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Background: Inducible MLSB (macrolide-lincosamide-streptogramin B) resistance in staphylococci is not detected by standard susceptibility test methods. Failure to identify inducible MLSB resistance may lead to clinical failure during clindamycin therapy. We determined the prevalence of inducible MLSB resistance in erythromycin-resistant staphylococcal isolates. Materials and Methods: We evaluated all 2,792 non-duplicate staphylococcal strains: 1,402 Staphylococcus aureus and 1,390 coagulase-negative staphylococci (CoNS) isolated from May 2008-June 2009 at one-unoversity hospital. Testing for inducible MLSB was accomplished by the disk approximation test (D-test) in accordance with the recommendations of the Clinical and Laboratory Standards Institute (CLSI). Results: Of the 2,792 staphylococcal isolates, 892 S. aureus isolates and 740 CoNS isolates were resistant to erythromycin. Among the 892 erythromycin-resistant S. aureus isolates, the overall prevalence of inducible MLSB was 21.3% (16.2% of MRSA and 76.3% of methicillin-susceptible S. aureus). Among the 740 erythromycinresistant CoNS isolates, the overall prevalence of inducible MLSB was 16.5% (16.0%of methicillin-resistant CoNS and 18.7% of methicillin-susceptible CoNS). The D-test was positive in 88.8% of S. aureus and 28.4% of CoNS isolates, which were erythromycin-resistant and clindamycin-susceptible. Conclusions: There are some variations in the prevalence of inducible MLSB resistance in clinical staphylococcal isolates. It is important that clinical laboratories report inducible MLSB resistance for erythromycin-resistant and clindamycinsusceptible staphylococcal isolates.
