained smears, which will
be the source of infection.
Laboratory utensils (dishes, test-tubes and bottles) are undergone preliminary
disinfection before usage (they are soaked in 3% solution of chloramine for 2-24
hours).
Your hands are disinfected after your work with infection materials. NB! Rub
your hands with wool or serviettes soaked in 0.5-1% solution of chloramine, after this
wash your hands with warm water and soap.
Theme 2. Classification of Microorganisms
Bacterial taxonomy or systematics comprises three components:
1. Classification, or the orderly arrangement of units. А group of units is called а
7
taxoп (рl. taxa), irrespective of its hierarchic level.
2. Identification of аn unknown with а defined and named unit, and
3. Nomenclature, or the naming of units.
For purposes of classification, it is necessary to determine as manу
characteristics of bacteria as possible. Such characteristics mау bе weighted, greater
importance being given to some than to others, or they mау bе assigned equal
importance, depending оn the method of classification. Оn the contrary, for purposes
of identifying bacterial isolates, it is important to devise а key using the minimum
number of important characteristics which саn bе easily tested.
Bacterial classification presents special problems.
Linnaeus (1735) divided all living beings into two kingdoms, plant and animal.
Bacteria had been placed in the plant kingdom and designated. Вat as bacteria present
features соmmоn to both plants and animals, it has been proposed that а new
kingdom, Monera, be created to accommodate аll microorganisms without true
nuclei, plastids and sexual reproduction (Stanier and van Niel 1941). This proposal
has nоt mеt with universal acceptance.
Кingdoms are divided successively into division, class, order, family, tribe,
genus and species. For example, the full taxonomical position of the typhoid bacil1us
is as follows:
Divisioп
Protophyta
Class
Schizoтycetes
Order
Eubacteriales
Faтi1y
Eпterobacteriaceae
Tribe
Sa1тoпellae
Geпus
Sa1тoпella
Species
Sa1тoпella typhi
The species concept in bacteria: Species is the standard taxonomical unit in
biology. With higher forms of life, а species unit constitutes а stage of evolution,
with а characteristic morphology, and is delimited bу the failure of interbreeding
outside the unit. Вut in bacteria, the species соncept is vague and ill defined. Due to
the absence of fossil remains in bacteria, the evolutionary status of species саn not bе
established. Morphological differences are insufficient for the definition of bacterial
species. Тhе general absence of sexual reproduction in bacteria prevents the use of
inbreeding, as а test for differentiation between species.
In spite of these difficulties, the concept of species provides а convenient unit in
bacterial taxonomy. Besides morphological features, criteria useful for the definition
of bacterial species are physiological, biochemical, antigenic and pathogenic
properties. As 'species' is а genetic concept, definitive information can bе obtained bу
comparison of the nucleotide base ratios, which are constant for аnу оnе species but
mау bе different in different species. Genetic homology can bе demonstrated bу
DNA hybridization between different individuals of the same species. Comparison of
rRNA sequences helps to arrange bacterial species into а phylogenetic tree.
An important difference between the classification of bacteria and that of higher
8
organisms is that in the former, the properties of а population are studied, and not of
аn individual. А population derived bу binary fission from а single cell is called а
clone. А single bacterial colony represents а clone. Though all the cells in а clone are
expected to bе identical in all respects, а few of them mау show differences due to
mutation. А population of bacteria derived from а particular-source, such as а
patient, is called а strain.
The general absence of sexual reproduction in bacteria serves to maintain their
character constant. But bacteria possess several features that contribute to some
degree of heterogeneity in their populations. Their short generation time and high
rate of mutation lead to the presence, in anу population, of cells with altered
characters. Methods of genetic exchange such − transformation, transduction and
conjugation cause differences in character. Prophage and plasmid DNA саn induce
new properties.
Phylogenetic classification: There are two approaches to bacterial classification.
The hierarchical classification represents а branching trее like arrangement, оnе
characteristic being employed for division at each branch or level. This system is
called phylogenetic because it implies аn evolutionary arrangement of species.
Depending оn the characteristic so chosen, the classification wou1d give different
patterns. For example, the intestinal Gram negative bacilli have been traditionally
classified depending оn whether they ferment lactose or not. While this provides а
useful distinction between the pathogenic and nonpathogenic groups of these bacilli,
а different but useful classification could bе obtained using fermentation of sucrose
as the criterion. While classification based оn weighted characteristic is а convenient
method, it has the serious drawback that the characters used mау not bе valid.
Fermentation of lactose, in the example cited, is not аn essential and permanent
characteristic. It mау bе acquired or lost upsetting the system of arrangement.
Adansonian classification: The Adansonian classification, so called after
Michael Adanson who introduced it in the eightenth century, avoids the use of
weighted characteristics. It makes по phylogenetic assumption but merely takes into
account all the characteristics expressed at the time of study. Неnсе it is called а
phenetic systeт. It gives equal weight to all measurable features, and groups
organisms оп the basis of similarities of several characteristics. The availability of
computers has extended the scope of phenetic classification bу permitting
comparisons of very large numbers of properties of several organisms at the same
time. This is known as nuтerical taxonoтy.
Molecular or genetic classification: This is based оn the degree of genetic
relatedness of different organisms. Since аll properties are ultimately based оn the
genes present, this classification is said to bе the most natural or fundamental
method. DNA relatedness саn bе tested bу studying the nucleotide sequences of
DNA and bу DNA hybridisation or recombination methods. The nucleotide base
composition and base ratio (Adenine- Тhyminе:Guаninе-Сytоsinе ratio) varies
widely among different groups of microorganisms, though it is constant for members
of the same species. Molecular classification has been employed more with viruses
than with bacteria.
9
Nо method of bacterial classification is universally accepted. Тhе method most
widely adopted is presented in successive editions of Bergey's Маnual of
Deterтiпative Bacteriology. Intraspecies classification: For diagnostic or
epiderniological purposes, it is often necessary to subclassify bacterial species. This
mау bе based оn biochemical properties (biotypes), antigenic features (serotypes),
bacteriophage susceptibility (phage types) or production of bacteriocins (colicin
types). А species mау bе divided first into groups and then into types, as for
example, in streptococci.
