Interactions between Free-Living Amoebae and Legionella in the Environment

Abstract

While their presence is common in the environment, culture and isolation of Legionella from environmental waters are fastidious. Free-living amoebae have identical aquatic habitats and are probable natural hosts for Legionella. In the laboratory it was shown that amoebae can feed on Legionella on solid and in liquid medium; both survived after several subcultures of amoebae. Amoebae were isolated from river waters and sediments. Cysts or trophozoites were subcultured; the amoebae were washed and harvested, then lysed by thermal shock and ultrasonic treatment. The lysates were positive for Legionella by IFD with different pools of antisera (A, B and C from CDC, Atlanta). Intra-peritoneal injection of the lysates in guinea-pigs allowed the isolation of L.pneumophila 1 from blood and various organs. Amoebae are likely to be natural hosts for Legionella and are convenient as an ecological model in the laboratory. Intra-cellular replication and inclusion in resistant cysts of amoebae give them a possibility of survival in unfavourable conditions.