Influence of subinhibitory concentrations of antibiotics on virulence of staphylococci.

The understanding and control of infections caused by staphylococci are still far from complete, and staphylococcal infections continue to be a serious problem. The organisms possess numerous virulence factors that can act independently to induce various symptoms and lesions. Chemotherapy has changed the clinical spectrum of staphylococci but has not eradicated serious staphylococcal infections. An evaluation of the interaction of antibiotics, staphylococci, and host defense will help to identify those factors that determine the success or failure of therapy for staphylococcal infections. The activity of antibiotics is usually expressed in terms of concentrations that either inhibit or kill microorganisms in vitro or in experimental infections. Subinhibitory concentrations of antibiotics may induce changes in bacterial properties both in vitro and in vivo. An understanding of the mechanism of such changes would allow a more rational application of antibiotics that have both specific antistaphylococcal action and positive effects on host defense mechanisms.