Vibrio cholerae O1 classical strains are facultative intracellular bacteria, which survive and multiply symbiotically inside the aquatic free-living amoebae

Abstract number: 1133_112

Abd H., Weintraub A., Sandström G.

Objectives:  

Cholera is a severe intestinal disease, caused by different spices of Vibrio cholerae. While cholera affects many millions of people around the world, the main reservoir of the bacterium is not completely known. Since both free-living amoeba and V. cholerae inhabit aquatic systems, an association between them would be possible. Our previous study has shown that the seventh-pandemic V. cholerae O1 El Tor- Inaba strain N16961 behaves as a facultative intracellular bacterium during its survival in free-living amoebae. Here we address the question if strains of V. cholerae O1 classical have the same ability as strain N16961 to grow and survive inside Acanthamoeba castellanii.

Methods:  

V. cholerae O1 classical strains were co-cultivated with A. castellanii for more than two weeks. The interaction between these microorganisms was followed by viable counts of alone- and co-cultivated microorganisms. Intra-amoebic growth and localization of each bacterial strain was estimated by gentamicin assay, viable count, microscopy, and PCR to detect cholera toxin gene and amoebic 18 s RNA gene disclosing symbiont-host association.

Results:  

The results show that examined V. cholerae O1 classical strains multiply and survive inside trophozoites and cysts of A. castellanii. The bacterial internalization was in cytoplasmic compartment of the amoebae cells. The relation between these microorganisms in co-cultures could be listed as symbiosis since, presence of the amoebae enhanced growth of bacteria, and the presence of the bacteria did not affect amoebic growth. In addition, V. cholerae strains could not survive without A. castellanii more than a few days.

Conclusions:  

The symbiotic relation between these bacterial strains and A. castellanii showing a new environmental host of V. cholerae and a facultative intracellular behaviour of V. cholerae O1 classical strains, which is in contrast to the general held view of the bacterium.