Abstract
Purpose :
Staphylococci are among the most frequently reported causative bacteria in ocular infections, and antibiotic resistance in these pathogens can complicate treatment. The Antibiotic Resistance Monitoring in Ocular micRoorganisms (ARMOR) study is a nationwide surveillance study on in vitro antibacterial resistance levels among ocular pathogens now in its 13th year. Here, we examined resistance trends over time among staphylococcal isolates collected from 2009 through 2021 to date in ARMOR.
Methods :
Each year as part of ARMOR, Staphylococcus aureus and coagulase-negative staphylococci (CoNS) from ocular infections were collected and sent to a central laboratory for species confirmation. Minimum inhibitory concentrations (MICs) were determined for up to 16 different antibiotics and interpreted as susceptible/resistant based on Clinical and Laboratory Standards Institute methods and breakpoints. Longitudinal trends in resistance were evaluated using Cochran-Armitage tests for linear trends in a proportion.
Results :
A total of 2847 S. aureus and 2416 CoNS were included in this analysis. Over the 13-year collection period, methicillin/oxacillin resistance decreased among both S. aureus (39 to 37%; P<0.001) and CoNS (53 to 37% P=0.003). Decreases in resistance were also observed for azithromycin (62% to 53%), ciprofloxacin (39% to 31%), and tobramycin (24% to 12%) among S. aureus, and for ciprofloxacin (46% to 20%) among CoNS (P<0.001 for all). In contrast, increases in resistance were noted for chloramphenicol among S. aureus (6% to 34%; P<0.001) and for trimethoprim among CoNS (26% to 29%; P=0.044). Of staphylococci collected in 2021 specifically, >80% of methicillin-resistant isolates exhibited multidrug resistance (≥3 antibiotic classes). Cumulative besifloxacin MIC90s (1 µg/mL for S. aureus and 2 µg/mL for CoNS) were 4- to 128-fold lower than other fluoroquinolones and comparable to vancomycin.
Conclusions :
Analyses of antibiotic resistance among staphylococci collected over 13 years in ARMOR indicate that in vitro resistance has decreased only slightly over this timeframe for several antibiotics and is still prevalent in 2021. Although the clinical relevance of in vitro data is unclear without consideration of the ocular pharmacokinetics of tested antibiotics, these findings warrant attention when choosing empiric therapy for the management of ocular staphylococcal infections.
This abstract was presented at the 2022 ARVO Annual Meeting, held in Denver, CO, May 1-4, 2022, and virtually.