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2023 OMIG Abstract

Methicillin-Resistant Staphylococcus Aureus Keratitis Is Mainly Caused by Multidrug-Resistant Lineages That Are Associated with Poor Outcomes

Olivia Cummings, Camille Andre, Jennifer Ling, Sonia N. Yeung, Titus Wong, Alfonso Iovieno,
and Paulo J.M. Bispo

Department of Ophthalmology, Massachusetts Eye & Ear; Department of Ophthalmology and Visual Sciences, University of British Columbia; Vancouver Coastal Health, Vancouver, BC, Canada

Purpose: Methicillin-resistant Staphylococcus aureus (MRSA) is an increasingly common cause of multi-drug resistant (MDR) keratitis. This combined retrospective and laboratory-based study investigated patient characteristics, management, antimicrobial resistance (AMR) patterns, and outcomes in cases of MRSA keratitis at two tertiary institutions. AMR testing and genomic analysis on the patient-derived MRSA isolates were performed to elucidate connections between patient characteristics, AMR determinants, and other genome-level data.

Methods: Patients with MRSA keratitis treated at our institutions between 2005-2022 were included. Bacterial isolates collected from corneal scrapings were used for laboratory investigation and genomic analysis.

Results: We included a total of 70 eyes (67 patients) with culture-proven MRSA keratitis. The median age at diagnosis was 63 years (range 13-96). Most patients had a history of ocular surface disease (N=44, 67.7%) or prior ocular surgery (N=45, 65.2%). Most had no history of MRSA infection or extensive healthcare exposures (both N=53, 79.1%). Fortified vancomycin/tobramycin was the most common initial treatment (N=48; 61.5%). Eighteen cases (29.0%) underwent surgical management, including penetrating keratoplasty (N=7), tarsorrhaphy (N=5), and corneal gluing (N=8). Grafts or implants were removed in three cases for source control. Post-treatment BCVA was <20/60 for 12 eyes (24.0%) and >20/60 for 38 eyes (54.3%; N=20, 28.6% lost to follow-up). Sixty (85.7%) tested isolates were multidrug resistant and exhibited in vitro resistance to antibiotics used empirically in the treatment of corneal ulcers such as moxifloxacin (80.3%), ciprofloxacin (87.0%), and tobramycin (72.7%). MIC₅₀/MIC₉₀ for vancomycin were 1 µg/mL and 2 µg/mL, respectively. MIC₅₀/MIC₉₀ for moxifloxacin were 8 µg/mL and >32 µg/mL, respectively. All isolates were susceptible to vancomycin in vitro. No isolates displayed the heterogeneous vancomycin intermediate resistance phenotype or exhibited tolerance to vancomycin in vitro. Clonal complexes 5 and 8 were present on multilocus sequence type (MLST) analysis, with CC5 predominant. Trends toward differences between patient characteristics and MLST were noted.

Conclusions: Corneal MRSA infection engendered a high risk of poor visual outcomes in our population despite treatment with the recommended antibiotic regimen. Most were infected with highly MDR MRSA strains despite minimal healthcare exposure. This points to the existence of community-level niches, which may be opportunistic and cause sight-threatening infection in older patients with multiple ocular surface risk factors.

Disclosure: S (Massachusetts Lions Eye Research Fund, New England Corneal Transplant Research Fund)

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