Abstract

Emergence of methicillin resistance in Staphylococcus aureus (S.aureus) has left us with very few therapeutic alternatives available to treat staphylococcal infection. The widespread use of macrolide-lincosamide-streptogramin B (MLSB) antibiotics has led to an increase in number of staphylococcal strains acquiring resistance to MLSB antibiotics. This study was done to investigate the infections by hospital and community acquired “erythromycin- induced clindamycin resistant” strains or D-test positives of clinical isolates of Staphylococcus aureus (S.aureus) in a hospital. Three hundred isolates of S.aureus were subjected to routine antibiotic susceptibility testing including Cefoxitin (30µg) by modified disc diffusion method. Inducible resistance to clindamycin in S.aureus was tested by D-test as per CLSI guidelines. Among 300 S.aureus isolates, 114 (38%) were methicillin resistant Staphylococcus aureus (MRSA) and 186 (62%) methicillin susceptible Staphylococcus aureus (MSSA). Forty one (13.67%) isolates showed induced clindamycin resistance, 49(16.33%) showed constitutive resistance and 94 (31.33%) showed the MS phenotype. Inducible resistance and constitutive resistance were found to be higher in MRSA compared to MSSA (22.81%, 23.68% and 8.1%, 11.8% respectively). D-test should be included as a part of routine antibiotic susceptibility testing to detect induced clindamycin resistance to prevent treatment failure.

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