Identification of erm and msrA genes in inducible clindamycin resistance of clinical isolates of staphylococcus aureus by polymerase chain reaction and D-test in Iran.

Background: Background: Resistance to macrolide can be mediated by erm and msrA genes in Staphylococcus aureus. There are the evidences that show erm genes may be causative agent of inducible or constitutive resistance. D-test as a simple phenotypic test can differentiate between S. aureus isolates with inducible clindamycin resistance. The aim of this study was to investigate the incidence of inducible clindamycin resistance and determine the most frequency of erm and msrA genes among S. aureus isolates. Methods & Materials: In this study a total of 124 non duplicate isolates of S. aureus collected from different clinical specimens were tested with disk diffusion method. All of isolates were tested by PCR for mecA, ermA, ermB, ermC and msrA genes. Results: According to PCR results 48.4% had mecA gene and 51.6% were mecA negative. By phenotypic D-test method, 32.3% revealed inducible resistance and recorded as D and D+. Sensitive and constitutive phenotypes were found in 54.8% and 12.9% of isolates respectively. Inducible clindamycin resistance was more prevalent in MRSA (29%) than MSSA isolates (2.4%). Among studied ermgenes, the most frequency genes were ermA and ermC with 41.1% and 17.7% respectively. Three isolates of them had D phenotype, while the PCR results of erm genes were negative. All isolates were negative for ermB or msrA genes. Conclusion: Since S. aureus isolates with inducible resistance maymutate and change to constitutive resistance, so for prevention of treatment failure, we suggest that inducible resistance test be performed in the isolates which are resistant to erythromycin and sensitive to clindamycin. [ABSTRACT FROM AUTHOR]