Prevalence of inducible clindamycin resistance among clinical isolates of Staphylococcus aureus detected by phenotypic method: A preliminary report

Clindamycin is one of the alternative antibiotics in the therapy of Staphylococcus aureus, particularly in methicillin resistant S. aureus (MRSA) infections. But inducible clindamycin resistance (iMLSB) has been described as a cause of clinical failure of such infections. The present study attempted to evaluate the prevalence of inducible clindamycin resistance among S. aureus isolates in a tertiary care centre in north eastern India. The study was carried out in the department of Microbiology, Era’s Lucknow Medical College and Hospital, Lucknow, India, during a period of one year from December 2008 to November 2009. It was a prospective cross sectional study. In total, 260 S. aureus isolates were subjected to routine antibiotic susceptibility testing, including cefoxitin (30 mg), by the Kirby Bauer disc diffusion method. Inducible resistance to clindamycin was tested by double disk diffusion assay (D test) as per Clinical and Laboratory Standards Institute (CLSI) guidelines. Overall, inducible clindamycin resistance was detected among sixty (23.2%) isolates, while 16(6.15%) showed constitutive resistance and the remaining 39 (15%) exhibited a MS phenotype. Inducible resistance and constitutive resistance were higher in MRSA than methicillin-susceptible S. aureus (MSSA). Therefore, owing to the high percentage of inducible clindamycin resistance, we recommend that a screening test such as the D test should be included in routine susceptibility testing for S. aureus.   Key words: Double disk diffusion assay (D test), inducible clindamycin resistance (iMLSB),Staphylococcus aureus.