Phenotypic and genotypic characterization of macrolide resistance among Staphylococcus aureus isolates in Isfahan, Iran.

Background and Objectives: Macrolide, lincosamide and streptogramin B (MLSB ) are noteworthy antibiotics for the treatment of Staphylococcus aureus infections. The purpose of this study, was to determine the phenotypic and genotypic characterization of macrolide resistance, among S. aureus , isolated from clinical samples and nasal swabs.

Materials and Methods: Totally, 162 non-duplicate S. aureus isolates were collected from clinical samples and nasal swabs, from patients and healthcare workers (HCWs), between March 2016 and September 2016, at four teaching hospitals in Isfahan. The antibiotic resistance profile was determined using disk diffusion test and the presence of resistance genes was detected, using PCR.

Results: Of 162 S. aureus isolates, 43.8% (71/162) and 34% (55/162) isolates were erythromycin-resistant and methicillin-resistant S. aureus (MRSA), respectively. The prevalence of constitutive MLSB (cMLSB ), inducible MLSB (iMLSB ), macrolide-streptogramin B-resistant (MSB ) and lincosamide-streptogramin-A resistance (LSA ) phenotype was 32%, 6%, 6% and 2%, respectively. The most common erythromycin resistance genes, in S. aureus isolates were erm C (35.2%), followed by erm A (20.4%) and msr A (17.3%). Meanwhile, msr A was detected in 43.6% of MRSA isolates. The frequency of coexistence of erm A+ erm C+ msr A, in S. aureus isolates was 7% and it was only detected in MRSA isolates.

Conclusion: In the current study, cMLSB phenotype was the most common erythromycin resistance pattern and erm C was the most prevalent gene in erythromycin-resistant isolates. The results revealed that the various mechanisms of erythromycin resistance are expanding in Isfahan.