Characterization of Coagulase-Negative Staphylococci Isolated from Cases of Ostitis and Osteomyelitis

Coagulase-negative staphylococci (CoNS) are often responsible for cases of chronic ostitis and osteomyelitis, especially in patients with orthopedic prosthesis/implants. The aim of this study was to characterize CoNS isolated from ambulatory patients with chronic ostitis/osteomyelitis and to compare them by PFGE (pulsed-field gel electrophoresis). Out of 263 bacterial strains isolated from wounds/sinuses of patients with chronic ostitis/osteomylitis, 41 were identified as CoNS. Twenty methicillin-resistant strains were selected for this study. Our results confirm the superior performance of cefoxitin disk test to detect methicillin resistance in heterogenous population of CoNS. High level of antibiotic resistance was observed among the studied strains: majority of CoNS were resistant to tetracycline and erythromycin and also to clindamycin and ciprofloxacin. Importantly, in 15 out of 20 studied CoNS different phenotypes of macrolides, lincosamides and streptogramin n MLS resistance was suggested. Eight strains demonstrated resistance to both erythromycin and clindamycin, suggesting constitutive MLS B phenotype. Seven remaining strains presented resistance to erythromycin and susceptibility to clindamycin with negative D-test results, suggesting the presence of macrolides and streptogramines type A efflux pump. All studied strains were sensitive to vancomycin (MIC 0.75 n 2.0 µg/ml), teicoplanin (MIC 0.125 n 8.0 µg/ml), and quinupristin/dalfopristin (MIC 0.19 n 1.0 µg/ml). No clonal relatedness was observed in PFGE patterns.