In Vitro Antibiotic Resistance Among Bacteria from the Cornea in the Antibiotic Resistance Monitoring in Ocular MicRoorganisms Surveillance Study

Purpose: This study aimed to report on in vitro susceptibility patterns among corneal isolates collected in the Antibiotic Resistance Monitoring in Ocular micRoorganisms (ARMOR) study.

Methods: Each year, from 2009 to 2019, Staphylococcus aureus, coagulase-negative staphylococci (CoNS), Streptococcus pneumoniae, Pseudomonas aeruginosa, and Haemophilus influenzae isolates cultured from patients with ocular infections at participating ARMOR sites were submitted to a central laboratory for species confirmation and antibiotic susceptibility testing. In this analysis of corneal isolates, odds ratios for concurrent resistance were based on sample proportions, one-way ANOVA was used to evaluate resistance by patient age, and Cochran-Armitage tests were used to examine changes in antibiotic resistance over time.

Results: A total of 1499 corneal isolates were collected from 61 sites over the 11-year period. Overall, 34.5% (148 of 429) of S. aureus and 41.9% (220 of 525) of CoNS isolates were methicillin resistant and had higher odds ratios for concurrent resistance to azithromycin (17.44 and 5.67), ciprofloxacin (39.63 and 12.81), and tobramycin (19.56 and 19.95), respectively, relative to methicillin-susceptible isolates (P < .001, all); also, a high proportion of methicillin-resistant S. aureus (85.1%) and methicillin-resistant CoNS (81.8%) were multidrug resistant (at least three classes of antibiotics). Resistance among S. pneumoniae isolates was highest for azithromycin (33.1%), whereas P. aeruginosa and H. influenzae isolates demonstrated low resistance overall. Among staphylococci, antibiotic resistance differed by patient age (S. aureus: F = 6.46, P < .001; CoNS: F = 4.82, P < .001), and few small changes in resistance (≤3.60% per year), mostly decreases, were observed over time.

Conclusions: Although rates of in vitro antibiotic resistance among presumed keratitis isolates obtained in ARMOR seemed stable between 2009 and 2019, resistance among staphylococci and pneumococci remains high (and should be considered when treating keratitis).