Exposure to antibiotics in the environment encourages resistance as small numbers of ‘resistant mutants’ will survive whilst susceptible organisms die off
Particularly likely to happen in the gut of someone taking antibiotics or in bacteria in a hospital environment
How bacteria aquire resistance
The ability to become resistant to an antibiotic is the result of a change in the bacterial DNA
Can occur by 2 mechanisms:
Genetic mutation
Misreading of DNA
Bacteria reproduce rapidly - lots of scope for misreading
Transfer of bacterial DNA
Transformation:when bacteria die and the cells break apart, ‘free-floating’ DNA released into surrounding environment may be ‘scavenged’ by other bacteria and incorporated into DNA - the DNA may contain genes for antibiotic resistance
Conjugation: replication and transfer of plasmid DNA - plasmid DNA may contain genes for resistance
Transduction:bacterial DNA transferred from one bacterium to the other inside a virus that infects bacteria (bacteriophages)
Mechanisms of resistance
Altered binding site
A change in bacterial DNA can cause a change in the gene product which is the target of the antibiotic
Destruction of antibiotic
Bacteria may possess genes which code for enzymes that chemically degrade or inactivate the antibiotic
β -lactamases and cephalosporinases target and disrupt the β-lactam ring of the antibiotics
ESBLs: enzymes that inactive almost all penicillins and cephalosporins
Produced by some Gram-negative bacteria
Increased efflux
Efflux pumps actively export antibiotics out of the bacterial cell
Genetic change may increase the rate of efflux - antibiotic pumped back out of the cell before it has time to act
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