Vancomycin Resistance Screening in Methicillin-Resistant Staphylococci: Comparison of Vancomycin Screen Agar, E-strip and Broth Microdilution

Background: Detection of vancomycin resistance in methicillin-resistant staphylococci is essential because resistance may affect therapeutic choices and infection-control decisions. Vancomycin screen agar is a screening method, whereas E-strip and broth microdilution (BMD) provide MIC-based results. Objective: To describe and compare vancomycin screen agar, E-strip and BMD findings among methicillin-resistant Staphylococcus aureus (MRSA) and methicillin-resistant coagulase-negative staphylococci (MRCoNS) reported in this study. Methods: This cross-sectional laboratory study was conducted at Government Medical College and associated hospitals, Kota, Rajasthan, from March 2025 to February 2026. Two hundred clinical staphylococcal isolates were identified by standard microbiological methods. Methicillin resistance was assessed using cefoxitin disk diffusion method. Vancomycin susceptibility was screened using vancomycin screen agar and MICs were assessed by E-strip and BMD method. The study included 116 MRSA and 21 MRCoNS isolates. Screen-agar positivity and MIC-based vancomycin susceptibility was detected among methicillin resistant isolates. Wilson 95% confidence intervals (CIs) were calculated for proportions, and two-sided Fisher exact tests compared MRSA and MRCoNS proportions. Results: Vancomycin Screen agar was positive in 1/116 MRSA and 1/21 MRCoNS. E-strip and BMD both reported one vancomycin-resistant MRSA (1/116) and no resistant MRCoNS (0/21). The MRCoNS screen-positive result was not confirmed by either MIC method. Conclusion: One MRSA isolate was reported as vancomycin-resistant by VSA method confirmed by both E-strip and BMD, whereas no MRCoNS isolate was resistant to vancomycin by either of these methods. One MRCoNS screen-agar-positive (Vancomycin Resistant) result was discordant with MIC testing (susceptible by both E-strip and BMD).