Legionella cardiaca sp. nov., isolated from a case of native valve endocarditis in a human heart

Abstract

A Gram-negative, rod-shaped bacterium, designated H63T, was isolated from aortic valve tissue of a patient with native valve endocarditis. 16S rRNA gene sequencing revealed that H63T belongs to the genus Legionella , with its closest neighbours being the type strains of Legionella brunensis (98.8 % similarity), L. londiniensis (97.0 %), L. jordanis (96.8 %), L. erythra (96.2 %), L. dresdenensis (96.0 %) and L. rubrilucens , L. feeleii , L. pneumophila and L. birminghamensis (95.7 %). DNA–DNA hybridization studies yielded values of <70 % relatedness between strain H63T and its nearest neighbours in terms of 16S rRNA gene sequence similarity, indicating that the strain represents a novel species. Phylogenetic analysis of the 16S rRNA, macrophage infectivity potentiator (mip) and RNase P (rnpB) genes confirmed that H63T represents a distinct species, with L. brunensis being its closest sister taxon. Fatty acid composition and biochemical traits, such as the inability to ferment glucose and reduce nitrate, supported the affiliation of H63T to the genus Legionella . H63T was distinguishable from its neighbours based on it being positive for hippurate hydrolysis. H63T was further differentiated by its inability to grow on BCYE agar at 17 °C, its poor growth on low-iron medium and the absence of sliding motility. Also, H63T did not react with antisera generated from type strains of Legionella species. H63T replicated within macrophages. It also grew in mouse lungs, inducing histopathological evidence of pneumonia and dissemination to the spleen. Together, these results confirm that H63T represents a novel, pathogenic Legionella species, for which the name Legionella cardiaca sp. nov. is proposed. The type strain is H63T ( = ATCC BAA-2315T  = DSM 25049T  = JCM 17854T).