Much greater discrimination in intraspecies typing has been achieved bу the
application of newer techniques from immunology, biochemistry and genetics.
Investigations of epidemiology and pathogenesis using these techniques have been
collectively referred to as тolecu1ar epideтiology. Тhе methods used are of two
types: phenotypic (study of expressed characteristics) and genotypic (direct analysis
of genes, chromosomal and extrachromosomal DNA). Molecular phenotypic
methods include electrophoretic typing of bacterial proteins and immunoblotting.
Genotypic methods include PCR and nucleotide sequence analysis.
Nomenklature
Тhе need for applying generally accepted names for bacterial species is selfevident. Two kinds of names are given to bacteria. Тhе first is the casual or common
namе which varies from country to country and is in the local language. Names such
as 'typhoid bacillus' and 'gonococcus' are casual names. Such names are useful for
communication at the local level. Тhе second is the scientific or international name
which is the same throughout the world. Тhе scientific name consists usually of two
words, the first being − the namе of the genus and the second one −the specific
epithet. Тhе generic name is usually а Latin noun. Тhе specific epithet is an adjective
or noun and indicates some property of the species (for example, albus, meaning
white), the animal in which it is found (for example, suis, means pig), the disease it
causes (tetaпi, of tetanus), the person who discovered it (welchii, after Welch) or the
place of its isolation (loпdoп). Тhе generic name always begins with а capital letter
and the specific epithet with а small letter, even if it refers to а person or place (for
example, Salтопеllа loпdoп).
Theme 3. Morphology of Bacteria
Bacteria (Gk. bakterion small staff) are, for the most part, unicellular organisms
lacking chlorophyll. Their biological properties and predominant reproduction by
binary fission relates them to prokaryotes.
The size of bacteria is measured in micrometres (mem) and varies from 0.1 mcm
(Spiroplasma, Acholeplasma) to 16-18 mem (Spirillum volutans). Most pathogenic
bacteria measure 0.2 to 10 mcm.
Morphologically, bacteria possess three main forms. They are either spherical
(cocci), rod-shaped (bacilli) or spiral-shaped (vibrios, spirilla and spirochetes).
10
Cocci (Gk. kokkos berry). These forms of bacteria (Fig. 1) are spherical,
ellipsoidal, bean-shaped, and lanceolate. Cocci are subdivided into six groups
according to cell arrangement, cell division and biological properties.
1. Micrococci (Micrococcus). The cells are arranged singly or irregularly. They
are saprophytes, and live in water and in air (M. agilis, M. roseus, M. luteus, etc.).
2. Diplococci (Gk. diplos double) divide in one plane and remain attached in
pairs. These include: meningococcus, causative agent of epidemic cerebrospinal
meningitis, and gonococcus, causative agent of gonorrhoea and blennorrhoea.
3. Streptococci (Gk. streptos curved, kokkos berry) divide in one plane and are
arranged in chains of different length. Some streptococci are pathogenic for humans
and are responsible for various diseases.
4. Tetracocci (Gk. tetra four) divide in two planes at right angles to one another
and form groups of fours. They very rarely produce diseases in humans.
5. Sarcinae (L. sarcio to tie) divide in three planes at right angles to one another
and resemble packets of 8, 16 or more cells. They are frequently found in the air.
Virulent species have not been encountered.
6. Staphylococci (Gk. staphyle cluster of grapes) divide in several planes
resulting in irregular bunches of cells, sometimes resembling clusters of grapes. Some
species of staphylococci cause diseases in man and animals.
Rods. Rod-shaped or cylindrical forms (Fig. 2) are subdivided into bacteria,
bacilli, and clostridia. Bacteria include those micro-organisms which, as a rule, do not
produce spores (colibacillus, and organisms responsible for enteric fever,
paratyphoids, dysentery, diphtheria, tuberculosis, etc.). Bacilli and clostridia include
organisms the majority of which produce spores (bacilli responsible for anthrax,
tetanus, anaerobic infections, etc.).
11
Figure 1
Spherical forms of bacteria
1 − micrococci; 2 − diplococei; 3 − streptococci; 4 − tetracocci; 5 − sarcinae;
6 − staphylococci
According to their arrangement, cylindrical forms can be subdivided into three
groups: (1) diplobacteria and diplobacilli occurring in pairs (bacteria of pneumonia);
(2) streptobacteria or streptobacilli occurring in chains of different length (causative
agent of anthrax); (3) bacteria and bacilli which are not arranged in a regular pattern
(these comprise the majority of the rod-shaped forms).
Figure 2
Rod-shaped bacteria
1 − diplobacteria; 2 − rods with rounded, sharpened and thickened ends;
3 − different rod-shaped forms and streptobacteria
Figure 3
Spiral-shaped bacteria
1 − vibriones; 2 − spirilla
Some rod-shaped bacteria have pin-head thickenings at the ends (causative
agents of diphtheria); others form lateral branchings (bacilli of tuberculosis and
leprosy). This is explained by the fact that in rod-shaped bacteria the ratio of surface
area to volume is higher. Thus, a larger surface area is in direct contact with nutrient
substances in the surrounding medium.
Spiral-shaped bacteria. Vibriones and spirilla belong to this group of bacteria
(Fig. 3).
1. Vibriones (L. vibrio to vibrate) are cells which resemble a comma in
appearance. Typical representatives of this group are Vibrio comma, the causative
12
agent of cholera, and aquatic vibriones which are widely distributed in fresh water
reservoirs.
2. Spirilla (L. spira coil) are coled forms of bacteria exhibiting twists with one
or more turns. Only one pathogenic species is known (Spirillum minor) which is
responsible for a disease in humans transmitted through the bite of rats and other
rodents (rat-bite fever, sodoku).
3. Spirohetes (from speiera meaning coil and chaite meaning hair) are flexuous
spiral forms. Treponema pallidum, the causative agent of syphilis.
