Inducible clindamycin resistance in staphylococcus aureus isolated from clinical samples at tertiary care hospital Ahmedabad

Introduction: Clindamycin is most commonly used drug in treatment of erythromycin resistant Staphylococcus aureus causing skin and soft tissue infection. In vitro routine tests for clindamycin susceptibility may fail to detect inducible clindamycin resistance due to erm genes leading to treatment failure. Thus it is necessary to detect such resistance by simple D test on regular basis. Aim: To study the induction of clindamycin resistance and characterize the Staphylococcus aureus phenotypes based on their susceptibility pattern and induction testing. Material & Methods: Total 400 Staphylococcus aureus strains were isolated from different clinical samples. All isolates were tested for MRSA using Cefoxitin (30µg) by Kirby Bauer disc diffusion method. All 400 S. aureus strains were tested to see different induction phenotypes by D test as per CLSI guidelines. Result: Out of 400 isolates of S. aureus, 75 (18.7%) isolates showed inducible clindamycin resistance, 117 (29.3%) isolates showed constitutive resistance, 79(19.7%) isolates showed MS phenotype of resistance and 129 (32.3%) isolates were sensitive to both erythromycin and clindamycin drugs. Inducible resistance was more in MRSA strain (32.3%) as compared to the MSSA strain (9.9%). Conclusion: This study showed that D test should be done as routine disc diffusion test to detect inducible clindamycin resistance in Staphylococcus aureus strains so clindamycin therapeutic failure can be reduced.