Discrimination between contaminating and commensal strains of Staphylococcus epidermidis (Search for phenotypic virulence criteria in Staphylococcus epidermidis)

Staphylococcus epidermidis strains are diverse in their pathogenicity. Some are invasive virulent strains causing serious nosocomial infections; some are skin commensals with a low virulence. The discrimination of them is of great clinical significance. To analyze the implication of different factors in virulence, phenotypical methods were applied. Comparative assessment of the enzymatic activity of nosocomial and commensal strains of S. epidermidis was performed: alkaline phosphatase (PHA), beta-glucosidase (LAC ), arginine dehydrolase (ARG), urease (URE), maltosidase (PAM), N-acetylglutamic acid hydrolase (FPY), N-acetylglucosaminehydrolase (FGA ) were studied. Differences were found in the urease activity, i.e. 93% and 77% of commensal and nosocomial strains, respectively, were positive.In sheep blood agar, the difference was more significant - only 16.7% of commensal strains demonstrated the haemolytic activity, but 52.4% of nosocomial strains occurred to be haemolytic.