Intracellular survival of Vibrio cholerae O1 El Tor strains in environmental protozoa- Acanthamoeba castellanii may induce bacterial phenotypic alterations

Abstract number: 1134_02_144

Sandström G., Weintraub A., Abd H.

Objectives:

Cholera is a severe and potentially life-threatening diarrheal disease caused by certain spices of the gram-negative bacterium Vibrio cholerae. Many millions of cases of cholera occur annually, in epidemic and pandemic forms due to V. cholerae O1 and O139, and also sporadically due to non-O1 and non-O139 V. cholerae strains. In this context, the survival of V. cholerae in nature is of interest from an epidemiological perspective. Although the natural reservoirs for survival and multiplication of V. cholerae are far from compeletly disclosed, our previous study has shown that free-living amoebae can be reservoirs for the seventh-pandemic V. cholerae O1 El Tor- Inaba strain N16961, which can survive and grow intracellularly in Acanthamoeba castellanii.The aim of this study was to examine the ability of different strains of V. cholerae O1 El Tor to grow and survive in Acanthamoeba castellanii, and to examine whether intra-amoebic survival of bacteria alter their pattern of resistance and sensitivity to different antibiotics.

Methods:

V. cholerae O1 El Tor strains were co-cultured 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 were estimated by gentamicin assay, viable count, microscopy, and PCR to detect cholera toxin gene and amoebic 18s RNA gene disclosing symbiont-host association.

Results:

The results show that examined V. cholerae O1 El Tor strains multiplied and survived 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 classified as symbiosis, since presence of the amoebae enhanced growth of bacterial strains, and presence of the bacteria did not affect amoebic growth. The intra-amoebic survival of bacteria did not alter their pattern of resistance and sensitivity to different antibiotics such as ampicillin, gentamicin, and tetracycline.

Conclusions:

This study shows a facultative intracellular behaviour of examined V. cholerae O1 El Tor strains, which is in contrast to the general held view, which considers the bacterium to be extracellular microorganisms. The clinical importance of free-living amoebae is their possible role as ‘Trojan horse’.