Summary auto-generated
Researchers identified five Leptospira strains isolated from reproductive tissues of pigs in Australian herds as a novel bacterial species, designated Leptospira fainei. These strains did not match any of the 24 known pathogenic Leptospira serogroups or saprophytic species through serological testing. Phenotypic characterization revealed growth characteristics intermediate between pathogenic and saprophytic leptospires—they grew at both 13°C and 30°C and were partially inhibited by 8-azaguanine. Extensive molecular analysis, including arbitrarily primed PCR fingerprinting, pulsed-field gel electrophoresis (PFGE), and mapped restriction site polymorphisms of the 16S rRNA gene, demonstrated the five strains were genetically identical and distinct from all known species. DNA-DNA hybridization yielded only 34-36% homology with the most closely related species, Leptospira inadai, meeting the criterion of at least 70% homology required for species delineation. Phylogenetic analysis of 16S rRNA sequences positioned L. fainei in a clade with L. inadai, separate from both pathogenic and saprophytic clades. The type strain was designated BUT 6T, and the organism was confirmed to contain the pathogenic Leptospira 16S rRNA gene signature, indicating potential pathogenic capacity despite its intermediate phenotypic characteristics.
Key findings
- Five genetically identical Leptospira strains from pig reproductive tissues represent a new species, L. fainei, with a new serogroup designated Hurstbridge
- DNA-DNA hybridization values of 34-36% with L. inadai and 0% with all other Leptospira species confirmed species status
- L. fainei demonstrates intermediate growth phenotypes between pathogenic and saprophytic leptospires (growth at 13°C and partial 8-azaguanine inhibition)
- Phylogenetic analysis reveals L. fainei clusters with L. inadai in a distinct clade separate from recognized pathogenic and saprophytic leptospire groups
- PCR assays confirmed L. fainei contains the pathogenic Leptospira 16S rRNA gene signature despite its intermediate characteristics
This summary was generated automatically from the article PDF and is not part of the original publication. Refer to the PDF for the authoritative text.
Abstract
Pathogenic leptospires can be causative agents of reproductive problems in pigs. Cultures of uteri and kidneys from two pig herds in New South Wales and Victoria (Australia) yielded five strains identified as Leptospira on morphological and cultural grounds. Phenotypic characteristics (growth at 13 and 30°C, growth in the presence of 8-azaguanine) were intermediate between those of pathogenic and saprophytic leptospires. No cross-agglutination was observed with reference antisera representing the 24 pathogenic serogroups and the main saprophytic ones. Antiserum against one of the strains did not agglutinate reference strains representative of any serogroup. This provided evidence of a new serovar, designated hurstbridge. Genomic characterization of the five strains was achieved using five molecular approaches. Mapped restriction site polymorphisms in the rrs (16S rRNA) gene were not related to those of any reference strains. Arbitrarily primed PCR fingerprints suggested clonality of the five strains. The strains all showed an identical and unique PFGE profile. PCR, using primers specific for the rrs gene of pathogenic leptospires, amplified corresponding sequences from the strains. DNA-DNA hybridization (and reciprocal experiments) using the S1 nuclease/TCA method was performed between one of the strains and the reference strains of Leptospira species. The homology ranged from 0 to 36% (the latter being with Leptospira inadai) thus satisfying the criterion of a new species, Leptospira fainei (type strain BUT 67). Phylogenetic analysis of 16S rRNA sequences showed that L. fainei and L. inadai formed a clade separate from the previously recognized saprophyte and pathogen clades.