Major Characteristics of Eukaryotes and Prokaryotes
Characteristic
Major groups
Size (approximate)
Nuclear structures
Nucleus
Chromosomes
Ploidy
Cytoplasmic structures
Mitochondria
Golgi bodies
Endoplasmic reticulum
Ribosomes
(sedimentation
coefficient)
Cytoplasmic
membrane
Cell wall
Reproduction
Eukaryote
Prokaryote
Algae, fungi, protozoa, Bacteria
plants, animals
> 5 µm
0,5 to 3 µm
Classic membrane
Strands of DNA
Diploid genome
No nuclear membrane
Single, circular DNA
Haploid genome
Present
Present
Present
80S (60S + 40S)
Absent
Absent
Absent
70S (50S + 30S)
Contains sterols
Does not contain
sterols
Is complex structure
containing protein,
lipid and peptidoglican
Asexual (binary
fission)
Is absent or composed
of chitin
Sexual and asexual
13
Theme 4. Bacteral Anatomi
Cellular structure
Further information: Bacterial cell structure
Fig.4
Fig. 4 shows the structure of an idealised bacterial cell. The outer layer or cell
envelope consists of two components - a rigid cell wall and beneath it a cytoplasmic or
plasma membrane. The cell envelope encloses the protoplasm, comprising the
cytoplasm, cytoplasmic inclusions such as ribosomes and mesosomes, granules,
vacuoles and the nuclear body. Besides these essential components, some bacteria may
possess additional structures. The cell may be enclosed in a viscid layer, which may be
a loose slime layer, or organised as a capsule. Some bacteria carry filamentous
appendages protruding from the cell surface — the flagella which are organs of
locomotion and the fimbriae which appear to be organs for adhesion.
Сell wall
The cell wall encases the protoplast and lies immediately external to the
cytoplasmic membrane. It is 10-25 nm thick, strong and relatively rigid, though with
some elasticity, and openly porous, being freely permeable to solute molecules
smaller than 10000 daltons and 1 nm in diameter. It supports the weak cytoplasmi
membrane against the high internal osmotic pressure of the protoplasm (usually
between 5 and 25 atmospheres) and maintains the characteristic shape of the
14
bacterium in its coccal, bacillary, filamentous or spiral form. From a mechanical
point of view the cell wall may be likened to the outer cover, and the plasma
membrane to the inner tube of the pneumatic tyre of a motor car.
The integrity of the cell wall is essential to the viability of the bacterium. If the
wall is weakened or ruptured, the protoplasm may swell from osmotic imbibition of
water and burst the weak cytoplasmic membrane. This process of lethal
disintegration and dissolution is termed lysis. When the rupture occurs locally in
some part of the cell wall and a bubble of protoplasm is extruded there, the process is
called plasmoptysis.
When intact bacteria, particularly Gram-negative bacteria, are placed in a
solution of very high solute concentration and osmotic pressure, water may be
withdrawn osmotically so that the protoplast shrinks, detaching and retracting the
plasma membrane from the cell wall. This process is called plasmofysis. A similar
process takes place when bacteria are dried, as in preparing a dry film on a
microscope slide. Plasmolysis may be reversible or it may be lethal. Weakening,
removal or defective formation of the cell wall is involved in the production of
the various abnormal forms called spheroplasls, free protoplasts, pleomorphic
involution forms, and L-forms or L-phase organisms.
The cell wall plays an important part in cell division. A transverse partition
of cell wall material grows inwards, like a closing iris diaphragm, from the lateral
wall at the equator of the cell and forms a complete cross-wall separating two
daughter cells. The cell wall is not seen in conventionally stained smears examined
with the light microscope; it generally remains unstained and lies, invisible, outside
the stained shrunken bacterial protoplast. It can be demonstrated by special
staining methods but most readily and clearly by electron microscopy; it is seen both
in ultrathin sections and, as an empty fold surrounding the shrunken protoplast, in
whole-cell preparations shadowcast with heavy metal.
Fig.5 The mucopeptide structure of the bacterial cell wall.
15
The chemical composition of the cell wall differs considerably between
different bacterial species, but in all species the main strengthening component (the
'basal structure') is а glycopeptides (mucopeptide) substance. The mucopeptide is
composed of N-acetylglucosamine and N-acetylmuramic acid molecules linked
alternately in a chain (Fig. 5), the N-acetylmuramic acid molecules each carrying a
short tri-, tetra-or penta-peptide side-chain containing D- and L-alanine, D-glutamic
acid and either L-lysine or diaminopimelic acid. These are further cross-linked by
peptide chains (Fig. 6). In Gram-positive bacteria the cell wall is generally simple and
large in amount, it consists of teichoic acid (ribitol phosphate and Yacetylglucosamine polymer) and glycine and makes up over 80 per cent of the wall
weight. In Gram-negative bacteria the cell wall is complex and minor in amount, it
comprises lipid, polysaccharide, protein and lipopolysaccharide (endotoxin) and
makes up only about 5-10 per cent of the weight of the wall. The special structure of
the cell wall may have an important role in protecting the mucopeptide from attack
by the body's lysozyme. In general, the walls of the Gram positive bacteria have
simpler chemical nature than those of Gram negative bacteria (Table 2). The cell wall
carries bacterial antigens that are important in virulence and immunity.
Fig.6 The mucopeptide structure of the bacterial cell wall/
16
Table 2 Comparison of cell walls of Gram positive and Gram negative bacteria
__________________________________________________________
Gram positive Gram negative
_____________________________________________________________
Thickness
16-20 nm
2 nm
Lipids
Absent
Present
Namber of layers
1-2
5-6
or
scant
Teichoic acid
Present
Absent
% of the weight of the wall
80%
5-10%
Fig. 7 Morphology and Ultrastructure of Microorganis
The outermost layer of Gram negative bacterial cell wall is called the outer
membrane, it has f lipid bilayer structure, which contains various proteins known as
outer membrane proteins (OMP). Among these are porins which form
transmembrane pores that serve as diffusion channels for small molecules. They also
serve as specific receptors for some bacteriophages.
17
The lipopolysaccharides (LPS) present on the cell walls of Gram negative
bacteria account for their endotoxic activity and О antigen specificity. The LPS
consists of three regions. Region I is the polysaccharide portion determining the О
antigen specificity. Region II is the core polysaccharide. Region III is the glycolipid
portion (lipid A) and is responsible for the endotoxic activities, that is, pyrogenicity,
lethal effect, tissue necrosis, anticomplementary activity, B-cell mitogemcity,
immunoadjuvant property and antitumour activity.
