Characterization of South Florida Nocardia Keratitis: Trends, Risk Factors, Susceptibilities and Response to Photodynamic Therapy

Abstract

Purpose : Nocardia are a diverse group of aerobic actinomyces, ubiquitous in nature. Nocardia keratitis (NK) is a rare, recalcitrant corneal infection associated with risk factors including trauma and contact lens abuse. The clinical diagnosis and treatment of NK is often difficult, lending itself to inappropriate medications and poorer outcomes. Photodynamic antimicrobial therapy (PDAT) presents an alternative treatment utilizing light-activated photosensitizer to generate reactive oxygen species.

Methods : A retrospective chart review assessed NK incidence and species between 1990-2019. A pointed review of the last 10 years of NK cases examined risk factors, treatments and antibiotic susceptibilities. Susceptibility data not available in the medical record were obtained with Sensititre RAPMYCO AST Plates performed according to company procedures. Polymerase chain reaction and 16S ribosomal DNA sequencing speciated Nocardia isolates. Three common isolates of NK at Bascom Palmer Eye Institute, N. amikacinitolerans, N. farcinica and N. asteroides complex, were selected and retrieved based availability for PDAT experimentation. Alongside concentration-matched water, photosensitizer and irradiation controls, prepared isolates were irradiated for 15 minutes with 0.1% rose bengal (RB) and a custom 525 nm light source and compared to treatment with 0.1% riboflavin and a 375 nm light source (6mw/cm² each).

Results : There were 61 total isolates from 1990-2019. N. asteroides (30), N. amikacinitolerans (11), N. arthritidis (3), N. beijingensis (3), N. asteroides complex (3), N. farcinica (2), N. brasiliensis (2), N. kruczakiae (2), N. veterana, N. harenae and N. bhagyanarayanae were identified. In the last 10 years of NK, 85% of cases were associated with contact lenses. The MIC₉₀ for tobramycin, amikacin, moxifloxacin and ciprofloxacin were 16, 64, 8, and 4μg/ml, respectively. All strains of Nocardia mixed with 0.1% RB and irradiated for 15-minutes demonstrated more inhibition of growth compared to all controls and 0.1% riboflavin PDAT (Figure 1).

Conclusions : We detected an increased incidence of NK over the last 30 years and a notable association of infection with contact lens use. Amongst all strains, 0.1% RB PDAT founded greater inhibition versus 0.1% riboflavin PDAT.

This is a 2020 ARVO Annual Meeting abstract.

 

Figure 1. Comparison of 525 nm PDAT with 0.1% RB vs. 375 nm PDAT with 0.1% riboflavin for N. amikacinitolerans.