A Prey–Bacterivore Interaction: CdtB Involvement in the Cytotoxicity Mechanism of Escherichia albertii Against Tetrahymena thermophila CU427

Abstract

Escherichia albertii is a Gram-negative, facultative anaerobic bacillus recognized as a zoonotic foodborne pathogen. Aquatic E. albertii populations likely coexist with protist hosts. Dynamic interactions between pathogenic bacteria and their protist predators may extend beyond shared growth spaces and involve host-directed cytotoxicity. E. albertii carries cytotoxicity-associated genes such as cdt, stx, and astA. This study aimed to elucidate the role of cdtB in E. albertii interaction within the Tetrahymena thermophila CU427 strain. Cytolethal distending toxins (CDTs) are tripartite protein exotoxins; CdtB requires CdtA and CdtC to bind to the glycosphingolipids ganglioside GM1 and GM3 and induce full cytotoxicity in mammalian cells. Ganglioside GM1 was highly distributed in CU427 in our study, whereas GM3 showed no comparable distribution, suggesting that ganglioside GM1 may act as a receptor for CdtB in Tetrahymena cells. However, cholera toxin B subunit treatment failed to inhibit E. albertii cytotoxicity against CU427. A LIVE/DEAD assay using Carboxyfluorescein succinimidyl ester/Propidium Iodide staining was conducted for CU427 infected with E. coli expressing recombinant E. albertii CdtB. CU427 viable cell number decreased half-fold after 24 h in a similar tendency with E. albertii infection. These results indicate that CdtB is involved in E. albertii cytotoxicity against protist hosts, particularly Tetrahymena, and suggest that the cytotoxic mechanism, especially its interaction with host cells, differs from that in mammalian cells. Thus, this study provides deeper insights into the involvement of CdtB in the E. albertii cytotoxicity mechanism.