Identification of the causative organisms in suspected bacterial
keratitis traditionally involves collecting multiple corneal scrapes, which are plated directly onto different solid
agar culture media. Difficulties have been reported with this practice, so the development of a simpler diagnostic method in suspected bacterial
keratitis would be useful. It is unclear whether a single corneal scrape sent to the microbiology laboratory in a liquid transport culture medium (indirect method) is as reliable for the diagnosis of bacterial
keratitis as inoculation of multiple scrapes directly onto
agar plates (direct method). To investigate this, bacterial recovery was assessed following transfer and transport of different concentrations and types of bacteria from an artificially contaminated surgical blade into brain heart infusion (BHI). Bacterial recovery rates between the proposed (indirect) and standard (direct) method were then compared after the in vitro inoculation of pig corneas and following specimen collection in patients with presumed bacterial
ulcerative keratitis. Recovery of bacteria from contaminated surgical blades was found to be the same from both solid and liquid
culture media. There was no significant difference in the numbers of positive cultures from solid (direct) and liquid (indirect)
culture media, both in the experimental pig cornea inoculation study (P = 0.34) and in experiments with patients with clinical
infections (P = 0.4), with an 85.2% agreement between methods (kappa = 0.61, P < 0.0001). In conclusion, therefore, the collection of two corneal scrapes, one used for Gram staining and the other transported in BHI followed by plating and subculturing in an enrichment medium, provides a simple method for the investigation of presumed bacterial
keratitis.