Detecting the frequency of aminoglycoside modifying enzyme encoding genes among clinical isolates of methicillin-resistant Staphylococcus aureus

Introduction: Methicillin-resistant Staphylococcus aureus (MRSA) plays an important role in causing many serious nosocomial infections. In this study, the antimicrobial susceptibility and the frequency of aminoglycoside modifying enzyme encoding genes among clinical isolates of methicillin-resistant Staphylococcus aureus was investigated from two university hospitals of Zanjan province of Iran.
Methods: In this study, the antimicrobial susceptibility of MRSA isolates to various antibiotics was investigated by the disk diffusion method. Multiplex PCR assays were used for the determination of aminoglycoside modifying enzyme (AME) genes and staphylococcal cassette chromosome mec (SCCmec) types in MRSA strains.
Results: All 58 MRSA isolates were sensitive to vancomycin. Resistance to penicillin G, oxacilin, gentamicin, erythromycin, clindamycin, kanamycin, and tobramycin was found in 96.4%, 98.3%, 51.7%, 53.4%, 55.2%, 62% and 58.6% of the isolates, respectively. The most prevalent AME genes were aac(6′)/aph(2′′) (48.3 %) followed by ant(4)-Ia (24%). The aph(3′)-Ia gene was the least frequent AME gene among MRSA isolates (19%). Of the 58 tested MRSA isolates, 5 (8.6%) were harboured SCCmec type I, 11 (19%) SCCmec type II, 20 (34.5%) SCCmec type III, 17 (29.3%) SCCmec type IVa, 1 (1.7%) SCCmec type IVb, 2 (3.4%) SCCmec type IVc, 11 (19%) SCCmec type IVd, and, 18 (31%) SCCmec type V. Nineteen isolates were not typeable.
Conclusion: In conclusion, the aac (6′)/aph (2′′) was the most common aminoglycoside modifying enzyme gene and SCCmec type II and V were the most frequent types detected in hospital isolates, respectively.