Free-living amoebae that belong to the genus Acanthamoeba are widespread in the environment, including water. They are responsible for human
infections and can host pathogenic microorganisms. Under unfavorable conditions, they form
cysts with high levels of resistance to disinfection methods, thus potentially representing a threat to public health. In the present study we evaluated the efficacies of various
biocides against trophozoites and
cysts of several Acanthamoeba strains. We demonstrated that
disinfectant efficacy varied depending on the strains tested, with environmental strains demonstrating greater resistance than collection strains. Trophozoites were inactivated by all treatments except those using
glutaraldehyde as an active compound: for these treatments, we observed resistance even after 30 min exposure.
Cysts resisted many treatments, including certain conditions with
glutaraldehyde and other
biocides. Moist heat at 55 degrees C was not efficient against
cysts, whereas exposure at 65 degrees C was. Several chemical formulations containing
peracetic acid,
hydrogen peroxide, or
ortho-phthalaldehyde presented greater efficacy than
glutaraldehyde, as did
ethanol and
sodium hypochlorite; however, some of these treatments required relatively long incubation times to achieve
cyst inactivation. Amoebal
cysts can be highly resistant to some high-level
disinfectants, which has implications for clinical practice. These results highlight the need to consider the effective disinfection of protozoa in their vegetative and resistant forms due to their intrinsic resistance. This is important not only to prevent the transmission of protozoa themselves but also due to the risks associated with a range of microbial pathogens that are found to be associated intracellularly with these microorganisms.