ARMOR Study: 4-year data on antibiotic resistance of ocular pathogens

TAKE HOME: Analyses of antimicrobial susceptibility testing of ocular isolates collected during 2012 in the Antibiotic Resistance Monitoring in Ocular MicroRganisms (ARMOR) surveillance study reinforce concern about bacterial resistance and provide guidance on agent selection.

By Cheryl Guttman Krader; Reviewed by Terrence P. O’Brien, MD

Miami-Results from the fourth year of data collection in the Antibiotic Resistance Monitoring in Ocular MicroRganisms (ARMOR) surveillance study show that resistance rates of ocular pathogens have remained relatively stable during the program’s history. However, the findings highlight that pathogen resistance to many commonly used antimicrobial agents, including multi-drug resistance, are important issues.

Researchers from Bausch + Lomb presented the information on antibacterial minimum inhibitory concentration (MIC) values and susceptibility profiles for different ocular isolates at the 2013 annual meeting of the Association for Research in Vision and Ophthalmology (ARVO) in Seattle. Terrence P. O’Brien, MD, holder of the Charlotte Breyer Rodgers Distinguished Chair in Ophthalmology and co-director of the Ocular Microbiology Laboratory, Bascom Palmer Eye Institute, University of Miami Miller School of Medicine, Miami, attended the ARVO microbiology session and discussed the findings of the study with Ophthalmology Times.

“Awareness of evolving trends in antimicrobial susceptibility patterns is essential for rationally choosing optimal agents for treatment and prevention of ocular infections,” he said. “As such, ARMOR, which was launched several years ago to monitor antimicrobial resistance in ocular pathogens and especially to follow bacterial resistance to the fluoroquinolones, is an important project.

“These latest data reinforce concern about resistance of common pathogens to some commonly used antimicrobial agents, including fluoroquinolones,” Dr. O’Brien added. “They suggest that in some cases, a single agent may not be sufficient and rather that a combination of antimicrobial drugs may be preferred when treating active infection or for prophylaxis.”

Data analyses

The ARMOR analyses included data from 455 ocular infection isolates that were submitted during 2012 by 25 sites across the United States. The samples included 160 coagulase-negative Staphylococcus sp. (CoNS), 153 Staphylococcus aureus, 61 Streptococcus pneumoniae, 44 Pseudomonas aeruginosa, and 37 Haemophilus influenzae.

Comparisons of MIC₉₀ values (MIC inhibiting the visible growth of 90% of all isolates) for all organisms showed the activity of besifloxacin was consistently as good as or better than the other agents tested. MIC₉₀ values for besifloxacin ranged from 0.03 to 4 mcg/ml, and were ≤2 mcg/mL for all organisms except P. aeruginosa.

The ARMOR data also showed that CoNS and S. aureus had high rates of resistance to multiple antibiotics, with both organisms having resistance rates exceeding 30% for 7 of the 15 antibiotics tested. The methicillin-resistant strains of CoNS and S. aureus were more likely to be non-susceptible to other antibiotics as compared with the methicillin-sensitive strains. The rate of multidrug resistance for methicillin-resistant S. aureus and methicillin-resistant CoNS isolates exceeded 70%.

“Knowing the type and proportion of ocular pathogens that are potentially resistant, as well as the antibiotics to which they are less susceptible, allows selection of agents that have a broad spectrum of activity and proven efficacy against potentially sight-threatening organisms,” Dr. O’Brien said.

“The finding of resistance of common ocular pathogens to the fluoroquinolones that have been widely used as the agents of choice for infection treatment and prophylaxis is concerning,” he said. “However, there is some comfort in the fact that the latest anti-infective agent introduced for ophthalmic use, the C8-chloro-fluoroquinolone besifloxacin, still shows reasonable activity against many of these resistant pathogens.”

Terrence P. O’Brien, MD

E: tobrien@med.miami.edu

Dr. O’Brien has served as a non-salaried advisory and ad hoc consultant during the past year to Bausch + Lomb and other companies that market antimicrobial agents for ophthalmic use.