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Flashcards in Antibiotic Resistance Deck (16):

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?

horizontal transfer
vertical transfer


What are the consequences of antibiotic exposure?

Sensitive strains exposed to antibiotics at sub-lethal concentrations

Chance of survival will be enhanced by development of resistance

Resistant strain will out-compete sensitive strains
Resistance perpetuated by vertical transfer

Mixtures of sensitive and resistant strains (e.g. normal flora in hospitalised patients) exposed to antibiotics