Abstract
BackgroundThe methicillin-resistant Staphylococcus aureus clone USA300 contains a novel mobile genetic element, arginine catabolic mobile element (ACME), that contributes to its enhanced capacity to grow and survive within the host. Although ACME appears to have been transferred into USA300 from S. epidermidis, the genetic diversity of ACME in the latter species remains poorly characterized.Methodology/Principal FindingsTo assess the prevalence and genetic diversity of ACME, 127 geographically diverse S. epidermidis isolates representing 86 different multilocus sequence types (STs) were characterized. ACME was found in 51% (65/127) of S. epidermidis isolates. The vast majority (57/65) of ACME-containing isolates belonged to the predominant S. epidermidis clonal complex CC2. ACME was often found in association with different allotypes of staphylococcal chromosome cassette mec (SCCmec) which also encodes the recombinase function that facilities mobilization ACME from the S. epidermidis chromosome. Restriction fragment length polymorphism, PCR scanning and DNA sequencing allowed for identification of 39 distinct ACME genetic variants that differ from one another in gene content, thereby revealing a hitherto uncharacterized genetic diversity within ACME. All but one ACME variants were represented by a single S. epidermidis isolate; the singular variant, termed ACME-I.02, was found in 27 isolates, all of which belonged to the CC2 lineage. An evolutionary model constructed based on the eBURST algorithm revealed that ACME-I.02 was acquired at least on 15 different occasions by strains belonging to the CC2 lineage.Conclusions/SignificanceACME-I.02 in diverse S. epidermidis isolates were nearly identical in sequence to the prototypical ACME found in USA300 MRSA clone, providing further evidence for the interspecies transfer of ACME from S. epidermidis into USA300.
Highlights
Staphylococcus epidermidis is a ubiquitous commensal of the human skin and mucosal surfaces and a major cause of indwelling medical device infections
In the present study we found that 52% (65/127) of S. epidermidis isolates representing the broad genetic and geographic diversity of the species contained one of three arginine catabolic mobile element (ACME) allotypes
There were extensive genetic diversity found in ACME islands of S. epidermidis, with 39 distinct variants identified by a PCR-based scanning method
Summary
Staphylococcus epidermidis is a ubiquitous commensal of the human skin and mucosal surfaces and a major cause of indwelling medical device infections. Many S. epidermidis strains carry the arginine catabolic mobile element (ACME), a novel genomic island that may contribute to enhanced capacity of this species to colonize the human skin and mucosal surfaces [4]. Mobilization of ACME is believed to be mediated by the cassette chromosome recombinases (ccrAB) encoded by SCC element [5,6] This element has been found in diverse S. aureus genetic backgrounds, suggesting frequent horizontal dissemination [4,5,6,7]. The methicillin-resistant Staphylococcus aureus clone USA300 contains a novel mobile genetic element, arginine catabolic mobile element (ACME), that contributes to its enhanced capacity to grow and survive within the host. ACME appears to have been transferred into USA300 from S. epidermidis, the genetic diversity of ACME in the latter species remains poorly characterized
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