AN INVESTIGATION OF THE PATHOGENIC AND NONPATHOGENIC FREE-LIVING AMEBAS IN AN ACTIVATED-SLUDGE PLANT

Pathogenic and non-pathogenic free-living amoebae from an activated-sludge plant were investigated. The greatest species diversity occurred in the raw, settled sewage and at the beginning of the aeration tank, whilst the lowest number of species occurred in the final sedimentation tanks. Thirteen species of free-living amoebae representing eleven genera were isolated; these included three species of Acanthamoeba (A. castellanii, A. culbertsoni and A. polyphaga), all of wich were pathogenic to mice with varying degrees of virulence. The implications for the public health risk of the presence of pathogenic free-living amoebae in activated-sludge plants are discussed.