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H. Sueke, S. Kaye, R. Gilbert, T. Neal; Evaluation of a Simplified Method for Obtaining Samples From Corneal Ulcers in Bacterial Keratitis Over a 10 Year Period. Invest. Ophthalmol. Vis. Sci. 2010;51(13):2419. doi: https://doi.org/.
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To evaluate the introduction of a simplified method for collecting and isolating organisms form cases of presumed bacterial keratitis over a 10 year period.
Data was collected by the department of medical microbiology at the Royal Liverpool University Hospital for all patients that had a corneal scrape for suspected bacterial keratitis for the period 1998-2008. Samples were collected from ulcers using standard methods: direct plating onto several agar plates in addition to a smear. For the period 2004 to 2008, corneal samples were using simplified method (Kaye SB et al, J Clin Microbiol 2003;41:3192-3197) taken by scraping the base of the ulcer with two separate surgical blades. The first blade was smeared onto a glass slide used for Gram staining and the other transported in brain heart infusion followed by plating and then subculturing in an enrichment medium in the laboratory.
A total of 1887 corneal scrapes were collected (mean of 172 per year, isolation rate 38% despite a significant proportion of patients receiving treatment at presentation). The introduction of a simplified method led to a significant increase in number of patients from whom samples were collected: 146 to 203 per year. There was a significant reduction in the isolation of Coagulase negative Staphylococci (CNS) (36.42% to 26.82%) using the simplified method. There were no significant changes in the isolation of the recognised pathogenic bacteria: Staphylococcal aureus (9.13% and 9.11%) Streptococcus spp. (8.01 and 9.19%) but an increase in Pseudomonas spp. (9.12% to 12.46%) and Enterobacteriaceae (6.80% to 15.75%).
The difficulties encountered with the collection of multiple scrapes with direct plating, has led to increased empirical treatment of microbial keratitis. The introduction of a simplified method has led to an increase in the collection of corneal samples in isolating the cause of microbial keratitis. The simplified method has been shown to be equivalent to standard method but is shown to be associated with a reduced contamination rate as reflected in the reduction of CNS, but no change in the isolation of recognised pathogenic bacteria
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