Abstract
In the aquatic environment, Vibrio spp. interact with many living organisms that can serve as a replication niche, including heterotrophic protists, or protozoa. Protozoa engulf bacteria and package them into phagosomes where the cells are exposed to low pH, antimicrobial peptides, reactive oxygen/nitrogen species, proteolytic enzymes, and low concentrations of essential metal ions such as iron. However, some bacteria can resist these digestive processes. For example, Vibrio cholerae and Vibrio harveyi can resist intracellular digestion. In order to survive intracellularly, bacteria have acquired and/or developed specific factors that help them to resist the unfavorable conditions encountered inside of the phagosomes. Many of these intra-phagosomal factors used to kill and digest bacteria are highly conserved between eukaryotic cells and thus are also expressed by the innate immune system in the gastrointestinal tract as the first line of defense against bacterial pathogens. Since pathogenic bacteria have been shown to be hypervirulent after they have passed through protozoa, the resistance to digestion by protist hosts in their natural environment plays a key role in enhancing the infectious potential of pathogenic Vibrio spp. This review will investigate the current knowledge in interactions of bacteria with protozoa and human host to better understand the mechanisms used by both protozoa and human hosts to kill bacteria and the bacterial response to them.
Highlights
Vibrio spp. are metabolically versatile bacteria that inhabit the aquatic environment
It was recently shown that OmpU is important for the expulsion of V. cholerae within food vacuoles of ciliate hosts, a fact that suggests that this protein might confer resistance to V. cholerae to the intra-phagosomal factors required for digestion (Espinoza-Vergara et al, 2019)
This review highlights that the strategies used to digest and inactivate bacteria in both protozoa and the GI tract of the human host are highly conserved and further emphasize how the resistance to the intracellular digestion in protozoa might enhance the pathogenicity of Vibrio spp
Summary
Vibrio spp. are metabolically versatile bacteria that inhabit the aquatic environment. The fact that the passage and release of pathogenic bacteria from the intracellular protozoan environment results in increased infectivity suggests that the exposure to intra-phagosomal factors may enhance virulence phenotypes.
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