Characterisation of Putative Outer Membrane Proteins from Leptospira borgpetersenii Serovar Hardjo-Bovis Identifies Novel Adhesins and Diversity in Adhesion across Genomospecies Orthologs

Leptospirosis is a zoonotic bacterial disease affecting mammalian species worldwide. Cattle are a major susceptible host; infection with pathogenic Leptospira spp. represents a public health risk and results in reproductive failure and reduced milk yield, causing economic losses. The characterisation of outer membrane proteins (OMPs) from disease-causing bacteria dissects pathogenesis and underpins vaccine development. As most leptospire pathogenesis research has focused on Leptospira interrogans, this study aimed to characterise novel OMPs from another important genomospecies, Leptospira borgpetersenii, which has global distribution and is relevant to bovine and human diseases. Several putative L. borgpetersenii OMPs were recombinantly expressed, refolded and purified, and evaluated for function and immunogenicity. Two of these unique, putative OMPs (rLBL0972 and rLBL2618) bound to immobilised fibronectin, laminin and fibrinogen, which, together with structural and functional data, supports their classification as leptospiral adhesins. A third putative OMP (rLBL0375), did not exhibit saturable adhesion ability but, together with rLBL0972 and the included control, OmpL1, demonstrated significant cattle milk IgG antibody reactivity from infected cows. To dissect leptospire host-pathogen interactions further, we expressed alleles of OmpL1 and a novel multi-specific adhesin, rLBL2618, from a variety of genomospecies and surveyed their adhesion ability, with both proteins exhibiting divergences in extracellular matrix component binding specificity across synthesised orthologs. We also observed functional redundancy across different L. borgspetersenii OMPs which, together with diversity in function across genomospecies orthologs, delineates multiple levels of plasticity in adhesion that is potentially driven by immune selection and host adaptation. These data identify novel leptospiral proteins which should be further evaluated as vaccine and/or diagnostic candidates. Moreover, functional redundancy across leptospire surface proteins together with identified adhesion divergence across genomospecies further dissect the complex host-pathogen interactions of a genus responsible for substantial global disease burden.

Growth dynamic of Leptospira spp. from Sejroe serogroup in different media formulae

The culturing of Leptospira strains from bovine clinical samples is challenging and has resulted in some gaps in securing an epidemiological understanding. Strains related to chronic reproductive leptospirosis in cattle belong to the Sejroe serogroup - not only Hardjoprajitno and Hardjobovis but also Guaricura genotypes. This study analyses the growth of Leptospira strains from serogroup Sejroe in different culture media, with the aim of suggesting better culturing approaches. To meet this objective, two culture media were applied: EMJH and T80/40/LH. In addition, three different cocktails of selective agents were chosen. The combinations of medium and selective additives resulted in 10 different tested formulae. The poor performance of Hardjobovis in EMJH indicated that its growth may represent a possible bias when culturing these strains from bovine samples. The most efficient medium for culturing Hardjobovis was T80/40/LH, while T80/40/LH medium + STAFF combination proved to be the best choice for growth, being recommended for obtaining a higher number of these strains from bovines.

Molecular epidemiology of Leptospira noguchii reveals important insights into a One Health context

Leptospirosis presents a complex and dynamic epidemiology. Bovine leptospirosis has been described as a major infectious disease impairing reproductive efficiency. Although infections by Leptospira interrogans, L. santarosai and L. borgpetersenii are frequently reported in cattle, the presence of L. noguchii in these animals should not be neglected. In this study, we describe serological (MAT) and molecular characterization (rrs and secY gene sequencing, multilocus sequence typing [MLST] and pulsed-field gel electrophoresis [PFGE]) of eight L. noguchii strains obtained from slaughtered cows. Intraspecific genetic diversity was evaluated, and haplotype networks were constructed based on hosts and geographical localizations. Strains were characterized as belonging to serogroups Australis, Autumnalis and Panama, and molecular characterization showed a high heterogeneity of these strains. Ten different STs were found (including nine new STs and 39 novel alleles) as well as nine different pulsotypes. Two clonal complexes were found. Phylogenetic trees based on secY locus and concatenated MLST loci showed two main clusters, with sequences from the present study included in the first. In general, there was no relationship between the geographical origin and the secY phylogenetic clusters, as well as between secY phylogenetic clusters and serogroups. Molecular diversity indexes confirmed a high variability (H > 0.8). This high intraspecific variation observed may be related to differences in virulence, pathogenicity and antigenicity or even adaptability of the strains. In addition, haplotype networks clearly demonstrated the circulation of genotypes between humans and animals, confirming the zoonotic potential. The present study provides relevant data for the study of leptospirosis in the One Health context, where human, animal and environmental health is closely connected.

The Successful Management of Leptospirosa hardjo Infection in a Beef Herd in Northern Ontario

Abortion, premature calving, hemolytic anemia and fatal hematuria were associated with high levels (titer > 10(-4)) of antibody to Leptospira interrogans serovar hardjo and with isolation of hardjo in a herd of 265 beef cattle in the Great Clay Belt of northern Ontario. This herd was bred by artificial insemination, after heat detection by vasectomized bulls. The antibody prevalence rate in the herd was 54 to 60% over a five year period. The rate tended to reach 100% by age three years and to be below 5% in yearlings, which were raised in isolation from older cattle. Hardjo was isolated from the urine of a cow that aborted in the eighth month of pregnancy, and from kidneys of yearling steers which had been exposed to an older cow. Maternal antibody levels in calves paralleled those in their dams, protecting calves while they were being naturally exposed to infection, thus contributing to the achievement of balance between host and parasite. A controlled vaccination trial was conducted in 50 initially seronegative yearling steers and heifers. Serological response to vaccine was limited to a maximum agglutinin titer of 10(-2) in 8% of vaccinated cattle. Vaccination reduced the infection rate from 86% in the controls to 46% in the treated group, indirectly reducing the number of calves for which colostral antibody against hardjo would be available. A vaccination program was not implemented in the herd. Hardjo infection appeared to die out over a period of six years following the initial five year study period, with antibody prevalence falling from 60% to 0.7% and reactors persisting only in two eight year old cows. Decline in infection was coincident with changes in management which protected heifers from exposure to infection until their third pregnancy, and which probably lowered the reservoir of infection by increased culling from older age classes.