Acanthamoeba castellanii: growth, encystment, excystment and biocide susceptibility.

Stages in the encystment and excystment processes of Acanthamoeba castellanii have been studied. The kinetics of encystment involved measurements of the three phases (pre-encystment, cyst initiation and cyst wall synthesis). Excystment, starting from a mature cyst, involved pre-emergence, penetration outwards of the cyst wall and free trophozoite. The sensitivity to biocides of trophozoites in the exponential growth phase, pre-encystment trophozoites, mature cysts and pre-excystment cysts has been investigated. Some differences in relative sensitivity to a bisbiguanide (chlorhexidine) and a polymeric biguanide (polyhexamethylene biguanide) were observed, but mature cysts were always the most resistant cellular form.