A study of various environmental factors on the growth, encystment and survival of free living amoebae : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Microbiology at Massey University

Abstract

Free-living amoebae (FLA) are soil organisms which have a worldwide distribution. Interest was raised when they were implicated in two fatal and several non-fatal infections in humans. This investigation involved examination of the role and/or effect of several environmental factors on growth, encystment and cyst survival

of FLA. The effect of K+, Na+ , Mg+2, Ca+2 and Fe+2/+3 on the growth of four species of amoebae (Naegleria gruberi, Naegleria fowleri, Acanthamoeba culbertsoni and Acanthamoeba castellanii) was investigated. Inhibition of growth rate increased as the cation concentration was increased.

The roles of Mg+2 and Ca+2 in encystment were investigated and it was found that rather than being necessary, they were inhibitory. The survival of cysts under low temperatures and high cation concentrations was studied. Acanthamoeba proved to be resistant to adverse conditions once encysted. Naegleria were not affected by high cation levels but were adversely affected by low temperatures. A preliminary identification of two isolates from Ngawha Springs hot pools was undertaken showing both amoebae to be temperature tolerant Naegleria species.