Abstract
Purpose::
Longitudinal surveillance of antimicrobial susceptibilities can detect emerging resistance trends and facilitate therapy selection. TRUST is an annual, ongoing, nationwide surveillance program recently expanded to ocular isolates. Ocular TRUST is the only nationwide surveillance program that prospectively collects and tests antimicrobial susceptibility in microbes cultured from eye infections. First-year results are presented for Streptococcus pneumoniae (SP) and Haemophilus influenzae (HI) ocular isolates.
Methods::
Samples were prospectively collected from geographically distributed U.S. institutions (28 community and 7 eye hospitals) between October 2005 and June 2006. All isolates were tested by broth microdilution according to CLSI methodology at a centralized independent laboratory. Microtiter panels included common ophthalmic antibiotics. MICs were interpreted as susceptible, intermediate, or resistant according to 2006 CLSI criteria.
Results::
All SP (n=49) and HI (n=32) isolates were 100% susceptible to the newer fluoroquinolones (FQs) levofloxacin, gatifloxacin, and moxifloxacin; ciprofloxacin SP susceptibility was 89.8%. Only one SP isolate was susceptible to tobramycin; all SP isolates were resistant to polymyxin B. Rank order of SP susceptibility to all antimicrobials tested: FQs > penicillin > trimethoprim > tobramycin > polymyxin B. All HI isolates were 100% susceptible to all antimicrobials tested except trimethoprim (81.3%). Prospective results for newer FQs (levofloxacin, gatifloxacin, moxifloxacin) correlated well with retrospective (1999-2006) susceptibility data in ocular isolates: ≥99.9% of SP (n=760) and 99.7% of HI (n=356).
Conclusions::
Susceptibility patterns in SP and HI ocular infections are identical for levofloxacin, gatifloxacin, and moxifloxacin, despite higher selection pressure for levofloxacin from a decade of widespread systemic use. Conversely, pathogen resistance limits the usefulness of polymyxin B and tobramycin in SP ocular infections (eg, bacterial conjunctivitis).
Keywords: bacterial disease • ocular irritancy/toxicity testing • antibiotics/antifungals/antiparasitics