Fluorescein-conjugated lectin visualization of fungi and acanthamoebae in infectious keratitis

The authors investigated the efficacy of two fluorescein-conjugated lectins (FCLs), concanavalin A (F-ConA) and wheat germ agglutinin (F-WGA), to visualize microorganisms from clinical specimens with documented mycotic and acanthamoebic keratitis. Corneal scrapings from 18 patients with culture-proven keratomycosis and deparaffinized histopathologic specimens from five culture-proven cases of acanthamoebic keratitis were evaluated. The F-ConA provided consistently bright staining of the mycotic structures in each of the corneal scrapings. Both F-ConA and F-WGA stained acanthamoebic trophozoites and cysts in the histopathologic specimens. In both the corneal scrapings and the histopathologic specimens, the microorganisms were easily differentiated from background corneal cells and tissue. These staining patterns correlate well with the results from experimental studies, and with the known cell wall carbohydrate compositions for fungi and acanthamoebae. This study provides further evidence that FCLs (particularly F-ConA) may eventually become effective first-line stains for the visualization of microorganisms in specimens from ocular infections.