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Survival of enterohemorrhagic Escherichia coli in the presence of Acanthamoeba castellanii and its dependence on Pho regulon.

ABSTRACT: Enterohemorrhagic Escherichia coli (EHEC) are involved in outbreaks of food-borne illness and transmitted to humans through bovine products or water contaminated by cattle feces. Microbial interaction is one of the strategies used by pathogenic bacteria to survive in the environment. Among protozoa, the free-living amoebae are known to host and protect several water-borne pathogens. In this study, the interaction between EHEC and the predacious protozoa Acanthamoeba castellanii was investigated. Using monoculture and cocultures, growth of both organisms was estimated for 3 weeks by total and viable cell counts. The numbers of EHEC were significantly higher when cultured with amoebae than without, and less EHEC shifted into a viable but nonculturable state in the presence of amoebae. Using several mutants, we observed that the Pho regulon is required for EHEC growth when cocultured with amoebae. In contrast, the Shiga toxins (Stx) were not involved in this association phenotype. Cocultures monitored by electron microscopy revealed a loss of the regular rod shape of EHEC and the secretion of multilamellar vesicles by the amoebae, which did not contain bacteria. As the interaction between A. castellanii and EHEC appears beneficial for bacterial growth, this supports a potential role for protozoa in promoting the persistence of EHEC in the environment.

SUBMITTER: Chekabab SM

PROVIDER: S-EPMC3535388 | biostudies-literature | 2012 Dec

REPOSITORIES: biostudies-literature

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Survival of enterohemorrhagic Escherichia coli in the presence of Acanthamoeba castellanii and its dependence on Pho regulon.

Chekabab Samuel Mohammed SM Daigle France F Charette Steve J SJ Dozois Charles M CM Harel Josée J

MicrobiologyOpen 20121030 4

Enterohemorrhagic Escherichia coli (EHEC) are involved in outbreaks of food-borne illness and transmitted to humans through bovine products or water contaminated by cattle feces. Microbial interaction is one of the strategies used by pathogenic bacteria to survive in the environment. Among protozoa, the free-living amoebae are known to host and protect several water-borne pathogens. In this study, the interaction between EHEC and the predacious protozoa Acanthamoeba castellanii was investigated. ...[more]

PMID: 23233434

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Project description:The respiratory pathogenic bacterium Bordetella bronchiseptica can persistently survive in terrestrial and aquatic environments, providing a source of infection. However, the environmental lifestyle of the bacterium is poorly understood. In this study, expecting repeated encounters of the bacteria with environmental protists, we explored the interaction between B. bronchiseptica and a representative environmental amoeba, Acanthamoeba castellanii, and found that the bacteria resisted amoeba digestion and entered contractile vacuoles (CVs), which are intracellular compartments involved in osmoregulation, to escape amoeba cells. In prolonged coculture, A. castellanii supported the proliferation of B. bronchiseptica. The avirulent Bvg- phase, but not the virulent Bvg+ phase, of the bacteria was advantageous for survival in the amoebae. We further demonstrate that two Bvg+ phase-specific virulence factors, filamentous hemagglutinin and fimbriae, were targeted for predation by A. castellanii. These results are evidence that the BvgAS two-component system, the master regulator for Bvg phase conversion, plays an indispensable role in the survival of B. bronchiseptica in amoebae. IMPORTANCE The pathogenic bacterium Bordetella bronchiseptica, which causes respiratory diseases in various mammals, exhibits distinct Bvg+ and Bvg- phenotypes. The former represents the virulent phase, in which the bacteria express a set of virulence factors, while the role of the latter in the bacterial life cycle remains to be understood. In this study, we demonstrate that B. bronchiseptica in the Bvg- phase, but not the Bvg+ phase, survives and proliferates in coculture with Acanthamoeba castellanii, an environmental amoeba. Two Bvg+ phase-specific virulence factors, filamentous hemagglutinin and fimbriae, were targeted by A. castellanii predation. B. bronchiseptica turns into the Bvg- phase at temperatures in which the bacteria normally encounter these amoebae. These findings demonstrate that the Bvg- phase of B. bronchiseptica is advantageous for survival outside mammalian hosts and that the bacteria can utilize protists as transient hosts in natural environments.

Dataset Information

Survival of enterohemorrhagic Escherichia coli in the presence of Acanthamoeba castellanii and its dependence on Pho regulon.

Publications

Survival of enterohemorrhagic Escherichia coli in the presence of Acanthamoeba castellanii and its dependence on Pho regulon.

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