Clonal dissemination of Staphylococcus aureus isolates causing nosocomial infections, Tehran, Iran

Objective(s): In the current research, the prevalence of Staphylococcus aureus clones and genes encoding antimicrobial resistance and toxins were examined among 120 S. aureus strains from nosocomial infections in tehran, Iran.Materials and Methods: Antimicrobial susceptibility was examined, based on disk diffusion and PCR method to identify resistance and toxin-encoding genes. Based on the polymorphisms in SCCmec, agr, spa, and MLST, the isolates were typed. Results: Among 120 S. aureus isolates, 85 (70.8%) were  methicilin resistant S. aureus (MRSA), and 35 (29.2%) were methicilin sensetive S. aureus (MSSA). The tested isolates contained resistance genes, including ant(4΄)-Ia (90%), aac(6΄)-Ie/aph(2˝) (80%), aph(3΄)-IIIa (30%), erm(A) (26.7%), erm(B) (10.8%), erm(C) (11.7%), msr(A) (40.8%), msr(B) (14.2%), tet(M) (45.8%), and mupA (8.3%). The MRSA strains were clustered into six different clones. The most common genotypes included ST239-SCCmec III/t037 (23.3%), ST239-SCCmec III/t388 (22.5%), ST22-SCCmec IV/t790 (8.3%), ST15-SCCmec IV/t084 (7.5%), ST585-SCCmec III/t713 (5%), and ST239-SCCmec III/t924 (4.2%), respectively. ST182/t196 (8.3%) and ST123/t171 (5%) belonged exclusively to MSSA strains. Overall, 10 (66.7%) and 5 (33.3%) out of 15 isolates with pvl genes were attributed to clones ST22-SCCmec IV/t790 and ST15-SCCmec IV/t084, respectively. ST22-SCCmec IV/t790, ST239-SCCmec III/t037, and ST15-SCCmec IV/t084, were related to high-level mupirocin-resistant phenotypes.  Conclusion: The genetic diversity of S. aureus was confirmed in our hospitals, and ST239-SCCmec III/t037 showed a relatively high prevalence in our study. It seems that assessment of resistance and virulence genes in different S. aureus molecular types is necessary for proper antibiotic consumption.