Abstract
Purpose :
As staphylococci are known causative pathogens in ophthalmic infections, antibiotic resistance among these bacteria is of clinical concern. The Antibiotic Resistance in Ocular MicRoorganisms (ARMOR) study is the only ongoing nationwide surveillance study which evaluates in vitro antibacterial resistance among ocular pathogens, now in its 11th year. We examined preliminary 2019 data along with previous years’ data for longitudinal trends in antibiotic resistance among staphylococcal isolates.
Methods :
Throughout the years of study, Staphylococcus aureus and coagulase-negative staphylococci (CoNS) isolates from ocular infections were collected and sent to a central laboratory for species confirmation and susceptibility testing. Minimum inhibitory concentrations (MICs) were determined by broth microdilution according to Clinical and Laboratory Standards Institute guidelines and interpreted as susceptible/resistant based on established systemic breakpoints. Data were evaluated using Cochran-Armitage tests for linear trends in a proportion.
Results :
161 S. aureus and 130 CoNS have been collected to date in 2019 for a cumulative total of 2350 S. aureus and 1895 CoNS isolates collected, respectively, since study start in 2009 and evaluated herein. Preliminary results showed that oxacillin/methicillin resistance (MR) has continued to decrease among S. aureus (39% to 29%; P<0.001) but continues not to change among CoNS (P=0.693) with approximately half of CoNS exhibiting MR each year. Resistance also decreased for azithromycin (62% to 52%), ciprofloxacin (39% to 26%), and tobramycin (24% to 10%) among S. aureus (P<0.001 for all) while tetracycline resistance increased (4% to 9%; P=0.009). Among CoNS, ciprofloxacin resistance continues to decrease (46% to 32%; P=0.001) while trimethoprim resistance increased (26% to 42%; P=0.002). As in previous years, a high proportion of methicillin-resistant staphylococci demonstrated multidrug resistance (MDR; ≥3 antibiotic classes). In 2019, besifloxacin MIC90s (0.5 µg/mL for S. aureus and 4 µg/mL for CoNS) were 4- to 64-fold lower than other fluoroquinolones.
Conclusions :
Longitudinal analyses confirm decreased MR among S. aureus, although MR remains significant among CoNS. In vitro findings for antibiotic resistance among CoNS bear consideration when making treatment choices, especially given MDR and potential concurrent resistance to trimethoprim.
This is a 2020 ARVO Annual Meeting abstract.