PC3014: In Vitro Antibiotic Resistance Among Bacterial Pathogens from Pediatric Patients with Eye Infections: 13-year Results from the ARMOR Study

Background: Antibiotic resistance may be problematic in eye infections and can complicate treatment. Antibiotic resistance data from large, multi-center, multi-year surveillance studies can provide clinicians with information to guide empirical therapy choices. The Antibiotic Resistance Monitoring in Ocular micRoorganisms (ARMOR) study is the only ongoing nationwide surveillance study focused exclusively on in vitro antibiotic resistance among common ocular pathogens. We report on ARMOR data among isolates collected from pediatric patients (≤17 years of age) from 2009 through 2021.

Methods: Each year in ARMOR, clinical centers across the US submit isolates of Staphylococcus aureus, coagulase-negative staphylococci (CoNS), Streptococcus pneumoniae, Haemophilus influenzae, and Pseudomonas aeruginosa, cultured from ocular infections in patients of any age, to a central laboratory for in vitro susceptibility testing. Minimum inhibitory concentrations (MICs) for up to 16 antibiotics (10 drug classes) are determined using broth microdilution methodology and interpreted as per Clinical and Laboratory Standards Institute (CSLI) guidelines and breakpoints. Here, data for isolates obtained from patients aged 0-17 were analyzed.

Results: A total of 1,658 isolates were collected from pediatric patients at 79 clinical sites across 36 states. Among S. aureus and CoNS, respectively, 58% and 74% were resistant to azithromycin and 24% and 46% were methicillin-resistant (MR); multidrug resistance (MDR; resistance to ≥3 drug classes) was found in 15% and 40%, and in 52% and 77% of MR strains thereof (Figure). Resistance to azithromycin (40%) and penicillin (36%) was noted among S. pneumoniae, while resistance was low ( < 2%) among H. influenzae to any of the tested antibiotics. Although all P. aeruginosa were resistant to polymyxin B, < 4% were resistant to other drugs. Respective MIC90s (MICs that inhibited 90% of isolates, in μg/mL) for besifloxacin/moxifloxacin/ciprofloxacin were 0.25/1/8 for S. aureus, 0.25/1/4 for CoNS, 0.06/0.25/1 for S. pneumoniae, 0.03/0.03/0.015 for H. influenzae, and 2/2/0.25 for P. aeruginosa.

Conclusion: In vitro antibiotic resistance is common among staphylococci and pneumococcal isolates collected from pediatric patients, with a high prevalence of MDR among staphylococci, especially in MR strains. Besifloxacin had the lowest MICs against staphylococcal and pneumococcal strains and a comparable MIC to other fluoroquinolones against H. influenzae; ciprofloxacin had the lowest MIC against P. aeruginosa. The clinical significance of these in vitro data is unclear without consideration of the ocular pharmacokinetics of tested antibiotics.