Bacteria

Question 1

Type 3 secretion system example

Answer 1

Salmonella

Question 2

Type 3 secretion system components

Answer 2

Basal body (crosses bacteria membranes)

Needle (crosses space between bacterial cell and host membrane)

V-tip complex (crosses the host membrane)

Question 3

Translocation

Answer 3

substance (bacterial effectors) moved from bacterial cell to host cell

Question 4

Secretion

Answer 4

substance simply secreted from bacterial cell

Question 5

Salmonella enterica causes…

Answer 5

food poisoning (most commonly)

Question 6

Salmonella typhi causes…

Answer 6

typhoid fever

Question 7

Types of type 3 secretion in Salmonella

Answer 7

Two different pathogenicity islands

SPI-1 & SPI-2

Different niches, induced by different stimuli

SPI-1 invasion and establishment

SPI-2 after invasion for translocation of effector proteins fr survival and replication

Question 8

Which serotypes of Salmonella can only affect humans?

Answer 8

S. typhi

S. paratyphi

Question 9

Distinctive features in exclusively human-infective Salmonella

Answer 9

presence of a capsule 
presence of the typhoid toxin
more pseudogenes
longer incubation
tryptophan and cysteine auxotrophy

Question 10

Marker of host specific Salmonella serotypes

Answer 10

presence of high number of pseudogenes

Question 11

Type 3 secretion system pseudogenes in S.typhi

Answer 11

sopA, sopE2, sopD2, slrP

Question 12

How do type 3 secretion system pseudogenes in S.typhi restrict it to humans?

Answer 12

mouse macrophages can destroy vesicle with Rab32-BLOC-3 dependent antimicrobial pathway

Rab32 would have been blocked by functional versions (sopD2 and GtgE absent in S. typhi)

Question 13

Roles of membrane proteins in bacterial survival (basic)

Answer 13

Sensing 
Transport
Defence
Stress Response
Attachment
Infection

Question 14

Bacterial membrane sensing example

Answer 14

2 component systems
Sensor histidine kinase (HPK) & response regulator (RR)

HPK - senses change in environment - often external to cell/membrane
located

HPK autophosphorylated by ATP → HPK-P on conserved His

HPK-P phosphorylates RR → RR-P + HPK

RR-P binds to DNA or to protein and changes cell behaviour

Question 15

Bacteria membrane transport and defence example

Answer 15

CusCBA
CusCBA (effluxes copper accumulated in periplasm)

Adaptor protein-mediated metal-responsive dynamic assembly–disassembly
model of CusCBA complex.

Two transporters - one on each membrane

• stress = linking protein and transport
• no stress = un-linked no transport

Question 16

Bacteria membrane stress response example

Answer 16

CpxAR and sigmaE

Question 17

sigmaE response bacteria

Answer 17

Stress response

Activity of σE is negatively controlled by anti-sigma factor RseA (inner membrane protein)
- held by it and when it is cleaved -> response

Many stress conditions activate σE pathway – all proposed to lead to
accumulation of outer membrane proteins -> signal via DegS protease

Question 18

CpxAR response bacteria

Answer 18

two-component

Responds to envelope stress conditions - inner membrane protein

Eg alkaline pH, adhesion,
pathogenesis