Molecular Characterization and Resistance Profile of Methicillin Resistant Staphylococcus aureus Strains Isolated from Hospitalized Patients in Intensive Care Unit, Tehran-Iran

Background: Staphylococcus aureus is an important opportunistic pathogen and can cause a wide range of infections. The ability of this pathogen to successfully persist within the hospital and the community is largely due to its remarkable ability to acquire resistance against various antimicrobial agents. Objectives: The aim of this study was to determine the carriage of antibacterial resistance genes and virulence markers of S. aureus isolates from hospitalized patients in intensive care units in Tehran, the capital of Iran. Methods: In this cross-sectional study that was conducted during an 11-month period since March 2015 to January 2016, a total of 105 S. aureus strains were investigated. MRSA screening was performed by phenotypic and genotypic methods. The Kirby-Bauer disk diffusion method was used to assess the sensitivity of S. aureus strains. The strains were typed based on the polymorphisms in SCCmec types. The presence of resistance (ermA, ermB, ermC, mupA, msrA, msrB, tetM, ant (4΄)-Ia, aac (6΄)-Ie/aph (2˝), aph (3΄)-IIIa) and toxin (etb, eta, pvl, tst) encoding genes were investigated by the polymerase chain reaction (PCR) technique. Results: In this study, 105 isolates of S. aureus were obtained from 299 various clinical specimens. Ninety five (90.5%) strains were confirmed as methicillin-resistant S. aureus. The lowest levels of resistance were related to quinupristin-dalfopristin (16.8%) while the highest levels of resistance were related to penicillin (94.7%). Multi-drug resistance was observed in 91.5% of the isolates. Type IV was the most prevalent SCCmec type (57.9%), followed by type III (22.1), type V (12.6%), I (5.3%), and II (2.1%). Overall, 25 isolates (26.3%) harbored PVL-encoding genes, and all of them belonged to SCCmec type IV. The presence of resistance genes ant(4΄)-Ia, aac(6΄)-Ie/aph(2˝), aph(3΄)-IIIa, ermA, ermB, ermC, msrA, msrB, and tetM was detected in 94.7%, 81.1%, 31.6%, 31.6%, 15.9%, 18.9%, 47.3%, 21.1%, 56.8%. The frequency of the etb, eta, and tst genes were 1.1%, 4.2%, and 32.6%, respectively. Conclusions: The results illustrated the diversity of antibacterial resistance and virulence gene profiles among different SCCmec types of S. aureus. The increased prevalence of methicillin-resistant S. aureus isolates containing different toxin and antibiotic resistance genes is a serious threat for the hospitalized patients in the intensive care units.