Antimicrobial Resistance Flashcards
How does bacterial resistance occur?
natural phenomenon
bacteria adapt to survive
bacteria rapidly multiple, mutate, and can generate resistance very quickly
Main mechanisms of antimicrobial resistance?
enzymatic inactivation of drug
modified targets for drugs - drug cant bind a effectively useless
reduced permeability to drug
efflux of drug
intrinsic resistance?
natural phenomenon
lactobacillus intrinsically to lactomycin
e.g. the bacteria has natural efflux pumps and this can be predicted by a microbiologist
cant do anything about intrinsic resistance
acquired resistance?
WT organism is susceptible to the drug but can acquire mobile genetic elements or genes
often transferred on plasmids and can jump between different bacteria
major cause for concern
e.g. fully susceptible e.coli and can acquire a plasmid with various resistance genes and become resistant
chromosomally mediated resistance?
more intrinsic or less likely to be transmitted between different organism
- Mutation in gene coding for drug target or membrane transport system.
- Frequency of spontaneous mutations 10-7 to 10-9
- Much lower than frequency of acquisition of plasmids.
- Less of a problem clinically.
- Basis for using multi-drug therapy eg TB.
plasmid mediated resistance?
mobile genetic elements and can carry genetic (resistance genes) between different bacteria
this is what microbiologist are trying to combat
- Plasmids are extra-chromosomal strands of DNA.
- Replicate independent of cell chromosome.
- May carry genes for enzymes which degrade antibiotics and modify
membrane transport systems. - May carry one or more resistance genes.
- Some plasmids have ability to conjugate
- Therefore they can transfer resistance genes to other species of bacteria
resistance vs failure therapy?
- Resistance = inabilitiy of antibiotic to kill/inhibit bacterial growth.
- Resistance can be detected in the lab by measuring MIC levels (Minimum
Inhibitory Concentration). - Clinical failure may occur despite lab reports of sensitivity. Why? Think of
the underlying infection and source control.
reasons for failure of therapy?
- Inadequate dose of antibiotic.
- Inappropriate route.
- Non-compliance with antibiotic.
- Bacteria walled off in abscess cavity.
- Foreign bodies e.g. surgical implants/prosthesis.
- Poor penetration of drug to site of infection.
- Lack of source control e.g. intestinal perforation.
conjugation?
transfer of plasmids between different bacteria
MIC aka?
minimum inhibitory concentration
