EFFECTS OF POLYHEXAMETHYLENE BIGUANIDE AND CHLORHEXIDIAE ON 4 SPECIESOF ACANTHAMOEBA IN-VITRO

We determined the relative minimal inhibitory and minimal amoebicidal concentrations of chlorhexidine digluconate and polyhexamethylene bigu anide for four species of Acanthamoeba. The amoebae were grown in pept one-glucose-yeast extract broth for 72 h in tissue culture flasks. Eit her washed trophozoites (similar to 10(5)) or cysts (similar to 10(5)) were incubated in the enrichment broth in 96 well microtiter trays. A ntimicrobial concentrations of the biguanides were determined from mic roscopic examinations of methylene blue uptake and from subcultures. I n general, killing was time dependent. Minimal amoebicidal concentrati ons at 24 h ranged from 50 to 100 mg/ml and to as low as 25 mg/ml by 7 2 h. Trophozoites were killed more rapidly than cysts. Both biguanides had similar levels of activity. A synergistic combination of chlorhex idine and polyhexamethylene biguanide (total concentration 25 mg/ml) w as most evident for A. castellanii and A. polyphaga. Cysts of A. culbe rtsoni and A. hatchetti stained more rapidly after exposure to the com bination of biguanides than to the single biguanides, but there were n o statistically significant differences in the final numbers of dead o r stained cysts after exposure to the combination or to the single big uanides.