Isolation and characterization of two novel plasmids from pathogenic Leptospira interrogans serogroup Canicola Serovar Canicola strain Gui44

Comparative Genomic Analysis and a Novel Set of Missense Mutation of the Leptospira weilii Serogroup Mini From the Urine of Asymptomatic Dogs in Thailand

Leptospira weilii belongs to the pathogenic Leptospira group and is a causal agent of human and animal leptospirosis in many world regions. L. weilii can produce varied clinical presentations from asymptomatic through acute to chronic infections and occupy several ecological niches. Nevertheless, the genomic feature and genetic basis behind the host adaptability of L. weilii remain elusive due to limited information. Therefore, this study aimed to examine the complete circular genomes of two new L. weilii serogroup Mini strains (CUDO6 and CUD13) recovered from the urine of asymptomatic dogs in Thailand and then compared with the 17 genomes available for L. weilii. Variant calling analysis (VCA) was also undertaken to gain potential insight into the missense mutations, focusing on the known pathogenesis-related genes. Whole genome sequences revealed that the CUDO6 and CUD13 strains each contained two chromosomes and one plasmid, with average genome size and G+C content of 4.37 Mbp and 40.7%, respectively. Both strains harbored almost all the confirmed pathogenesis-related genes in Leptospira. Two novel plasmid sequences, pDO6 and pD13, were identified in the strains CUDO6 and CUD13. Both plasmids contained genes responsible for stress response that may play important roles in bacterial adaptation during persistence in the kidneys. The core-single nucleotide polymorphisms phylogeny demonstrated that both strains had a close genetic relationship. Amongst the 19 L. weilii strains analyzed, the pan-genome analysis showed an open pan-genome structure, correlated with their high genetic diversity. VCA identified missense mutations in genes involved in endoflagella, lipopolysaccharide (LPS) structure, mammalian cell entry protein, and hemolytic activities, and may be associated with host-adaptation in the strains. Missense mutations of the endoflagella genes of CUDO6 and CUD13 were associated with loss of motility. These findings extend the knowledge about the pathogenic molecular mechanisms and genomic evolution of this important zoonotic pathogen.

Spatial and Simultaneous Seroprevalence of Anti-Leptospira Antibodies in Owners and Their Domiciled Dogs in a Major City of Southern Brazil

Although leptospirosis has been considered a major concern in urban areas, no study to date has spatially and simultaneously compared both owner and dog serology in households of major cities. Accordingly, the aim of the present study was to assess the seroprevalence of Leptospira antibodies, evaluate associated risk factors and conduct spatial analyses in 565 randomly selected households, which included 597 dog owners and 729 dogs in Londrina, Southern Brazil. Seropositivity by MAT were detected in in 11/597 (1.84%) owners and in 155/729 (21.26%) dogs. The risk factors were evaluated with logistic regression analysis and spatial factors and case distribution were evaluated with kernel density analyses. The sera of 14/155 (9.03%) dogs reacted for more than one serovar with the same titer. Canicola was the most frequent serogroup, detected in 3/11 (27.27%) owners and 76/155 (49.03%) dogs. The highest titer among the owners was 1:3,200 and was detected in the same household with a titer of 1:800 in the dog. Simultaneous owner-dog seropositivity was found in 7/565 (1.23%) households, with three reacted against serogroup Canicola. Positive owners were detected in 4/565 (0.70%) households and positive dogs were detected in 141/565 (24.95%) households. The associated risks of infection for dogs were different from those associated with infection in owners. Risk analyses for Canicola also identified specific factors of infection. Regardless of owner and dog cases were not statistically clustered, the kernel map has shown dog positivity occurrence in the same hot locations and near positive owners. The dependent variable analysis and logit model suggested a greater likelihood of peri-domiciliary contact with Leptospira. In conclusion, exposure to Leptospira infection was significantly higher in dogs than in their owners and human cases spatially overlapped dog cases, implicating dogs as potential environmental sentinels for this disease. In addition, the associated risk may vary according to serogroup, and the observed simultaneous Canicola seropositivity of owner and dog has suggested intradomicile-transmitted infection.

Crawling Motility on the Host Tissue Surfaces Is Associated With the Pathogenicity of the Zoonotic Spirochete Leptospira

Bacterial motility is crucial for many pathogenic species in the process of invasion and/or dissemination. The spirochete bacteria Leptospira spp. cause symptoms, such as hemorrhage, jaundice, and nephritis, in diverse mammals including humans. Although loss-of-motility attenuate the spirochete's virulence, the mechanism of the motility-dependent pathogenicity is unknown. Here, focusing on that Leptospira spp. swim in liquid and crawl on solid surfaces, we investigated the spirochetal dynamics on the host tissues by infecting cultured kidney cells from various species with pathogenic and non-pathogenic leptospires. We found that, in the case of the pathogenic leptospires, a larger fraction of bacteria attached to the host cells and persistently traveled long distances using the crawling mechanism. Our results associate the kinetics and kinematic features of the spirochetal pathogens with their virulence.

