The use of fluorescein-conjugated lectins for visualizing atypical mycobacteria

We investigated the feasibility of using fluorescein-conjugated lectins for visualizing and differentiating two species of atypical mycobacteria. Pure cultures of Mycobacterium fortuitum and Mycobacterium chelonei were established, as was an experimental model of infectious keratitis involving these two organisms. Samples from the pure cultures and corneal scrapings were placed on glass slides, fixed, and incubated with one of a panel of 22 fluorescein-conjugated lectins. The slides were examined using an epifluorescence microscope. Fluorescein-conjugated concanavalin A brightly stained both species of atypical mycobacteria, in both the pure culture and experimental keratitis samples. Several additional fluorescein-conjugated lectins (wheat germ agglutinin, succinylated wheat germ agglutinin, Phaseolus vulgaris erythroagglutinin, and Psophocarpus tetragonolobus agglutinin) brightly stained M chelonei, but only moderately stained M fortuitum. These staining patterns are consistent with the known carbohydrate compositions of the cell walls of atypical mycobacteria and suggest that fluorescein-conjugated lectins may be useful for the visualization of these organisms in corneal infections.