antibiotic resistanc

Question 1

development of MRSA

Answer 1

pre-antibiotic days = poor prognosis for staph aureus -> penicillin discovered, effective treatment -> 70% staph acquire gene encoding b-latamase breaking down penicillin -> staph becomes resistant to streptomycin -> methicillin (lactamase resistant penicillin made -> staph becomes resistant to methicillin and gentamicin. Now can only use vacomycin.
organism almost untreatable

Question 2

mechanisms of resistance to an antibiotic

Answer 2

1 - mechanism aimed at antibiotic itself (eg enzyme degrade/modify drug
2- alter drug target (bacteria alters antibiotic’s target so that it can no longer bind)
3 - altered transport (eg bacteria develops efflux pumps to get rid of antibiotic or alters porins so cannot get in)

Question 3

how do antibiotics become resistant

Answer 3

1 - genetic mechanism (e.g. mutation, or acquired genes from other bacteria)
2 - non genetic (e.g. when bacteria not growing, inhibiting cell wall synthesis will not make a difference)
3 - natural resistance (eg membrane is resistant to the antibiotic entering)

Question 4

how may mutations come about in bacteria

Answer 4

1 - chromosome mediated

2 - plasmid mediated

Question 5

how may chromosomes mediate mutations in bacteria leading to antibiotic resistance

Answer 5

spontaneous mutation in bacterial genome e.g. mutation in PBP or in efflux pumps/porins. when using antibiotic we kill off non-mutated bacteria &select the drug resistant mutant.

Question 6

how may plasmids mediate mutations in bacteria leading to antibiotic resistance

Answer 6

obtaining genes from other bacterial plasmids. is common in gram -ve.

Question 7

how does using antibiotics select resistant bacteria

Answer 7

bacteria replicates and has some spontaneous mutations. by chance one of these mutations gives it resistance to an antibiotic. continues to grow normally, making up a small proportion of the bacterial pop. when we start antibiotics non mutated bacteria is killed off and resistant ones survive and continue to replicate so become dominant population

Question 8

how can bacteria transfer bacteria

Answer 8

1- transformation (bacteria ingest dna from environment left from dead bacteria and insert it into their dna)
2 - transduction (when bacteria is infected by a virus and virus takes up some bacterial dna. when it infects next bacteria it can pass on that dna)
3 - conjugation (bacteria transfer plasmids via their sex pilli)

Question 9

ways in which a bacterium may become resistant to b-lactam

Answer 9

contain b-lactamase
gram +ve bac often alter their PBP .’. cannot bind
gram -ve bac often alter their porins so antibiotic cannot pass through

Question 10

how have we responded to development of b-lactamase in bacteria

Answer 10

developed augmentin, which is a mix of clavulanic acid and amoxicillin. amoxicillin is the antibiotic and have b-lactam ring. clavulanic acid binds to and inhibits b-lactamase

Question 11

ways in which gram -ve bacteria can become resistant to penicillin

Answer 11

1 - mutation in the porin .’. antibiotic cannot pass through .’. can’t reach PBP
2 - mutation in PBP or acquires new PBP that the antibiotic cannot bind to .’. antibiotic does not work
3 - bacteria acquires b-lactamase .’. degrades antibiotic before it can inhibit the PBP

Question 12

how to prevent antibiotic resistant

Answer 12

• control use of antibiotics
• complete antibiotic course
• prescribe antibiotics properly
• combination therapy (so multiple drug target .’. likely to kill all bacteria)
• infection control