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Phase 2a > Microbiology > Flashcards

Microbiology Flashcards

1
Q

What is a pathogen?

A

Organism that causes or is capable of causing disease.

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2
Q

What is a Commensal?

A

Organism which colonises the host but causes no disease in normal circumstances.

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3
Q

What is a Opportunist Pathogen?

A

Microbe that only causes disease if host defences are compromised.

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4
Q

What is the definition of Virulence/ Pathogenicity?

A

The degree to which a given organism is pathogenic.

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5
Q

What is the definition of asymptomatic carriage?

A

When a pathogen is carried harmlessly at a tissue site where it causes no disease.

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6
Q

What areas are open to bacterial colonisation?

A

Skin, areas with mucosal surfaces, tract stomach, gut, vaginal tract, mouth, urethra

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7
Q

What are the 2 main forms of bacterial morphology?

A

Coccus (small sphere) an Bacillus (rod)

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8
Q

What does it indicate when bacteria remains purple when stained with gram stain (purple dye)?

A

Bacteria is Gram positive.

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9
Q

What does it indicate if bacteria turns red when stained with gram stain (purple dye)?

A

Bacteria is Gram negative.

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10
Q

What are the different structures of bacteria that coccus/ cocci (multiple coccus) can form?

A
  • Dipplococcus
  • Chain of Cocci
  • Cluster of Cocci
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11
Q

What are the different structures of bacteria that structures of bacteria that are bacillus can form?

A
  • Chain of rods
  • Vibrio (curved rod)
  • Spirochaete (spiral rod)
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12
Q

What structures are found in a bacteria cell?

A
  • Inner membrane
  • Outer membrane
  • Cell wall
  • Pilli
  • Chromosome of circular double stranded DNA
  • Capsule
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13
Q

What are Bacterial Endotoxins?

A

Component of the outer membrane of bacteria e.g. lipopolysaccharide in Gram negative bacteria

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14
Q

What are bacterial exotoxins?

A

Secreted proteins of Gram positive and Gram negative bacteria

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15
Q

Is Tetanus an exotoxin or endotoxin? What does it do?

A

A exotoxin.

It stimulates nerves and causes muscles to go into spasm, characterised in babies by an arched back.

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16
Q

What is the structural difference between gram positive and gram negative bacteria?

A

Gram positive bacteria cell have only 1 membrane; a thick peptidoglycan layer.

Gram negatie bacteria cell have 2 membranes; a thin peptidoglycan layer and an outer lipopolysaccharide membrane.

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17
Q

What is the ideal bacterial environment?

A
  • Temperature; < -80 to +80 degrees 9120 degrees for spores)
  • pH; < 4-9
  • Water/ desiccation; 2 hours to 3 months 9>50 years for spores)
  • Light; UV
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18
Q

What are bacterial toxins?

A

Chemicals released by bacteria.

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19
Q

Compare exotoxin and endotoxins for:

  • Composition
  • Action
  • Effect of heat
  • Antigenicity
  • Produced by
  • Covertibility to toxoid
A
  • Composition; exo = protein, endo = lipopolysaccharide
  • Action; exo = specific, endo = non-specific
  • Effect of heat; exo = labile, endo = stable
  • Antigenicity; exo = strong, endo = weak
  • Produced by; exo = mostly gram positive, endo = LPS - gram negative
  • Coveritbility to toxoid; exo = yes, endo = no
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20
Q

What is a toxoid?

A

A toxin treated (usually with formaldehyde) so that it loses its toxicity but retains its antigenicity.

21
Q

How does bacterial transcription occur?

A

RNA polymerase is used to extract mRNA from the circular bacterial chromosome. A 30S/50S ribosome is used to turn the mRNA into a protein.

22
Q

What does a plasmid contain?

A
  • Transfer promotion genes
  • Plasmid maintenance genes
  • Antibiotic virulence determinant genes
23
Q

How does genetic variation occur in bacteria?

A

Mutation:

  • Base substitution
  • Deletion
  • Insertion

Gene transfer:

  • Transformation e.g. via plasmid
  • Transduction e.g. via phage
  • Conjugation e.g. via sex pilus
24
Q

What can bacteria be classified into:

A
  1. obligate intracellular bacteria

2. bacteria that may be cultivated on artificial media

25
Q

Give examples of obligate intracellular bacteria

A
  • Rickettsia
  • Chlamydia
  • Coxiella
26
Q

How can bacteria that may be cultured on artificial media be further divided?

A
  1. with a cell wall

2. no cell wall

27
Q

Give examples of bacteria with no cell wall

A
  • Mollicutes
28
Q

How can bacteria with a cell wall be divided further?

A
  1. Growing as single cells

2. Growing as filaments

29
Q

Give examples of bacteria with a cell wall that can grow as filaments

A
  • Actinomyces
  • Nocardia
  • Streptomyces
30
Q

What can bacteria with cell walls that grow as single cells be further divided into?

