Objective: To identify resistance patterns to the fluoroquinolones for pati
ents with bacterial keratitis.
Design: Retrospective observational case series,
Participants: All cases of bacterial keratitis presenting to the Charles T.
Campbell Ophthalmic Microbiology Laboratory at the Eye and Ear Institute o
f Pittsburgh from January 1993 to December 1997 were reviewed, A total of 1
053 ocular isolates from 825 cases of bacterial keratitis were identified,
Main Outcome Measures: 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 Clin
ical 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 org
anisms 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-nega
tive Staphylococcus species showed significant resistance to both fluoroqui
nolones but no change in resistance over the study period, The gram-negativ
e organisms showed good susceptibility to the fluoroquinolones.
Conclusions: This in vitro study shows a significant increased resistance o
f S. aureus to the fluoroquinolones from 1993 to 1997, In addition, gaps in
fluoroquinolone coverage for Streptococcus and coagulase-negative Staphylo
coccus species raise concern for the use of monotherapy in treating bacteri
al keratitis, Contrary to what might be expected, the distribution of gram-
positive to gram-negative organisms has shifted, with a decrease in the num
ber of gram-positive organisms identified, while the number of gram-negativ
e isolates has remained stable.