Isolation, Purification, and Characterization of Leptophages

To date, only three bacteriophages of leptospires-leptophages-are known. Nonetheless, numerous prophages have been found in the genus, especially in the genomes of pathogenic species. Thus, some laboratories attempt to isolate leptophage particles from environmental samples or following mitomycin C induction of bacterial cultures. Here, we propose multiple procedures to isolate, purify, and characterize bacteriophages, based on protocols used for LE3 and LE4 characterization.

Comparative genomic analysis of Chinese human leptospirosis vaccine strain and circulating isolate

LEPTOSPIRA INTERROGANS

serogroup Canicola is one of the most important pathogens causing leptospirosis and is used as a vaccine strain of the current Chinese human leptospirosis vaccine. To characterize leptospiral pathogens, L. interrogans serogroup Canicola vaccine strain 611 and circulating isolate LJ178 from different hosts at different periods were sequenced using a combined strategy of Illumina X10 and PacBio technologies, and a comprehensive comparative analysis with other published Leptospira strains was conducted in this study. High levels of genomic similarities were observed between vaccine strain 611 and circulating isolate LJ178; both had two circular chromosomes and two circular extrachromosomal replicons. Compared with the strain 611 genome, 132 single nucleotide polymorphisms and 92 indels were found in strain LJ178. The larger lipopolysaccharide biosynthesis locus of serogroup Canicola was identified in both genomes. The phylogenetic analysis based on whole-genome sequences revealed that serogroup Canicola was not restricted to a specific host or geographic location, suggesting adaptive evolution associated with the ecologic diversity. In summary, our findings provide insights into a better molecular understanding of the component strains of human leptospirosis vaccine in China. Furthermore, these data detail the genetic composition and evolutionary relatedness of Leptospira strains that pose a health risk to humans.

Leptospira and Leptospirosis

Leptospira spp. are morphologically and phylogenetically unique bacteria that are ubiquitous in the environment. Pathogenic species are the agents of leptospirosis, an emerging zoonotic disease transmitted to both human and animals from the environment contaminated with the urine of reservoir animals. The taxonomy of Leptospira has recently undergone extensive revisions with the use of whole-genome sequences, thus expanding considerably the number of species.

Toolbox of Molecular Techniques for Studying Leptospira Spp

This chapter covers the progress made in the Leptospira field since the application of mutagenesis techniques and how they have allowed the study of virulence factors and, more generally, the biology of Leptospira. The last decade has seen advances in our ability to perform molecular genetic analysis of Leptospira. Major achievements include the generation of large collections of mutant strains and the construction of replicative plasmids, enabling complementation of mutations. However, there are still no practical tools for routine genetic manipulation of pathogenic Leptospira strains, slowing down advances in pathogenesis research. This review summarizes the status of the molecular genetic toolbox for Leptospira species and highlights new challenges in the nascent field of Leptospira genetics.

Comparative genomics of pathogenic Leptospira interrogans serovar Canicola isolated from swine and human in Brazil

Leptospira interrogans serovar Canicola is one of the most important pathogenic serovars for the maintenance of urban leptospirosis. Even though it is considered highly adapted to dogs, serovar Canicola infection has already been described in other animals and even a few human cases. Here, we present the genomic characterisation of two Brazilian L. interrogans serovar Canicola strains isolated from slaughtered sows (L0-3 and L0-4) and their comparison with human strain Fiocruz LV133. It was observed that the porcine serovar Canicola strains present the genetic machinery to cause human infection and, therefore, represent a higher risk to public health. Both human and porcine serovar Canicola isolates also presented sequences with high identity to the Chinese serovar Canicola published plasmids pGui1 and pGui2. The plasmids identification in the Brazilian and Chinese serovar Canicola strains suggest that extra-chromosomal elements are one more feature of this serovar that was previously unnoticed.

Antibiotic susceptibilities of livestock isolates of leptospira

Leptospirosis is the most common zoonotic disease and is endemic worldwide. The antibiotic susceptibilities of Leptospira strains isolated from both humans and animals are poorly documented. This issue is particularly important for isolates from food-producing animals which are regularly exposed to antibiotic treatments. This study assessed the susceptibility of 35 leptospira strains isolated from food-producing animals of diverse geographical origins between 1936 and 2016 to the antimicrobial agents used most commonly in animals. A broth microdilution method was used to determine the susceptibilities of Leptospira strains isolated from livestock to 11 antibiotics. All isolates were susceptible to penicillin, amoxicillin, clavulanate, cephalexin, ceftriaxone, doxycycline, tetracycline, streptomycin, enrofloxacin and spectinomycin, but not polymyxin [minimum inhibitory concentration (MIC) ≥ 4 μg/L]. For tetracycline and doxycycline, the MIC was significantly higher for the recent isolates from Sardinia, Italy than for the other isolates. Antimicrobial susceptibilities were also determined with 10- and 100-fold higher inocula. High inocula significantly diminished the antibacterial effect by at least 10-fold for enrofloxacin (MIC ≥256 μg/L), streptomycin (MIC ≥16 μg/L) and tetracycline (MIC ≥32 μg/L), suggesting selection of resistant strains for high inocula. These findings contribute to the assessment of whether certain antibiotics are potentially useful for the treatment of leptospirosis, and point out the risk of failure for some antibiotics during infection with a high inoculum in both animals and humans. This study strengthens the need to detect and prevent the emergence of antimicrobial resistance of this major emerging zoonotic pathogen.

