A combined approach of VNTR and MLST analysis: improving molecular typing of Argentinean isolates of Leptospira interrogans.

Leptospirosis is an emerging infectious disease that has been identified as both a human and animal health problem worldwide. Regular outbreaks associated with specific risk factors have been reported in Argentina. However, there are no available data concerning the genetic population level for this pathogen. Therefore, the aim of this work was to describe the genetic diversity of Leptospira interrogans through the application of two molecular typing strategies: variable number of tandem repeats (VNTR) and multilocus sequence typing (MLST). For this purpose, seven reference strains and 18 non-epidemiologically related isolates from diverse hosts and Argentinean regions were analysed. Among them, nine genotypes and seven sequence types (STs), including three unreported STs, were described using VNTR and MLST, respectively. eBURST analysis demonstrated that ST37 was the most frequent and founder genotype of a clonal complex (CCs) containing STN1 and STN3, suggesting the importance of studying the serovars belonging to this CC in Argentina. The data from maximum parsimony analysis, which combined both techniques, achieved intra-serovar discrimination, surmounted microscopic agglutination test discrepancies and increased the discriminatory power of each technique applied separately. This study is the first to combine both strategies for L. interrogans typing to generate a more comprehensive molecular genotyping of isolates from Argentina in a global context.

Simplified MLST scheme for direct typing of Leptospira human clinical samples.

Leptospirosis is a globally distributed zoonosis. Epidemiological data are scarce and present major challenge because of the varied clinical presentations. Multilocus Sequence Typing has already proven to be a robust molecular typing method providing accurate results for strain characterization. We have adapted our MLST scheme by reducing the set of loci to facilitate Leptospira typing directly from human clinical samples. The application of this 3-locus scheme provides Leptospira species and allelic profiles of the samples retaining the power of discrimination of the whole scheme. Moreover, an approach to the serogroups was also achieved. Our results contribute to the epidemiological study of Leptospirosis, since the direct typing on clinical specimens could detect and update allelic variants and serogroups present in a region. The simplified scheme allowed at the same time to take advantage of limited genetic material available in clinical samples that may increase the sources of information for epidemiological monitoring.

Isolation and clinical sample typing of human leptospirosis cases in Argentina.

Leptospira typing is carried out using isolated strains. Because of difficulties in obtaining them, direct identification of infective Leptospira in clinical samples is a high priority. Multilocus sequence typing (MLST) proved highly discriminatory for seven pathogenic species of Leptospira, allowing isolate characterization and robust assignment to species, in addition to phylogenetic evidence for the relatedness between species. In this study we characterized Leptospira strains circulating in Argentina, using typing methods applied to human clinical samples and isolates. Phylogenetic studies based on 16S ribosomal RNA gene sequences enabled typing of 8 isolates (6 Leptospira interrogans, one Leptospira wolffii and one Leptospira broomii) and 58 out of 85 (68.2%) clinical samples (55 L. interrogans, 2 Leptospira meyeri, and one Leptospira kirschneri). MLST results for the L. interrogans isolates indicated that five were probably Canicola serogroup (ST37) and one was probably Icterohaemorrhagiae serogroup (ST17). Eleven clinical samples (21.6%), provided MLST interpretable data: five were probably Pyrogenes serogroup (ST13), four Sejroe (ST20), one Autumnalis (ST22) and one Canicola (ST37). To the best of our knowledge this study is the first report of the use of an MLST typing scheme with seven loci to identify Leptospira directly from clinical samples in Argentina. The use of clinical samples presents the advantage of the possibility of knowing the infecting strain without resorting to isolates. This study also allowed, for the first time, the characterization of isolates of intermediate pathogenicity species (L. wolffii and L. broomii) from symptomatic patients.

First Genome Sequence of Leptospira interrogans Serovar Pomona, Isolated from a Bovine Abortion.

Leptospirosis is a widespread zoonosis and a re-emergent disease of global distribution with major relevance in veterinary production. Here, we report the whole-genome sequence of Leptospira interrogans serovar Pomona strain AKRFB, isolated from a bovine abortion during a leptospirosis outbreak in Argentina.

Reassessment of MLST schemes for Leptospira spp. typing worldwide.

Leptospirosis is a neglected zoonosis of global importance. Several multilocus sequence typing (MLST) methods have been developed for Leptospira spp., the causative agent of leptospirosis. In this study we reassessed the most commonly used MLST schemes in a set of worldwide isolates, in order to select the loci that achieve the maximum power of discrimination for typing Leptospira spp. Global eBURST algorithm was used to detect clonal complexes among STs and phylogenetic relationships among concatenated and individual sequences were inferred through maximum likelihood (ML) analysis. The evaluation of 12 loci combined to type a subset of strains rendered 57 different STs. Seven of these loci were selected into a final scheme upon studying the number of alleles and polymorphisms, the typing efficiency, the discriminatory power and the ratio dN/dS per nucleotide site for each locus. This new 7-locus scheme was applied to a wider collection of worldwide strains. The ML tree constructed from concatenated sequences of the 7 loci identified 6 major clusters corresponding to 6 Leptospira species. Global eBURST established 8 CCs, which showed that genotypes were clearly related by geographic origin and host. ST52 and ST47, represented mostly by Argentinian isolates, grouped the higher number of isolates. These isolates were serotyped as serogroups Pomona and Icterohaemorrhagiae, showing a unidirectional correlation in which the isolates with the same ST belong to the same serogroup. In summary, this scheme combines the best loci from the most widely used MLST schemes for Leptospira spp. and supports worldwide strains classification. The Argentinian isolates exhibited congruence between allelic profile and serogroup, providing an alternative to serological methods.

A combined approach of VNTR and MLST analysis: improving molecular typing of Argentinean isolates of Leptospira interrogans

Leptospirosis is an emerging infectious disease that has been identified as both a human and animal health problem worldwide. Regular outbreaks associated with specific risk factors have been reported in Argentina. However, there are no available data concerning the genetic population level for this pathogen. Therefore, the aim of this work was to describe the genetic diversity of Leptospira interrogans through the application of two molecular typing strategies: variable number of tandem repeats (VNTR) and multilocus sequence typing (MLST). For this purpose, seven reference strains and 18 non-epidemiologically related isolates from diverse hosts and Argentinean regions were analysed. Among them, nine genotypes and seven sequence types (STs), including three unreported STs, were described using VNTR and MLST, respectively. eBURST analysis demonstrated that ST37 was the most frequent and founder genotype of a clonal complex (CCs) containing STN1 and STN3, suggesting the importance of studying the serovars belonging to this CC in Argentina. The data from maximum parsimony analysis, which combined both techniques, achieved intra-serovar discrimination, surmounted microscopic agglutination test discrepancies and increased the discriminatory power of each technique applied separately. This study is the first to combine both strategies for L. interrogans typing to generate a more comprehensive molecular genotyping of isolates from Argentina in a global context.