Leptospira genomics

Detection of Genes Related to Antibiotic Resistance in Leptospira

Leptospirosis is a disease caused by the bacteria of the Leptospira genus, which can usually be acquired by humans through contact with urine from infected animals; it is also possible for this urine to contaminate soils and bodies of water. The disease can have deadly consequences in some extreme cases. Fortunately, until now, patients with leptospirosis have responded adequately to treatment with doxycycline and azithromycin, and no cases of antibiotic resistance have been reported. However, with the extensive use of such medications, more bacteria, such as Staphylococci and Enterococci, are becoming resistant. The purpose of this study is to determine the presence of genes related to antibiotic resistance in the Leptospira genus using bioinformatic tools, which have not been undertaken in the past. Whole genomes from the 69 described Leptospira species were downloaded from NCBI's GeneBank and analyzed using CARD (The Comprehensive Antibiotic Resistant Database) and RAST (Rapid Annotations using Subsystem Technology). After a detailed genomic search, 12 genes associated with four mechanisms were found: resistance to beta-lactamases, vancomycin, aminoglycoside adenylyltransferases, as well as multiple drug efflux pumps. Some of these genes are highly polymorphic among different species, and some of them are present in multiple copies in the same species. In conclusion, this study provides evidence of the presence of genes related to antibiotic resistance in the genomes of some species of the genus Leptospira, and it is the starting point for future experimental evaluation to determine whether these genes are transcriptionally active in some species and serovars.

Molecular evolution and mosaicism of leptospiral outer membrane proteins involves horizontal DNA transfer

Leptospires belong to a genus of parasitic bacterial spirochetes that have adapted to a broad range of mammalian hosts. Mechanisms of leptospiral molecular evolution were explored by sequence analysis of four genes shared by 38 strains belonging to the core group of pathogenic Leptospira species: L. interrogans, L. kirschneri, L. noguchii, L. borgpetersenii, L. santarosai, and L. weilii. The 16S rRNA and lipL32 genes were highly conserved, and the lipL41 and ompL1 genes were significantly more variable. Synonymous substitutions are distributed throughout the ompL1 gene, whereas nonsynonymous substitutions are clustered in four variable regions encoding surface loops. While phylogenetic trees for the 16S, lipL32, and lipL41 genes were relatively stable, 8 of 38 (20%) ompL1 sequences had mosaic compositions consistent with horizontal transfer of DNA between related bacterial species. A novel Bayesian multiple change point model was used to identify the most likely sites of recombination and to determine the phylogenetic relatedness of the segments of the mosaic ompL1 genes. Segments of the mosaic ompL1 genes encoding two of the surface-exposed loops were likely acquired by horizontal transfer from a peregrine allele of unknown ancestry. Identification of the most likely sites of recombination with the Bayesian multiple change point model, an approach which has not previously been applied to prokaryotic gene sequence analysis, serves as a model for future studies of recombination in molecular evolution of genes.

Leptospirosis: a zoonotic disease of global importance

In the past decade, leptospirosis has emerged as a globally important infectious disease. It occurs in urban environments of industrialised and developing countries, as well as in rural regions worldwide. Mortality remains significant, related both to delays in diagnosis due to lack of infrastructure and adequate clinical suspicion, and to other poorly understood reasons that may include inherent pathogenicity of some leptospiral strains or genetically determined host immunopathological responses. Pulmonary haemorrhage is recognised increasingly as a major, often lethal, manifestation of leptospirosis, the pathogenesis of which remains unclear. The completion of the genome sequence of Leptospira interrogans serovar lai, and other continuing leptospiral genome sequencing projects, promise to guide future work on the disease. Mainstays of treatment are still tetracyclines and beta-lactam/cephalosporins. No vaccine is available. Prevention is largely dependent on sanitation measures that may be difficult to implement, especially in developing countries.

Leptospirosis

Leptospirosis is a worldwide zoonotic infection with a much greater incidence in tropical regions and has now been identified as one of the emerging infectious diseases. The epidemiology of leptospirosis has been modified by changes in animal husbandry, climate, and human behavior. Resurgent interest in leptospirosis has resulted from large outbreaks that have received significant publicity. The development of simpler, rapid assays for diagnosis has been based largely on the recognition that early initiation of antibiotic therapy is important in acute disease but also on the need for assays which can be used more widely. In this review, the complex taxonomy of leptospires, previously based on serology and recently modified by a genotypic classification, is discussed, and the clinical and epidemiological value of molecular diagnosis and typing is also evaluated.

Penicillin-binding proteins in Leptospira interrogans

The Leptospira interrogans ponA and pbpB genes were isolated and characterized. ponA and pbpB encode the penicillin-binding proteins (PBPs) 1 and 3, respectively. There is little sequence variation between the PBP genes from two L. interrogans strains (serovar icterohaemorrhagiae strain Verdun and serovar pomona strain RZ11). The deduced L. interrogans PBP 1 and PBP 3 protein sequences from the two strains shared over 50% similarity to homologous proteins from Escherichia coli. It was demonstrated for strain Verdun that ponA and pbpB are transcribed individually from their own promoter. The ponA and pbpB genes from both strains are separated by 8 to 10 kb and oriented such that their transcription is convergent. The L. interrogans PBP 1 and PBP 3 proteins were synthesized in E. coli and were modified with ampicillin using a digoxigenin-ampicillin conjugate. These data show that both genes encode functional PBPs.

Identification of new repetitive element in Leptospira interrogans serovar copenhageni and its application to PCR-based differentiation of Leptospira serogroups

A new repetitive DNA element was identified in an isolate of Leptospira interrogans serovar copenhageni from a patient in Salvador, Brazil. A Sau3A genomic library from this strain was constructed and screened for repetitive DNA elements. An insert of 438 bp (Rep1) from one library clone hybridized to multiple chromosomal DNA fragments resolved electrophoretically after digestion with BamHI, HindIII, and MfeI. A single oligonucleotide primer, designated iRepl, was designed to generate multiple PCR amplicons of various electrophoretic mobilities in a PCR typing method. The method distinguished strains belonging to the eight pathogenic and three saprophytic species of the genus Leptospira. Clinical isolates obtained during urban epidemics between 1996 and 1998 in Salvador, Brazil, were analyzed by this PCR method. Although the iRep1 primer was unable to discriminate strains among L. interrogans serovar copenhageni isolates, it was able to differentiate strains belonging to different species and serogroups of Leptospira identified in Salvador. This PCR-based method may provide a faster and less expensive alternative to serologic tests used in reference laboratories.