4.0 Bacteriology

Question 1

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

Answer 1

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>

Question 2

Define endemic:

Answer 2

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

Question 3

Define epidemic:

Answer 3

Sudden appearance of disease (or ↑ above endemic levels)

Question 4

Define pandemic:

Answer 4

Global epidemic

Question 5

Define point source outbreaks:

Answer 5

Bacterial infections arising from single origin

Question 6

Define continuous source:

Answer 6

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

Question 7

Define propagated outbreaks:

Answer 7

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

Question 8

Cell size range for bacteria:

Answer 8

0.5 - 3 um

Question 9

Comment on the genome of bacteria:

Answer 9

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

Question 10

What colour are gram positive bacteria?

Answer 10

Violet/blue

Question 11

What colour are gram negative bacteria?

Answer 11

Pink

Question 12

What bacteria do not gram stain well?

Answer 12

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>

Question 13

What is bacterial cell wall made up of?

Answer 13

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

Question 14

Functions of bacterial cell membrane:

Answer 14

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

Question 15

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

Answer 15

<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)

Question 16

What enzymes are found in the gram -ve periplasm?

Answer 16

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

Question 17

What does the Gram -ve outer membrane?

Answer 17

<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

Question 18

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

Answer 18

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

Question 19

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

Answer 19

Use N-terminal secretion signal + Sec pathway

Question 20

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 ___________________

Answer 20

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

Question 21

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

Answer 21

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

Question 22

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

Answer 22

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)

Question 23

Define transposons:

Answer 23

Segment of DNA containing useful genes that benefit bacteria

Question 24

Define plasmids:

Answer 24

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

Question 25

Define pathogenicity islands:

Answer 25

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

Question 26

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

Answer 26

1) Transduction
- From bacteriophage (bacterial virus)

2) Transformation
- Uptake from dead (lysed) bacteria

3) Conjugation
- Direct transfer between 2 bacteria

Question 27

Direct vs indirect damage:

Answer 27

Direct damage = caused by toxins/bacterial invasion

Indirect damage = caused by host response

Question 28

What do UPEC use to bind to bladder receptors?

Answer 28

Common (type I) pili

Question 29

What do UPEC use to bind to kidney receptors?

Answer 29

Pap (p-pilli)

Question 30

Why are UTIs from UPEC recurrent?

Answer 30

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

Question 31

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

Answer 31

Tighter than for UPEC

EPEC and EHEC inject Tir into host cell

Intimin on bacteria binds to Tir → polymerisation of actin

Question 32

Give some examples of bacteria that cause biofilms:

Answer 32

1) Strep. mutans - caries
2) Staphyloccoci
3) Psedomonas aeruginosa - opportunistic (burns, wounds, cystic fibrosis)

Question 33

What are the two methods of cellular invasion?

Answer 33

1) Zipper mechanism
- Receptor mediated endocytosis
- Invasins mimic normal ligands (e.g. fibronectin) → endocytosis

Example = Listeria

2) Trigger mechanism
- Injected effector proteins (mimic SipA, SipC + SptP) → cytoskeleton rearrangements → internalisation

Example = Salmonella

Question 34

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

Answer 34

Listeria

Question 35

Example of bacteria that stay and replicate in entry vacuoles:

Answer 35

Salmonella

Question 36

What is the mechanism of entry and replication by Chalmydia?

Answer 36

1) Enters as elimentary body (EB) form
- Injects protein Tarp to do this

2) EB is taken up into endosome

3) In endosome EB → RB (reticulate body)

4) RB replicates → ↑ RB + ↑ EB

5) Cell lyses and releases EB → infect new cells