Acanthamoeba is a free-living, fresh-water protozoan that can cause severe corneal disease. Acanthamoeba keratitis can closely mimic epithelial and stromal Herpes simplex keratitis. Three cases of severe keratitis, were referred for treatment. One patient presented with a pseudodendritic epithelial lesion that gradually progressed to stromal involvement. A second patient presented with central stromal infiltrate and necrosis, while a third exhibited features of a disciform lesion with the later development of an immune ring. Acanthamoeba was recovered from the cornea in each case. The distinctive characteristics of the history and clinical findings in Acanthamoeba keratitis can aid the clinician in distinguishing between these two clinical entities. Cytopathology and special staining and culture techniques can confirm the diagnosis.
Chitin, a unique structural polysaccharide found in fungi and arthropods, is not produced by vertebrates. Thus, the potential applications of a specific and sensitive assay for chitin are numerous, including the evaluation of the extent of fungal keratitis. Chitin is a homopolymer of beta (1, 4) linked D-N-acetylglucosamine. We have developed a simple and reproducible assay for chitin and applied it to Candida albicans cultures. The assay involves homogenization of the culture and treatment with 21.1 M KOH to remove soluble materials, including proteins. This base treatment also deacetylates the chitin to the glucosamine polymer, chitosan. Chitosan is hydrolyzed by 0.5 M H2SO4 to glucosamine monomers which are then deaminated by the addition of NaNO2 to the acid solution. The resulting 2,5-anhydromannose is reduced by NaB[3H]4 to 1-[3H] 2,5-anhydromannitol. This radiolabelled sugar is isolated by paper chromatography and quantified via liquid scintillation. The sensitivity of this assay is assessed by comparison of colony forming units (CFU's) with a glucosamine standard. A typical run of the assay detects 53.1 CFU/c.p.m., and 356,000 c.p.m. per nanomole of N-acetylglucosamine. The specificity of the assay is very high because of the unique nature of chitin. This method of chitin determination may be a useful alternative method for future investigations involving the study of fungal infections in mammalian tissues.
We compared the efficacy of two polyenes, amphotericin B and natamycin, in two models of yeast infection. In one, treatment was begun immediately after inoculation, in the other it was delayed 24 hours. In each model infection with Candida albicans was established in the corneal stroma of dutch-belted rabbits and treated topically with 5% natamycin or amphotericin B 0.15% and 0.075%. Quantitative isolate recovery techniques were used to assess response after 5 days of treatment. A significant therapeutic effect was present for amphotericin B in both models. However, delayed treatment with natamycin was ineffective using treatment schedules efficacious when begun 1 hour after inoculation. A therapeutic effect was present only with administration of the drug every 1/2 hr. This altered response may reflect a difference in susceptibility between different growth phases in yeasts.
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