Distribution of erm genes and low prevalence of inducible resistance to clindamycin among staphylococci isolates

Introduction: Resistance to macrolides, lincosamides and streptogramins B (MLSB antibiotics) in staphylococci may be due to modification in ribosomal target methylase encoded by erm genes. The expression of MLSB resistance lead to three phenotypes, namely constitutive resistance (cMLS(B)), inducible resistance (iMLS(B)), and resistance only to macrolides and streptogramins B (MSB). The iMLS(B) resistance is the most difficult to detect in the clinical laboratory. Objective: This study investigated the expression of MLSB resistance and the prevalence of the erm genes among 152 clinical isolates of Staphylococcus aureus and coagulase-negative Staphylococcus (CNS) from Hospital de Clinicas de Porto Alegre. Methods: Primary MLSB resistance was detected by the disk diffusion method. Isolates with iMLS(B) phenotype were tested by double-disk induction method. All isolates were tested by a genotypic assay, PCR with specific primers. Results: A total of 46.7% of staphylococci were positive for cMLS(B); 3.3% for iMLS(B) and 3.3% for MSB. One or more erm genes were present in 50.1% of isolates. The gene ermA was detected in 49 isolates, ermC in 29 and ermB in 3. Conclusion: The prevalence of the ermA, ermB and ermC genes were 29.6%, 17.1% and 0.66% respectively, and constitutive resistance was the most frequent as compared to the other two phenotypes.