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MedST IB: Biology of Disease (BoD) > 4.0 Bacteriology > Flashcards

4.0 Bacteriology Flashcards

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1
Q

What four criteria are needed to identify the causative agent of a particular disease (Koch’s postulates)?

A
  1. Bacterium must be <b>present in every case</b> of the disease<br></br>2. Bacterium must be <b>isolated</b> from the disease and <b>grown</b> in pure culture<br></br>3. Bacterium from pure culture must <b>cause disease when inoculated into a healthy</b>, susceptible host<br></br>4. Bacterium must be <b>reisolated from the new host</b>
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2
Q

Define endemic:

A

Occurs regularly<br></br>At low or moderate levels

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3
Q

Define epidemic:

A

Sudden appearance of disease (or ↑ above endemic levels)

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4
Q

Define pandemic:

A

Global epidemic

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5
Q

Define point source outbreaks:

A

Bacterial infections arising from single origin

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6
Q

Define continuous source:

A

Point source outbreaks can be continuous outbreaks if source is not eradicated

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7
Q

Define propagated outbreaks:

A

Host-to-host transmission → even greater numbers of infections

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8
Q

Cell size range for bacteria:

A

0.5 - 3 um

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9
Q

Comment on the genome of bacteria:

A

Haploid<br></br>Single + circular<br></br>Plasmids<br></br>Bacteriophage

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10
Q

What colour are gram positive bacteria?

A

Violet/blue

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11
Q

What colour are gram negative bacteria?

A

Pink

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12
Q

What bacteria do not gram stain well?

A

1) Treponema<br></br>2) <b>Mycobacterium</b><br></br>3) <b>Mycoplasma</b><br></br>4) Leigonella pneumoniae<br></br>5) Rickettsia<br></br>6) <b>Chlamydia</b>

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13
Q

What is bacterial cell wall made up of?

A

<b>Peptidoglycan</b><br></br><br></br>Alternating NAG + NAM sugars with oligopeptide cross-links

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14
Q

Functions of bacterial cell membrane:

A

1) Osmotic barrier<br></br>2) Signal transduction<br></br>3) Nutrient transport<br></br>4) Respiration

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15
Q

Differences between Gram +ve and Gram -ve cell envelope:

A

<b>Gram +ve</b><br></br>Thicker cell wall<br></br><br></br><b>Gram -ve</b><br></br>Thinner cell wall<br></br>Periplasm<br></br>Outer membrane (with porins and LPS)

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16
Q

What enzymes are found in the gram -ve periplasm?

A

Hydrolytic enzymes:<br></br>1) Proteases<br></br>2) Lipases<br></br>3) Phosphatases<br></br>4) <b>β lactamases</b>

17
Q

What does the Gram -ve outer membrane?

A

<b>1) Porins</b><br></br><b>2) Lipopolysaccarhide (LPS)</b><br></br>- O-antigen (v. variable)<br></br>- Lipid A = endotoxin → TNF and IL-1

18
Q

What is the bacterial capsule made out of?<br></br><br></br>Role of bacterial capsule?

A

Polysaccharides<br></br><br></br>Prevents drying out and provides protection

19
Q

How are proteins secreted across the cell membrane (inner membrane)?

A

Use N-terminal secretion signal + Sec pathway

20
Q

Complete the blanks:<br></br><br></br>Bacteria use _____ for mobility. Receptors on the bacterial nose sense chemicals and move towards ______ and away from _________.<br></br><br></br>__________ rotation of the _______ causes _________ movement. __________ rotation of the _______ causes ___________________

A

Bacteria use flagella for mobility. Receptors on the bacterial nose sense chemicals and move towards nutrients and away from toxic chemicals.<br></br><br></br>Counter-clockwise (CCW) rotation of the falgella causes forward movement. Clockwise (CW) rotation of the flagella causes tumbling + changing of direction

21
Q

What is the signal transduction pathway used by bacteria to sense the environment?

A

<b>Histidine-aspartate phosphorelay (HAP)</b>

22
Q

What is <b>Quorom Sensing?</b>

A

Sensing cell density<br></br>Some pathogens switch on their virulence only when cell population is high<br></br>Bacteria recognise a ‘quorum’ by secreting small signal molecules and sensing its concentration (communication)

23
Q

Define transposons:

A

Segment of DNA containing useful genes that benefit bacteria

24
Q

Define plasmids:

A

Extra-chromosomal genetic elements<br></br><br></br>(may contain transposons)

25
Q

Define pathogenicity islands:

A

Genes required for survival and virulence are usually in pathogenicity islands (higher G+C content)

26
Q

What are 3 techniques by which bacteria can acquire and transfer DNA?

A

<b>1) Transduction</b><br></br>- From bacteriophage (bacterial virus)<br></br><br></br><b>2) Transformation</b><br></br>- Uptake from dead (lysed) bacteria<br></br><br></br><b>3) Conjugation</b><br></br>- Direct transfer between 2 bacteria

27
Q

Direct vs indirect damage:

A

Direct damage = caused by toxins/bacterial invasion<br></br><br></br>Indirect damage = caused by host response

28
Q

What do UPEC use to bind to bladder receptors?

A

Common (type I) pili

29
Q

What do UPEC use to bind to kidney receptors?

A

Pap (p-pilli)

30
Q

Why are UTIs from UPEC recurrent?

A

Acute infection → superficial bladder cells exfoliate → allows UPEC to invade underlying epithelial cells where they can persist in a quiescent reservoir + are protected from Abs → resurge and cause recurrence

31
Q

What is the nature of cell adhesion in EPEC and EHEC?

A

Tighter than for UPEC<br></br><br></br>EPEC and EHEC inject <b>Tir</b> into host cell<br></br><br></br><b>Intimin</b> on bacteria binds to Tir → <b>polymerisation of actin</b>

32
Q

Give some examples of bacteria that cause biofilms:

A

<b>1) Strep. mutans</b> - caries<br></br><b>2) Staphyloccoci</b><br></br><b>3) Psedomonas aeruginosa</b> - opportunistic (burns, wounds, cystic fibrosis)

33
Q

What are the two methods of cellular invasion?

A

<b>1) Zipper mechanism</b><br></br>- Receptor mediated endocytosis<br></br>- <b>Invasins</b> mimic normal ligands (e.g. fibronectin) → endocytosis<br></br><br></br>Example = Listeria<br></br><br></br><b>2) Trigger mechanism</b><br></br>- Injected effector proteins (mimic SipA, SipC + SptP) → cytoskeleton rearrangements → internalisation<br></br><br></br>Example = Salmonella

34
Q

Example of bacteria that escapes the entry vacuole to move and replicate in cytosol:

A

Listeria

35
Q

Example of bacteria that stay and replicate in entry vacuoles:

A

Salmonella

36
Q

What is the mechanism of entry and replication by Chalmydia?

A

<b>1) Enters as elimentary body (EB) form</b><br></br>- Injects protein Tarp to do this<br></br><br></br><b>2) EB is taken up into endosome</b><br></br><br></br><b>3) In endosome EB → RB (reticulate body)</b><br></br><br></br><b>4) RB replicates → ↑ RB + ↑ EB</b><br></br><br></br><b>5) Cell lyses and releases EB → infect new cells</b>

MedST IB: Biology of Disease (BoD) (9 decks)

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