Listeria weihenstephanensis sp. nov., isolated from the water plant Lemna trisulca taken from a freshwater pond.

The phylogenetic position and phenotypic characteristics of two non-spore-forming bacilli similar to members of the genus Listeria were studied. The gram-reaction-positive, slightly motile, facultatively anaerobic strains were isolated from the water plant Lemna trisulca sampled from a freshwater pond in Bavaria, Germany. Although no identification was possible employing the API Listeria test (bioMérieux), 16S rRNA sequence analysis confirmed a close phylogenetic similarity to Listeria rocourtiae DSM 22097(T) (99.0 % sequence similarity) and a more distant relationship to other Listeria species (96.0 % to Listeria monocytogenes DSM 20600(T) and 95.0 % similarity to Listeria grayi DSM 20601(T)). DNA-DNA hybridization analysis between the isolates and Listeria rocourtiae DSM 22097(T) yielded a similarity of 22.5 %. Analysis of partial sequences of sigB, prs, recA and HSP60 were studied and compared with those of other members of the genus Listeria and Brochothrix thermosphacta DSM 20171(T) supporting the relationships indicated by 16S rRNA gene sequences. The studied isolates were non-haemolytic and were not associated with cases of human or animal disease. While the results demonstrate that the strains belong to the genus Listeria, phenotypic and genotypic differences from Listeria rocourtiae DSM 22097(T) suggest that the strains represent a novel species for which the name Listeria weihenstephanensis sp. nov. is proposed; the type strain is WS 4560(T) ( = DSM 24698(T) = LMG 26374(T)), with WS 4615 ( = DSM 24699 = LMG 26375) as a second strain of the species.