Boyle-Vavra, S., Jones, M., Gourley, B. L., Holmes, M., Ruf, R., Balsam, A. R., Boulware, D. R., Kline, S., Jawahir, S., Devries, A., Peterson, S. N., Daum, R. S.
Comparative Genome Sequencing of an Isogenic Pair of USA800 Clinical MRSA Isolates Obtained Before and After Daptomycin Treatment Failure
Antimicrob Agents Chemother. 2011 Feb 22;
Here we describe a clinical daptomycin treatment failure in a patient with recurrent methicillin-resistant Staphylococcus aureus (MRSA) bacteremia in whom daptomycin was administered after a failed empiric treatment course with vancomycin and piperacillin/tazobactam. We had the opportunity to compare the genome sequences of an isogenic pair of daptomycin-susceptible and -resistant MRSA isolates obtained before and after initiation of daptomycin therapy, respectively. The genotype of both isolates was USA800, ST5, SCCmec type IV, agr type II. There was no increase in cell-wall thickness in the daptomycin-resistant strain despite having decreased susceptibility to both vancomycin and daptomycin. By comparing the genome sequences by pyrosequencing, we identified a polymorphism (S337L) in the 10th transmembrane segment of the multiple peptide resistance factor, MprF, encoding lysyl phosphatidylglycerol transferase. This enzyme has been shown previously to promote repulsion of daptomycin at the cell surface by addition of positively charged lysine to phosphatidyl glycerol. Also, the hlb ORF encoding the beta-toxin was interrupted by a prophage in the daptomycin-susceptible strain; this phage was missing in the daptomycin-resistant isolate and the hlb ORF was restored. Loss of the phage in the resistant isolate also resulted in loss of virulence factor genes, clpP, scn and sak. This is the first study to use pyrosequencing to compare the genomes of a daptomycin susceptible/resistant MRSA isolate pair obtained during failed daptomycin therapy in humans.