Genetic characteristics of vancomycin intermediate Staphylococcus aureus isolated from patients in Tehran, Iran: CC/ST8 is a serious threat

Abstract

Vancomycin-intermediate Staphylococcus aureus (VISA) strains represent a serious public health concern. It is crucial to investigate the genetic diversity, biofilm formation, and virulence analysis of VISA isolated from hospitalized patients. During the two-year study period, 42 VISA were obtained from 520 S. aureus isolates collected from various clinical samples, corresponding to a prevalence of 8.1%, as determined by the broth microdilution method. These VISA isolates were further characterized using biofilm formation, antimicrobial susceptibility tests, SCCmec typing, spa typing, multilocus sequence typing (MLST), and PCR analysis for detecting resistance (erm(B), tet(M), mecC, msr(B), mecA, mupA, vanA, aac(6')-Ie/aph(2˝), mupB, msr(A), erm(C), erm(A), vanB, ant(4')-Ia, and aph(3')-IIIa), biofilm (clfA, clfB, fnbA, fnbB, ebp, cna and bap) and virulence (eta, etb, pvl, and tst) genes. Our results indicated that the 42 VISA isolates belonged to three clonal complexes, including CC8 (78.6%), CC22 (11.9%), and CC5 (9.5%). The vast majority of S. aureus isolates belonged to CC8/ST239-SCCmec III/t037 (42.9%). Our result revealed that PVL-positive strains belonged to CC/ST5-SCCmec IV/t002 (9.5%), CC/ST8-SCCmec IV/t008 (19%), and CC/ST22-SCCmec IV/t790 (7.1%) while TST-positive isolates belonged to CC8/ST239-SCCmec III/t030 (9.5%) and CC8/ST239-SCCmec III/t037 (35.7%). The majority of HLMUPR isolates belonged to CC8/ST239-SCCmec III/t037 (14.3%), followed by CC/ST8-SCCmec IV/t008 (7.1%), CC8/ST239-SCCmec III/t030 (4.8%), and CC/ST5-SCCmec IV/t002 (2.4%) lineages carrying mupA. The highest frequency of VISA strain with iMLSB phenotype belonged to the CC8/ST239-SCCmec III/t037 (11.9%) clonal lineage. The study highlights that genetic diversity and characteristics of the VISA strains should be closely and continuously monitored. Besides that, importance of measures to prevent the transmission of VISA to treat such infection were urgently needed.

Keywords: Staphylococcus aureus; hospitals; methicillin-resistant Staphylococcus aureus; multilocus sequence typing; vancomycin.