In Vitro Antibiotic Resistance Among Ocular Bacterial Pathogens from Children in the ARMOR Surveillance Study

Background: Bacterial eye infections are frequently encountered in pediatric medicine, and antibiotic resistance among causative pathogens may complicate empirical treatment. In vitro data from large, multi-center, multi-year antibiotic resistance surveillance studies are useful for tracking resistance to commonly used antibiotics. The Antibiotic Resistance Monitoring in Ocular Microorganisms (ARMOR) study is the only ongoing nationwide antibiotic resistance surveillance program specific to ocular bacteria. Here, we report on in vitro antimicrobial susceptibility data for isolates collected from pediatric patients (≤17 years of age) in ARMOR from 2009 through 2020.

Methods: Clinical centers across the United States submitted isolates of Staphylococcus aureus, coagulase-negative staphylococci (CoNS), Streptococcus pneumoniae, Haemophilus influenzae, and Pseudomonas aeruginosa, cultured from ocular infections in patient of any age, to a central laboratory for susceptibility testing. Minimum inhibitory concentrations (MICs) were determined by broth microdilution methodology for up to 16 antibiotics according to the Clinical and Laboratory Standards Institute guidelines, and isolates were categorized as susceptible or resistant to the antibiotics tested based on systemic breakpoints, where available. Data for isolates obtained from patients aged 0-17 and the subset thereof for patients aged 0-3 years were extracted and analyzed.

Results: A total of 1532 isolates were collected from pediatric patients at 78 clinical sites across 36 states. Among S. aureus and CoNS, respectively, 57% and 74% were resistant to azithromycin and 22% and 50% were methicillin-resistant (MR); multidrug resistance to ≥3 drug classes (MDR) was prevalent among MR strains (51% and 72%). Resistance among S. pneumoniae was notable for azithromycin (40%) and penicillin (35%), while resistance to tested antibiotics was <2% among isolates of H. influenzae. Although all isolates of P. aeruginosa were resistant to polymyxin B, <5% were resistant to other agents. Besifloxacin was found to have 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 (Table). Resistance rates were similar among isolates from patients aged 0-3 years, with the exception of a lower rate of MDR among MR S. aureus and CoNS (2% and 44%).

Conclusion: In vitro antibiotic resistance appears common among staphylococcal and pneumococcal isolates collected from pediatric patients, with MR staphylococci exhibiting high levels of MDR. The clinical relevance of these data are unclear without additional consideration of the ocular pharmacokinetics of tested antibiotics.