Antibiotic resistance among ocular pathogens: current trends from the ARMOR surveillance study (2009-2016)

The Antibiotic Resistance Monitoring in Ocular micRoorganisms study is an ongoing surveillance study that tracks antibiotic resistance among bacterial isolates from ocular infections across the United States. We report antibiotic resistance rates and trends from 2009 through 2016.

Staphylococcus aureus, coagulase-negative staphylococci (CoNS), Streptococcus pneumoniae, Pseudomonas aeruginosa, and Haemophilus influenzae from various ocular infections were obtained from participating United States centers. Isolates were sent to a central laboratory for determination of antibiotic resistance profiles. Minimum inhibitory concentrations were determined by broth microdilution according to the Clinical and Laboratory Standards Institute for drugs from more than ten antibiotic classes, and isolates were classified as susceptible or resistant based on systemic breakpoints, wherever available. Resistance rates were also evaluated based on decade of patient life and longitudinally over the 8-year time period.

A total of 1,695 S. aureus, 1,475 CoNS, 474 S. pneumoniae, 586 H. influenzae, and 599 P. aeruginosa were collected from 87 sites. Resistance was high among staphylococci and pneumococci, with methicillin resistance detected in 621 (36.6%) S. aureus and 717 (48.6%) CoNS isolates. Multidrug resistance (≥3 drug classes) was observed among staphylococci, particularly in methicillin-resistant (MR) isolates (MR S. aureus [MRSA]: 76.2%; MR CoNS [MRCoNS]: 73.5%). Differences in methicillin resistance among staphylococci were observed based on patient age, with higher rates observed in older patients (P<0.0001). For certain organism-antibiotic combinations, there were significant changes in resistance over time, including a decrease in methicillin resistance among S. aureus (but not CoNS); no notable trends were observed for S. pneumoniae.

Antibiotic resistance was prevalent among gram-positive organisms, and MR staphylococcal isolates were more likely to be multidrug resistant. Although a small decrease in methicillin resistance was observed among S. aureus over time, the continued high prevalence of in vitro methicillin resistance should be considered when treating patients with ocular infections.