Antibiotic Resistance Patterns in Cold-Adapted Bacillus subtilis From the Southern Ocean and Comparative Genomic Insights.

Background: Antibiotic resistance is a contemporary public health issue that poses significant environmental and public health concerns. The presence of antimicrobial-resistant (AMR) microbes has been reported across media irrespective of geography and landscape. This study aimed to analyze the antibiotic susceptibility of Bacillus subtilis obtained from the Indian Sector of the Southern Ocean (39°19' S, 57°30' E to 66°38' S, 76°22' E).

Methods: Bacillus subtilis was revived and cultured on Mannitol Yolk Polymyxin Agar. Antibiotic susceptibility was assessed via the agar well diffusion assay against 10 therapeutically significant antibiotics. Whole-genome sequencing was performed to identify the presence of AMR genes. A total of 12 AMR genes were identified via the Comprehensive Antibiotic Resistance Database (CARD). A comparative genomics approach was employed to investigate the global distribution of AMR genes from 2014 to 2024.

Results: Antibiotic susceptibility testing indicated complete resistance to metronidazole, while the isolates remained susceptible to ampicillin, doxycycline, tetracycline, ciprofloxacin, norfloxacin, cefixime, azithromycin, meropenem, and cotrimoxazole. Whole-genome sequencing and comparative analysis identified 12 AMR genes, including aadK, vanT (within the vanG cluster), ykkC, ykkD, vanW (within the vanI cluster), FosBx1, qacJ, qacG, tet(45), vanY (within the vanM cluster), and blt. The observed resistance mechanisms included antibiotic efflux, target modification, and enzymatic inactivation. Comparative genomic analysis of 15 closely related strains revealed variability in the distribution of AMR genes, with B. subtilis strain MB415 carrying all 12 resistance genes.

Conclusion: The detection of antibiotic-resistant B. subtilis in the Southern Ocean suggests potential anthropogenic influences on microbial communities, underscoring the need for continuous surveillance of AMR in remote marine environments to prevent its proliferation and mitigate its ecological consequences.