|High rates of in vitro resistance has only slightly decreased over 13 years. Photo: Delaney Kent, OD. Click image to enlarge.|
In ocular infections, staphylococci are among the most frequently reported bacteria. Two analyses of the ongoing Antibiotic Resistance Monitoring in Ocular micRoorganisms (ARMOR) study found that antibiotic resistance remains prevalent. These findings were recently presented during the 2022 ARVO annual meeting in Denver.
ARMOR, a nationwide surveillance study of in vitro antibacterial resistance levels among ocular pathogens, is currently in its 13th year. As part of this trial, Staphylococcus aureus and coagulase-negative staphylococci (CoNS) from ocular infections were collected each year and sent to a laboratory to confirm the species.
In one analysis, researchers examined longitudinal trends of the staphylococcal isolates collected, which included 2,847 S. aureus and 2,416 CoNS. Over the course of the 13-year collection period, data revealed that methicillin/oxacillin resistance decreased among both S. aureus and CoNS. The study authors also observed decreases in resistance 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.1
The researchers reported increases in resistance for chloramphenicol among S. aureus (6% to 34%) and for trimethoprim among CoNS (26% to 29%). When examining the staphylococci collected in 2021 specifically, they found that more than 80% of methicillin-resistant isolates exhibited resistance to three or more antibiotic classes.
Preliminary findings from an interim analysis of 446 isolates collected in 2021 were also presented. Among S. aureus, in vitro resistance was 53% to azithromycin, 37% to oxacillin/methicillin and 31% to ciprofloxacin. Among CoNS, in vitro resistance was 60% to azithromycin, 37% to oxacillin/methicillin, 20% to ciprofloxacin and 29% to trimethoprim.2
The data showed multi-drug resistance among 32% of S. aureus and 40% of CoNS isolates. Additionally, the rate of multi-drug resistance more than doubled in methicillin-resistant isolates. These initial findings revealed high rates of in vitro antibiotic resistance in ocular staphylococci collected in 2021 and are consistent with 2020 ARMOR data, according to the investigators.
“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,” the study authors wrote in their abstract. “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.”
Original abstract content © Association for Research in Vision and Ophthalmology 2022.
1. Asbell P, Sanfilippo C, DeCory H. Antibiotic resistance among ocular staphylococcal pathogens: longitudinal trends in the ARMOR study. ARVO 2022 annual meeting.
2. Sanfilippo C, DeCory H, Asbell P. Preliminary antibiotic resistance data among ocular bacterial pathogens in the ARMOR 2021 study. ARVO 2022 annual meeting.