Purpose:
Antibiotic resistance is a serious concern in the treatment of bacterial infections of the eye. The ARMOR (Antibiotic Resistance Monitoring in Ocular MicRoorganisms) surveillance study was initiated in 2009 to monitor resistance trends among bacterial pathogens of ocular significance. Here we report the study results for the year 2011.
Methods:
Thirty-two sites were enrolled to submit ocular isolates of Streptococcus pneumoniae, Staphylococcus aureus, coagulase-negative staphylococci (CoNS), Pseudomonas aeruginosa, and Haemophilus influenzae for antibiotic susceptibility testing. Broth microdilution minimum inhibitory concentrations were determined for 14-16 representative antibiotics against 517 isolates per Clinical and Laboratory Standards Institute methods. Isolates were categorized as susceptible, intermediate, or resistant based on systemic breakpoints (where available).
Results:
While almost 46% of S. pneumoniae isolates were resistant to azithromycin, fewer than 6% of isolates were non-susceptible to imipenem, ceftriaxone, chloramphenicol, or penicillin. All isolates were susceptible to the fluoroquinolones. Resistance among the staphylococci was highest for azithromycin (63-66%), oxacillin (39-41%), and ciprofloxacin (30-42%). Among the fluoroquinolones, besifloxacin had the lowest MIC90, which was within one serial dilution of vancomycin. More than 37% of the CoNS and over 42% of the S. aureus isolates were intermediate or resistant to three or more drug classes; 7% and 13%, respectively, were non-susceptible to six or more drug classes. Among P. aeruginosa isolates, 27% were non-susceptible to polymyxin B, followed by ciprofloxacin (7%), imipenem (2%), and tobramycin (0%). No resistance was detected among the H. influenzae isolates.
Conclusions:
Multi-drug resistance in staphylococci remains prevalent among ocular pathogens. However, compared to the data from the two previous ARMOR studies, the current surveillance data show similar or decreased levels of non-susceptibility for most bacteria / drug combinations. Future studies will be needed to determine if this indicates a true decrease in resistance across the US or simply reflects sampling variations, e.g. due to geographical differences in participating study sites between each year of the study.
Keywords: bacterial disease • antibiotics/antifungals/antiparasitics • clinical (human) or epidemiologic studies: prevalence/incidence