Cytoplasmic Membrane
The bacterial protoplast is limited externally by a thin, elastic cytoplasmic
membrane, which is 5-10 nm thick, consists mainly of lipoprotein and is visible in
some ultrathin sections examined with the electron microscope. Membranes are
important features of prokaryotic and eukaryotic cells. In cross-section they
generally appear in suitably stained electronmicroscope (EM) preparations as two
dark lines about 2-5 nm wide separated by a lighter area of similar width. The
classical model of a 'unit membrane' is illustrated in Fig. 8; lipid molecules are
arrayed in a double layer with their hydrophilic polar regions externally aligned
and in contact with a layer of protein at each surface. The functions of membranes
differ widely in nature and it is clear that this simplified model cannot account for
all of the variations of function that are already known. In bacteria, the
cytoplasmic membrane lacks cholesterol which is a normal constituent of animal
cell membranes. The cytoplasmic membrane constitutes an osmotic barrier that is
impermeable to many small molecular solutes and is responsible for maintaining
the differences in solute content between the cytoplasm and the external
environment. It permits the passive diffusion inwards and outwards of water and
certain other small molecular substances, especially lipid-soluble ones, and it
actively effects the selective transport of specific nutrient solutes into the cell and
that of waste products out of it. In addition to the enzymes, or permeases,
responsible for the active uptake of nutrients, the cytoplasmic membrane contains
many other kinds of enzymes, notably respiratory enzymes and pigments
(cytochrome system), certain enzymes of the tricarboxylic acid cycle and, probably,
polymerizing enzymes that manufacture the substances of the cell wall and
extracellular structures. It has little mechanical strength and is supported on the
outside by the cell
wall (Fig. 8).
Phospholipids
bilayer
Protein
Lipid
18
Fig.8 Cytoplasmic Membrane
Cytoplasm of Bacteria
The cytoplasm of the bacterial cell is a viscous, watery solution, or soft gel,
containing a variety of organic and inorganic solutes, and numerous small granules
called ribosomes. The cytoplasm of bacteria differs from that of the higher eukaryotic
organisms not containing an endoplasmic reticulum or membrane bearing
microsomes, in not containing mitochondria and in not showing signs of internal
mobility such as cytoplasmic streaming, the formation, migration and disappearance
of vacuoles, and amoeboid movement.
Ribosomes
Bacterial ribosomes are slightly smaller (10-20 nm) than those of eukaryotic
cells and they have a sedimentation constant of 70S, being composed of a 30S and a
50S subunit (cf. 40S and 60S in the 80S eukaryotic counterparts). They may be seen
with the electron microscope and number tens of thousands per cell. They are strung
together on strands of mRNA to form polysomes and it is at this site that the code of
the mRNA is translated into peptide sequences. Thus the ribosomal components link
up and travel along the mRNA strand and here determine the sequence of amino
acids brought to the site on tRNA molecules and built into specific polypeptides.
Although there are many similarities between bacterial ribosomes and those of
cellular tissues, there are some considerable differences. This fortunately allows us
to use antibacterial agents, such as streptomycin, which interfere with bacterial
metabolism at the ribosomal level without unduly upsetting human ribosomal
function.
Inclusion Granules
Numerous inclusions are located in the cytoplasm comprising volutin granules,
lipoprotein bodies, glycogen, amylose, accumulations of pigment, sulphur, calcium,
etc.
Volutin granules which contain metaphospate stain more intensely than the
cytoplasm. They possess high electron density. The volutin granules vary in size from
several hundreds of 0.1 to 0.5 mcm.
A characteristic feature of the granules of volutin is their metachromatic stain.
They are stained reddish-purple, with methylene blue while the cytoplasm is stained
blue.
Volutin was first discovered in the cell of Spirillum volutans (from which it was
named), then in Corynebacterium diphtheriae and other organisms. The presence of
volutin is taken into account in laboratory diagnosis of diphtheria.
Lipoprotein bodies are found quite frequently as droplets of fat in certain bacilli
and spirilla. They disappear when the cells are deprived of nutrients, and appear when
19
bacteria are grown on nutrient media of high carbohydrate content. They are
discernible if stained with Sudan or fuchsin.
The presence of volutin granules and lipoprotein bodies is biologically important
since they serve as sources of stored food for the bacterium in the case of starvation.
Glycogen and granulose are intracellular inclusions which can be identified by
treating the cell with Lugol's solution. Glycogen stains reddish-brown and granulose
grey-blue. Glycogen granules are prominent in aerobic bacilli. Granulose is
frequently found in butyric-acid bacteria, and I especially in Clostridium
pectinovorum.
Mesosomes
Mesosomes (chondroids) a r e v e s i c u l a r , convoluted or multilaminated
structures formed as invaginations of the plasma membrane into the cytoplasm.
They are more prominent in Gram positive bacteria. They are the principal sites of
respiratory enzymes in bacteria and are analogous to the mitochondria of
eukaryotes. Mvsosomes are often seen in relation to the nuclear body and the site of
synthesis of cross wall septa, suggesting that they coordinate nuclear and
cytoplasmic division during binary fission.
Nucleoid
The nucleoid (nucleoplasm, karyoplasm) in prokaryotes is a ball of double
twisted DNA threads; it has no membrane separating it from the cytoplasm and is not
connected with the main protein of the bacterial cell.
Since the nucleoid of bacteria differs in structure and function from the nuclei of
fungi, Protozoa, and plant and animal cells, the term genophore has been introduced
to designate it.
The nucleoid of bacteria is diffuse in character and is filled with DNA fibrils
which are 300-500 nm in diameter and are arranged to form a closed loop. It is
located in the central part of the cell.
Capsules, Microcapsules and Loose Slime
Many bacteria are surrounded by a discrete covering layer of a relatively firm
gelatinous material that lies outside and immediately in contact with the cell wall.
When this layer, in the wet state, is wide enough to be resolved with the light
microscope, it is called a capsule. When it is narrower, and detectable only by indirect,
serological means, or by electron microscopy, it may be termed a microcapsule. The
capsular gel consists largely of water and has only a small content (e.g. 2 per cent) of
solids. In most species, the solid material is a complex polysaccharide, though in some
species its main constituent is polypeptide or protein.
