Genomic Insights into Isolates Exhibiting Diminished Daptomycin Susceptibility.

Daptomycin is one of the last therapeutic resources for multidrug-resistant gram-positive bacteria. Despite its structural similarities with glycopeptides, its mechanisms of action and resistance are different and in some respects are not completely understood. Mutations in several genes have been associated with daptomycin resistance, especially in , , and , but their role and importance remain to be elucidated. We have studied mutations in 11 genes, which have been previously associated with daptomycin non-susceptibility, in nine daptomycin-non-susceptible clinical isolates (daptomycin MIC: >1 mg/L). Susceptibility to daptomycin, vancomycin, linezolid, oxacillin, telavancin and dalbavancin was studied. , , , , , , , , and were amplified by PCR and sequenced. The sequences were compared with the ATCC 25923 complete genome (GenBank gi: 685631213) by using BLAST software. We did not find any changes in , , and . All isolates excepting isolate MSa5 showed a high number of significant mutations (between 13 and 25 amino acid changes) in . Most isolates also showed mutations in the genes, the genes and . Daptomycin non-susceptibility in clinical isolates seems to be reached through different mutation combinations when compared to ATCC 25293. Especially and showed very high polymorphism in most isolates. Meanwhile, one isolate, MSa5, showed only single mutation in (P314T).