Antibiotic Resistance in Microbial Keratitis: Ten-Year Experience of Corneal Scrapes in the United Kingdom

Abstract

To determine the scale of antibiotic resistance in microbial keratitis in East Kent, United Kingdom. Retrospective, observational case series. Corneal scrapes over a 10-year period to December 2008 were identified using the local microbiology database, which provided culture results and antibiotic sensitivity-resistance profiles. Isolate sensitivity to chloramphenicol, cefuroxime, gentamicin, and ciprofloxacin was determined by microdilution using the Microscan System (Siemens Diagnostics, Dearfield, IL). Isolates were graded as sensitive, intermediate, or resistant to the tested antibiotics, with minimal inhibitory concentrations interpreted against breakpoints from the Clinical and Laboratory Standards Institute. There were 476 scrapes from 440 patients (female, 57.6%; mean age, 53.5 years). All samples were cultured. Culture was positive in 163 samples (34.2%), growing 172 organisms. Bacterial keratitis accounted for 162 isolates (94.2%), of which 99 (61.1%) were gram-negative. There was a general increase in the number of gram-negative isolates with time (P=0.003). In vitro testing showed widespread gram-negative resistance to chloramphenicol (74.1%), with reducing sensitivity over the study period (P=0.004). There was 97.3% sensitivity to combination gentamicin and cefuroxime, and 94.4% sensitivity to ciprofloxacin. Ciprofloxacin resistance was found in 8 (17.0%) of 47 gram-positive isolates tested, with no trend toward increasing resistance. This study has documented the highest levels of gram-negative keratitis in any open retrospective survey to date and highlights a trend of increasing gram-negative infection. We have demonstrated reducing chloramphenicol sensitivity, with high sensitivity to combination gentamicin and cefuroxime, as well as ciprofloxacin. Gram-positive fluoroquinolone resistance was higher than previously reported in the United Kingdom, but showed no evidence of increasing resistance. Second-generation fluoroquinolone monotherapy remains the recommended empirical treatment in microbial keratitis in the United Kingdom, and a change to fourth-generation compounds is not advised. Continued testing is essential to monitor for increasing resistance. The author(s) have no proprietary or commercial interest in any materials discussed in this article.