Download BACTERIAL CELL STRUCTURE Microbiology Lecture 2 Professor

11/24/13
BACTERIAL CELL SHAPES
AND SIZES
BACTERIAL CELL
STRUCTURE
coccus
e.g. Staphylococcus
aureus
bacillus
e.g. Escherichia coli
Microbiology Lecture 2
spirillum
Professor T.J. Foster
GRAM STAIN
e.g. Treponema
pallidum
Mixed culture showing
(1) spherical cocci
(2) rod-shaped bacilli and
(3) spiral or
helical-shaped bacteria (Gram stained).
THE GRAM STAIN
•  CRYSTAL VIOLET + IODINE
FORM COMPLEX
•  WASH ETHANOL
•  COUNTERSTAIN FUSCHIN
•  GRAM POSITIVE, PURPLE
CRYSTAL VIOLET-IODINE RETAINED
•  GRAM NEGATIVE, RED
CRYSTALVIOLET-IODINE WASHED OUT
Escherichia coli, Gram negative rod.
Staphylococcus aureus, Gram positive coccus
Mixtures of Gram positive and Gram negative bacteria
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STRUCTURE OF THE BACTERIAL
(PROKARYOTIC) CELL
•  NO MITCHONDRIA
–  FUNCTIONS PERFORMED BY
CYTOPLASMIC MEMBRANE
G
G
M
G
M
G
M
M
Disaccharide
repeat
G
G
M
G
M
G
M
Peptido
-glycan
M
•  RIBOSOMES FREE IN CYTOPLASM
G
–  NO ENDOPLASMIC RETICULUM
M
G
M
G
M
G
M
•  HAPLOID
–  SINGLE CIRCULAR CHROMOSOME
–  NO NUCLEAR MEMBRANE
•  CELL WALL PEPTIDOGLYCAN
G, N-acetyl glucosamine
M, N-acetyl muramic acid
–  UNIQUE WALL POLYMER
Peptidoglycan
LYSOZYME, an enzyme
that cleaves
polysaccharide
G
G
M
G
G
M
M
G
G
M
M
G
Peptide bridge
Amino acid
Peptidogycan Disaccharide
N-acetyl muramic acid
N-acetyl glucosamine
M
M
G
M
PENICILLIN, an antibiotic
inhibits formation of peptide cross bridge
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NAG
NAM
Summary of Peptidoglycan Structure
NAG
NAM
Two tetrapeptide
Chains
crosslinked
Two tetrapeptide chains
cross-linked by peptide bridge
FUNCTION OF CELL WALL
FUNCTION OF CELL WALL
•  MECHANICAL STRENGTH
•  STRUCTURAL INTEGRITY
•  MECHANICALSTRENGTH
•  STRUCTURAL INTEGRITY
–  DISRUPT PEPTIDOGLYCAN
–  CELLS BURST
–  HIGH INTERNAL OSMOTIC PRESSURE
–  DISRUPT PEPTIDOGLYCAN
–  CELLS BURST
–  HIGH INTERNAL OSMOTIC PRESSURE
Protoplast
Bacterial cell
Wall
Lysozyme
Isotonic solution
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GRAM-POSITIVE BACTERIAL CELL WALL
FUNCTION OF CELL WALL
Lipoteichoic acid
Wall teichoic acid
negatively charged
polymers
•  MECHANICALSTRENGTH
•  STRUCTURAL INTEGRITY
Proteins
Covalently bound
to peptidoglycan
–  DISRUPT PEPTIDOGLYCAN
–  CELLS BURST
–  HIGH INTERNAL OSMOTIC PRESSURE
Protoplast
Peptidoglycan
H2O
Lysozyme
Isotonic solution
Cytoplasmic membrane
Hypotonic
Protoplast bursts
Gram-Positive Bacterial Wall Structure
Protein
Attached covalently
to cell wall
peptidoglycan.
Lipoteichoic acid
Cytoplasm
GRAM-POSITIVE BACTERIAL CELL
Thick single-layered cell wall
Nuclear material
(no nuclear membrane)
Wall teichoic acid
Thick
Peptidoglycan
Cytoplasmic
Membrane.
