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R. Ventura, D. Miller, E. Alfonso; Laboratory Update on Microbial Keratitis in South Florida. Invest. Ophthalmol. Vis. Sci. 2009;50(13):3115.
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To evaluate the impact of culture media selection and prior antibiotic use on recovery of pathogens in patients with microbial keratitis.
Laboratory records of patients examined at our institution between January 2007 and June 2008 to R/O microbial keratitis were reviewed and data extracted on culture positive rates, pathogen frequency, prior antibiotic exposure, contact lens wear, media selection, detection time and emerging antibiotic resistance. Statistical evaluations were performed using 2 x 2 tables and chi square.
The culture positive rate for this group was 57% (437/766). Of the 437 positive cultures, pathogen frequency included gram negatives-46.2% (N=202), gram positives-25.4% (N=111), fungi-19.0% (N=83), amoeba-7.1% (N=31) and mixed infections-2.3% (N=10). Among 364 patients, 46.9% (N=167) were exposed to at least one antibiotic prior to the culture. Choices included moxifloxacin and gatifloxacin 52.1%, aminoglycosides 11.4% and fortified 9.5%. Gram negative rods were more likely to be recovered from patients with no antibiotic history (60.9% vs 30.4%). Fungi (28.7% vs 11.7%) and Acanthamoeba (13.8% vs 1.5%) was more frequently recovered patients with prior exposure to antibiotics. History of contact lens wear (CL) was positive in 48.8% of the cases (N= 295).Gram negative pathogens were significantly more likely to be recovered from CL (60.4%) vs none CL 39.1%,( p=0.000) wearers, while gram positive isolates were more likely to be associated with NCL.( 35% vs 10%, p=0.000) There was no significant difference between recovery of fungi (CL-16.7% vs NCL 19.1%, p=0.5708) or acanthamoeba (9.9% vs 4%, p=0.077). between the two groups. 90% or more of the isolates were recovered on a combination of chocolate, blood agar and thioglycollate. Detection rates at 48 hours were 72.3%-gram negatives, 70.3%-gram positives, 49.4%-fungi and 35.5% acanthamoeba. Greater than 75% of isolates were recovered in 3 days. Less than half of the isolates were recovered in 48 hrs for patients on prior treatment vs those who were not (44.9 vs 72.3%, p=0.000). Greater than 95% of gram negatives (96.2% N=195/202) but less than 75% for gram positives (72.3% N= 86/119) remained susceptible to the fluoroquinolones, overall: 87.2% (N=281/321). 93.1% of isolates were susceptible to the aminoglycosides (N=256/275), gram negatives =96.5% (195/202) and gram positives 65.8% (64/76).
There is an increase trend in the recovery of nonbacterial and mixed microbial infections in patients presenting with microbial keratitis in S. Florida. Treatment options for gram positive pathogens are becoming more limited.
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