Genotypic, phenotypic, biochemical, physiological and pathogenicity-based categorisation of Acanthamoeba strains

Abstract. The genus Acanthamoeba includes more than 20 morphological species, but classification is problematical. Recently, the discovery of substantial interstrain differences in ribosomal DNA (rDNA) sequences has prompted questions about the relatedness of strains of the same species. In this study, therefore, we have investigated relationships between two isolates of A. polyphaga, CCAP 1501/3c and ATCC 30871, using morphological, biochemical, physiological, molecular and cytotoxicity assays. We observed that A. polyphaga ATCC 30871 exhibited up to six arms in endocyst while A. polyphaga CCAP 1501/3c exhibited a maximum of 5 arms thus indicating their position in group 2 and 3, respectively. Acanthamoeba polyphaga ATCC 30871 exhibited growth at 37°C and growth on 1M mannitol plates while A. polyphaga CCAP 1501/3c did not. In addition, both isolates exhibited differences in isoenzyme banding patterns and rDNA restriction fragment polymorphisms. More importantly, A. polyphaga ATCC 30871 produced cytotoxicity on corneal epithelial cells while A. polyphaga CCAP 1501/3c had no effects, suggesting differences in pathogenicity. Thus, all the results provide evidence for significant differences between the strains and further provided the basis for reclassification of the isolates. Implications of these results in the clinical diagnosis of pathogenic Acanthamoeba are discussed. Species of the genus Acanthamoeba Volkonsky, 1931 are present in diverse environments including swimming pools, surface waters, thermally polluted dis-charges, ocean waters, soil, air and tap waters. Based on epidemiological information to date, they can be consid-ered as waterborne pathogens (De Jonckheere 1980, 1983, Marciano-Cabral 2000, Khan et al. 2001). Although the species of Acanthamoeba can caus