INDUCIBLE CLINDAMYCIN RESISTANCE AMONG CLINICAL ISOLATES OF STAPHYLOCOCCUS AUREUS

Abstract

Introduction: The resistance to antimicrobial agents among staphylococci is an increasing problem. This has led to renewed interest in the usage of macrolide- lincosamide- streptogramin B (MLSB) antibiotics to treat Staphylococcus aureus infections. Clinical failure has been reported due to multiple mechanisms that confer resistance to MLSB antibiotics.

Aims: The present study was aimed to detect inducible clindamycin resistance among S. aureus isolates and to study the relationship between clindamycin and methicillin resistance.

Materials and Methods: During a period of 6 months, a total 297 S. aureus isolates from various clinical specimens were included in the study. Antimicrobial susceptibility test was done by Kirby-Bauer’s disc diffusion method as per Clinical and Laboratory Standards Institute (CLSI) guidelines. For detection of inducible clindamycin resistance, D test using erythromycin and clindamycin as per CLSI guidelines was performed, and three different phenotypes were interpreted as MS phenotype (D test negative), inducible MLSB (iMLSB) phenotype (D test positive), and constitutive MLSB phenotype.

Results: Of the total 297 S. aureus isolates, majority were obtained from pus 35% (104), from swab 52% (153) followed by blood, tissue samples and body fluids 13% (40). Out of 297, 71% (211) were erythromycin resistant. Out of the total 297 isolates, 30.30% (90) were methicillin-resistant S. aureus (MRSA) and 69.69% (207) were methicillin-sensitive S. aureus (MSSA). MLSB phenotype in 13.46%, MS phenotype in 32.65%, and constitutive MLSB phenotype was observed in 24.91% of isolates. Inducible clindamycin resistance was more among MRSA than MSSA isolates.

Conclusion: D test should be included as a mandatory method in routine disc diffusion testing to detect inducible clindamycin resistance in staphylococci for the optimum treatment of patients.