Emerging fluoroquinolone resistance in bacterial keratitis: a 5-year review.
OBJECTIVE
To identify resistance patterns to the fluoroquinolones for patients with bacterial keratitis.


METHODS
Retrospective observational case series.


METHODS
All cases of bacterial keratitis presenting to the Charles T. Campbell Ophthalmic Microbiology Laboratory at the Eye and Ear Institute of Pittsburgh from January 1993 to December 1997 were reviewed. A total of 1053 ocular isolates from 825 cases of bacterial keratitis were identified.


METHODS
In vitro laboratory susceptibility testing of ocular isolates to ciprofloxacin and ofloxacin was determined by the Kirby-Bauer disk diffusion method and interpreted using the National Committee for Clinical Laboratory Standards serum standards.


RESULTS
The number of cases of bacterial keratitis per year decreased from 284 in 1993 to 75 in 1997. The ratio of gram-positive to gram-negative organisms changed from 81.8%:18.2% in 1993 to 51.4%:48.6% in 1997 (chi-square, 66.00; degrees of freedom, 4; P < 0.000001). Resistance of Staphylococcus aureus to ciprofloxacin significantly increased annually from 5.8% in 1993 to 35.0% in 1997 (chi-square, 19.80; degrees of freedom, 4; P < 0.0001) and for ofloxacin from 4.7% to 35.0% over the same period (chi-square, 21.32; degrees of freedom, 4; P < 0.001). Streptococcus species and coagulase-negative Staphylococcus species showed significant resistance to both fluoroquinolones but no change in resistance over the study period. The gram-negative organisms showed good susceptibility to the fluoroquinolones.


CONCLUSIONS
This in vitro study shows a significant increased resistance of S. aureus to the fluoroquinolones from 1993 to 1997. In addition, gaps in fluoroquinolone coverage for Streptococcus and coagulase-negative Staphylococcus species raise concern for the use of monotherapy in treating bacterial keratitis. Contrary to what might be expected, the distribution of gram-positive to gram-negative organisms has shifted, with a decrease in the number of gram-positive organisms identified, while the number of gram-negative isolates has remained stable.
University of Pittsburgh Eye and Ear Institute, Pennsylvania, USA. mgoldstn@eye1.eye.ufl.edu
M H
MH
Goldstein
R P
RP
Kowalski
Y J
YJ
Gordon
D000890:Anti-Infective Agents / Q000494:pharmacology*; D002939:Ciprofloxacin / Q000494:pharmacology*; D003320:Corneal Ulcer / Q000188:drug therapy / Q000453:epidemiology / Q000382:microbiology*; D004352:Drug Resistance, Microbial; D015818:Eye Infections, Bacterial / Q000188:drug therapy / Q000453:epidemiology / Q000382:microbiology*; D006090:Gram-Negative Bacteria / Q000187:drug effects* / Q000302:isolation & purification; D006094:Gram-Positive Bacteria / Q000187:drug effects* / Q000302:isolation & purification; D006801:Humans; D008826:Microbial Sensitivity Tests; D015242:Ofloxacin / Q000494:pharmacology*; D010414:Pennsylvania / Q000453:epidemiology; D012189:Retrospective Studies
D000890:Anti-Infective Agents; D002939:Ciprofloxacin; D015242:Ofloxacin