Vibrio species utilise Acanthamoeba castellanii as an environmental host

Abstract number: P1240

Abd H., Saeed A., Sandström G.

Objectives:Vibrio is a genus of Gram-negative bacteria found in water and it may be carried by sea living animals. The genus comprises nearly 70 species. Vibrio cholerae O1 and V. cholerae O139 produce cholera toxin and cause cholera. V. cholerae non-O1/O139 strains and other vibrio species such as V. parahaemolyticus, V. vulnificus and V. mimicus can cause gastroenteritis, open wounds infection, and septicaemia. The prevalence rate of infections caused by vibrios increases globally. The combination of increased water temperature and salinity may contribute to increased association rates of the bacteria with sea living animals or protozoa. Our recent studies have shown that Vibrio cholerae O1 and O139 have the ability to grow and survive in the aquatic free-living amoeba Acanthamoeba castellanii. The aim of the current study was to highlight interaction of different vibrio clinical isolates with A. castellanii. Vibrio species were isolated from Bangladesh, India and Sweden and they included V. cholerae O1, V. cholerae O139 MO10, V. cholerae O139 SG24, V. mimicus and V. vulnificus.

Methods:Acanthamoeba castellanii and Vibrio strains were alone and co-cultivated for two weeks. Gentamicin assay was used to kill extracellular vibrios as well as to examine ability of amoeba to protect intracellular vibrios from antibiotic killing. Interaction between microorganisms was studied by viable count, necrosis assay, fluorescence microscopy, electron microscopy and statistical analysis.

Results: The results showed that Acanthamoeba castellanii grew in the presence of Vibrio species and the amoeba numbers enhanced during 2 weeks.

Growth of the bacterial strains was enhanced significantly in the presence of A. castellanii compared to alone cultivated bacteria, which died within few days.

The examined vibrio species grew intracellularly to 10⁴–10⁶ CFU/ml in A. castellanii and the intracellular bacteria survived for >2 weeks.

Electron microscopy showed that the intracellular localisation of the bacteria was in vacuoles of the trophozoites a few hours after co-cultivation. Multiplication of bacterial cells occurred in the cytoplasm of trophozoites one day after co-cultivation and the bacteria were found in the cysts of A. castellanii 6 and 7 days after co-cultivation.

Conclusions:Vibrio cholerae, V. mimicus and V. vulnificus grew and survived in A. castellanii disclosing the role of acanthamoebae as environmental hosts for Vibrio species.