Legionella drancourtii sp. nov., a strictly intracellular amoebal pathogen

Abstract

A Legionella-like amoebal pathogen (LLAP), formerly named LLAP12(T), was characterized on the basis of microscopic appearance, staining characteristics, growth in Acanthamoeba polyphaga at different temperatures, DNA G+C content, serological cross-reactivity and 16S rRNA and macrophage infectivity potentiator (mip) gene sequence analysis. LLAP12(T) was found to be a motile, Gram-negative bacterium that grew within cytoplasmic vacuoles in infected amoebae. The infecting bacteria induced lysis of their amoebal hosts and time taken to do so was dependent on incubation temperature. Recovery of LLAP12(T) from amoebae onto axenic media could not be achieved. Phylogenetic analysis of LLAP12(T), based on 16S rRNA and mip gene sequence analysis, indicated that it lay within the radiation of the Legionellaceae and that it clustered specifically with Legionella lytica and Legionella rowbothamii. The divergence observed between LLAP12(T) and these two species was of a degree equal to, or greater than, that observed between other members of the family. In support of this delineation, LLAP12(T) was found not to cross-react serologically with any other Legionella species. The mip and 16S rRNA gene sequence-based analyses also indicated that LLAP12(T) was related very closely to two other previously identified LLAP isolates, LLAP4 and LLAP11. Taken together, these results support the proposal of LLAP12(T) as the type strain of Legionella drancourtii sp. nov.