2 Antibiotic resistance Flashcards
What is ESBL?
extended spectrum beta-lactamase-producing Enterobacteriacae
What is VRE/GRE?
Vancomycin/glycopeptide-resistant enterococci
Why do sensitivity testing?
Target therapy.
Explain Rx failures.
Provide alternatives.
Provide oral not IV.
How is sensitivity testing carried out?
Culture micro-organism in presence of differing strengths of agent and determine if MIC is above breakpoint level.
What is clinical resistance?
1 example.
Resistance genes are only expressed in vivo - so Rx is ineffective.
AmpC beta-lacatamase genes in enterobacteriacae.
What are the 6 mechanisms of antibiotic resistance?
No target. Reduced permeability. Altered target. Over-expression of target. Enzymatic degradation. Efflux pump.
Why do these combinations not work?
Vancomycin and g-ve bacilli.
Gentamicin and anaerobes.
Impermeable outer membrane.
Gentamicin requires O2 dependant active transport.
Why is MRSA resistant to flucloxacillin?
Altered penicillin binding protein won’t bind B lactams.
Which antibiotics do beta-lactamases degrade?
Penicillins and cephalosporins.
What is horizontal transfer?
Circular DNA sequences exchanged via plasmids by conjugation. Using transposons and integrons.
How do you avoid antibiotic resistance?
Never use unless necessary.
Use most narrow-spectrum available.
Use combination therapy if indicated.
Consult expert sources.
Why are VRE resistant to vancomycin?
Altered peptide sequence. D-ala D-lac.
Why are G-ves resistant to trimethoprim?
Dihydrofolate reductase gene (dhr) mutations.
Which enzyme enables bacterial resistance to gentamicin?
Aminoglycoside modifying enzymes.
Which enzyme enables bacterial resistance to chloramphenicol?
Chloramphenicol acetyltransferase.