Loose slime, or free slime is in amorphous, viscid colloidal material that is secreted
extra-cellularly by some non-capsulate bacteria and also, outside their capsules, by
20
many capsulate bacteria. In capsulate bacteria the slime is generally similar in
chemical composition and antigenic character to the capsular substance. When slimeforming bacteria are grown on a solid culture medium, the slime remains around the
bacteria as a matrix in which they are embedded and its presence confers on the
growths a watery and sticky 'mucoid ' character. The slime is freely soluble in water
and, when the bacteria are grown or suspended in a liquid medium, it passes away
from them and disperses through the medium
Demonstration. Capsules and slime have little affinity for basic dyes and are
usually invisible in films stained by ordinary methods. Capsules are most likely to be
visualized by these stains, as either clear or coloured haloes, when the bacteria are
contained in blood, pus or serous fluid. Special methods are available for the
'positive' or 'negative' staining of capsules and loose slime, some being applied to
dry, and some to wet films. Since capsules consist largely of water, they shrink very
greatly on drying. For this reason, dry-film methods of demonstrating capsules are
unreliable, the capsules may shrink so much that they become invisible or, on the
other hand, shrinkage artefacts may give the appearance of capsules on noncapsulate bacteria. The most reliable method of demonstration is by negative
staining in wet films with India ink: the carbon particles of the ink make a dark
background in the film, but cannot penetrate the capsule, which thus appears as a clear
halo around the bacterium (Fig.9). When bacteria that have been grown on solid
medium are being examined for capsules, it is important that they should first be
washed or suspended for a sufficient time in water to ensure the removal of any loose
slime which can be observed when films are made directly from the solid medium.
Because of their low solid content and tendency to shrink greatly on drying,
capsules and microcapsules are not easily demonstrated with the electron microscope.
The large capsule is commonly seen only as an indefinite narrow zone of slight
opacity that blurs the otherwise clear tin edge of the cell wall. Microcapsules may
not be seen at all and for this reason the presence of microcapsules has generally to be
deduced from serological evidence that the cell-wall antigen (e.g. the O, or somatic
antigen) is masked by a covering layer (e.g. of K, or "capsular" antigen).
Function. It is not known with certainty what are the functions of capsules and
microcapsules, but it is probable that their principal action is in protecting the cell wall
against attack by various kinds of antibacterial agents, e.g. bacteriophages, colicines,
complement, lysozyme and other lytic enzymes, that otherwise would more readily
damage or destroy it. The capsule protects the bacteria against ingestion by the
phagocytes of the host. The capsule is thus an important agent determining virulence,
and non-capsulate mutants of these bacteria are found to be non-virulent. The capsular
substance is usually antigenic and the capsular antigens play a very important part in
determining the antigenic specificity of bacteria.
21
Fig.9 . Chain of bacilli with large capsule and pair with very small capsule in wet
film with India inc.
Flagella.
Motile bacteria are subdivided into creeping and swimming bacteria. Creeping
bacteria move slowly (creep) on a supporting surface as a result of wave-like
contractions of their bodies, which cause periodic alterations in the shape of the cell.
These bacteria include Myxobacterium, Beggiatoa, Thiothrix. Swimming bacteria
move freely in a liquid medium. They possess flagella, thin hair-like cytoplasmic
appendages measuring 0.02 to 0.05 mcm in thickness and from 6 to 9 mcm in length.
In some spirilla they reach a length of 80 to 90 mcm.
Investigations have confirmed that the flagella are made up of protein (flagellin)
the composition of which differs considerably from that of the bacterial cell proteins.
With the aid of paper chromatography, it has been discovered that the flagellate
material contains several amino acids: lysine, aspartic and glutamic acids, alanine,
etc. It has been suggested that the flagella are attached to basal granules which are
found in the outlying zones of the cytoplasm.
The flagella can be observed by dark-field illumination, by special methods
involving treatment with mordants. According to a pattern in the attachment of
flagella motile microbes can be divided into 4 groups (Fig.11): (1) monotrichates,
bacteria having a single flagellum at one pole of the cell (cholera vibrio, blue pus
bacillus), (2,4) amphitrichates, bacteria with two polar flagella or with a tuft of
flagella at both poles (Spirillum volutans),(3) lophotrichates, bacteria with a tuft of
flagella at one pole ( Alcaligenes faecalis), (5) peritrichates, bacteria having flagella
distributed over the whole surface of their bodies (colibacillum, salmonellae of
enteric fever and paratyphoids A and B).
22
Fig. 10. Type of flagellar arrangement: 1. single flagellum at one pole. 2. single
flagellum at each pole 3. tuft of flagella at one pole 4. tufts of flagella at both poles
5. peritrichous flagella
The flagella can be observed by dark-field illumination, by special
methods involving treatment with mordants. According to a pattern in the attachment
of flagella motile microbes can be divided into 4 groups (Fig.10): (1) monotrichates,
bacteria having a single flagellum at one pole of the cell (cholera vibrio, blue pus
bacillus), (2,4) amphitrichates, bacteria with two polar flagella or with a tuft of
flagella at both poles (Spirillum volutans),(3) lophotrichates, bacteria with a tuft of
flagella at one pole ( Alcaligenes faecalis), (5) peritrichates, bacteria having flagella
distributed over the whole surface of their bodies (colibacillum, salmonellae of
enteric fever and paratyphoids A and B).
Fimbriae
Certain Gram-negative bacilli, including saprophytic, intestinal commensal
and pathogenic species in the family Enterobacteriaceae, possess filamentous
appendages of a different kind from the flagella. These are called fimbriae or pili,
and they occur in some non-motile, as well as in some motile strains. They are far
more numerous than flagella (e.g. 100-500 being borne peritrichously by each cell)
and are much shorter and only about half as thick. They do not have the smoothly
curved spiral form of flagella and are mostly more or less straight. They cannot be
seen with the light microscope but are clearly seen with the electron microscope
23
in preparations that have been metal-shadowed or negatively stained with
phosphotungstic acid (Fig 11).
Function. There is evidence that fimbriae may function as organs of adhesion.
