Legionella sheltonii sp. nov., a novel species isolated on a cruise ship during routine monitoring

Journal article, 2025

Legionella-like isolates, HB10 and PATHC038T, were isolated from a cold water distribution system on a cruise ship in 2017. The strains have been characterized by employing discriminatory genome typing, matrix-assisted laser desorption/ionization time-of-flight MS technique, fatty acid profiling and biochemical tests, thus identifying a new species in the genus Legionella. Colonies displayed phenotypic characteristics typical of the family Legionellaceae, including a requirement for l-cysteine and testing catalase positive. Fatty acid methyl ester analysis showed that the predominant fatty acids detected in the studied strains are C16:0 iso, C16:1 ω7c, C16:0 and C15:0 anteiso. The obtained MIC values showed antimicrobial susceptibility to the antimicrobial drugs ciprofloxacin and erythromycin (0.8 and 2 µg ml-1, respectively). The bacteria were also Gram-negative, rod-shaped, grew aerobically on buffered charcoal yeast extract agar and weakly grew on glycine-vancomycin-polymyxin-cycloheximide media at 36 °C with the ability to autofluoresce a blue-white colour when placed under a long-wavelength UV light (365 nm). The whole-genome sequencing performed displayed a G+C content of 38.2 mol%. The digital DNA-DNA hybridization analysis demonstrated a separation from the phylogenetically most related Legionella cherrii, with 54.7% DNA-DNA relatedness. The identity percentage measured by average nucleotide identity between the PATHC038T strain and its respective closest species, L. cherrii, was 93.9%, also confirming the distinctiveness of the novel species. The 16S rRNA gene, mip and rpoB sequences showed a similarity of 98.7, 98.4 and 96.2%, respectively, with L. cherrii NCTC 11976T. Additionally, average amino acid identity and percentage of conserved proteins analyses further supported their classification as a novel species. The results obtained in this study confirm the status of an independent species. The name proposed for this species is Legionella sheltonii sp. nov. with PATHC038T (CCUG 76918T, ATCC TSD-370) as the type strain.