Molecular Characterizations, Virulence Determinants and Antimicrobial Resistance Profiles of Methicillin-Resistant Staphylococcus aureus (MRSA) in the North of Iran

Abstract

Background: Emergence and prevalence of Methicillin-Resistant Staphylococcus aureus (MRSA) has become a major universal health concern, limiting therapeutic options. Methods: In the North side of Iran, during the years 2015 to 2017, a total number of 37 MRSA isolates, including 19 clinical isolates from hospitalized patients and 18 colonizing isolates from health care workers were identified from three hospitals, in Gorgan, North of Iran. Antimicrobial susceptibility test was performed using the disk diffusion method and E-test. The presence of virulence and antibiotic resistance determinants were evaluated by PCR. The genotypic characterization was further analyzed using multi-locus sequence, spa, SCCmec, and agr typing.Results: The frequency of MRSA among S. aureus isolates was 38.14% (37/97). The most frequent S. aureus resistant isolates were found to be obstinate against penicillin (98%) and gentamicin (82.5%). Additionally, the lowest resistance rates were found against daptomycin (0%), vancomycin (2.7%), and quinupristin-dalfopristin (5.4%). All MRSA isolates were susceptible to daptomycin with MIC50/MIC90 of 0.25/0.5 µg/ml. One isolate belonging to the ST239-SCCmecIII/t037 clone (MIC≥16μg/ml) was resistant to vancomycin. All but one isolate that shares the ST22-SCCmec IV/t790 strain were positive for both tsst and pvl genes. The most predominant MRSA isolates (27%) were associated with the ST239-SCCmec III/t037 clone; and followed by ST239-SCCmec III/t924 (16.2%).Conclusions: In our study, circulating MRSA strains were genetically diverse with a high prevalence of the ST239-SCCmecIII/t037 clone. These findings emphasize the need for future and continuous surveillance studies on MRSA to prevent the dissemination of multidrug resistance and existing MRSA clones in an effective manner.

Clonal Diversity and Epidemiological Characteristics of ST239-MRSA Strains

“…Previous studies from Iran had indicated that a variant of ST-239 (named as ST1283 strain) was resistant to vancomycin (MIC of 512 mg/mL) (Azimian et al, 2012), and ST239-SCCmec-III/t037 from a university hospital showed resistance to vancomycin (Shekarabi et al, 2017). The latter clone was also reported to be resistant to vancomycin from hospitalized patients in Iran (Kouhsari et al, 2020). Similar to other bacteria, it is evidenced that the emergence of ST239 VRSA is a multifactorial phenomenon that could result from factors such as the intensive use of vancomycin in treating lifethreatening infections (McDonald et al, 1997), bacterial genetic background, and yet-unknown evolutionary mechanisms.…”