The possession of fimbriae confers on bacilli the power of adhering firmly to solid
surfaces of various kinds, including those of the cells of animals, plants and fungi.
Comparable non-fimbriate bacilli do not adhere when they collide with such
surfaces. Moreover, bacteria growing in stagnant liquid medium under air are
assisted by the possession of fimbriae to grow attached together in the form of a
pellicle that floats on the surface of the medium where the growth is greatly
enhanced by the free supply of atmospheric oxygen.
Sex fimbriae (sex pili). The fertility factors of enterobacteria, such as the F
factor, which confer 'maleness', or conjugating and DNA-donor abilities on the
bacteria in which they are present, determine the formation by the bacterium of a few
exceptionally long, specialized fimbriae. These sex fimbriae appear to attach
specifically to non-male bacteria and may play a part in the transfer of DNA. They
also act as receptor sites for certain bacteriophages described as being 'malespecific'.
FIG 11. Salmonella typhy. Dividing bacillus from log-phase culture bears about
fifteen long wavy flagella and over a hundred short fimbriae.
24
Spores and sporulation
Endospores are small spherical or oval bodies formed within the cell. A spore is
formed at a certain stage in the development of some micro-organisms and this
property was inherited in the process of evolution in the struggle for keeping the
species intact. Some micro-organisms, principally rod-shaped (bacilli and clostridia),
are capable of sporulation. These include the causative agents of anthrax, tetanus,
anaerobic infections, botulism.
Sporulation occurs in the environment (in soil and on nutrient media), and is not
observed in human or animal tissues. The sporulation process occurs in four
successive stages: (1) preparatory stage; (2) forespore stage; (3) stage of cell wall
formation; and (4) maturation stage.
Under certain conditions, particularly unfavourable ones, structural changes take
place inside the bacillus cell. The process is characterized by a thickening of the
cytoplasm in a certain region and the formation of a forespore, which becomes
surrounded by a thick poorly permeable multilayered wall. The rest of the cell
gradually disappears. Instead of a vegetative cell, a mature spore, one-tenth the size
of the parental cell, is produced. Sporulation is completed within 18 to 20 hours.
Spores are characterized by their high refractive index. If observed unstained
under a microscope, they appear as glistening granules which stain poorly. Because
of the presence of a thick multilayered wall having a laminated structure, minimal
free water content, and a high calcium and lipid content, the spores are capable of
resisting unfavourable environmental conditions for many years. The spores of
certain bacilli are capable of withstanding boiling and high concentrations of
disinfectants. They are killed in an autoclave exposed to saturated steam, at a
temperature of 115-125°C, and also at a temperature of 150-170°C in a Pasteur hotair oven.
When conditions become favourable, the spores germinate and transform again
into vegetative cells. When germination occurs, the spores swell, enlarge in size, their
water content increases, the rate of metabolic processes rises, and they stain easily
with aniline dyes. From the wall at the pole, in the centre, or between the pole and the
centre an outgrowth begins to protrude which transforms into a rod. Usually
germination takes place more quickly than sporulation (within 4 to 5 hours).
The sporulation process in bacilli is not one of multiplication since most rodshaped forms produce only one spore each.
In bacilli and clostridia, spores are located (1) centrally, in the centre of the cell
(causative agent of anthrax); (2) terminally, at the ends of the rod (causative agent of
tetanus); (3) subterminally, towards the ends (causative agents of botulism, anaerobic
infections, etc.) (Fig.12).
25
Fig.12
Shapes and arrangement of spores in bacilli and clostridia
1 — central; 2— terminal; 3 — subterminal
Theme 5. Morphology and Ultrastructure of Spirochaetes.
Spirochaetes are constructed in а far more complicated manner than ordinary
bacteria. Тhеу аrе slender spiral cells that have an intrinsic active undulating motility
although they lack flagella. Тhеу mау consist of regularly spaced tight coils or loose
irregular spirals of varying amplitude. Some рrореl themselves with rapid lashing
movements, others bу slow twisting and bending. Тhеу differ in length from 4 to 14
µm and in thickness from 0·1 to 0·6 µm. Larger spirochaetes саn easily bе seen in
stained films but the very thin ones are barely detectable bу this means and are best
demonstrated bу dark field microscopy in wet preparations.
Тhе protoplasmic core of these spiral cells is enclosed within а сеll wall and аn
inner cytoplasmic membrane; between these two layers there are overlapping sets of
fine fibrils which are anchored bу knobs at the two poles of the organism. Тhе
number of fibrils varies according to the genus from а single pair to six or more pairs.
It is probable that the spiral shape of the organisms depends оn the tension in the
fibrils for if they havе been ruptured the coiled арpearance is lost and the сеll
straightens out. Тhе serpentine movement of spirochaetes mау also depend оn the
integrity of the fibres.
Spirochaetes belong to the order Spirochaetales which is divided into two families
Spirochaetaceae and Treponemataceae. Тhе former are free-living saprophytes and
are not associated with disease. Тhе latter consist of several genera that are
pathogenic for man and animals; they include Trеропета, Borrelia and Leptospira.
Theme 6. Morphology and Ultrastructure of Rickettsiae.
Rickettsiae are included in the order Rickettsiales of obligate intracellar bacteria
containing DNA and RNA, and are pleomorphic organisms. They live and multiply
only within the cells (in the cytoplasm and nucleus) of the tissues of humans,
animals, and vectors.
26
Coccoid forms resemble very fine, homogeneous, or single-grain ovoids about
0,5 mcm in diameter, quite often they occur as the diploforms.
Rod-shaped rickettsiae are short organisms from 1 to 1,5 mcm in diameter with
granules on the ends; or long and usually curved thin rods from 3 to 4 mcm in length.
Filamentous forms are from 10 to 40 mcm and more in length; sometimes they
are curved and multigranular filaments.
Rickettsiae are non-motile, do not produce spores and capsules and stain well by
the Romanowsky-Giemsa stain and the Ziehl-Neelsen stain.
Electron microscopy and cytochemical study have shown that the rickettsiae
have an inner (0,06 mcm) and an outer membrane acting as a wall and consisting of
three layers. Granules of the ribosome type measuring 2-7 mcm and vacuole-like
structures 0,06-0,08 mcm in diameter have been found in the cytoplasm or rickettsiae.
