Distribution of erm genes among Staphylococcus aureus isolates with inducible resistance to clindamycin in Isfahan, Iran

BACKGROUND: The rising frequency of methicillin resistant Staphylococcus aureus (MRSA) has led to an increased use of antibiotics such as macrolide, lincosamide, streptogramin B (MLS(B)) for the treatment of S. aureus infections. Resistance to MLS(B) in S. aureus is commonly encoded by erm genes, which can be constitutive MLS(B) (cMLS(B)) or inducible MLS(B) (iMLS(B)). The purpose of this study was to determine the frequency of cMLS(B), iMLS(B), and MS phenotypes using D-test and polymerase chain reaction (PCR) methods. MATERIALS AND METHODS: A total of 215 isolates of S. aureus were collected from January 2010 to May 2012 from Al-Zahra Hospital in Isfahan. PCR was performed for detection of mecA gene on all isolates using specific primers. The frequency of MLS(B)-resistant isolates was determined using D-test, and then a multiplex PCR was performed for detection of ermA, ermB, and ermC genes. RESULTS: Among 215 S. aureus isolates examined, 82 (40.9%) were MRSA, and iMLS(B), cMLS(B), and MS resistance phenotypes had a frequency of 9 (4.18%), 58 (26.9%), and 11 (5.1%), respectively. Among nine isolates with iMLS(B) resistance phenotype, four isolates contained ermC gene, two isolates ermB gene, and one isolate ermA gene. Two isolates did not have any erm gene. CONCLUSION: In the current study, cMLS(B) was the most frequent phenotype and ermC was the most common gene in iMLS(B) resistant phenotypes.