Status of inducible clindamycin resistance among macrolide resistant Staphylococcus aureus

Clindamycin has long been an option for treating both methicillin sensitive Staphylococcus aureus (MSSA) and methicillin resistant S. aureus (MRSA) infections. So, it is utmost important to perform the susceptibility test for erythromycin and clindamycin. And, there is concern on use of this antibiotic in the presence of erythromycin resistance because of the possibility of induction of cross-resistance among members of macrolide, lincosamide and streptogramin B (MLSB) group. During August 2011 to May 2012, a total of 207 isolates of S. aureus were isolated and among which 29.47% (61) isolates were confirmed as MRSA by cefoxitin (30 µg) disc. All the isolates were further processed for MLSB resistance test by double disc diffusion test of erythromycin (2 µg) and clindamycin (15 µg) at a distance of 15 and 22 mm between them. This study result show 12.56% (26) and 14.49% (30) of inducible macrolide-lincosamide-streptogramin B phenotype (iMLSB) resistance type at 22 and 15 mm disc distance, respectively, showing 15 mm disc distance is potential than 22 mm and 17.39% (36) of cMLSB resistance type. Similarly, both iMLSB and cMLSB are greater in MRSA than MSSA and constitutes 18.05 (11) and 36.06% (22), respectively. Thus, this study concludes that D-test should be used as a mandatory method and is more potential in 15 mm disc apart.