Ricketsiae multiply by division of the coccoid and rod-shaped forms wich give
rise to homogeneous populations of the corresponding type, and also by the breaking
down of the filamentous forms giving rise to coccoid and rod-shaped entities.
Pathogenic rickettsiae invade various species of animals and man. The diseases
caused by rickettsiae are known as rickettsioses. A typical representative is
Ricckettsia prowazekii, the causative agent of typhus fever.
The order Rickettsiales consists of 3 families: Rickettsiaceae, wich has been
characterized above; Bartonellaceae, parasites of human erythrocytes;
Anaplasmaceae, parasites of animal erythrocytes.
.
Theme7. Morphology and Ultrastructure of Mycoplasmas.
The mycoplasmas belong to the class Mollicutes, order Mycoplasmatales. These
bacteria measure 100-150 nm, sometimes 200-700 nm, are non-motile and do not
produce spores.
Mycoplasmas are the smallest micro-organisms. They were first noticed by
Pasteur when he studied the causative agent of pleuropneumonia in cattle. However,
at the time he was unable to isolate them in pure culture on standard nutrient media,
or to see them under a light microscope. Because of this, these micro-organisms were
regarded as viruses. In 1898 Nocard and Roux established that the causative agent of
pleuropneumonia can grow on complex nutrient media which do not contain cells
from tissue cultures. Elford using special filters determined the size of the microbe to
be within the range of 124-150 nm. Thus, in size mycoplasmas appeared to be even
smaller then some viruses.
Since they do not possess a true cell wall, mycoplasmas are characterized by a
marked pleomorphism. They give rise to coccoid, granular, filamentous, cluster-like,
ring-shaped, filterable forms, etc. Pleomorphism is observed in cultures and in the
bodies of animals and man. The nuclear apparatus is diffuse. There are both
pathogenic and non-pathogenic species. The most representative of the pathogenic
species in the causative agent of pleuropneumonia in cattle.
27
At the present time more than 36 representatives of this order have been
isolated. They are found in the soil, sewage waters, different substrates and in the
bodies of animals and humans. Since mycoplasmas pass through many filters, and yet
grow on media which do not contain live tissue cells, they are considered to be
micro-organisms intermediate between bacteria and viruses. Chemically,
micoplasmas are closer to bacteria. They contain up to 4 per cent DNA and 8 per cent
RNA.
The most typical representatives of the pathogenic species are the causative
agents of pleuropneumonia in cattle (Mycoplasma mycoides), acute respiratory
infections (Mycoplasma hominis), and atypical pneumonia in humans (Mycoplasma
pneumoniae).
Theme 8. Morphology and Ultrastructure of Fungi.
Fungi (L. fungus a mushroom) belong to plant heterotrophic organisms
(eukaryotes) devoid of chlorophyll. The cells of fungi have a differentiated nucleus
and many of them multiply by sporulation. They differ greatly from bacteria.
The fungi are marked by various morphology. The main structural component of
the vegetative body is the mycelium which is composed of branching colourless
filaments (hyphae). In some species the mycelium is non-septate, i.e. formed of a
single cell (Mucor mould), in others (higher fungi) it is polycellular (septate). Yeasts
are oval or rounded and lack mycelium.
Fungi resemble algae in structure. They have a firm membrane consisting of
cellulose, pectin substances, and carbohydrates. Various inclusions are found in the
cytoplasm: glycogen, volutin, drops of fat.
The cells of fungi may be mononucleate and polynucleate. The nuclei undergo
both direct and indirect division.
Fungi reproduce by rupture of the mycelium into pieces capable of germinating,
by means of chlamydospores and conidia, by sporulation, and by the sexual way.
The group of fungi includes saprophytes, parasites, and facultative parasites of
plants, animals, and humans.
Oomycetes are fungi with non-cellular (non-septate) mycelium. Some species
live in water, others in the soil. Water inhabiting oomycetes cause diseases among
fish and destroy the roe of fish and frogs. Other oomycetes parasitize on plants and
cause phytophtorosis of potatoes and the fruit of grapes.
The genus Mucor or bread mould belongs to the class Oomycetes. It consists of
a non-septate mycelium in the shape of a much-branched cell, from which branch out
the fruiting hyphae — sporangiophores with round dilatations at the tips —
sporangia. The latter are filled with endospores which provide a means of
reproduction. Mucor mould may also reproduce sexually. It is widespread in nature,
is often found on vegetables, moist surfaces of objects, and in manure.
A typical representative of Mucor mould is Mucor mucedo.
28
Pathogenic species of this mould may cause infections of the lungs and middle
ear, and a general severe infectious process in humans.
Zygomycetes are soil fungi with a non-cellular mycelium. They reproduce by
means of sporangiospores, less frequently by means of conidia. Enzymes secreted by
these fungi are used for clarifying juices and preparing alcoholic beverages.
The class Zygomycetes includes the order Entomophiles, parasites of insects;
they cause the death of the larvae of mosquitoes and flies and are used as insecticides.
Ascomycetes or sac fungi (35 000 species) have a multicellular mycelium. They
reproduce sexually by means of ascospores (spores which develop in special spore
cases, asci). The organisms reproduce asexually by means of conidia (exospores
which bear the function of asexual reproduction in many fungi).
The genus Aspergillus belongs to the class Ascomycetes. The fungi have divided
septate mycelium, and a unicellular conidiophore which terminates in a fan-like row
of short sterigmata from which the spores are pinched off in chains — conidia (Gk.
konidion particle of dust).
A typical representative of aspergilla is Aspergillus niger which is widespread in
nature. It is found on moist objects, on bread and jam. Certain species may cause
aspergillosis of the lungs, ear, and eye in humans or may infect the whole body.
The genus Penicillium belongs to the class Ascomycetes. The mycelium and
conidiophore are multicellular while the fruiting body is in the shape of a brush. The
conidiophore branches towards its upper part and terminates in sterigmata from
which even-rowed chains of conidia are pinched off. This genus of fungi is
widespread in nature. It is found in fodder, milk products, ink and jam, on moist
objects, and old leather. The type species is Penicillium glaucum. Certain species
(Penicillium notatum, Penicillium chrysogenum, etc.) are used for producing
penicillin which is widely employed in treating many infectious diseases. Some
species of this genus of fungi are pathogenic for humans. They cause infections of the
skin, nails, ears, upper respiratory tract, lungs, and other organs.
