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

Abstract

Objectives: 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.

Keywords: Agr; MLST; MRSA; SCCmec; Spa; Staphylococcus aureus.

Figure 1

Resistance pattern of Staphylococcus aureus obtained from clinical samples

Figure 2

A) Lane M, 100-bp DNA Ladder (Fermentas, UK); Lane 1 PCR product of aac(6΄)-Ie/aph(2˝) encoding gene, Lane 2 PCR product of PCR product of aph(3΄)-IIIa encoding gene, Lane 3 PCR product of erm(A) encoding gene, Lane 4 PCR product of erm(B) encoding gene, Lane 5 PCR product of erm(C) encoding gene, Lane 6 PCR product of msr(A) encoding gene, Lane 7 PCR product of msr(B) encoding gene, Lane 8 PCR product of mupA encoding gene, and Lane 9 PCR product of tet(M) encoding gene. B) Lane M, DNA Ladder; lane 1 negative control, Lane 2 the 323 bp PCR product of agr type III, lane 3 the 575 bp PCR product of agr type II, lane 4 the 441 bp PCR product of agr type I, lane 5 the 518 bp PCR product of SCCmec Type III, lane 6 the 937 and 415 bp PCR products of SCCmec Type IV. C) Lane M, DNA ladder; lane 1-5, variable PCR product of spa. D) Lane M, DNA Ladder; Lane 1the 270 bp PCR product of nucA gene, Lane 2the 93 bp PCR product of eta gene, Lane 3the 226 bp PCR product of etb gene, Lane 4the 398 bp PCR product oftst-1 gene, Lane 5the 180 bp PCR product of luk-PV gene, Lane 6the 583 bp PCR product of mecA gene

Figure 3

Distribution of spa types in methicilin resistant S. aureus (MRSA) and methicilin sensetive S. aureus (MSSA) strains isolated from nosocomial infections

Figure 4

Distribution of molecular types in 85 methicilin resistant S. aureus (MRSA) strains isolated from nosocomial infections