Genotypic and phenotypic differences between nosocomial and commensal Staphylococcus epidermidis isolates from northern Portugal

Abstract

Staphylococcus epidermidis is a common causative agent of relapsing and persistent hospital-acquired infections, not only because this bacterium belongs to the patients’ microbiota(causing autoinfection) but also because it is easily transmitted by healthcare workers (causing cross-infections). The goal of the present study was to characterize, for the first time, the biofilm-forming ability and virulence associated traits of several S. epidermidis strains circulating in a Portuguese hospital, as well as in the Portuguese community (northern region). To achieve that, bacteria were isolated from October 2011 to January 2013 and identified by biochemical tests and rpoB sequencing. Confirmed S. epidermidis strains were then tested for biofilm formation, antimicrobial resistance and carriage of biofilm-associated genes. The majority of clinical and skin isolates were resistant to erythromycin followed by penicillin. Regarding the presence of virulence-associated genes there was an equal distribution between the clinical and commensal isolates. The aap gene was the most prevalent (48% and 50%, respectively) followed by ica operon (37% and 33%, respectively) and bhp gene (15% and 17%, respectively). These results are in agreement with the ones obtained for the biofilm formation. Our results highlight slight differences between isolates obtained from the hospital setting and those obtained from the community. The emergence of antibiotic resistance and the frequent presence of virulence-associated genes among commensal Portuguese strains, reported in this study, raises serious clinical implications and should be considered to re-evaluate preventive measures against nosocomial infections.