Isolation of small colony variants of Staphylococcus aureus following gentamicin bead placement for osteomyelitis as a possible cause for recurrence

Aim: Recently, S. aureus small colony variants (SCVs) were reported to persist within cultured endothelial cells and to cause persistent and antibiotic resistant infections in humans. Because gentamicin call very reproducably select for electron transport deficient SCVs as shown in earlier in vitro experiments, we searched for SCVs in a patient with chronic osteomyelitis, who received gentamicin beads. Method: Special culture and identification procedures for determination of SCVs were used, including testing of the S. aureus specific nuc gene, pulsed field gel electrophoresis (PFGE) as a typing method and characterization of the auxotrophism of the SCVs. Results:In a case of a 34-year-old patient with chronic osteomyelitis who had previously been treated with gentamicin beads, menadione auxotrophic S. aureus SCVs as well as wild type S. aureus were recovered in multiple bone specimen. All different colony types isolated from simultaneous or from sequential specimen were shown to be clonal by PFGE. Conclusion: Recovery of S. aureus SCVs from a patient treated with gentamicin beads suggests that the slow release of gentamicin into the local environment may be an efficient way to select for and/or induce SCVs. These data should alert physicians to also consider SCVs when a treatment failure occurs in a patient that has received gentamicin beads.