A D-test is set up on a S.aureus isolate.There was no zone around the Erythromycin disk and the zone of inhibition around the clindamycin disk adjacent to the erythromycin disk was interpreted as susceptible.Thus,the resistance mechanism for the erythromycin is due to:
A)altered target.
B)increased efflux.
C)decreased porin channels.
D)degradative enzymes.

Question

Quizplus · Accepted Answer

This describes a negative D zone test.Thus,the erythromycin-R is due to msrA gene,which results in increased efflux of erythromycin from the bacterial cell and does not induce clindamycin (macrolide-lincosamide-streptogramin B)resistance mediated by products of the erm genes (i.e. ,erthryomycin ribosomal methylase)which alters the MLS antibiotic target.

A D-Test Is Set Up on a S