Detection and Prevalence of Inducible Clindamycin Resistance in Staphylococcus Species: Insights from a Tertiary Care Centre in Kerala

Introduction: With the emergence of many multidrug resistant organisms like methicillin resistant Staphylococci, therapeutic options for treating skin and soft tissue infections have become severely limited. Clindamycin is an attractive option for the treatment of such cases especially Community-acquired MRSA (CA-MRSA) because of its excellent tissue penetration and it can be used in penicillin-allergic patients also. But clinical failure can occur due to multiple mechanisms that confer resistance to Macrolide, Lincosamide and Streptogramin B antibiotics. This study was conducted to detect inducible clindamycin resistance in Staphylococci as well as to detect the prevalence of erythromycin induced clindamycin resistance in staphylococcal isolates in the institute. Materials and Methods: It was a prospective cross-sectional study conducted on the Staphylococcal isolates obtained from routine clinical samples during a period of 1½ years in the Department by systematic sampling method. A total of 300 non-duplicate Staphylococcal isolates from various clinical samples were subjected to antimicrobial susceptibility testing as per the CLSI guidelines. The prevalence of inducible clindamycin resistance in these isolates were tested by using Double disk approximation test (D test), which was supported by automated method (Vitek 2 compact systems) and agar dilution method. Results: Out of the 300 Staphylococcal isolates included in the study, 90.7% were coagulase positive and 9.3% coagulase negative. It consisted of 34.7% MRSA, 56% MSSA, 5.7% MRCONS and 3.6% MSCONS. Out of the 154 Erythromycin resistant staphylococcal isolates tested, 39 (13%) were found to be D test positive. Inducible clindamycin resistance was exhibited by 18.26% of MRSA, 11.30% of MSSA and 6.66% of MRCONS. Constitutive resistance phenotype, MS phenotype and Susceptible phenotype was exhibited by 27 (9%), 89 (29.7%) and 144 (48%) staphylococcal isolates respectively. Conclusion: D test is simple and reliable test to detect inducible clindamycin resistance which can be missed if not looked for specifically. Clinical microbiology laboratories should use the double disc approximation test as standard practice with all Erythromycin resistant strains which will help to prevent treatment failure.