Cytopathogenicity of Naegleria fowleri and Naegleria gruberi for Established Mammalian Cell Cultures

Abstract

Amebae of Naegleria fowleri and Naegleria gruberi were cytopathic for nine established mammalian cell cultures, including mouse and human fibroblasts, rabbit and monkey kidney cells, rat and mouse neuroblastoma cells, baby hamster kidney cells, and human epithelioma and carcinoma cells. Nine strains of N. fowleri were equally cytopathic for rodent neuroblastoma cells. As few as one ameba per million neuroblastoma cells destroyed the mammalian target cells after 9 days. The N. fowleri grew and destroyed rat neuroblastoma cells at 30 to 37 C whereas N. gruberi grew and destroyed the target cells at 25 to 30 C. Both N. fowleri and N. gruberi attached efficiently to the target cells at 30 to 37 C; N. gruberi but not N. fowleri attached efficiently at 25 C. Electron microscopic observations of mixed cultures of N. fowleri and neuroblastoma cells established that the amebae, after 12 hr, had ingested portions of the neuroblastoma target cells without causing cell lysis. Conversely, N. gruberi amebae, after attaching to target cells, disrupted the plasma membrane and cytoplasm of the target cells although the target cell nucleus remained intact. The amebae then ingested the target cell debris.

Scanning electron microscopic study of human neuroblastoma cells affected with Naegleria fowleri Thai strains

“…Cytopathogenicity of N. fowleri in mammalian cell cultures has been studied since 1982 (Marciano-Cabral et al 1982). The formation of CPE on cell monolayers depends on susceptibility of the monolayer type.…”

Pathogenic Naegleria fowleri and non-pathogenic Naegleria lovaniensis exhibit differential adhesion to, and invasion of, extracellular matrix proteins

“…The ability to elicit cytopathic effects on cells in culture does not appear to define pathogenicity for Naegleria. That is, while species of Naegleria such as N. lovaniensis and Naegleria gruberi destroy mammalian cells in vitro (Marciano-Cabral et al, 1982;Marciano-Cabral & Fulford, 1986), they have yet to be shown to be causative of human disease. Also, the ability to tolerate temperatures of 37 u C or higher does not appear to be a defining marker of pathogenicity for Naegleria.…”

Role of the Nfa1 Protein in Pathogenic Naegleria fowleri Cocultured with CHO Target Cells

“…It is, therefore, intimately involved in pathogenesis (12). The process has been named trogocytosis, the piecemeal engulfment of mouse embryo cells by N. fowleri (12). It is now known that trogocytosis is accomplished by amoebastomes (2), which amoebae use to engulf particles of various sizes, including cultivated mammalian cells.…”

“…Phagocytosis is a basic function of this amoeba and one that causes the destruction of cells, whether in cell culture or in human tissue. It is, therefore, intimately involved in pathogenesis (12). The process has been named trogocytosis, the piecemeal engulfment of mouse embryo cells by N. fowleri (12).…”

“…fowleri is cytopathogenic to a variety of cultured mammalian cells (12,18,20). The proposed mechanism(s) of the cytopathic action of this organism for mammalian cells includes active phagocytosis of cells by pseudopodium formation (11).…”