Effects of biocides on Acanthamoeba castellanii as measured by flow cytometry and plaque assay

The lethal effects of various biocides, in particular two agents (chlorhexidine diacetate and polyhexamethylene biguanide) on cysts and trophozoites of Acanthamoeba castellanii have been measured by both plaque assay and flow cytometry (FCM). Minimum amoebicidal concentrations against trophozoites were generally the same by the two methods whereas minimum cysticidal concentrations were occasionally higher by FCM. Concentrations of biguanides required to produce an equal reduction in viability were also higher by FCM than by plaque assay.