Prevalence and characterization of vancomycin-resistance genes in Staphylococcus spp. isolated from clinical samples

Background: Vancomycin has been the cornerstone for treating multidrug-resistant Staphylococcus infections. However, the emergence of vancomycin-resistant Staphylococcus spp. (VRSA and resistant CoNS) poses a growing clinical challenge. Early detection of vancomycin-resistance genes is crucial for guiding therapy and preventing spread. Objectives: To determine the prevalence and molecular characterization of vancomycin-resistance genes among Staphylococcus spp. isolated from clinical samples in a tertiary care hospital in Bhubaneswar, India. Methods:A total of 124 Staphylococcus spp. isolates were obtained by streaking from culture plates of diverse clinical samples, collected from patients at IMS and SUM Hospital, Bhubaneswar, India, between January to June 2025.Antimicrobial susceptibility testing was performed using the disc diffusion method according to CLSI guidelines. PCR amplification targeting the vanA gene was conducted to confirm vancomycin-resistance determinants at the molecular level. Results:Pus accounted for the largest source of isolates (33.87%), followed by BAL fluid (20.9%) and blood (18.54%). Antimicrobial susceptibility testing showed high resistance rates to penicillin (70.96%), cefazolin (67.74%), and chloramphenicol (62.9%). Vancomycin disc diffusion, a preliminary screening test, indicated reduced susceptibility/resistance in 27 isolates (21.7%). In contrast, PCR amplification revealed 86 positive bands among all isolates (), and specifically, 70 out of 100 S. aureus isolates (70%) carried vancomycin-resistance determinants (vanA gene). Newer antimicrobials retained strong activity, with teicoplanin (89.51%), linezolid (86.29%), and tigecycline (85.4%) showing the highest sensitivity. Conclusion:Molecular detection revealed a substantially higher prevalence of vancomycin-resistance determinants (the vanA gene) than disc diffusion screening, suggesting that unvalidated phenotypic assays may significantly underestimate the presence of resistance genes. These findings emphasize the urgent need for routine molecular surveillance, other phenotypic methods like MIC, E tests, etc , rational antibiotic use, and robust infection control practices to mitigate the growing threat of vancomycin-resistant Staphylococcus spp. in clinical settings.