Ocular Microbiology and Immunology Group
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2026 OMIG Abstract

Virulence Factor Signatures of Ocular Staphylococcus aureus Clinical Isolates from India and the United States

Jordan N Reed¹, Divya TejSowpati², Karthik Bharadwaj Tallapaka², Prashant Garg³, Joveeta Joseph⁴,
and Rachel Wozniak¹

¹University of Rochester School of Medicine, Rochester, New York; ²CSIR Centre for Cellular and Molecular Biology, Hyderabad, India; ³Shantilal Shanghvi Cornea Institute, LV Prasad Eye Institute, Hyderabad, India; ⁴Jhaveri Microbiology Centre, LV Prasad Eye Institute, Hyderabad, India

Purpose: Staphylococcus aureus is a major causative organism of infectious keratitis (corneal infection). The survival, pathogenicity, and response to treatment of S. aureus in ocular tissue is likely due to acquired, physiological niche-driven virulence and antibiotic resistance factors, which may differ across diverse geographic regions. We sought to leverage bacterial whole-genome sequencing to identify resistance and virulence factor signatures in ocular clinical isolates from the US and India to provide further insight into the pathogenesis and diversity of S. aureus keratitis.

Methods: 65 S. aureus ocular isolates from India and 80 from the USA were collected between 2019-2025. Whole genome sequencing was performed, and using a custom in silico pipeline, genomes were assembled and interrogated for traditional strain typing markers (Multilocus Sequence Type (MLST), agr, spa, SCCmec). Antibiotic resistance signatures for each strain were defined using a custom database of 80 mutations and genes that confer antibiotic resistance in S. aureus. Virulence factor signatures were constructed using our custom database of 448 genes with a known or putative virulence function in S. aureus.

Results: India and US ocular S. aureus populations varied widely in strain type; the most common MLST in India was ST22 (n=12) and in US was ST8 (n=18). Only five ST groups were identified in both populations, and the spa types were similarly distinct. Considering antibiotic resistance, Indian strains had significantly higher rates of fluoroquinolone resistance markers compared to US strains (96.9% vs 33.8%, p < 0.001). Additionally, the mechanism of fluoroquinolone resistance significantly varied between populations; for example, the S80F mutation in gene grlA was nearly exclusively identified in Indian strains (93.8% vs 1.3%, p < 0.001), while only US strains had the E84G mutation (13.8% vs 0.0%, p = 0.003). Indian strains also had higher rates of trimethoprim resistance (44.6% vs 6.3%, p < 0.001), while USA strains had higher resistance to Fosfomycin (80.0% vs 41.5%, p < 0.001). Virulence profiles were also distinct between countries. 30 virulence factors were significantly more present in Indian strains, including collagen adhesin (cna), enterotoxins sec3, sel, seh, seb, sel26, and sea, and toxins psmb2, sak, ete, and edinB. Conversely, 29 virulence factor genes were significantly more present in USA isolates, including lipoprotein-like lpl3, lpl1, lpl4, and lpl9, proteases splC and splF, and toxin secretion genes esaG1 and esaD.

Conclusions: Ocular S. aureus strains from India and the US have distinct antibiotic resistance and virulence profiles. The differences suggest unique pathogenic mechanisms and may ultimately provide insight into disease prognosis and treatment.