OBJECTIVETo determine whether Acanthamoeba polyphaga could affect the survival and growth of Vibrio cholerae O139 in low temperature.

METHODSV. cholerae O139 was co-cultured with the Acanthamoeba polyphaga to be examined on its intracellular growth and survival rate within cysts at low temperature, using methods as Gram-staining, electron microscope and passage culture.

RESULTSV. cholerae O139 were observed to enter into the trophozoites and grow the within the vacuoles after 8 hour incubation with Acanthamoeba polyphaga. The germs survived in the vacuole and/or endo-layer of wall and could be re-isolated from the excystment of Acanthamoeba polyphaga. At 30 degrees C, V. cholerae O139 could survive for 120 days with the amoeba while less than 45 days in PAS. At 4 degrees C, the number of viable bacteria decreased and reached undetectable levels for both study and control groups after a 30-day incubation. V. cholerae O139 could be re-isolated from the 30-, 45-, 60- and 75-day's infected cysts after excystment. However the ability of excystment for 90-day's infected cysts decreased and V. cholerae O139 within the cyst could not be isolated again because the amoebae had lysed.

CONCLUSIONThese findings indicated that V. cholerae O139 could grow within Acanthamoeba polyphaga and the survival time could be increased in the cysts at low temperature. It seemed that Acanthamoeba can provide an environmental reservoir for V. cholerae O139.