Investigation of the VISA and hVISA Presence in Methicillin-Resistant Staphylococcus aureus Isolates by Various Methods

Abstract

Staphylococcus aureus is an important human pathogen that causes community and hospital-acquired infections. The role of vancomycin in the treatment of methicillin-resistant S.aureus infections is indisputable. However, vancomycin intermediate susceptible S.aureus (VISA) and heterogeneously VISA (hVISA) isolates, that cause treatment failures during the use of vancomycin, cannot be detected by routine laboratory methods. The gold standard method for the detection of these isolates is the population profile analysis-area under the curve (PAP-AUC) method. In this study, it was aimed to determine the presence of mecA and mecC gene regions that cause methicillin resistance, the clonal relationship between isolates, and the presence of VISA and hVISA. A total 68 methicillin-resistant S.aureus (MRSA) strains were included in this study which were isolated in the microbiology laboratory of the hospital between 2015- 2020. Identification of the isolates were determined by matrix assisted laser desorption ionization-time of flight mass spectrophotometry (VITEK MS, BioMérieux, France). Methicillin resistance was investigated by disk diffusion method using cefoxitin (30 µg, Bioanalyse, Türkiye) disk and vancomycin MIC values were determined by broth microdilution method. mecA and mecC gene regions were investigated by polymerase chain reaction (PCR) method. The presence of VISA and hVISA were investigated by modified agar screening, macro gradient diffusion test and confirmated by PAP-AUC methods, and the clonal relationship between isolates were investigated by pulsed field gel electrophoresis method. The mecA gene region was determined in all isolates, but the mecC gene region was not found in any of the isolates. The MIC50 value of the isolates was determined as 1 μg/mL and the MIC90 value was determined as 2 μg/mL by broth microdilution method. Six VISA and four hVISA suspected strains were detected by a modified agar screening method. Among the isolates identified as suspicious by the modified agar screening method, one isolate was evaluated as VISA and one isolate was evaluated as hVISA by the gold standard PAP-AUC method. No dominant epidemic isolate has been identified by PFGE. As a result, VISA and hVISA were determined in the hospital. The increase in these isolates is a serious concern. For this reason, it is believed that it would be beneficial to investigate the VISA/hVISA ratios in MRSA isolates at certain periods, and to take necessary infection control measures to implement measures and practices to prevent the spread of these isolates in the community and hospital environment.