Shifting trends in bacterial keratitis in south Florida and emerging resistance to fluoroquinolones.
OBJECTIVE
To study the distribution, current trends, and patterns of resistance to antimicrobial agents of bacterial keratitis isolates in South Florida.


METHODS
Retrospective, observational, case series.


METHODS
The microbiology records of all patients with bacterial keratitis seeking treatment at the Bascom Palmer Eye Institute from January 1, 1990 through December 31, 1998 were reviewed.


METHODS
In vitro laboratory minimum inhibitory concentration testing of the corneal isolates to the fluoroquinolones (ofloxacin and ciprofloxacin) and to the aminoglycosides (tobramycin and gentamicin) was performed using the Vitek (Automatic Microbial System Biomerieux Vitek, Inc., Hazelwood, Missouri) method.


RESULTS
During this 9-year period, 2920 consecutive corneal cultures were obtained, and a pathogen was recovered in 1468 cultures (50%). The number of corneal ulcers scraped, positive cultures, recovered bacterial isolates, and ratio of gram-positive to gram-negative isolates per year remained approximately equal throughout the study period. Staphylococcus aureus and Pseudomonas aeruginosa represented 19.4% and 25.7%, respectively, of the total bacterial isolates during this period. However, we documented a gradual increase in the number of S. aureus keratitis isolates (29% of gram-positive organisms in 1990 versus 48% in 1998, P = 0.01) coupled with a decrease in the number of P. aeruginosa isolates (54% of gram-negative organisms in 1990 versus 46% in 1998). A decrease in the incidence of contact lens-associated keratitis and P. aeruginosa isolates in this group of patients was documented. Serratia marcescens and P. aeruginosa were most commonly isolated in contact lens-associated keratitis (18% each). There was increasing laboratory resistance of S. aureus keratitis isolates to the fluoroquinolones (11% in 1990 to 28% in 1998), but resistance patterns to the aminoglycosides remained unchanged. There was a three-fold increase in the percentage of resistant S. aureus isolates to fluoroquinolones between 1990 and 1994 and between 1995 and 1998. Both fluoroquinolones and aminoglycosides exhibited low in vitro effectiveness against P. aeruginosa throughout the study period.


CONCLUSIONS
The increased recovery of S. aureus keratitis isolates and decreased laboratory effectiveness against fluoroquinolones to these pathogens present an important therapeutic challenge.
Bascom Palmer Eye Institute, University of Miami School of Medicine, Miami, Florida, USA. galexandrakis@med.miami.edu
G
G
Alexandrakis
E C
EC
Alfonso
D
D
Miller
D000900:Anti-Bacterial Agents / Q000494:pharmacology / Q000627:therapeutic use; D000890:Anti-Infective Agents / Q000494:pharmacology / Q000627:therapeutic use*; D001419:Bacteria / Q000187:drug effects* / Q000302:isolation & purification; D002939:Ciprofloxacin / Q000494:pharmacology / Q000627:therapeutic use; D003315:Cornea / Q000382:microbiology; 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*; D005431:Florida / Q000453:epidemiology; D005839:Gentamicins / Q000494:pharmacology / Q000627:therapeutic use; D016905:Gram-Negative Bacterial Infections / Q000188:drug therapy / Q000453:epidemiology / Q000382:microbiology*; D016908:Gram-Positive Bacterial Infections / Q000188:drug therapy / Q000453:epidemiology / Q000382:microbiology*; D006801:Humans; D008826:Microbial Sensitivity Tests; D015242:Ofloxacin / Q000494:pharmacology / Q000627:therapeutic use; D012189:Retrospective Studies; D014031:Tobramycin / Q000494:pharmacology / Q000627:therapeutic use
D000900:Anti-Bacterial Agents; D000890:Anti-Infective Agents; D005839:Gentamicins; D002939:Ciprofloxacin; D015242:Ofloxacin; D014031:Tobramycin