A Phenotypic and Genotypic Study of Prevalence of Inducible Clindamycin Resistance in Staphylococcus Aureus Strains Isolated from Clinical Samples at a Tertiary Care Centre

Background: Clindamycin, a lincosamide represents a common choice of drug for skin and soft tissue infections as an alternative in case of resistance to methicillin. The routine invitro tests may fail to detect inducible clindamycin resistance resulting in therapeutic failure which can be detected by a simple D test routinely in laboratory. Materials and Methods: 281 Staphylococcus aureus were isolated and subjected to phenotypic and genotypic detection of erm genes by antibiotic susceptibility testing with cefoxitin (30mg) and confirming its growth on MRSA screen agar. The isolates were subjected to double disc diffusion test with erythromycin and clindamycin discs placed adjacently at a distance of 15 to 20 mm and observed for the D zoning after overnight incubation. The ermA, ermB, ermC genes were detected from the isolates by PCR assay. Results: Out of 281 Staphylococcus aureus isolates 93 (33%) were MRSA, 188 (66.9%) were MSSA. Inducible clindamycin resistance was found in 22 (23.6%) MRSA and 12 (6.3%) MSSA isolates. ermA, ermC genes are found more in MRSA when compared to MSSA (22.5%, 67.7% and 6.3%, 0.5% respectively). Conclusion: This study shows the importance of D test to be used routinely to detect inducible clindamycin resistance. Since the isolates with inducible resistance have the ability to mutate and change to constitutive resistance, it may lead to treatment failure.