The investigation of low-level resistance to vancomycin in methicillin-resistant staphylococcus aureus isolates

ABSTRACT Aim: S. aureus is one of the leading pathogens causing community and hospital-acquired infections. Vancomycin is the first antibiotic of choice in the treatment of MRSA infections. VISA and hVISA strains that cause treatment failure in patients receiving vancomycin therapy can't be detected by routine laboratory methods. The gold standart method for the detection of these strains is the PAP-AUC method. In our study, we aim to investigate the presence of VISA and hVISA with the PAP-AUC method. Materials and Methods: 68 MRSA strains isolated from various samples sent to our hospital's microbiology laboratory between 2015-2020 and stocked at -80 degrees were included in our study. First of all, the presence of mecA and mecC genes was investigated by PCR method in all showers with methicillin resistance determined by cefoxitin disk diffusion method. The presence of VISA and hVISA was investigated in these strains by macro E-test, agar screening, broth microdilution and PAP-AUC methods. The clonal relationship between strains was investigated by PFGE method. Results: Although all strains contain the mecA gene, no mecC gene was found in any strain. All strains were in the susceptible category, except for one strain of which MIC value was 4 μg/ml by broth microdilution method. No suspicious isolate was found as a result of the scanning performed with the macro E-test method. As a result of the screening performed with brain heart infusion agar containing 2 μg/ml vancomycin, 6 VISA and 4 hVISA suspect strains were detected. With the PAP-AUC method, which is the gold standart method, one of these suspicious strains, the strain with a MIC value of 4 μg/ml, were evaluated as VISA and one as hVISA. No dominant outbreak strain detected with PFGE. Conclusion: The possibility of VISA and hVISA in patients who fail during vancomycin treatment used in MRSA infections should be considered and vancomycin should be used more rationally in order to avoid treatment failure. Keywords: hVISA, mecA, mecC, MRSA, PAP-AUC, S. aureus, VISA