Antibiotic susceptibility of bacterial pathogens isolated from the aqueous and vitreous humour in the Antibiotic Resistance Monitoring in Ocular micRoorganisms (ARMOR) Surveillance Study: 2009–2020 update

ABSTRACT: Objectives: We evaluated antibiotic resistance among intraocular isolates obtained from presumed endophthalmitis cases collected from 2009 through 2020 in the Antibiotic Resistance Monitoring in Ocular micRoorganisms (ARMOR) study, the only ongoing nationwide surveillance study tracking in vitro resistance in ocular pathogens. Methods: Presumed endophthalmitis isolates obtained from the aqueous humour and vitreous humour were collected from participating centres, and minimum inhibitory concentrations were determined and interpreted per Clinical and Laboratory Standards Institute methods and available breakpoints. Results: A total of 307 presumed endophthalmitis isolates (aqueous humour, n = 88; vitreous humour, n = 219) were obtained from 43 clinical sites, including 188 coagulase-negative staphylococci (CoNS), 61 Staphylococcus aureus, 31 Streptococcus pneumoniae, 14 Pseudomonas aeruginosa, and 13 Haemophilus influenzae isolates. Of the CoNS isolates, 47.9% (90/188) were methicillin resistant, 58.0% (109/188) were azithromycin resistant, and 46.3% (87/188) were ciprofloxacin resistant. Of the S. aureus isolates, 45.9% (28/61) were methicillin resistant, 57.4% (35/61) were azithromycin resistant, and 44.3% (27/61) were ciprofloxacin resistant. Multidrug resistance (MDR; i.e., resistance to ≥3 antibiotic classes) was prevalent among staphylococci, particularly methicillin-resistant strains, of which >70% exhibited MDR. Resistance among S. pneumoniae isolates was notable for azithromycin and penicillin, each 38.7% (12/31), and for polymyxin B among P. aeruginosa 100.0% (14/14), whereas no resistance was observed for H. influenzae isolates to the antibiotics tested. Conclusion: In vitro antibiotic resistance was common among presumed endophthalmitis isolates collected in the ARMOR surveillance study. These data could inform antibiotic selection for infection prophylaxis and/or treatment of intraocular infections.