Occurrence of Inducible Clindamycin Resistance in Clinical Isolates of Staphylococcus aureus in a Tertiary Care Hospital

Background: Staphylococcus aureus causes wide range of infections, ranging from minor skin infections, chronic bone infection to devastating septicemia and endocarditis. In vitro, S. Aureus isolates with constitutive resistance are resistant to both erythromycin and clindamycin whereas those with inducible resistance are resistant to erythromycin and appear sensitive to clindamycin (iMLSB). There are limited reports on prevalence of inducible clindamycin resistance among S.aureus from this geographical area. Aim: To study the occurrence of inducible clindamycin resistance among clinical isolates of Staphylococcus aureus Method: Isolates of S. aureus obtained from various clinical samples were subjected to routine antibiotic sensitivity testing by Kirby Bauer disc diffusion method. The clinical isolates were tested for Methicillin resistance using cefoxitin 30 μg discs. Inducible clindamycin resistance was detected by ‘D’ test as per CLSI guidelines. Result: A total 161, S. aureus were isolated and identified from various clinical samples out of which 118 (73%) were MRSA and 43 (27%) were MSSA. Erythromycin resistance was seen in 99 (61.4%) isolates. Among the erythromycin resistant S.aureus, iMLSB resistance was observed in 34 (21.1%) isolates and constitutional resistant types cMLSB in 51 (31.67%) and MS phenotype in 76 (47.20%). Conclusion: Occurrence of Inducible Clindamycin resistance was observed in isolates of S.aureus. D test is a simple and comparatively easy method which can be used in a routine laboratory and will enable in guiding the clinicians regarding judicious use of clindamycin.