Antimicrobial resistance trends in bacterial keratitis over 5 years in Sydney, Australia

IMPORTANCE: Antimicrobial resistance (AMR) patterns in bacterial keratitis may fluctuate in a geographic location over time. BACKGROUND: To investigate any change in AMR patterns in Sydney, Australia. DESIGN: Retrospective case series. PARTICIPANTS: All patients with microbial keratitis who underwent a corneal scrape and culture from 2012 to 2016 at the Sydney Eye Hospital. METHODS: Matrix-assisted laser desorption ionization-time of flight (MALDI-TOF) mass spectrometry identified organisms. The Calibrated Dichotomous Susceptibility method determined antibiotic susceptibilities. MAIN OUTCOME MEASURES: Isolated organisms and antibiotic susceptibilities. RESULTS: There were 1084 corneal scrapes from 957 patients. The mean age was 54 years (range 18-100) and 52% were male. Cultures were positive in 711 of 1084 scrapes (66%), with 884 organisms identified. Of the bacteria isolated, 685 of 884 (78%) were Gram-positive and 199 of 884 (22%) were Gram-negative. Overall, the most common bacteria were coagulase-negative Staphylococci (CoNS) (405/884, 46%). Methicillin-resistance was detected in 7% of Staphylococcus aureus isolates (7/103). Methicillin-resistance in CoNS (ie, also cefalotin resistance) was reported in 19% of isolates and ciprofloxacin 8%. For methicillin-sensitive S aureus (MSSA), 5% of isolates were resistant to ciprofloxacin. For Corynebacterium spp., 34% of isolates were resistant to chloramphenicol and 9% to ciprofloxacin. The most common Gram-negative bacteria was Pseudomonas aeruginosa (109/199, 55%). One case was resistant to ciprofloxacin. CONCLUSIONS AND RELEVANCE: Coagulase-negative staphylococcal species were the most frequently suspected of causing bacterial keratitis. Increased resistance to cefalotin was identified for CoNS and to ciprofloxacin for Corynebacterium spp., MSSA and P aeruginosa compared to a previous study in Sydney in 2002 to 2003.