Differential growth of Legionella pneumophila strains within a range of amoebae at various temperatures associated with in-premise plumbing

Aims: The potential effect of in-premise plumbing temperatures (24, 32, 37 and 41 degrees C) on the growth of five different Legionella pneumophila strains within free-living amoebae (Acanthamoeba polyphaga, Hartmannella vermiformis and Naegleria fowleri) was examined. Methods and Results: Compared with controls that actively fed on Escherichia coli prey, when Leg. pneumophila was used as prey, strains Lp02 and Bloomington-2 increased in growth at 30, 32 and 37 degrees C while strains Philadelphia-1 and Chicago 2 did not grow at any temperature within A. polyphaga. Strains Lp02, Bloomington-2 and Dallas 1E did not proliferate in the presence of H. vermiformis nor did strain Philadelphia-1 in the presence of N. fowleri. Yet, strain Bloomington-2 grew at all temperatures examined within N. fowleri, while strain Lp02 proliferated at all temperatures except 41 degrees C. More intriguing, strain Chicago 2 only grew at 32 degrees C within H. vermiformis and N. fowleri suggesting a limited temperature growth range for this strain. Conclusions: Identifying the presence of pathogenic legionellae may require the use of multiple host amoebae and incubation temperatures. Significance and Impact of the Study: Temperature conditions and species of amoeba host supported in drinking water appear to be important for the selection of human-pathogenic legionellae and point to future research required to better understand Legionella ecology.