AVR Funded Grant – 2022

Project Title:

The Bacterial Ocular Surveillance System (BOSS)

Chief Investigator:

Professor Stephanie Watson

Co-Investigators:

Prof Monica Lahra, A/Prof Richard Mills, Dr Steve Wiffen, Dr Maria Cabrera- Aguas

Aim

The aim of this study was to report the type of bacteria and antibiotic resistance of bacteria isolated from corneal scrapings in bacterial keratitis (corneal infections) from 2019 to 2022.

Methods

A retrospective analysis of bacteria isolated from cornea scrapings from 12 centres in Sydney, Melbourne, Adelaide, and Perth from January 1, 2019 to December 31, 2022 was conducted. Bacteria were identified by MALDI-TOF mass spectrometry. Antibiotic susceptibilities were determined using standard methodology.

Key results

There were 1791 organisms isolated. Of these, 1311 (73%) were Gram-positive and 480 (27%) Gram-negative organisms. Coagulase-negative staphylococci (CoNS) 32% (569/1791), Staphylococcus aureus 22% (398/1791), including 26 methicillin-resistant S. aureus (MRSA), Corynebacterium spp. 5% (83/1791); and Pseudomonas aeruginosa 14% (252/1791) were the most common organisms.

Antimicrobial non-susceptibility was found for CoNS to cefalotin 25%, chloramphenicol 12%, ciprofloxacin 7% and gentamicin 5%; methicillin-sensitive S. aureus (MSSA) to ciprofloxacin 6%, chloramphenicol 5%, gentamicin 1%; MRSA to ciprofloxacin 42% and gentamicin 8% and chloramphenicol 6%; Corynebacterium spp. to cefalotin 29%, ciprofloxacin 12%, chloramphenicol 9%; Pseudomonas aeruginosa to ciprofloxacin 2%, gentamicin 1.2%, and tobramycin 1%. All Gram-positive isolates were susceptible to vancomycin.

Implications for Clinical Practice/Science and Future Research

Results from this study will inform ophthalmologists on treating patients with bacterial keratitis according to antibiotic susceptibilities in each region in Australia. It is known that antibiotic susceptibilities change according to climate and geographical regions.

Next steps are to continue this surveillance program nationwide including other sites such Tasmania, Australian Capital Territory, Queensland, and Northern Territory. We also aim to include other infectious conditions such as conjunctivitis and endophthalmitis.

Conclusion

Coagulase negative Staphylococci were the main causal organisms of bacterial keratitis. Of these, one-quarter of these were resistant to cefalotin. An ongoing antimicrobial resistance surveillance program in ocular infections across Australia is needed to provide evidence-base therapy recommendations according to geographic locations..

Lay Summary of Outcomes

This study investigated the trends of bacteria and their antibiotic susceptibility from corneal scrapes from patients with corneal infection in Australia. Coagulase negative staphylococci were the main causal bacteria. Of these, 25% were resistant to cefalotin and 7% to ciprofloxacin.