Cytopathogenesis of Naegleria fowleri Thai strains for cultured human neuroblastoma cells

Extracellular Vesicles from Naegleria fowleri Induce IL-8 Response in THP-1 Macrophage

Extracellular vesicles (EVs) released from pathogenic protozoans play crucial roles in host–parasite communication and disease pathogenesis. Naegleria fowleri is a free-living protozoan causing primary amoebic meningoencephalitis, a fatal disease in the central nervous system. This study aims to explore the roles of N. fowleri-derived EVs (Nf-EVs) in host–pathogen interactions using the THP-1 cell line as a model. The Nf-EVs were isolated from the N. fowleri trophozoite culture supernatant using sequential centrifugation and characterized by nanoparticle tracking analysis and transmission electron microscopy. The functional roles of Nf-EVs in the apoptosis and immune response induction of THP-1 monocytes and macrophages were examined by flow cytometry, quantitative PCR, and ELISA. Results showed that Nf-EVs displayed vesicles with bilayer membrane structure approximately 130–170 nm in diameter. The Nf-EVs can be internalized by macrophages and induce macrophage responses by induction of the expression of costimulatory molecules CD80, CD86, HLA-DR, and CD169 and the production of cytokine IL-8. However, Nf-EVs did not affect the apoptosis of macrophages. These findings illustrate the potential role of Nf-EVs in mediating the host immune cell activation and disease pathogenesis.

A Search for Anti-Naegleria fowleri Agents Based on Competitive Exclusion Behavior of Microorganisms in Natural Aquatic Environments

Naegleria fowleri causes deadly primary amoebic meningoencephalitis (PAM) in humans. Humans obtain the infection by inhaling water or dust contaminated with amebae into the nostrils, wherefrom the pathogen migrates via the olfactory nerve to cause brain inflammation and necrosis. Current PAM treatment is ineffective and toxic. Seeking new effective and less toxic drugs for the environmental control of the amoeba population to reduce human exposure is logical for the management of N. fowleri infection. On the basis of the concept of competitive exclusion, where environmental microorganisms compete for resources by secreting factors detrimental to other organisms, we tested cell-free culture supernatants (CFSs) of three bacteria isolated from a fresh water canal, i.e., Pseudomonas aeruginosa, Pseudomonas otitidis, and Enterobacter cloacae, were tested against N. fowleri. The CFSs inhibited growth and caused morphological changes in N. fowleri. At low dose, N. fowleri trophozoites exposed to P. aeruginosa pyocyanin were seen to shrink and become rounded, while at high dose, the trophozoites were fragmented. While the precise molecular mechanisms of pyocyanin and products of P. otitidis and E. cloacae that also exert anti-N. fowleri activity await clarification. Our findings suggest that P. aeruginosa pyocyanin may have a role in the control of amphizoic N. fowleri in the environment.