Coagulase-negative staphylococci. Pathogens have major role in nosocomial infections.

Coagulase-negative staphylococci live naturally on the skin and mucous membranes of humans and are therefore often found in clinical specimens. Distinguishing clinically significant, pathogenic strains from contaminant strains is one of the major challenges facing clinical microbiology laboratories. S epidermidis and other novobiocin-susceptible coagulase-negative staphylococci have emerged as a major cause of nosocomial infections, particularly of nosocomial bacteremia in immunocompromised patients. S epidermidis also is common in injecting drug users, who are particularly susceptible to right-sided endocarditis, and--most important--in patients with such indwelling foreign bodies as intravenous catheters. Depending on the kind of device and its insertion site, different infection syndromes generate a variety of clinical presentations. In these patients, the host defense mechanisms often seem unable to handle the infection and, in particular, to eliminate the staphylococci from the infected device because of a biofilm on the foreign body surface. S saprophyticus, the most commonly isolated bacterium of the novobiocin-resistant coagulase-negative staphylococci, is a common pathogen of the urogenital tract; it generally infects immunocompetent patients, particularly young, sexually active men and women.