A genomic island of the pathogen Leptospira interrogans serovar Lai can excise from its chromosome.

An examination of the two Leptospira interrogans genomes sequenced so far reveals few genetic differences, including an extra DNA region, 54 kb in length, in L. interrogans serovar Lai. This locus contains 103 predicted coding sequences that are absent from the genome of L. interrogans serovar Copenhageni, of which only 20% had significant BLASTP hits in GenBank. By analyzing the L. interrogans serovar Lai genome by pulsed-field gel electrophoresis, we also found that this 54-kb DNA fragment exists as a circular plasmid. This was confirmed by amplification of a DNA fragment corresponding to that of the predicted fragment if this region excised from the chromosome and its left and right ends joined together. In addition, cloning of the putative rep gene of this DNA region was responsible for autonomous replication in Leptospira spp., therefore generating a new Escherichia coli-Leptospira sp. shuttle vector. Taken together, our results show that this genomic island can excise from the chromosome and form a replicative plasmid. Analysis of the distribution of this genomic island revealed that highly related sequences exist in other L. interrogans virulent strains. This genomic island, containing a high proportion of novel genes, may have an important role in spreading genes, including virulence factors, among bacterial populations.

Application of multilocus variable-number tandem-repeat analysis for molecular typing of the agent of leptospirosis.

Leptospirosis is a worldwide-distributed zoonosis, endemic in tropical areas. Epidemiologic investigations of leptospirosis still rely on tedious serological identification tests. Recently, molecular typing systems based on variable-number tandem-repeat (VNTR) analysis have been described and have been used to identify Leptospira interrogans strains. Although L. interrogans is the most common Leptospira species encountered in human infections around the world, other pathogenic species, such as Leptospira kirschneri and Leptospira borgpetersenii, are also frequently associated with human leptospirosis. In this study, we aimed to extend multilocus VNTR analysis (MLVA) identification of strains to species other than L. interrogans. We designed primers for VNTR loci found in L. interrogans, L. kirschneri, and L. borgpetersenii. The discriminatory power of the redefined primers was evaluated on collection strains and then on clinical strains. We also carried out a retrospective study on 156 strains isolated from patients and animals from New Caledonia, an area of high endemicity in the South Pacific. Our results show that this simple PCR-based MLVA typing technique is a powerful methodology for the epidemiology of leptospirosis.

Population-associated differences between the phase variable LPS biosynthetic genes of Helicobacter pylori.

BACKGROUND: Population structures are normally determined using genes under minimal functional selection. In this study we have assessed genes that are not always essential, show differences in alleles between strains, and are involved in the directly host-selectable phenotype of LPS biosynthesis. RESULTS: Eight complete LPS biosynthesis genes, seven of which are associated with phase variation in some or all strains of Helicobacter pylori, have been sequenced and their divergence analyzed. The differences observed indicate that recombination within these genes largely reflects exchange between strains within the population lineages previously determined on the basis of MLST using housekeeping genes. This indicates that the differences that are used for MLST are likely to broadly associate with genes under functional selection, and differences in strain behaviour. However, instances of exchange between the subpopulations were identified, including the hpAfrica2 subpopulation. Further, there were other differences in gene complements and the chromosomal location of genes indicative of greater diversity within the population than is revealed by the available genome sequences and comparative genome hybridization studies. CONCLUSION: These results indicate that the described population structure based upon MLST is broadly a good basis for studying the biology of H. pylori, but that individual alleles may not follow these associations. As a consequence, when working in unsequenced strains, it is necessary to carefully check the presence, sequence, and distribution of any individual gene of interest.

Phase variation mediated niche adaptation during prolonged experimental murine infection with Helicobacter pylori.

Changes in the repeats associated with the recently redefined repertoire of 31 phase-variable genes in Helicobacter pylori were investigated following murine gastric colonization for up to one year in three unrelated H. pylori strains. Between the beginning and end of the experimental period, changes were seen in ten genes (32 %), which would alter gene expression in one or more of the three strains studied. For those genes that showed repeat length changes at the longest time points, intermediate time points showed differences between the rates of change for different functional groups of genes. Genes most likely to be associated with immediate niche fitting changed most rapidly, including phospholipase A (pldA) and LPS biosynthetic genes. Other surface proteins, which may be under adaptive immune selection, changed more slowly. Restriction-modification genes showed no particular temporal pattern. The number of genes that phase varied during adaptation to the murine gastric environment correlated inversely with their relative fitness as previously determined in this murine model of colonization. This suggests a role for these genes in determining initial fitness for colonization as well as in subsequent niche adaptation. In addition, a coding tandem repeat within a phase-variable gene which does not control actual gene expression was also investigated. This repeat was found to vary in copy number during colonization. This suggests that changes in the structures encoded by tandem repeats may also play a role in altered protein functions and/or immune evasion during H. pylori colonization.

