Whole genome characterization of the mechanisms of daptomycin resistance in clinical and laboratory derived isolates of Staphylococcus aureus.

Anton Y Peleg,Ashlee M Earl,Aileen Rubio,David R Cameron,Spiros Miyakis,Doyle V Ward,George M Eliopoulos,Robert C Moellering,Satish Pillai,Niyaz Ahmed

doi:10.1371/journal.pone.0028316

Abstract

BackgroundDaptomycin remains one of our last-line anti-staphylococcal agents. This study aims to characterize the genetic evolution to daptomycin resistance in S. aureus.MethodsWhole genome sequencing was performed on a unique collection of isogenic, clinical (21 strains) and laboratory (12 strains) derived strains that had been exposed to daptomycin and developed daptomycin-nonsusceptibility. Electron microscopy (EM) and lipid membrane studies were performed on selected isolates.ResultsOn average, six coding region mutations were observed across the genome in the clinical daptomycin exposed strains, whereas only two mutations on average were seen in the laboratory exposed pairs. All daptomycin-nonsusceptible strains had a mutation in a phospholipid biosynthesis gene. This included mutations in the previously described mprF gene, but also in other phospholipid biosynthesis genes, including cardiolipin synthase (cls2) and CDP-diacylglycerol-glycerol-3-phosphate 3-phosphatidyltransferase (pgsA). EM and lipid membrane composition analyses on two clinical pairs showed that the daptomycin-nonsusceptible strains had a thicker cell wall and an increase in membrane lysyl-phosphatidylglycerol.ConclusionPoint mutations in genes coding for membrane phospholipids are associated with the development of reduced susceptibility to daptomycin in S. aureus. Mutations in cls2 and pgsA appear to be new genetic mechanisms affecting daptomycin susceptibility in S. aureus.

Highlights

Staphylococcus aureus is one of the most significant human bacterial pathogens, causing immense morbidity and mortality in hospitalised patients, as well as in the community
The increase in MIC to daptomycin for the laboratory exposed strains was equivalent to that seen for the clinical isolates, with no differences observed between agr+ S. aureus (A8115) and its isogenic agr2 (A8117) mutant strain (Table 2)
We have performed whole genome sequencing of the largest collection of daptomycin exposed S. aureus strains to date

Summary

Introduction

Staphylococcus aureus is one of the most significant human bacterial pathogens, causing immense morbidity and mortality in hospitalised patients, as well as in the community. It causes a diverse range of clinical disease, with mortality from infection reported as high as 35% [1]. Compounding this severity of disease is the constant adaptation of the bacteria to antibiotic pressure, with the emergence of resistance in S. aureus being one of the most important public health problems in the developed world. This study aims to characterize the genetic evolution to daptomycin resistance in S. aureus

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