Coagulase-negative staphylococci (CoNS) are part of the normal flora of human skin . These organisms have relatively low virulence but are increasingly recognized as agents of clinically significant infection of the bloodstream and other sites.
Risk factors for CoNS infection include the presence of foreign devices (such as intravascular catheters) and immune compromise. Treatment of CoNS infections can be challenging given limitations of antimicrobial resistance and the frequent presence of foreign material.
Issues related to antimicrobial resistance and treatment of CoNS infections will be reviewed here. The epidemiology, microbiology, pathogenesis, and clinical manifestations of CoNS are discussed separately (See "Microbiology, pathogenesis, and epidemiology of coagulase-negative staphylococci" and "Endocarditis due to coagulase-negative staphylococci".)
Microbiology — Resistance to methicillin and semisynthetic penicillins has been observed in more than 80 percent of coagulase-negative staphylococcal (CoNS) isolates . Such isolates are often resistant to multiple classes of antibiotics in addition to beta-lactams. The genes responsible for resistance are often found on plasmids, facilitating horizontal exchange of resistance genes among strains.
The mecA gene encoding a low-affinity penicillin-binding protein (PBP 2a) is responsible for mediating methicillin or oxacillin resistance in CoNS, as in S. aureus . This resistance is heterotypic, since only a minority of the bacterial population (as few as one in 103 or 106 organisms) expresses the resistant phenotype; this makes detection of resistance especially challenging . (See "Microbiology of methicillin-resistant Staphylococcus aureus".)