A
  • Rods
  • Cocci
  • Spirochates
31
Q

Give examples of spirochaetes bacteria

A
  • Leptospira
  • Treponema
  • Borrelia
32
Q

How do you carry out a gram stain?

A
  1. Apply a primary stain such as crystal violet (purple) to het fixed bacteria.
  2. Add iodide which binds to crystal violet and helps to fix it to the cel wall.
  3. Decolorise with ethanol or acetone.
  4. Counterstain with safranin (pink).
33
Q

What happens to gram negative bacteria when gram stain s applied?

A

The decolouriser interacts with the lipids and cells lose their outer lipopolysaccharide membrane and the crystal violet-iodide (CV-I) complexes, thus they appear pink/ red with counterstain.

34
Q

What happens to gram positive bacteria when gram stain is applied?

A

The decolouriser dehydrates the cell wall and the CV-I get trapped in the multi-layered petidoglycan.

35
Q

Give examples of both anaerobic and aerobic Gram Negative Cocci.

A

Anaerobic; Veillonella

Aerobic; Neisseria

36
Q

Give examples of both anaerobic and aerobic Gram Positive Cocci.

A

Aerobic; Staphylococcus, Streptococcus

Anaerobic; Peptostreptococcus

37
Q

What is the catalase test?

A
  • Flavoproteins reduce O2 using superoxide dismutase producing H2O2
  • Superoxide is converted in the following reaction by catalase 2H2O2 –> 2H2O + O2
  • Staphylococci are catalase +
  • Streptococci are catalase -
38
Q

What is the coagulase test?

A
  • Distinguishes S. aureus (coagulase positive) from other staphylococci (coagulase negative)
  • Coagulase activates prothrombin to convert fibrinogen to fibrin
  • Free coagulase is released and identified by tube coagulase test
  • Bound coagulase (clumping factor) is identified by a slide coagulase test
39
Q

What other test can be done for Staphylococcus aureus?

A
  • Latex test

- Positive coagulase test

40
Q

What is the result of the coagulase test on S. epidermis?

A
  • negative coagulase test
41
Q

What is haemolysis?

A
  • The ability of bacteria to break down red blood cells in blood agar.
  • Requires expression of hemolysin.
  • Particularly useful for classifying streptococci.
  • Alpha-hemolysis causing by production of hydrogen peroxide oxidising hemoglobin to methemoglobin (the agar appears green).
  • Beta-hemolysis results because of lysis of red blood cells by hemolysin such as Streptolysin O produced by S. pyogenes.
  • Gamma-hemolysis implies no hemolysis.
42
Q

What can Rods growing as single cells be further divided into?

A
  • Gram positive
  • Gram negative
  • Ziehl-Neelsen Stain positive
43
Q

Give examples of Ziehl - Neelsen stain positive bacteria

A 
- Mycobacteria; 
M. tuberculosis 
M. leprae 
M. avium-intracellulare
M. ulcerans 
M. kansasii
44
Q

Give examples of both aerobic and anaerobic Gram Positive Rods (Bacilli).

A

Anaerobic:

  • Clostridium
  • Proprioinibacterium

Aerobic:

  • Corynebacterium
  • Listeria
  • Bacillus
  • Erysipelothrix
45
Q

Give examples of both aerobic and anaerobic Gram Negative Rods (Bacilli).

A

Anaerobic:
- Bacteroides

Aerobic:
'Coliforms'
- Eschericia 
- Klebsiella 
- Shigella

‘Pseudomonads’
- Pseudomonas

‘Vibrio’

  • Vibrio
  • Campylobacter
  • Helicobacter

‘Parvobacteria’

  • Haemophilus
  • Brucella
  • Bordetella
  • Pasteurella
46
Q

What selective indicator media can be used for Gram-Negative Bacilli (Rods)?

A

MacConkey Agar:

  • Bile salts inhibit g+ve bacteria and inhibits swarming of a g-ve bacterium
  • Crystal violet also inhibits some g+ve bacteria
  • Neutral red acts as a pH indicator so that bacteria that ferment lactose (Lac=) and release H+ appear pink or red
  • Lactose available for Lac+ micro-organisms
  • Peptone for Lac- micro-organisms, means production of NH3 and a rise in pH

Cysteine lactose electrolyte deficient (CLED) media

  • used as media for urinary pathogens
  • Electrolyte deficient media stops swarming of Proteus Miribillis
  • Bromothymol blue = indicator, Lac. fermentation means the blue changes to yellow,
47
Q

What significance does motility have in distinguishing bacteria?

A
  • Flagella (used for bacteria motility) has staining patterns
  • Swarming motility patterns can be seen on agar
48
Q

What is the oxidase test?

A
  • Tests if micro-organism contains a cytochrome oxidase or indophenol oxidase
  • Uses a redox indicator
  • In oxidised state, indicator is dark blue or maroon
  • This implies the organism is able to use oxygen as the terminal electron acceptor

Phase 2a (8 decks)

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