Date Published: November 6, 2009
Publisher: Public Library of Science
Author(s): Maria Miragaia, Herminia de Lencastre, Francoise Perdreau-Remington, Henry F. Chambers, Julie Higashi, Paul M. Sullam, Jessica Lin, Kester I. Wong, Katherine A. King, Michael Otto, George F. Sensabaugh, Binh An Diep, Frank R. DeLeo. http://doi.org/10.1371/journal.pone.0007722
Abstract: 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. Although ACME appears to have been transferred into USA300 from S. epidermidis, the genetic diversity of ACME in the latter species remains poorly characterized.
Partial Text: Staphylococcus epidermidis is a ubiquitous commensal of the human skin and mucosal surfaces and a major cause of indwelling medical device infections. This organism is notorious for its capacity to accumulate antibiotic resistance determinants and to produce biofilm, making infections caused by this opportunistic pathogen particularly difficult to treat. The large gene pool of antibiotic resistance and virulence determinants in S. epidermidis is shared with other more pathogenic species such as S. aureus. In particular, multidrug-resistant conjugative plasmids and staphylococcal chromosome cassette mec (SCCmec) elements conferring β-lactam resistance are transferred frequently between S. epidermidis and S. aureus, enabling rapid evolution and adaptation against antibiotic selection pressure , , .
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 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. Only one of these variants was represented by more than one isolate in the S. epidermidis population; this variant, ACME-I.02, contained both the arc and opp-3 gene clusters. All the other variants of ACME are likely to derive from the ancestral ACME-I.02 variant. ACME-I.02 was found in 21% (27/127) of the isolates recovered from seven countries. Importantly, a 24-kb DNA fragment of ACME-I.02 in five S. epidermidis isolates was virtually identical to a homologous contig of the ACME-I.01 variant found in USA300, suggesting the interspecies transfer of ACME from S. epidermidis into USA300. A similar observation was made for the interspecies transfer of SCCmec type IV from S. epidermidis strains to S. aureus, indicating that S. epidermidis provides a reservoir for genetic exchange with S. aureus.