Antibiotic resistance determinants among ocular vs non-ocular Staphylococcus aureus clinical isolates

Staphylococcus aureus is an important pathogen, and the etiologic agent of more than 70% of ocular and peri-orbital infections causing severe tissue damage including permanent blindness. Ocular infections may be confounded by antibiotic resistance, and the breadth and nature of resistance among ocular S. aureus isolates is an area of active investigation. Therefore, we harnessed whole genome sequencing of 163 ocular S. aureus isolates from around the world and the CARD antimicrobial resistance database to investigate the prevalence of 21 classes of resistance genes. In order to identify emerging circulating resistance determinants that may be of particular importance among ocular S. aureus we utilized a collection of 116 publicly available non-ocular S. aureus genomes as a comparator strain set.

Among ocular and non-ocular isolates, antimicrobial efflux pumps associated with fluoroquinolone (Oc: N = 151, 92%; NonOc: N = 116, 100%) and tetracycline (Oc: N = 151, 92%; NonOc: N = 115, 99%) resistance were the most prevalent. However, aminoglycoside and macrolide efflux systems (NonOc: N = 109 (94%) vs Oc: N = 79, 48%; P < 0.0001), and the tetracycline resistance gene tetM (NonOc: N = 26 (23%) vs Oc: N = 2 (1%), P < 0.0001) were found more commonly among non-ocular isolates. Moreover, resistance determinants for daptomycin (N = 3, 2%), rifampin (N = 12, 11%), and trimethoprim/sulfamethoxazole (N = 10, 8%) were only present among non-ocular isolates. In contrast, blaZ-like b-lactamases were significantly more prevalent among ocular isolates (Oc: N = 115, 71%; NonOc: N = 33, 28%; P < 0.0001).

Antimicrobial resistance prediction software was able to detect significant differences in the antimicrobial resistance profiles between ocular and non-ocular S. aureus isolates perhaps reflecting different therapeutic selection pressures in these two groups, and supporting the need for further exploration of S. aureus isolates causing ocular disease.