The most recent analyses of data from the ARMOR (Antibiotic Resistance Monitoring in Ocular micRoorganisms) Surveillance Program can guide clinicians choosing antibiotic therapy for initial empiric therapy and infection prophylaxis. The information also reinforces the importance of prudent antibiotic prescribing to limit the development of bacterial resistance to existing options, according to Penny Asbell, MD.
Analyses of data collected during the first 10 months of 2016 show that the level of antibiotic resistance continues to be high among staphylococcal isolates and especially among strains that are methicillin-resistant (MR). Furthermore, the rate of multidrug resistance for these microorganisms, i.e., resistance to 3 or more classes of antibiotic, remained high, especially among the MR strains.
“Susceptibility data collected during ARMOR provide information on current antibiotic resistance levels and trends over time for common ocular pathogens. Based on the reported data, ophthalmologists can make informed decisions when selecting effective treatments for their patients,” said Penny Asbell, MD, Professor of Ophthalmology, Icahn School of Medicine at Mount Sinai, and Director, Cornea and Refractive Surgery Center, Mount Sinai Hospital, New York, NY.
“These most recent data from the ARMOR study also emphasize previous findings that antimicrobial resistance continues to be a serious threat to ocular health, with many strains demonstrating resistance to multiple drug classes, and clinicians are encouraged to exercise judicious antibiotic use.”
The 2016 analysis included 359 isolates that were collected from 11 US centers that participate in ARMOR. The review of the minimum inhibitory concentration (MIC) data showed that all isolates of Haemophilus influenzae were susceptible to all antibiotics tested. Resistance among Pseudomonas aeruginosa isolates to fluoroquinolones was 7%, and although the rate is relatively low, it is more than twofold greater than the resistance rate in 2015.
For Streptococcus pneumoniae, about one-third of isolates exhibited non-susceptibility to azithromycin and to penicillin, but the susceptibility of these Gram-positive organisms to fluoroquinolones and chloramphenicol remained high.
Resistance rates for Staphylococcus aureus and coagulase-negative staphylococci (CoNS) were generally unchanged in 2016 compared to the year before. Across all staphylococcal species, the highest rates of resistance were seen for azithromycin (47% to 63%), oxacillin/methicillin (27% to 43%), and ciprofloxacin (25% to 30%). CoNS isolates also showed high levels of nonsusceptibility to tobramycin (20%) and trimethoprim (36%).
In 2016, besifloxacin continued to show the lowest MIC90 value for both S. aureus and CoNS isolates when compared with other topical fluoroquinolones. MIC90 values for besifloxacin, moxifloxacin, gatifloxacin, ciprofloxacin, and levofloxacin against S. aureus were 1, 4, 8, 64, and 32 μg/mL, respectively, and 2, 32, 32, 64, and 128 μg/mL, respectively, against CoNS isolates.
Multidrug resistance was observed in 24% of S. aureus isolates, 36% of CoNS isolates, 70% of MR-S. aureus, and 77% of MR-CoNS.