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With rare exceptions, exposure of a microorganism to a drug promotes selection of genes that confer resistance to that drug. In a recent study involving daptomycin-susceptible and -resistant isolates from the blood of a patient with fatal bacteremia, researchers examined daptomycin resistance in Enterococcus faecalis. The blood samples were obtained before and after daptomycin treatment.
Comparative genomic sequencing and allelic replacement were performed on the isolate pair to define the genetic basis of resistance. In addition, the daptomycin-susceptible pretreatment isolate was exposed to increasing daptomycin concentrations in vitro to obtain a daptomycin-resistant derivative.
The researchers identified three mutations underlying the dev…