Small colony variants in staphylococcal infections: diagnostic and therapeutic implications

The discovery of S. aureus small colony variants as persistent and intracellular has provided new insight into the understanding of pathogenesis associated with staphylococcal diseases. Survival advantages are afforded to SCVs on the basis of their ability to hide within host cells, which provide protection from the immune system and some antibiotics. In addition, because most clinical SCVs are defective in electron transport, their uptake of positively charged antimicrobial substances is reduced. The atypical clinical microbiologic characteristics make identification and susceptibility testing difficult. SCVs have been recovered from patients with unusually persistent infections, particularly those patients with long disease-free intervals, and from patients who are chronically exposed to aminoglycosides and TMP-SMZ, suggesting that these clinical situations are those in which SCVs should be suspected and the clinical laboratory should carefully search for them.