40 - Coagulase Negative Staphylococci and their Role in Infection

Abstract

The differentiation between virulent staphylococci and those of the normal commensal flora has long depended on the production of coagulase and this has for many years formed part of the diagnostic armory of microbiologists. Some of the new species introduced, such as Staphylococcus xylosus and S. capitis are only occasionally isolated from normal human and animal skin and mucosal surfaces and rarely or never cause infections. It is, however, difficult to define the borderline between pathogenic and non-pathogenic microorganisms in the context of modern medicine and surgery, when the immune systems of patients are often suppressed. Few attempts are made to define the virulence potential of such strains, which belong to the skin flora and commonly contaminate clinical specimens, including abscess material and blood cultures. The association of some species of coagulase-negative staphylococci with infection is so well established that attention should be focused not so much on their isolation and identification but on their ability to cause infection. They therefore live in an intimate relationship with their host, producing only a moderate inflammatory response, which allows them to develop a long-term relationship in situations such as infected joint replacements and prosthetic valve endocarditis. This chapter has attempted to place the various virulence attributes of CNS into some perspective and to suggest how colonization can progress to infection.