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Classification of medically
important bacteria
Bacteria
Unicellular, Microscopic, Prokaryotic Organisms,
Multiply By Binary Fission.
Comparison Between Bacteria And Fungi
And Protozoa
Bacteria
Type
Chromosome One
(Number)
Nuclear
Membrane
Prokaryotic
Fungi & Protozoa
Eukaryotic
Multiple
Absent
Present
Comparison Between Bacteria and Fungi and Protozoa (Continued)
Bacteria
Fungi & Protozoa
Mitochondria
Absent
Present
Ribosomes
70s
80s
Sterols
Absent (Except
In Mycoplasma)
Usually
Present
Cell Wall
Rigid Layer Of
Peptidoglycan
(Absent In
Mycoplasma)
No PeptidoGlycan
(In some cases
cellulose present)
Bacteria can be divided into:
1. Filamentous Bacteria (Actinomycete) Most capable of
branching
2. True (Euobacteria): Divide by Binary Fission
Cocci
Bacilli (rods)
Vibrio (coma shape)
3. Spirocheates: Divide by Transverse Binary Fission
4. Mycoplasma Which Lack Rigid Cell Wall
5. Ricketssiae, and Chlamydia
Intracellular parasites
which
are
strict
Taxonomic Ranks
Formal Rank
________________________________________________________________________________________________________________________
Kingdom
Division
Class
Order
Family
Example
Prokaryotae
Gracilicutes
Scotobacteria
Eubacteriales
Enterobacteriae
Genus Eschirichia, Streptococcus, Staphylococcus, Streptococcus, Klebsiella
Species
coli
Pyogenes
aureus
pneumoniae pneumonia
 The
Gram stain, t bacteria into two main
groups, is the first step in bacterial
classfication & identification.
 Bacteria
stained purple are Gram + - their
cell walls have thick petidoglycan and
teichoic acid.
stained pink are Gram – their cell
walls have have thin peptidoglycan and
lipopolysaccharides with no teichoic acid.
 Bacteria
The Gram stain has four steps:
 1. crystal violet, the primary stain:
followed by
 2.grams
iodine, which acts as a mordant
by forming a crystal violet-iodine complex,
then
 3.
alcohol, which decolorizes, followed by

4. safranin, the counterstain.
Is this gram stain positive or negative?
Identify the bacteria.
Is this gram stain positive or negative?
Identify the bacteria.

Gram staining tests the bacterial cell wall's
ability to retain crystal violet dye during solvent
treatment.
Iodine is added as a mordant to form the crystal
violet/iodine complex in order to render the dye
impossible to remove.
 Ethyl-alcohol solvent acts as a decolorizer and
dissolves the lipid layer from gram-negative
cells. This enhances leaching of the primary
stain from the cells into the surrounding solvent.
 Ethyl-alcohol will dehydrate the thicker grampositive cell walls, closing the pores as the cell
wall shrinks.
 For this reason, the diffusion of the crystal violetiodine staining is inhibited, so the bacteria
remain stained.
Classification based on
 Shape
 Gram
reaction
 Oxygen
 Free living & non free living
Simplified Classification of Medically – Important
Gram-positive Bacteria
Free living
Aerobes or
facultative
Anaerobes
Cocci
Arranged in
clusters
Micrococcus
Staphylococcus
Arranged in
chains
Streptococcus
Anaerobes Peptostreptococcus
Simplified Classification of Medically –
Important Gram-positive bacteria
Sporing
Aerobes or
facultative
anaerobes
Nonsporing
Bacillus
Corynebacterium
Listeria
Lactobacillus
Nocardia
Mycobacterium
RODS
Sporing
Clostridium
Nonsporing
Actinomycosces
Anaerobes
Simplified Classification Of Medically –
Important Gram-negative Bacteria
Aerobes
Neisseria
Anaerobes
Veillonella
Cocci
Important Gram-negative Bacteria
Aerobes
Pseudomonas
Salmonella
Shigella
enterKlebsiella
obac Proteus
teriae Escherichia
Facultative
Anaerobes
BACILLI
cae Yersinia
respir leigonella
Bordetella
Haemophilus
zoonot Brucella
Pasteurella
francisella
yersinia
Vibrio(curved)
Anaerobes
Microaerophilic
Bacteroids
Fusobacterium
Camplylobacter
Simplified Classification Of Medically –
Important Gram-negative Bacteria
Aerobes
Leptospira
Anaerobes
Treponema
Borrelia
Spirochetes
Cell wall deficient bacteria------- Mycoplasma
2.Non- free living intra cellular—
Rickettsia &chlamydia
Capsule
Present in Certain Bacteria.
Polysaccharide;

occasionally protein
e.g. Bacillus anthracis
importance
a. Inhibit Phagocytosis
b. Antigenic

Study template for bacteria
Diagrams Showing The Structure Of Bacterial
Cell Walls
Microbiology And The Patient
Medical Microbiology – concerned with:
(i) Aetiology (cause)
(ii) Pathogenesis (Mechanism of production of
disease)
(iii) Laboratory Diagnosis
(iv) Treatment of infection
(v) Epidemiology (spread, distribution, prevalence
of infection in the community)
(vi) Control and prevention in community
Laboratory Methods: Collection of specimens
(i)
Microscopy
Stained Specimens
Unstained Specimens
(ii)
(iii)
(iv)
(v)
Culture
Identification of the organism
Tests for Antimicrobial agents serology
Demonstration of Abs
6) Understand the proper use of Clinical Lab.
a)
b)
c)
Specimen collection and handling
Requesting appropriate tests
Interpretation of results of Lab. tests
7) Correct selection, use, monitoring of antimicrobial therapy
8) Understand methods of prevention of
infection e.g. Vaccine, chemoprophylaxis,
hygiene, isolation etc.