3. Definition
Bacteriology: scientific study of bacteria
Medical bacteriology: is the scientific study of
medically relevant bacteria
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4. General characteristics
Typical prokaryotic cell
Contain both DNA and RNA
Most grow in artificial media
Replicate by binary fission
Almost all contain rigid cell wall
Sensitive to antimicrobial agent
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5. Structure of the Bacteria
Bacterial structure is considered at 3 levels.
Cell envelope proper: Cell wall and cell
membrane.
Cellular element enclosed with in the cell
envelope: Mesosomes, ribosomes, nucleiod and
cytoplasmic granules.
Cellular element external to the cell envelope:
Flagellum, Pili and Glycocalyx.Mr. Vincent Ejakait
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8. Cell wall
The bacteria cell wall is rigid
It is made up of a peptidoglycan layer
Functions of cell wall
1. Provides shape to the bacterium
2. Gives rigidity to the organism
3. Protects from environment
4. Provides staining characteristics to the
bacteriumMr. Vincent Ejakait
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12. Cell membrane
Also named as plasma membrane or
cytoplasmic membrane
It is composed of protein, lipids and
carbohydrate. (phospholipid layer)
Functions of cell membrane
Regulates the transport of nutrients and waste
products into and out of the cell.
Synthesis of cell wall components
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14. Cellular elements
Mesosomes: functions in cell division or
excretion
Ribosomes: protein synthesis
Cytoplasm: provision of nutrient
Nucleiod: Genetic material
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15. Glycocalyx (capsule and slime
layer)
Capsule is gel firmly adherent to cell envelope.
Slime is gel easily washed off from cell envelope.
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16. Flagellum
It is a whip-like
structure
It is the organ of
locomotion in
bacterial cell
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17. Pili (fimbriae)
It is hair like structure
composed of protein
It is the structure for
adherence to cell surface
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18. Size of Bacteria
The average diameter of spherical bacteria is 0.5-
2.0 µm.
For rod-shaped or filamentous bacteria, length is 1-
10 µm and diameter is 0.25-1.0 µm.
The bacterium, Epulosiscium fishelsoni , can be
seen with the naked eye
The Mycoplasmas, are the smallest cells known so
far.
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20. Classification of Bacteria
Bacteria can be classified depending on the
following features.
1. Morphology of bacterial cells
2. Arrangement of bacterial cells
3. Staining of the bacteria
4. Oxygen need
NB: Morphology and staining of bacteria are the
commonly used characteristics to classify bacteria.
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21. 1. Morphological classification
Cocci (singular coccus): Round or oval shaped
Bacilli (singular bacillus): Rod or cylindrical shaped
Coccobacilli (singular coccobacillus): Short rods
Spirillum: spiral shaped, non-flexible
Spirochete: spiral shaped, flexible
Vibrio: coma shapedMr. Vincent Ejakait
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25. 3. Staining classification
Gram positive bacteria:
The bacteria stains
purple or blue under
gram staining
Gram negative bacteria:
The bacteria stains pink
or red under gram
stainingMr. Vincent Ejakait
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26. Gram positive bacteria
Examples of common Gram +ve bacteria:
Mycobacterium: M leprae, M tuberculosis
Clostridium: C tetani, C perfringens
Bacillus: B anthracis
Staphylococcus: S aureus
Streptococcus: S pyogenes, S pneumonia
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27. Gram negative bacteria
Examples of Gram –ve bacteria
Salmonella: S typhi, S paratyphi
Bortadella: B pertussis
Chlamydia
Escherechia (E. coli)
Helicobacter: H pylori
Haemophilus influenza b (Hib)
Kleibssiela
Neisseria: N gonorrheae, N meningitidis
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28. 4. Oxygen need
On this basis bacteria have been divided into 4
groups:
1. Obligate anaerobes
2. Facultative anaerobes
3. Obligatory aerobes
4. Microaerophilic
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29. Anaerobes
a. Obligate anaerobes
Bacteria that can grow only in the complete
absence of molecular oxygen.
Ex. Clostridium, Actinomyces
b. Facultative anaerobes
Bacteria that can live and grow with or without
molecular oxygen
Ex. Escherichia coli, Staph spp, Strep spp, salmonelaMr. Vincent Ejakait
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30. Aerobes
c. Obligatory aerobes
Bacteria that need oxygen because they
cannot ferment or respire anaerobically.
Ex. Pseudomonas
d. Microaerophilic
Bacteria that can grow under conditions with
low oxygen tension
Ex. Clostridium tetaniMr. Vincent Ejakait
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32. Pathogenesis
Bacteremia: is the circulation of bacteria in the
blood.
For their optimal growth, bacteria requires
proper:
Nutrition
Oxygen (or absence of it)
pH (neutral)
Appropriate temperatureMr. Vincent Ejakait
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