Distribution of Plasmids in Distinct Leptospira Pathogenic Species

Leptospirosis, caused by pathogenic Leptospira, is a worldwide zoonotic infection. The genus Leptospira includes at least 21 species clustered into three groups--pathogens, non-pathogens, and intermediates--based on 16S rRNA phylogeny. Research on Leptospira is difficult due to slow growth and poor transformability of the pathogens. Recent identification of extrachromosomal elements besides the two chromosomes in L. interrogans has provided new insight into genome complexity of the genus Leptospira. The large size, low copy number, and high similarity of the sequence of these extrachromosomal elements with the chromosomes present challenges in isolating and detecting them without careful genome assembly. In this study, two extrachromosomal elements were identified in L. borgpetersenii serovar Ballum strain 56604 through whole genome assembly combined with S1 nuclease digestion following pulsed-field gel electrophoresis (S1-PFGE) analysis. Further, extrachromosomal elements in additional 15 Chinese epidemic strains of Leptospira, comprising L. borgpetersenii, L. weilii, and L. interrogans, were successfully separated and identified, independent of genome sequence data. Southern blot hybridization with extrachromosomal element-specific probes, designated as lcp1, lcp2 and lcp3-rep, further confirmed their occurrences as extrachromosomal elements. In total, 24 plasmids were detected in 13 out of 15 tested strains, among which 11 can hybridize with the lcp1-rep probe and 11 with the lcp2-rep probe, whereas two can hybridize with the lcp3-rep probe. None of them are likely to be species-specific. Blastp search of the lcp1, lcp2, and lcp3-rep genes with a nonredundant protein database of Leptospira species genomes showed that their homologous sequences are widely distributed among clades of pathogens but not non-pathogens or intermediates. These results suggest that the plasmids are widely distributed in Leptospira species, and further elucidation of their biological significance might contribute to our understanding of biology and infectivity of pathogenic spirochetes.

Complete Genome Sequences of Low-Passage Virulent and High-Passage Avirulent Variants of Pathogenic Leptospira interrogans Serovar Manilae Strain UP-MMC-NIID, Originally Isolated from a Patient with Severe Leptospirosis, Determined Using PacBio Single-Molecule Real-Time Technology

Here, we report the complete genome sequences of low-passage virulent and high-passage avirulent variants of pathogenic Leptospira interrogans serovar Manilae strain UP-MMC-NIID, a major causative agent of leptospirosis. While there were no major differences between the genome sequences, the levels of base modifications were higher in the avirulent variant.

A replicative plasmid vector allows efficient complementation of pathogenic Leptospira strains

Leptospirosis, an emerging zoonotic disease, remains poorly understood because of a lack of genetic manipulation tools available for pathogenic leptospires. Current genetic manipulation techniques include insertion of DNA by random transposon mutagenesis and homologous recombination via suicide vectors. This study describes the construction of a shuttle vector, pMaORI, that replicates within saprophytic, intermediate, and pathogenic leptospires. The shuttle vector was constructed by the insertion of a 2.9-kb DNA segment including the parA, parB, and rep genes into pMAT, a plasmid that cannot replicate in Leptospira spp. and contains a backbone consisting of an aadA cassette, ori R6K, and oriT RK2/RP4. The inserted DNA segment was isolated from a 52-kb region within Leptospira mayottensis strain 200901116 that is not found in the closely related strain L. mayottensis 200901122. Because of the size of this region and the presence of bacteriophage-like proteins, it is possible that this region is a result of a phage-related genomic island. The stability of the pMaORI plasmid within pathogenic strains was tested by passaging cultures 10 times without selection and confirming the presence of pMaORI. Concordantly, we report the use of trans complementation in the pathogen Leptospira interrogans. Transformation of a pMaORI vector carrying a functional copy of the perR gene in a null mutant background restores the expression of PerR and susceptibility to hydrogen peroxide comparable to that of wild-type cells. In conclusion, we demonstrate the replication of a stable plasmid vector in a large panel of Leptospira strains, including pathogens. The shuttle vector described will expand our ability to perform genetic manipulation of Leptospira spp.