THE LETHAL EFFECTS OF BIGUANIDES ON CYSTS AND TROPHOZOITES OF ACANTHAMOEBA-CASTELLANII

The effects of a range of biocides on trophozoite and encysted forms o f Acanthamoeba castellanii were investigated. Viable acanthamoebae wer e enumerated by a plaque assay technique. The cyst form of Acanthamoeb a castellanii was more resistant to all biocides tested than the troph ozoite form. Of the biocides tested, chlorhexidine diacetate (CHA) and polyhexamethylene biguanide (PHMB) were the most effective. Their let hal effects were time- and concentration-dependent. CHA was very effec tive when formulated in 0.1% EDTA combined with Tris buffer pH 7.8 whe reas PHMB activity was reduced by 0.1% EDTA. Three per cent dimethylsu lphoxide (DMSO) enhanced the activity of CHA but not of PHMB.