Strugnelltown

Question 1

Horizontal gene transfer

Answer 1

Ability of bacterium to respond to new selective pressures, to survive adverse environmental conditions, or to exploit new environments from modification of gene function or acquisition of new genes

Question 2

Phase variation

Answer 2

Changes in expression of important virulence proteins that occur at relatively high frequency compared to spontaneous mutations

Question 3

Internal DNA recombination

Answer 3

E.g. Neisseria pili
pilE has a promoter
pilS lacks promoter
pilE and pilS recombine which results in new version of pilE gene, new pilin protein produced not recognised by existing antibodies

Question 4

Transformation

Answer 4

DNA from donor cell released into environment and taken up by recipient cell

Question 5

Competent bacteria e.g.

Answer 5

S. pneumoniae

Question 6

DNA uptake sequences (DUS)

Answer 6

Recognition sites for binding and uptake of DNA into cell - bacteria only take up own DNA with DUS sequence

Question 7

Conjugation

Answer 7

Transfer of DNA directly from one cell to another by mating bridge

Question 8

Transduction

Answer 8

DNA transferred by virus - phage take up chromosomal DNA accidentally and inject into a new cell–> recombination

Question 9

Koch’s postulates and problems (4)

Answer 9

1. microbe must be associated with symptoms of disease and be present at site of infection. PROBLEM: asymptomatic, affect different areas
2. Microbe must be isolated from lesions of disease and grown as pure culture. PROBLEM: Can’t always get pure culture
3. Pure culture, when inoculated into host, must reproduce same disease. PROBLEM: not all good animal models
4. Microbe must be reisolated in pure culture from experimentally infected host

Question 10

Virulence measured by:

Answer 10

Lethal Dose

Infectious Dose

Question 11

Competition Assay

Answer 11

Selects for more virulent of 2 strains: the more important the gene that has been mutated, the stronger the selection

Question 12

Signature tagged mutagenesis

Answer 12

Determines which genes in a pathogen are involved in virulence
Mutant missing transposon must have hit key virulence gene

Question 13

T/F: Acquisition of genes horizontally can give rise to major shifts in virulence, if the genes encode for a toxin

Answer 13

TRUE: bacterium may acquire one gene or several and become a pathogen

Question 14

T/F: In bacterial pathogenesis, bacterium is much more important than host in determining outcome of host-bacterium interaction

Answer 14

FALSE: dependent on both bacterial and host factors

Question 15

T/F In transposon mutagenesis, it is possible to inactivate all genes within a bacterium through transposon insertional

Answer 15

FALSE: Insertion of transposon into some genes will make bacterium non-viable

Question 16

T/F: Measuring virulence of human pathogens is straightforward

Answer 16

FALSE

Question 17

In molecular Koch’s postulates, to test the impact of a mutation you usually need 2 groups - WT and mutant

Answer 17

FALSE: According to molecular Koch’s postulates, ideal is to exam WT, mutant and mutant which carries functional version of gene specifically mutated

Question 18

Etiology:

Answer 18

It is necessary to culture the bacterium to fulfill Koch’s postualtes

Question 19

Animal models

Answer 19

Same correlates of protection should be used in humans and in animal model, if the model is being used to model human disease

Question 20

Pathogenicity islands:

Answer 20

contain different GC% from rest of chromosome

Question 21

Slipped-strand synthesis/misrepair

Answer 21

Frameshift during DNA replication in regions of highly repetitive sequence e.g. N.gonorrhoeae

Question 22

Antigenic variation

Answer 22

Ability of some bacteria to change aa composition of their adhesins or other surface proteins to avoid host immune system by gene shuffling e.g. N.gonorrhoeae pili: recombination pilS and pilE

Question 23

DtxR: toxin repressor

Answer 23

Diptheria toxin not required ex vivo
Iron is limiting in host (Transferrins)
Low iron causes disassembly of DtxR dimer and toxin is produced
DtxR/Fe2+ binds to -10 of promoter, blocking RNA polymerase

Question 24

Two component system

Answer 24

Common in GN
Sensor kinase in membrane
Regulator in cytoplasm
Cue sensed in periplasm –> S dimerises –> kinase autophosphorylates histidine residue
Transferred to aspartic acid on regulator, which activates R as a transcription factor e.g. Bvg of bordatella pertussis

Question 25

Quorum sensing

Answer 25

Autoinducers - positive feedback e.g. LuxI

Question 26

T/F: Transcriptional regulation is an inefficient means of a bacterium manipulating its environmental response

Answer 26

FALSE