Inducible clindamycin resistance among Staphylococcal clinical isolates from Tripoli Central Hospital, Libya

BACKGROUND: The resistance to antimicrobial agents among Staphylococci is an increasing problem. This has led to a renewed interest in the usage of macrolide-lincosamide-streptogramin B (MLSB) antibiotics to treat staphylococcal infections. Clinical failure has been reported due to multiple mechanisms that confer resistance to clindamycin antibiotics. The present study was to investigate the inducible clindamycin resistance among isolates of methicillin resistant Staphylococci by the D-test method. MATERIALS & METHODS: This study was conducted on 218 staphylococcal isolates obtained from different clinical specimens of outpatients and inpatients admitted to Tripoli Central Hospital (TCH), Libya. Methicillin resistance was detected by oxacillin, cefoxitin disc diffusion test (Kirby Bauer method) and confirmed by other biochemical tests. Detection of inducible clindamycin resistance was performed by D-test using erythromycin and clindamycin. RESULTS: Eighty-six out of 218 staphylococcal isolates were resistant to erythromycin,26 (11.9%) isolates were D-test positive indicating inducible (iMLSB) phenotype, 24 (11%) isolates exhibited constitutive (cMLSB) phenotype, while 36 (16.5%) showed true sensitivity to clindamycin indicating (MS) phenotype. The distribution of isolates showing iMLSB phenotype was 12 (19.4%) for methicillin-resistant Staphylococcus aureus (MRSA), 8 (17.0%) for methicillin-resistant coagulase-negative Staphylococci (MRCNS), 6 (6.4%) for methicillin-sensitive Staphylococcus aureus (MSSA) and 0 (0%) for methicillin-sensitive coagulase-negative Staphylococci (MSCNS). CONCLUSION: Higher prevalence of iMLSB phenotype was mainly associated with methicillin-resistant than methicillin-sensitive isolates. We recommend that D-test should be performed to facilitate the appropriate treatment of patients infected with Staphylococci.