Prevalence and Detection of Heteroresistant Vancomycin-Intermediate Staphylococcus aureus (hVISA) Among Clinical Isolates: A Comparative Evaluation of Screening Methods.

BACKGROUND

Staphylococcus aureus is a major human pathogen, with methicillin-resistant S. aureus (MRSA) posing a significant challenge due to its resistance to multiple antibiotics. Vancomycin remains the drug of choice for MRSA infections; however, resistance mechanisms such as vancomycin-intermediate S. aureus (VISA) and heteroresistant VISA (hVISA) have emerged, leading to treatment failures. This study aimed to determine the prevalence of hVISA among clinical isolates and compare the efficacy of different screening methods.

METHODS

A prospective, observational study was conducted over 1.5 years, analyzing 102 non-duplicate clinical isolates of S. aureus from various specimens. Identification and antimicrobial susceptibility testing were performed using standard microbiological methods. MRSA detection was done using cefoxitin disc diffusion, while vancomycin susceptibility was assessed using minimum inhibitory concentration (MIC) determination. hVISA screening was performed using four methods: brain heart infusion agar with 4 µg/mL vancomycin (BHIV4), gradient plate method (GPM), macro E-test (MET), and E-test GRD, as these methods have been shown to be more effective than other screening techniques in previous studies. The PAP-AUC ratio was used as the gold standard for hVISA confirmation.

RESULTS

Among the 102 isolates, 49.02% were MRSA, and all were susceptible to vancomycin based on MIC values. However, 8.82% exhibited the hVISA phenotype out of the total S. aureus (102) isolates. hVISA was more prevalent in hospital-acquired infections (100% of hVISA isolates) than in community-acquired cases. The BHIV4 method showed the highest sensitivity (88.89%), while the gradient plate method had the highest specificity (94.62%).

CONCLUSION

The detection of hVISA is critical for optimizing treatment strategies and preventing therapeutic failures. The study suggests that BHIV4 screening can serve as an effective method for initial hVISA detection. Continuous surveillance and judicious antimicrobial use are essential to curb the emergence of resistance.