Antibiotic Resistance Flashcards
What is the ‘antibiotic era’?
Term used to describe the time since the widespread availability of antibiotics to treat infection
What is the ‘post-antibiotic era’?
Term used to describe the time after widespread antibiotic resistance has reduced the availability of antibiotics to treat infection
What does V/GRE stand for?
Vancomycin/glycopeptide-resistant enterococci
What does (ESBL) stand for?
Extended-spectrum β-lactamase-producing Enterobacteriaceae
Reasons for sensitivity testing
To enable transition from “empiric” to “targeted” antibiotic therapy
To explain treatment failures
To provide alternative antibiotics in case of treatment failure
or intolerance/adverse effects
To provide alternative oral antibiotics when IV therapy no longer required
What is the basic principles of sensitivity testing?
Culture of micro-organism in the presence of antimicrobial agent
Determine whether MIC is above a predetermined “breakpoint” level
When would you use a liquid media for a sensitivity test?
When you want an actual numerical measurement of the MIC
What are some limitations of sensitivity testing?
The infection may not be caused by the organism that has been tested.
The correlation between antimicrobial sensitivity and clinical response is not absolute.
Certain organisms are “clinically resistant” to antimicrobial agents even where in vitro testing indicates susceptibility
What are some mechanisms of resistance?
Absent target Decreased permeability Target modification Enzymatic degradation Drug efflux
Give examples of resistance by absent target
Antibacterial agents:fungi
Antibacterial agents:viruses
One explanation of treatment failure is the possibility that the infection is non-bacterial
Give examples of resistance by reduced permeability
Vancomycin: Gram-negative bacilli
(Gram-negatives have an outer membrane that is impermeable to vancomycin)
Gentamicin: anaerobic organisms
(Uptake of aminoglycosides requires an O2 dependent active transport mechanism)
Give some examples of resistance by target alteration
Flucloxacillin: MRSA
Vancomycin: VRE
Trimethoprim: Gram-negative bacilli
Give some examples of resistance by enzyme degradation
Penicillins and cephalosporins: β-lactamases (including ESBLs and NDM-1)
Gentamicin: aminoglycoside modifying enzymes
Chloramphenicol: chloramphenicol acetyltransferase (CAT)
Give some examples of resistance by drug efflux
Multiple antibiotics, specially in Gram-negative organisms1
Antifungal triazoles and Candida spp
How is resistance transferred?
plasmids:
horizontal transfer
vertical transfer
