Campylobacter magnus sp. nov., isolated from caecal contents of domestic pigs (Sus scrofa domesticus).

During the 2021 European Food Safety Authority coordinated harmonized monitoring of antimicrobial resistance in Campylobacter species in Slovenia, five Campylobacter-like strains were cultured from caeca of a total of 104 domestic pigs that could not be identified using the standard-prescribed biochemical tests or MALDI-TOF MS. The isolates were obtained using the standard ISO 10272 procedure for the isolation of thermotolerant Campylobacter with prolonged cultivation time. Small Campylobacter-like colonies were observed on mCCDA and CASA agar plates after 2-4 days of incubation; dark-field microscopy revealed relatively big spirilli-shaped bacteria exhibiting characteristic Campylobacter-like motility. The cells were 1.5-3 µm long and 0.5-0.7 µm wide, Gram-negative, oxidase-positive and catalase-positive. MALDI-TOF mass spectra were distinctive and consistent, but with low MALDI-TOF MS log scores and the closest matches being those of Campylobacter hyointestinalis and Campylobacter fetus. All five strains underwent whole-genome sequencing. Analysis of 16S rRNA gene sequences revealed that the isolates were most similar (98.3-98.4 % identity) to Campylobacter lanienae. Pairwise average nucleotide identity (ANI) values revealed that the five studied strains shared pairwise ANI of 96.2-96.5 % but were clearly distinct from the previously described Campylobacter species (ANI ≤72.8 %). The core genome-based phylogeny confirmed that the new strains form a distinct and well-supported clade within the genus Campylobacter. The conducted polyphasic taxonomic analysis confirmed that the five strains represent a novel Campylobacter species for which the name Campylobacter magnus sp. nov. is suggested, with strain 46386T (=DSM 115534T=CCUG 76865T) as the type strain.