The conundrum of ocular corynebacteria: are Corynebacterium macginleyi and Corynebacterium bovis commensals?

This study sought to establish the prevalence of Corynebacterium macginleyi and Corynebacterium bovis ocular colonisation in healthy adult individuals. Eye swabs and contact lenses were collected from adults with no symptoms or signs of active eye infection or inflammation. Specimens were cultured on both solid and liquid media. Isolates were identified by matrix-assisted laser desorption ionisation-time of flight mass spectrometry. Susceptibility testing was performed according to European Committee on Antimicrobial Susceptibility Testing methods. A total of 106 participants were included in the study who provided 212 eye swabs. Two sets of contact lenses were received. Coagulase-negative staphylococci and Corynebacterium species were the most frequently isolated organisms in our healthy participants. C. bovis was isolated in eight of 106 (7.5%) healthy individuals with no symptoms of eye disease. C. macginleyi colonisation rates were similar: five of 106 (4.7%). All C. macginleyi isolates tested susceptible to linezolid, tetracycline and vancomycin, with variable susceptibilities to clindamycin. All C. bovis isolates were susceptible to linezolid, tetracycline and vancomycin. All C. macginleyi and C. bovis isolates tested susceptible increased exposure to ciprofloxacin and penicillin. This study demonstrates C. macginleyi and C. bovis colonisation in the absence of eye infections in healthy individuals. This study highlights the complexity of the organisms and ocular health, underscoring the need for clinical correlation when isolated in low abundance in clinical specimens.