Abstract
Purpose :
Staphylococci are among the most common causative bacteria in ocular infections, and antibiotic resistance in these pathogens may lead to treatment failure. The Antibiotic Resistance Monitoring in Ocular micRoorganisms (ARMOR) surveillance study informs on evolving antimicrobial susceptibility patterns in ocular bacterial pathogens. Here, we analyzed in vitro antibiotic resistance among staphylococcal isolates collected from 2009 through 2020 to date in ARMOR for trends over time.
Methods :
Each year in ARMOR, Staphylococcus aureus and coagulase-negative staphylococci (CoNS) isolated from ocular infections are collected and sent to a central laboratory for species confirmation and susceptibility testing. Minimum inhibitory concentrations (MICs) are determined and interpreted as susceptible/resistant to 16 different antibiotics based on Clinical and Laboratory Standards Institute methods and breakpoints. Data for resistance to various drugs among 2599 S. aureus and 2143 CoNS were evaluated here using the Cochran-Armitage test for linear trends in a proportion.
Results :
Trend analysis showed a decrease in methicillin resistance (MR) among S. aureus (39 to 36%; P<0.001) but no change in MR among CoNS (~50% each year P=0.176). Additional decreasing trends in resistance were noted to azithromycin (62% to 57%), ciprofloxacin (39% to 33%), and tobramycin (24% to 16%) among S. aureus (P<0.001 for all), and to ciprofloxacin among CoNS (46% to 26%; P<0.001). In contrast, resistance increased to tetracycline among S. aureus (4% to 7%; P=0.034) and to trimethoprim among CoNS (26% to 28%; P=0.026). Multidrug resistance (≥3 antibiotic classes) among methicillin-resistant strains remained prevalent in 2020, although no isolates were vancomycin resistant. Besifloxacin retained consistently low MICs, with 2020 MIC90s (1 µg/mL for S. aureus and 2 µg/mL for CoNS) up to 128-fold lower than other fluoroquinolones.
Conclusions :
Over a 12-year span, staphylococci generally exhibited minimal or no change in in vitro antibiotic resistance. Although a small decrease in MR was observed among S. aureus (but not CoNS), the high level of MR in staphylococci warrants attention when selecting empiric antibiotic therapy, particularly with respect to multidrug resistance in these organisms.
This is a 2021 ARVO Annual Meeting abstract.