Emergence of vancomycin-intermediate and -resistant Staphylococcus aureus among methicillin-resistant S. aureus isolated from clinical specimens in the northwest of Iran

Abstract

Objectives: The aim of this study was to evaluate the frequency as well as the phenotypic and molecular characteristics of methicillin-resistant Staphylococcus aureus (MRSA) and vancomycin-resistant S. aureus (VRSA) isolates from clinical specimens at three university teaching hospitals in Urmia, Northwest Iran, from 2012-2015.

Methods: Following identification of the isolates, antibiotic susceptibility testing was performed. The presence of the mecA, vanA and pvl genes was evaluated, and staphylococcal cassette chromosome mec (SCCmec) typing was performed.

Results: A total of 177 S. aureus isolates were collected from various clinical specimens. Antibiotic susceptibility testing revealed high resistance rates to penicillin (98.9%), followed by erythromycin (61.6%). A total of 95 isolates (53.7%) were confirmed as MRSA. Among the initially screened vancomycin-intermediate S. aureus (VISA) isolates, one isolate with a minimum inhibitory concentration (MIC) of 6μg/mL harboured the vanA gene. Eleven MRSA isolates (11.6%) were also VRSA. A majority (23/95; 24.2%) of MRSA were classified as SCCmec type III. Only 6 MRSA isolates (6.3%) harboured the pvl gene.

Conclusions: This study highlights the presence of MRSA along with VISA and VRSA in our setting. To our knowledge, this is the first report showing that a strain can be defined as VISA phenotypically and as VRSA by molecular analysis. Such a finding raises major concerns with regard to control measures and reliable laboratory tests for screening of resistant strains.

Keywords: Methicillin-resistant; SCCmec; Staphylococcus aureus; Vancomycin-resistant.