Genetic analysis of methicillin-susceptible Staphylococcus aureus clinical isolates: High prevalence of multidrug-resistant ST239 with strong biofilm-production ability

J Clin Lab Anal. 2020 Nov;34(11):e23494. doi: 10.1002/jcla.23494. Epub 2020 Jul 21.


Background: The distributions of methicillin-susceptible Staphylococcus aureus (MSSA) are divers geographically with different genetic backgrounds. Data related to molecular characteristics of MSSA compare to methicillin-resistant Staphylococcus aureus (MRSA) is sparse.

Methods: In this cross-sectional study, antimicrobial susceptibility testing, virulence genes analysis, biofilm formation, accessory gene regulator (agr) typing, and multilocus sequence typing (MLST) characterized on 75 MSSA isolates.

Results: Multidrug-resistance MSSA was found to be 84%. Forty-eight (64%) isolates were toxinogenic with 34 and 14 isolates carrying pvl and tst representing 45.3% and 18.7%. The most common SE genes were sed (20%), sec (16%), and sea (16%). Fifty-five (73.3%) isolates were confirmed as biofilm producer with a markedly high prevalence of fnbA (93.3%), fnbB (86.7%), icaA (65.3%), icaD (53.3%), can (24%), ebp (10.7%), and bap (1.3%). A total of 3 agr types (I, 73.3%; III, 16%; II, 10.7%) and 4 clonal complexes (CCs) and sequence types (STs), namely CC8/ST293 (45.3%), CC/ST22 (28%), CC/ST30 (16%), and CC/ST5 (10.7%) were detected in this study. All the high and low-level mupirocin resistance strains belonged to ST239 and ST22 strains, respectively. All the fusidic acid-resistant isolates carried fusC and belonged to ST30.

Conclusions: These findings indicated that ST239 with strong biofilm production ability is the most common type in MSSA strains isolated from patients. It seems that the antimicrobial resistance profiles, toxin, and biofilm formation were closely associated with specific STs. Further studies are required to identify and control of these clonal lineages in our area.

Keywords: Staphylococcus aureus; Biofilm; Methicillin-susceptible S aureus; agr allotype; multilocus sequence typing.

MeSH terms

  • Biofilms
  • Cross-Sectional Studies
  • Drug Resistance, Multiple, Bacterial / genetics*
  • Humans
  • Iran
  • Microbial Sensitivity Tests
  • Molecular Epidemiology
  • Multilocus Sequence Typing
  • Staphylococcal Infections* / epidemiology
  • Staphylococcal Infections* / microbiology
  • Staphylococcus aureus* / drug effects
  • Staphylococcus aureus* / genetics
  • Staphylococcus aureus* / pathogenicity
  • Virulence Factors / genetics


  • Virulence Factors