Inducible Clindamycin Resistance in Staphylococcus aureus Isolates in a Community Setting

Background: 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 (S. aureus) infections. The resistance to macrolide can be mediated by msr A gene coding for efflux mechanism or via erm gene encoding for enzymes that confer inducible or constitutive resistance to MLSB antibiotics. In vitro routine tests for clindamycin susceptibility may fail to detect inducible clindamycin resistance due to erm genes resulting in treatment failure, thus necessitating the need to detect such resistance by a simple D test on a routine basis. Objective: This study was carried out to determine the prevalence of MLSBi resistance in both S. aureus isolates, including Methicillin Resistant Staphylococcus aureus (MRSA) and Methicillin Sensitive Staphylococcus aureus (MSSA). Results: Out of the 88 Staphylococcus aureus isolates, 18 (20%) were MRSA and 70 (80%) were MSSA. 41 (47%) isolates were erythromycin resistant. These erythromycin resistant isolates, when subjected to ‘D’ test, 17 isolates showed MS phenotype, 13 showed inducible MLSB phenotype and 11isolates showed constitutive MLSB phenotype. Out of 18 MRSA isolates 08 (44%) showed Inducible MLSB phenotype and 02 (11%) showed Constitutive MLSB phenotype, while in 70 methicillin sensitive Staphylococcal isolates 05 (7%) showed Inducible MLSB phenotype and 09 (13%) showed Constitutive MLSB phenotype. The percentage of inducible resistance was higher amongst MRSA isolates as compared to MSSA isolates. Conclusions: Clindamycin is kept as a reserve drug and is usually advocated in severe MRSA infections depending upon the antimicrobial susceptibility results. This study showed that D test should be used as a mandatory method in routine disc diffusion testing to detect inducible clindamycin resistance in Staphylococci for the optimum treatment of patients.