A total of 13 strains of Naegleria fowleri were cytopathogenic for lung, kidney, foreskin, ovary, connective tissue, neuroblastoma, laryngeal carcinoma, and cervical carcinoma mammalian cell lines. The strains of N. fowleri varied considerably in their ability to produce a cytopathic effect (CPE). Likewise, the different mammalian cell lines exhibited varying degrees of susceptability to the cytopathogenicity of the amebae. The African green-monkey kidney (Vero) cell line proved to be useful for assessing the cytopathogenic potential of N. fowleri strains. Although one strain failed to produce CPE in Vero-cell cultures, it did so in the two neuroblastoma cell lines. Other factors affecting the extent of CPE produced were incubation temperature, ameba: mammalian cell ratio, and the length of time during which amebae were maintained in cell culture.
The virulence of Naegleria fowleri for mice decreases with prolonged maintenance in axenic culture. Would the virulence be affected if amebas were grown in African green-monkey kidney (Vero)-cell cultures rather than in axenic culture? The weakly virulent LEE strain of N. fowleri was cultivated with Vero cells for 6 mo and tested in mice for changes in virulence. We found that continuous growth in Vero-cell cultures enhanced the virulence of the LEE strain and we propose that, as an alternative to serial passage in mice, the virulence of weakly virulent strains of N. fowleri may be enhanced by maintenance in Vero-cell cultures.
Abstract. This is a follow-up report on the viability of pathogenic Naegleria fowleri, Naegleria australiensis and Acanthamoeba castellanii isolates during 5 to 10 years of cryopreservation at -70°C. The greatest decrease in viability occurred with N. fowleri and the least occurred with N. australiensis. At 10 years of cryostorage, viability was 21% for N. fowleri, 32% for A. castellanii and 51% for N. australiensis.
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