Prevalence of Macrolide-Lincosamide-Streptogramin B (MLSB) Resistance in Staphybcoccus aureus Isolated from Patients in Tehran, Iran

Background and Objectives: Staphylococcus aureus is an important cause of nosocomial and community-acquired infections in every region of the world. Clindamycin is one of the alternativeagents used to treat S. aureus infections and accurate identification of clindamycin resistance isimportant to prevent therapeutic failure. Unfortunately, inducible clindamycin resistance is notdetected by standard susceptibility tests. This study aimed to determine the prevalence of themacrolides-lincosamides-streptogramins B (MLSB) resistance in S. aureus isolated in four universityhospitals in Tehran, Iran. Material & Methods: Two hundreds and forty-four non-duplicate clinical isolates of S. aureus [133 methicillin resistant S. aureus (MRSA) and 111 methicillin susceptible (MSSA) S. aureus] werecollected in 2008. Antimicrobial susceptibilities were determined by the D-test.Results: Altogether, 68% and 61.1% of isolates were resistant to erythromycin and clindamycin, respectively; with higher resistance in MRSA isolates compared to MSSA isolates. The constitutiveMLSB (cMLSB) resistance phenotype was recognized in 61.1%, while 5.3% had shown inducibleMLSB (iMLSB) resistance phenotype. Constitutive MLSB resistance phenotype predominated over inducible MLSB resistance phenotype and susceptible phenotype (83.9, 9.3 and 6.8%, respectively)among the MRSA isolates, whereas susceptible phenotype predominated over constitutive MLSBresistance phenotype and inducible MLSB resistance phenotype (62.6, 31.3 and 2%, respectively) among the MSSA isolates. Conclusion: Considering the higher prevalence of clindamycin resistance in MRSA isolates compared MSSA isolates, routine D-test of MRSA isolates is strongly recommended to prevent treatment failure.