Flow cytometry for determination of the efficacy of contact lens disinfecting solutions against Acanthamoeba spp.

Flow cytometric analyses of cellular staining with fluorescent viability dy es and direct microscopic observations of methylene blue exclusion were com pared for evaluation of the effects of a chlorhexidine gluconate-based cont act lens disinfectant solution and a polyhexamethylene biguanide solution a gainst cysts and trophozoites of Acanthamoeba castellanii and Acanthamoeba polyphaga. The flow cytometric procedure with propidium iodide (used to sta in dead cells) indicated that more than 90% of trophozoites of both species (inocula of 10(5) to 10(6)/ml) at 22 degrees C lost their viability after 4 h of exposure to chlorhexidine. When propidium iodide was used in combina tion with fluorescein diacetate (for live cells), the apparent number of pr opidium iodide-stained cells was reduced, but the relative efficacies of th e two biguanide solutions appeared unchanged from those evident with the si ngle dyes; the chlorhexidine solution was more effective than the polyhexam ethylene biguanide solution. Similar data were obtained with the more cumbe rsome methylene blue exclusion procedure. Flow cytometric analyses provided a statistically reproducible and rapid procedure for determining the relat ive antiamoebal efficacies of the disinfecting solutions.