Reveral of resistance

Question 1

Mutations will have a negative effect on the fitness of bacteria because:

Answer 1

• Impaired functioning upon change of essential target

- Increased energy costs upon (over) expression of resistance genes

Question 2

Bacterial resistance mechanisms and reduced fitness

Answer 2

• Overproduction target&raquo_space; Lesser energy
• Target modification&raquo_space; Ribosome works lesser optimal
• Enzymatic inactivation or modification&raquo_space; cause energy
• Decreased penetration&raquo_space; More difficult to get nutrition
• Increased efflux&raquo_space; Efflux of important compounds
• Bypass pathways

Question 3

Reversal of resistance

Answer 3

What they early thought : Antibiotic resistance results in reduced fitness > When selection stopped > Non pathogenic revertant will emerge and back sensitive
But WRONG

Question 4

Two experiments to look if reversal of resistance takes place

Answer 4

I : Samples persons H. pylori infection > Treated with macrolide > Determine resistance clarithromycines (=macrolide)
» 3 years later still these macrolide resistant aanwezig

II : Gave trimethoprim > What happened with resistant bacteria ? > No real change in trimethoprim resistance E.coli strains in two years

Question 5

Why no reverse resistance?

5 reasons

Answer 5

1. Relative fitness: Only relative fitness against wild type is important.
2. Co-resistance: Resistance to more antibiotics. One plasmid carries genes to different antibiotics.» This is important for survival of plasmid.
3. Adapt regulation:
4. Compensatory mutations : Secondary mutations makes resistance bacteria more fit.
   Same MIC > So same resistance
5. No cost mutations: Resistant mutant, with no fitness costs.

Question 6

Test relative fitness (in vitro and in vivo)

Answer 6

In vitro mix wild type and resistance one
» Resistance strains grow slower than susceptible, but in competition they survive

In vivo: Mix wild type and resistance bacteria&raquo_space; inject in mouse, in healthy mouse wild types more fit.

Question 7

Example of adapt regulation:

AmpC and VanA

Answer 7

• Introduction of AmpC in Salmonella enterica (from enterobactericea)&raquo_space; Sense problems peptidoglycan > To inner membrane > Produce AmpC.
  AmpC is in tight regulation to avoid fitness costs.
• VanA from enterococci to S. Aureus (here tightly regulated)
  Without VanA grow realy fast
  With VanA grow slower.
  &laquo_space;When needed transcripted.

Question 8

Compensatory mutations

Inner/ outer

Answer 8

• Intragenic (in same gene)

- Exogenic (in another gene)

Question 9

Example tuberculosis

Compensatory mutation

Answer 9

Tuberculosis: Exogenic
- Resistant strains against isonaizid: Have KatG null mutation. But normal function of KatG = degradation hydrogenperoxide &laquo_space;Can’t do this after mutation.

Compensatory exogenic mutation:
» Upregulation aphC > More black > Resistance isolates have low levels and some have high amount of aphC and can protect against oxygen radicals.

Question 10

KatG315 mutation

Answer 10

No cost mutation
Thr315 bigger than SER315 > So isoniazid can’t bind anymore.
But KatS315 is as good as wild type of KatG, so also can degrade hydrogenperoxide.

Question 11

Antibiotic resistance isolates in patients rather than in vitro strains.

Answer 11

Those are directly subjected to selection and therefore often have only minimal fitness effects.
- In clinical isolates see no cost mutations or compensatory mutations.

Question 12

Resistance genes spread

Answer 12

• Via transfer

- Via clonal spread