Mucor
Penicillium
29
Axpergillm
To the class Ascomycetes, the order Saccharomycetales (primary sac fungi)
belong the yeasts which are large, oval, round, and rod-shaped cells. Yeast cells have
a double-cell wall and a well defined nucleus. The cytoplasm is homogenous,
sometimes of a fine granular structure. It contains inclusions (glycogen, volutin,
lipid) and vacuoles, and also filamentous bodies — chondriosomes, which are
involved in synthetic processes in the cell. Yeasts multiply by budding, fission,
sporulation. Some species of yeasts reproduce sexually. Daughter cells produced by
budding from the parent cell transform into independent individuals.
Basidiomycetes, fungi with a multicellular mycelium. These organisms
predominantly reproduce sexually by basidiospores. The majority of them live on
decaying humus and vegetable matter.
Deuteromycetes are a rather large group of fungi consisting of a multicellular
mycelium without either the asco- or basidio-sporangiophore.
Pathogenic species of imperfect fungi are causative agents of derma-tomycoses:
favus (Trichophyton schoenleini), trichophytosis (Trichophyton violaceum),
microsporosis (Microsporum canis).
Comparison of fungi and bacteria
Feature
Diameter
Nucleus
Cytoplasm
Fungi
Approximately 4 µm
(Candida)
Eukaryotic
Mitochondria
and
endoplasmic reticulum
present
30
Bacteria
Approximately 1 µm
(Staphylococcus)
Prokaryotic
Mitochondria
and
endoplasmic reticulum
absent
Cell membrane
Sterols present
Cell wall content
Spores
Chitin
Sexual and asexual
spores for reproduction
Thermal dimorphism
Metabolism
Yes (some)
Require
carbon; no
anaerobes
organic
obligate
Sterols absent (except
Micoplasma)
Peptidoglycan
Endospores
for
survival,
not
for
reproduction
No
Many do not require
organic carbon; many
obligate anaerobes
Theme 9. Morphology and Ultrastructure of Actinomycetes
Actinomycetes (Gk. mykes fungus, actis ray) are unicellular microorganisms
which belong to the class Bacteria, the order Actinomycetales. The body of
actinomycetes consists of a mycelium which resembles a mass of branched, thin (0.21.2 mcm in thickness), non-septate, filaments — hyphae (Fig. 13).
In some species the mycelium breaks up into poorly branching forms. In young
cultures the cytoplasm in the cells of actinomycetes is homogeneous, it refracts light
to a certain extent, and contains separate chromatin grains. When the culture ages,
vacuoles appear in the mycelial cells, and granules, droplets of fat and rod-shaped
bodies also occur. The cell wall becomes fragile, breaks easily, and a partial lysis of
the cells occurs. In actinomycetes, as in bacteria, differentiated cell nuclei have not
been found, but the mycelial filaments contain chromatin granules. The
actinomycetes multiply by means of germinating spores attached to sporophores, and
by means of fragmentation where they break up into hyphae.
31
Figure 13.
Morphology and structure of actinomycetes
1-general view of the mycelium; 2—germination of spores; 3 — structure of
sporophores
Differentiating Characteristics of Actinomycetaceae
Staining
characteristics
Oxygen
requirement
Epidemiology
Clinical disease
Reproduction
Actinomyces
Gram-positive
Strict of
facultative
anaerobes
Part of normal
flora
(oropharynx,
gastrointestinal
tract)
Produce
abscesses with
yellow granules
Non-spore
former
Nocardia
Gram-positive
(stain poorly);
weakly acid-fast
Strict aerobes
Streptomyces
Gram-positive
Prevalent in soil;
occasionally
found in sputum
of normal
individuals
Cause
subcutaneous
and pulmonary
infection
Prevalent in soil
and water
Non-spore
former
32
Strict aerobes
Cause
subcutaneous
infections with
granules
(mycetoma)
Spore former
Bibliography
1. Medical Microbiology. G.G.A. Thomas. London, Bailliere Tindall, 1985.
2. Medical Microbiology. Cedric Mims. Toronto, 2004.
3. Microbiology, a human perspective. Eugene W. Nester. Published by
McGraw-Hill, 2004.
4. Microbiology. V.M. Korshunov. Moscow, 2002.
5. Textbook of Microbiology. R. Ananthanarayan. Orient Longman, 2007.
6. Medical Microbiology. Mackie and McCartney Longman Group (FE) Ltd
33
Contents
Introduction……………………………………………………………... 6
Theme 1. Microbiological laboratory. Safety regulations at work with
7
gas and microorganisms…………………………………………………
7
Theme 2. Classification of Microorganisms……………………………...
10
Theme 3. Morphology of Bacteria……………………………………….
Theme 4. Bacterial Anatomy…………………………………………….
14
Theme 5. Morphology and Ultrastructure of Spirochaetes……………… 26
Theme 6: Morphology and Ultrastructure of Rickettsiae………………... 26
Theme7: Morphology and Ultrastructure of Mycoplasmas……………...
27
Theme8: Morphology and Ultrastructure of Fungi……………………… 28
Theme 9. Morphology and Ultrastructure of Actinomycetes……………
31
Bibliography……………………………………………………………... 33
34
Общая микробиология.
Морфология и ультраструктура микроорганизмов
Учебное пособие
для студентов лечебного факультета англоязычного отделения
General Microbiology.
Morphology and ultrastructure of microorganisms.
The Manual
for the Students of General Medicine
of the English-speaking Medium
Базиков И.А., Лысогора Е.В.,
Климанович И.В., Селиванова И.С.
I.A. Bazikov, E.V.Lysogora, I.V. Klimanovich, I.S. Selivanova
Сдано в набор 2010 г. Подписано в печать 2010 г.
Формат 60х841/16. Бумага офсетная. Печать офсетная .
Гарнитура Times New Roman. Усл. печ. л.
Заказ № . Тираж экз.
Отпечатано в типографии Ставропольской государственной медицинской академии
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35