Emergence of High-Level Vancomycin Resistance in Staphylococcus aureus: Dissemination of vanA and vanB genes in Clinical MRSA and VRSA Isolates from Pakistan

Abstract

Background: The emergence of vancomycin-resistant Staphylococcus aureus (VRSA) poses a significant threat to public health, severely limiting therapeutic options for life-threatening infections. This study aimed to determine the prevalence of VRSA among clinical isolates, characterize their antimicrobial resistance profiles, and detect the presence of key vancomycin resistance genes, vanA and vanB. Methods: A cross-sectional study was conducted on 203 non-duplicate S. aureus isolates collected from a tertiary care hospital in Islamabad, Pakistan. Isolates were identified using standard microbiological techniques (Gram stain, catalase, coagulase) and confirmed by 16S rRNA sequencing. Antimicrobial susceptibility testing (AST) was performed using the Kirby-Bauer disk diffusion method, with MRSA identified by cefoxitin resistance. Minimum inhibitory concentrations (MICs) for vancomycin were inferred from disk diffusion, and isolates showing resistance were further analyzed. Conventional PCR was employed to detect the vanA and vanB resistance genes. Results: Of the 203 S. aureus isolates, 41 (20.2%) were identified as methicillin-resistant S. aureus (MRSA). The MRSA isolates exhibited high levels of resistance to multiple antibiotic classes, including penicillin G (100%), erythromycin (87.5%), ciprofloxacin (75.7%), and co-trimoxazole (59.5%). Alarmingly, 2 (4.9%) of the MRSA isolates were confirmed as VRSA. Molecular analysis revealed a high prevalence of resistance determinants in the VRSA strains, with vanA detected in both isolates (100%), vanB in one isolate (50%), and one isolate harboring both genes. Among all MRSA isolates, the prevalence of vanA was 12.2% (5/41), vanB was 4.9% (2/41), and 14.6% (6/41) carried at least one of these genes. Conclusion: This study confirms the presence of VRSA in a major healthcare facility in Pakistan, with resistance mediated by the transferable vanA and vanB genes. The co-existence of multidrug resistance (MDR) in these isolates presents a critical clinical challenge. These findings underscore the urgent need for enhanced antimicrobial stewardship, routine surveillance for VRSA, and molecular characterization of resistance mechanisms to guide infection control policies and preserve the efficacy of last-resort antibiotics.

Keywords: VRSA, MRSA, Antimicrobial Resistance, vanA, vanB, Vancomycin Resistance, Pakistan