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Sydney researchers identify improved topical therapy for microbial keratitis

An ongoing clinical study in Sydney has uncovered an alternative topical therapy to treat microbial keratitis in lieu of the antibiotics recommended by Therapeutic Guidelines Australia.

The Bacterial Ocular Surveillance System study (BOSS) found chloramphenicol in combination with ciprofloxacin/ofloxacin or gentamicin appears to be a suitable alternative, allowing eyecare professionals to choose the best antimicrobials for the corneal infection.

Stephanie Watson.

The findings come at a time when the World Health Organisation has called antimicrobial resistance (AMR) a global health threat. Resistant organisms can lead to ocular infection that can irreversibly damage eye structures, resulting in vision loss and even blindness.

However, prompt use of appropriate antimicrobials can preserve vision.

Professor Stephanie Watson, a corneal specialist and the head of the Corneal Research Group at the University of Sydney’s Save Sight Institute, and the head of the Corneal Unit at the Sydney Eye Hospital, is leading the BOSS study alongside Professor Monica Lahra from NSW Health Pathology.

Their 2017-2018 results have been published in Communicable Diseases Intelligence, a peer-reviewed scientific journal published by the Federal Department of Health.

Previously known as Keratitis Antimicrobial Resistance Surveillance Program, BOSS examined 374 bacteria isolated from cases of microbial keratitis at Sydney Eye Hospital from 1 January 2017 to 31 December 2018.

The central cornea has a white opacity known as ‘infiltrate’ with an epithelial defect and conjunctival injection.

AMR profiles were analysed in the context of the current Australian empiric regimens for topical therapy: ciprofloxacin/ofloxacin monotherapy versus combination therapy of cefalotin/cephazolin plus gentamicin.

At the Sydney Eye Hospital, combinations of chloramphenicol plus gentamicin, and chloramphenicol plus ciprofloxacin, are alternatively used, so they were also analysed in the study.

According to Watson and Lahra, the study reported no significant difference between antimicrobial cover provided either with ciprofloxacin/ofloxacin versus cefalotin/cephazolin plus gentamicin. Though greater toxicity and prolonged healing times have been associated with the latter.

Maria Cabrera-Aguas.

However, importantly, a treatment with chloramphenicol plus ciprofloxacin/ofloxacin or gentamicin, had significant improved cover.

Dr Maria Cabrera-Aguas, who compiled the report, said BOSS had allowed the research team to choose the best antimicrobials for microbial keratitis.

“I am looking forward to reporting BOSS data for 2019-2020 in 2021. We will need to watch for any further increases in resistance to cefalotin and whether fluoroquinolone resistance emerges, as has happened in the USA and India.”

The researchers said it was also important to understand why infection occurs, in order to prevent sight loss from microbial keratitis.

“Our review of 1052 cases of microbial keratitis cases from the Sydney Eye Hospital from 2012 to 2016 was published in Graefe’s Archive for Clinical and Experimental Ophthalmology journal in April 2020,” they said.

“Nearly nine out of 10 people had at least one predisposing factor; with contact lens wear the most common factor found in two-thirds of the cases.”

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