Clonal Analysis of Staphylococcus epidermidis Isolates Carrying or Lacking Biofilm-Mediating Genes by Multilocus Sequence Typing

Abstract

Staphylococcus epidermidis is part of the normal microflora of the human skin but is also a leading cause of device-associated infections in critically ill patients. Commensal and clinical S. epidermidis isolates differ in their ability to form biofilms on medical devices; the synthesis of biofilms is mediated by the icaADBC operon. Currently, the epidemiological relatedness between ica-positive and -negative isolates is not known; neither is it known whether the ica genes can spread to biofilm-negative strains through horizontal gene transfer. In this study, multilocus sequence typing (MLST) was employed for the clonal analysis of 118 S. epidermidis icapositive and -negative strains. MLST revealed that the majority of ica-positive and -negative strains were closely related and formed a single clonal complex. Within this complex one sequence type (ST27) was identified which contained exclusively ica-positive isolates and represented the majority of clinical strains tested. ST27 and related ica-positive clones carried different SCCmec cassettes (conferring methicillin resistance) and the insertion sequence IS256. The findings suggest that the S. epidermidis infections analyzed in this report are mainly caused by a single clone (ST27) which occurs preferentially in hospitals and differs from clones in the community. It is hypothesized that the successful establishment of ST27 within nosocomial environments has been facilitated by the presence of genes encoding biofilm and resistance traits.Staphylococcus epidermidis is a bacterium that constitutes a major component of the normal skin and mucosal microfloras of humans. It is a leading cause of hospital-acquired infections, mostly associated with the use of medical devices in seriously ill or immunocompromised patients. Staphylococcus epidermidis pathogenesis relies on the ability of the bacteria to form thick multilayered biofilms on a wide variety of polymer and metal surfaces (12). In general, biofilms consist of bacteria embedded into a polysaccharide matrix which protects bacteria against hostile environments, including antibiotics and the action of the host immune system, and therefore are an important factor in the development of chronic and recurrent infections (13,30). Although the production of staphylococcal biofilm is dependent upon multiple regulatory proteins, an essential factor is the presence and expression of the four-gene icaADBC operon (15). The operon encodes enzymes necessary for production of polysaccharide intercellular adhesin (PIA), which is required for biofilm formation and is involved in hemagglutination and bacterial aggregation (7,19,20). In animal models, PIA-negative mutants were significantly less likely to cause catheter-associated infections than their PIA-positive isogenic counterparts (27). Epidemiological studies have clearly shown that the majority of commensal Staphylococcus epidermidis isolates lack the ica operon, whereas clinical strains obtained from device-associated infections harbor the genetic information for biofilm ...

Staphylococcal Biofilms

“…Strains with IS256 integrated into ica and agr genes have been isolated from infection (Kozitskaya et al 2004;Vuong et al 2004b). In addition, the presence of IS256 appears to be correlated with the invasiveness of S. epidermidis strains (Gu et al 2005;Kozitskaya et al 2005). However, although IS256 might have a genuine role in the adaptation of the bacterial population to a different ecological niche, and thus to bacterial versatility, one can probably not call it a true regulator.…”

<I>Staphylococcus epidermidis</I> device-related infections: pathogenesis and clinical management

“…S. epidermidis possesses superb recombination potential and the ability to transfer genetic material, resulting in the spread and evolution of resistance traits within nosocomial bacterial communities (Ziebuhr et al 2006). The evolving nature of S. epidermidis and its adaptation to the dynamic nosocomial environment has recently been highlighted by Kozitskaya et al (2005) who reported that S. epidermidis infections were mainly caused by a single intercellular adhesin (ica)-positive clone of S. epidermidis (Sequence type 27) whose presence was widespread within hospital settings in Germany. The ST27 clone was rarely found outside medical facilities and differed from commensal strains in the community and it was hypothesised that the successful establishment of ST27 within nosocomial environments was facilitated by the presence of genes encoding biofilms and resistance traits.…”

Genetic determinants and biofilm formation of clinicalStaphylococcus epidermidisisolates from blood cultures and indwelling devises

“…Kozitskaya et al [27] sequenced S. epidermidis isolates which were collected from German, Irish, Norwegian, and North American population. ST27 was the dominant sequence type they identifi ed, followed by ST2 and sporadically ST5.…”

“…SCCmec types I to IV were determined by a multiplex PCR with specifi c primers and subseque nt visualization of the amplifi ed DNA fragment patterns by agarose gel electrophoresis as described by Oliveira et al [26] and Kozitskaya et al [27].…”