Lipid bilayer
Dividing cell
Membrane proteins
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GRAM-NEGATIVE BACTERIAL CELL WALL
Lipopolysaccharide
(endotoxin)
Gram-Negative Bacterial Wall Structure
Porin
Fimbria (pilus)
Polysaccharide chain
Lipopolysaccharide
LPS, endotoxin
Outer Membrane
Outer membrane
Pore
Outer membrane protein porin
Thin peptidoglycan
Periplasmic space
Peptidoglycan
Periplasm
Cytoplasmic membrane
Cytoplasmic membrane
Cytoplasm
GRAMNEGATIVE
BACTERIAL
CELL WALL
Molecules and Structures on
the Surface
of Gram-Negative Bacteria
Outer
Membrane
PeptidoGlycan
Periplasm
Cytoplasmic
Membrane
Cytoplasm
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Lipopolysaccharide
(Endotoxin)
eg. There are 100s of different
serotypes of the species
Salmonella enterica
FIMBRIAE (PILI)
Flagellum
Polysaccharide chain (highly variable)
Defines O (somatic) antigen
Core polysaccharide
fimbriae
Lipid A (toxic moiety)
Outer membrane
Promotes adhesion to mammalian cells
eg intestinal epithelium, Vibrio cholerae
Tip of Pilus of Escherichia coli
FimG tip protein – adhesin
Pilus of Escherichia coli
Tip fibrillum
3 nm thick tip fibrillum
Composed of 2 proteins
7 nm thick helical rod.
Subunits of FimA
Attached to outer
membrane basal
structure (not shown)
Shaft. Identical FimA subunits
Attached to outer membrane by
usher
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Flagella
Flagellum
Movement towards substrate
chemotaxis
Flexible. Beating flagella
Motility
Peritrichous
Rotates
polar
Motility; Polar
Number and arrangement of flagella characteristic of species
CAPSULE
•  Outer layer
•  Polysaccharide usually (sometimes
polypeptide)
•  Unstructured : loose association
•  Promotes virulence in pathogenic (diseasecausing) bacteria
–  Inhibits phagocytosis by leucocytes
–  Streptococcus pneumoniae.
–  Bacillus anthracis
• Cap+
virulent
• Capnon-virulent
Capsule
Bacillus anthracis
Streptococcuss
pneumoniae
Polysaccharide capsule
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CAPSULE
SPORES
Bacterial cell
•  Resistance to heat and dessication
Capsule
•  Clostridium
Bacillus
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Infections of Humans by Spore-Forming Bacteria.
Tetanus
Clostridium tetani. Obligate anaerobe.
Commensal of intestine of horses.
Spores in soil.
Contaminate deep wound.
Anaerobic environment. Germination.
Synthesize tetanus neurotoxin.
Enters nerve cells.
Inactivate neurons that trigger muscle relaxation.
Spasms - face, then limbs.
Vaccine (lecture 8)
You should take some time to reflect on the differences in structure, composition & organization of prokaryotic
and eukaryotic cells, referring back to earlier lectures on cell biology.
Anthrax
Bacillus anthracis Aerobic.
Ingestion or inhalation of spores.
Pneumonia or septicaemia.
Poly-D-glutamic acid capsule and potent “Lethal Toxin”
essential virulence factors
Biological weapon : bioterrorism
It is very important that you know the detailed structure of the cell wall of Gram-positive and Gram-negative
bacteria.
Not only is this knowledge of fundamental importance in its own right, but it is essential for the full
understanding of susceptibility of and resistance of microbes to antimicrobial drugs (lecture 3), and of
interactions between pathogenic bacteria and the mammalian host (lecture 4).
Note the different mechanisms of action of penicillin in inhibiting the formation of peptidoglycan (lecture 3), and
lysozyme, an enzyme which destroys peptidoglycan. Lysozyme is part of the innate immunity of mammals
(lecture 7/8)
Several appendages are found on bacterial cells that are of importance in colonization of the host (fimbriae or
pili of Gram-negative bacteria and surface proteins of Gram-positive bacteria – see lecture 4). The capsule of
Streptococcus pneumoniae is a major virulence factor because it prevents phagocytosis of bacteria by
neutrophils, unless there are specific antibodies present that bind to the capsule (see lecture 7/8).
Lipopolysaccharide of Gram- negative bacteria is an important antigenic determinant (lecture 7) but is also toxic
(it is called endotoxin) and is of importance in the pathogenesis of diseases caused by Gram-negative bacteria
(lecture 4) and is recognized by the host as a signal that infection is occurring – triggering inflammation
The ability of some Gram-positive bacteria to form spores is the reason why the autoclave must be used to
completely sterilize media and materials for laboratory use (lecture 1). Spores are very important in the
dissemination of the bacteria that cause tetanus and anthrax, the latter is currently of concern because of the
possibility of using it for bioterrorism.
Further Reading
Campbell does not have much detail on the structure of prokaryotes
Chapter 4 of Totora is an excellent chapter covering this lecture in some depth.
Todor’s On-line Textbook of Bacteriology
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