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

Objective: 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.

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.

Conclusions: 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.