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Subject: search.filters.subject.Meningoencephalitis

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    Environmental factors affecting encystment of P.F.L.A. together with disinfection studies: a thesis is presented in partial fulfilment of the requirements for the degree of Master of Science in Microbiology at Massey University, Palmerston North, New Zealand
    (Massey University, 1986) Harvey, Dawn
    ABSTRACT Free living amoebae from the genera Naegleria and Acanthamoeba have been implicated in fatal and several non-fatal infections of the human central nervous system, and other organs. They can be isolated from a worldwide range of environments. The common occurance of these organisms in nature may be attributed to the ability to form resistant cysts to withstand adverse environmental conditions. Research was performed to determine factors that will promote the encystment of amoebae, particularly Naegleria species. The parameters examined for the induction of encystment were: the type of substrate amoebae were growing on liquid or solid, the presence of bacteria, the cell concentration and nutrient availability and incubation at temperatures other than the optimal growth temperature. Higher percentages of amoebae encysted on solid surface environ­ments in comparison to the liquid media. In liquid media a greater percentage of trophozoites only formed a pre-encystment or roundform stage. The factor required for the complete encyst­ment of roundforms was not present. The encystment of Naegleria fowleri was not significantly influenced by the presence or absence of the bacterial species used (E. cloacae). Encystment of Naegleria spat different cell concentrations, using a nutrient media, a soil extract broth and a non-nutrient media was examined. Complete encystment of cells did not occur where nutrients were either high or absent, and the cell concentration was low. The ability of trophozoites of N. fowerli, N. gruberi, culbertsoni, and A. castellanii to encyst at a range of temperatures from 4°C - 44°C was studied. The trophozoites of Acanthamoeba sp could encyst over a wider temperature range in comparison to the trophozoites of Naegleria sp. The effect of disinfection using Baquacil was studied. Previously isolated strains of baquacil resistant N. fowleri, still had higher disinfection survival rates compared to sensitive strains. Resistance of trophozoites to Baquacil was not affected even after storage as a cyst. Baquacil resistant strains of N. fowleri were still sensitive to chlorination. Disinfection of amoebic cysts using chlorine and Baquacil was investigated. Amoebic cysts require higher levels of disinfection for inactivation in comparison to trophozoites. Acanthamoeba cysts have a greater tolerance to chlorination than Naegleria sp.
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    Classification and identification of the aetiological agents of primary amebic meningo-encephalitis, together with preliminary investigations of public health measures : a thesis presented in partial fulfillment of the requirements for the degree of Master of Science in Microbiology at Massey University
    (Massey University, 1974) Cursons, Raymond Thomas Michael
    The taxonomy of the aetiological agents of Primary Amebic Meningo-encephalitis (PAM) was investigated to determine the reliability of the common features of the three current schemes. It is concluded that the scheme of Singh & Das (1970) is the most suitable and should be generally adopted. The acceptance of one scheme will remove much of the confusion which characterizes the classification of these organisms. Current identification methods that differentiate between Naegleria gruberi (the non-pathogen) and Naegleria fowleri (the pathogen) were also investigated over a wider range of parameters than previously, to establish their relative usefulness. The conclusions of this investigation are presented in Tables XXII and XXIII. The controversial identification of the 1968 New Zealand cases (isolates BK & BL) as a Myxomycete by Mandal et al. (1970) was re-examined. Evidence is presented to demonstrate that they are N. gruberi. It was established that there was no general selection for the non-pathogen over the pathogen at 37°C as indicated by their respective QO2 values at 27°C and 37°C. That there is potential for adaptation to a range of temperatures was shown. The failure of chlorine as a disinfectant for these soil-amebae was also examined. The ineffectiveness of normal levels of chlorination was confirmed and therefore the use of NaCl and the basic dyes Malachite Green and Brilliant Green investigated. It was found that no amebae could survive a concentration of (1.5%)(W/V) of NaCl in axenic culture, of 1.5 µg/cm 3 of Malachite Green and of 3.0 µg of Brilliant Green.