Explain the mechanisms by which a bacterium may become resistant to an antimicrobial agent and provide an example (organism and antimicrobial) of each mechanism. (60% of marks)

How is antimicrobial resistance spread? (40% of marks)

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College Answer

Candidates were expected to explain and provide an example of an antimicrobial agent for
mechanisms such as enzyme inactivation of the antimicrobial, alteration of antimicrobial
binding/target sites, reduction of antimicrobial drug uptake or active efflux of drug by the
bacteria and alteration in enzymatic pathways. Use of a table aided candidates expressing this
information. Examples of the methods of spread of antibiotic resistance in bacteria that were
expected were: transfer of resistant bacteria from person to person; horizontal gene transfer;
transduction - acquisition of bacterial DNA from a phage (a virus that propagates in bacteria);
transformation - uptake and incorporation of free DNA released into the environment by
other bacterial cells; conjugation - gene transfer (usually on plasmids), by direct cell-to-cell
contact through a bridge.
Most candidates could name various mechanisms of resistance but many failed to gain marks
as they did not provide an example of an organism and antimicrobial. The second part of the
question concerning the spread of resistance was generally done quite well.
Syllabus - M2a2c
Reference: Pharmacology, Rang and Dale Ch 46, Goodman & Gillman, Ch42