The diversity within an expanded and redefined repertoire of phase-variable genes in Helicobacter pylori.

Phase variation is a common mechanism used by pathogenic bacteria to generate intra-strain diversity that is important in niche adaptation and is strongly associated with virulence determinants. Previous analyses of the complete sequences of the Helicobacter pylori strains 26695 and J99 have identified 36 putative phase-variable genes among the two genomes through their association with homopolymeric tracts and dinucleotide repeats. Here a comparative analysis of the two genomes is reported and an updated and expanded list of 46 candidate phase-variable genes in H. pylori is described. These have been systematically investigated by PCR and sequencing for the presence of the genes, and the presence and variability in length of the repeats in strains 26695 and J99 and in a collection of unrelated H. pylori strains representative of the main global subdivisions recently suggested. This provides supportive evidence for the phase variability of 30 of the 46 candidates. Other differences in this subset of genes were observed (i) in the repeats, which can be present or absent among the strains, or stabilized in different strains and (ii) in the gene-complements of the strains. Differences between genes were not consistently correlated with the geographic population distribution of the strains. This study extends and provides new evidence for variation of this type in H. pylori, and of the high degree of diversity of the repertoire of genes which display phase-variable switching within individual strains.

Modification in the ppk gene of Helicobacter pylori during single and multiple experimental murine infections.

The bacterial pathogen Helicobacter pylori is highly adapted to the human stomach, and a high level of polymorphism is observed among clinical isolates. This polymorphism may be the consequence of adaptive changes during colonization, making a strain better able to survive, to evade the immune system, and to provoke a chronic infection. To investigate the mechanisms involved in the acquisition of diversity in H. pylori, mouse models of single infections, coinfections, and superinfections were developed. These experimental infections were conducted with strain SS1, well known to be mouse adapted, and with two strains freshly isolated from infected patients: Hp141 and Hp145. Genetic modifications occurring in these strains were studied over time by comparing randomly selected colonies of the emerging strains to those of the infecting strains by using randomly amplified polymorphic DNA fingerprinting with six different primers and by using PCR to amplify the vacA and cagA genes. We showed that, regardless of the number of infecting strains, only one emerged from the animals and that the establishment of a first strain thwarted the implantation of a second strain. During both a single infection and a coinfection with SS1, Hp141 was replaced by a genetic variant (Hp141v) that overcame SS1 in coinfection experiments. Hp141v exhibited a deletion of a 102-bp repeated sequence within the ppk gene, which encodes polyphosphate kinase (PPK), an enzyme involved in the physiological adaptation of the microbial cell to nutritional and environmental stresses. The deletion led to higher enzymatic activity of PPK, and the variant exhibited a better capacity to colonize mice. Considering that the modified gene is known to be involved in adaptation to a new environment, our results are consistent with an adaptive change in strain Hp141 and suggest that PPK is an important virulence factor in H. pylori.

CD4+CD25+ T(R) cells suppress innate immune pathology through cytokine-dependent mechanisms.

CD4(+)CD25(+) regulatory T (T(R)) cells can inhibit a variety of autoimmune and inflammatory diseases, but the precise mechanisms by which they suppress immune responses in vivo remain unresolved. Here, we have used Helicobacter hepaticus infection of T cell-reconstituted recombination-activating gene (RAG)(-/-) mice as a model to study the ability of CD4(+)CD25(+) T(R) cells to inhibit bacterially triggered intestinal inflammation. H. hepaticus infection elicited both T cell-mediated and T cell-independent intestinal inflammation, both of which were inhibited by adoptively transferred CD4(+)CD25(+) T(R) cells. T cell-independent pathology was accompanied by activation of the innate immune system that was also inhibited by CD4(+)CD25(+) T(R) cells. Suppression of innate immune pathology was dependent on T cell-derived interleukin 10 and also on the production of transforming growth factor beta. Thus, CD4(+)CD25(+) T(R) cells do not only suppress adaptive T cell responses, but are also able to control pathology mediated by innate immune mechanisms.