2. Bacteria lecture

BACTERIA
By Mr. Vincent Ejakait

Content
 Definitions
 Structure
 Characteristics
 Classification
 Pathogenesis
Mr. Vincent Ejakait
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Definition
 Bacteriology: scientific study of bacteria
 Medical bacteriology: is the scientific study of
medically relevant bacteria
Mr. Vincent Ejakait
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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
Mr. Vincent Ejakait
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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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Bacteria structure
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Bacteria cell structure
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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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Cell wall
Mr. Vincent Ejakait
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Gram +ve vs Gram -ve
Gram positive
bacteria
 Thick peptidoglycan layer
 Has no outer membrane
 Peptidoglycan
 Teichoic acid
Gram negative
bacteria
 Thin peptidoglycan layer
 Has an outer membrane
 Peptidoglycan
 Lipoprotein
 Phospholipid
 LipopolysaccharideMr. Vincent Ejakait
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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
Mr. Vincent Ejakait
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Cellular elements
 Mesosomes: functions in cell division or
excretion
 Ribosomes: protein synthesis
 Cytoplasm: provision of nutrient
 Nucleiod: Genetic material
Mr. Vincent Ejakait
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Glycocalyx (capsule and slime
layer)
 Capsule is gel firmly adherent to cell envelope.
 Slime is gel easily washed off from cell envelope.
Mr. Vincent Ejakait
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Flagellum
 It is a whip-like
structure
 It is the organ of
locomotion in
bacterial cell
Mr. Vincent Ejakait
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Pili (fimbriae)
 It is hair like structure
composed of protein
 It is the structure for
adherence to cell surface
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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.
Mr. Vincent Ejakait
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Bacteria sizes
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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.
Mr. Vincent Ejakait
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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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2. Arrangement classification
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Arrangement of bacillus
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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
25

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
Mr. Vincent Ejakait
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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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4. Oxygen need
On this basis bacteria have been divided into 4
groups:
1. Obligate anaerobes
2. Facultative anaerobes
3. Obligatory aerobes
4. Microaerophilic
Mr. Vincent Ejakait
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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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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
30

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
32

2. Bacteria lecture

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2. Bacteria lecture