Nosocomial infections by Staphylococcus epidermidis: how a commensal bacterium turns into a pathogen.

Staphylococcus epidermidis is a commensal bacterium of the human skin. However, S. epidermidis and other coagulase-negative staphylococci (CNS) emerge also as common nosocomial pathogens infecting immunocompromized patients carrying medical devices. Antibiotic resistance and the ability of many nosocomial S. epidermidis isolates to form biofilms on inert surfaces make these infections hard to treat. Epidemiological analyses using multilocus sequence typing (MLST) and genetic studies suggest that S. epidermidis isolates in the hospital environment differ from those obtained outside of medical facilities with respect to biofilm formation, antibiotic resistance, and the presence of mobile DNA elements. Since S. epidermidis isolates exhibit high genome flexibility, they are now regarded as reservoirs for the evolution and spread of resistance traits within nosocomial bacterial communities.