The data showed that pathogenic free-living amoebae contain the proteolytic enzyme elastase. The levels of enzyme were similar in Naegleria fowleri, N. australianis italica, and Acanthamoeba culbertsoni A-1. No difference was found between elastase levels in a highly pathogenic N. fowleri and those in the same organism which had lost pathogenicity as a result of long-term axenic maintenance.
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Ferrante et al. (1988) studied this question.