Distinct virulence ranges for infection of mice by Bordetella pertussis revealed by engineering of the sensor-kinase BvgS

The whooping cough agent Bordetella pertussis coordinately regulates the expression of its virulence factors with the two-component system BvgAS. In laboratory conditions, specific chemical modulators are used to trigger phenotypic modulation of B. pertussis from its default virulent Bvg+ phase to avirulent Bvg- or intermediate Bvgi phases, in which no virulence factors or only a subset of them are produced, respectively. Whether phenotypic modulation occurs in the host remains unknown. In this work, recombinant B. pertussis strains harboring BvgS variants were tested in a mouse model of infection and analyzed using transcriptomic approaches. Recombinant BP-BvgΔ65, which is in the Bvgi phase by default and can be up-modulated to the Bvg+ phase in vitro, could colonize the mouse nose but was rapidly cleared from the lungs, while Bvg+-phase strains colonized both organs for up to four weeks. These results indicated that phenotypic modulation, which might have restored the full virulence capability of BP-BvgΔ65, does not occur in mice or is temporally or spatially restricted and has no effect in those conditions. Transcriptomic analyses of this and other recombinant Bvgi and Bvg+-phase strains revealed that two distinct ranges of virulence gene expression allow colonization of the mouse nose and lungs, respectively. We also showed that a recombinant strain expressing moderately lower levels of the virulence genes than its wild type parent was as efficient at colonizing both organs. Altogether, genetic modifications of BvgS generate a range of phenotypic phases, which are useful tools to decipher host-pathogen interactions

Molecular Evolution of the Two-Component System BvgAS Involved in Virulence Regulation in Bordetella

The whooping cough agent Bordetella pertussis is closely related to Bordetella bronchiseptica, which is responsible for chronic respiratory infections in various mammals and is occasionally found in humans, and to Bordetella parapertussis, one lineage of which causes mild whooping cough in humans and the other ovine respiratory infections. All three species produce similar sets of virulence factors that are co-regulated by the two-component system BvgAS. We characterized the molecular diversity of BvgAS in Bordetella by sequencing the two genes from a large number of diverse isolates. The response regulator BvgA is virtually invariant, indicating strong functional constraints. In contrast, the multi-domain sensor kinase BvgS has evolved into two different types. The pertussis type is found in B. pertussis and in a lineage of essentially human-associated B. bronchiseptica, while the bronchiseptica type is associated with the majority of B. bronchiseptica and both ovine and human B. parapertussis. BvgS is monomorphic in B. pertussis, suggesting optimal adaptation or a recent population bottleneck. The degree of diversity of the bronchiseptica type BvgS is markedly different between domains, indicating distinct evolutionary pressures. Thus, absolute conservation of the putative solute-binding cavities of the two periplasmic Venus Fly Trap (VFT) domains suggests that common signals are perceived in all three species, while the external surfaces of these domains vary more extensively. Co-evolution of the surfaces of the two VFT domains in each type and domain swapping experiments indicate that signal transduction in the periplasmic region may be type-specific. The two distinct evolutionary solutions for BvgS confirm that B. pertussis has emerged from a specific B. bronchiseptica lineage. The invariant regions of BvgS point to essential parts for its molecular mechanism, while the variable regions may indicate adaptations to different lifestyles. The repertoire of BvgS sequences will pave the way for functional analyses of this prototypic system

Monocyte-Derived Interleukin-10 Depresses the Bordetella pertussis- Specific Gamma Interferon Response in Vaccinated Infants▿

Antigen-specific gamma interferon (IFN-γ) has been demonstrated to participate in protection against Bordetella pertussis infection. Circulating mononuclear cells from B. pertussis-infected and from pertussis-vaccinated infants secrete high amounts of IFN-γ after in vitro stimulation by B. pertussis antigens, but with a large variation in the secreted IFN-γ levels between individuals. We show here that the inhibition of the specific IFN-γ response can be at least partially attributed to IL-10 secretion by monocytes. This IL-10 secretion was not associated with polymorphisms at positions −1082, −819, and −592 of the IL-10 gene promoter, suggesting that other genetic or environmental factors affect IL-10 expression and secretion

Seroprevalence of pertussis in Senegal : a prospective study

Background: Pertussis, also known as whooping cough, is a vaccine-preventable respiratory disease caused by Bordetella pertussis infection, against which Senegalese children are immunized with the diphtheria-tetanus-whole cell pertussis vaccine (DTwP). Seroepidemiology of pertussis has been widely described in industrialized countries, but rare are the studies referring to it in developing countries. Methods: We conducted a longitudinal survey in Northern Senegal to investigate the epidemiology of B. pertussis by evaluating the IgG antibody (Ab) response against pertussis toxin (PT). A cohort of 410 children aged 1 to 9 from five villages in the Middle Senegal River Valley were followed-up for 18 months. During that period, five visits were made to assess the immunological status of the children. Principal Findings: PT-specific IgG responses were significantly different according to age. Until the age of 3, there was a decrease in the Ab response, which then increased in the older groups. Assessment of IgG antibodies to PT (IgG-PT) suggested evidence of recent exposures to the pathogen. Surprisingly, in one of the five villages the average Ab response to PT was very low at all ages during the first 6 months of the study. At the third visit, IgG-PT concentrations peaked to very high levels, to slightly decline at the end of the survey. This indicates an outbreak of B. pertussis, whereas in the other villages a pertussis endemic profile could be observed. Conclusions: Pertussis is endemic in Northern Senegal despite the introduction of vaccination. The circulation of the bacteria seems to differ between geographic locations and over time. A more complete understanding of the epidemiology of pertussis and its environmental determinants could provide information to adapt vaccination programs

Mycobacterial heparin-binding hemagglutinin and laminin-binding protein share antigenic methyllysines that confer resistance to proteolysis

Mycobacterium tuberculosis and Mycobacterium bovis bacillus Calmette–Guérin produce a heparin-binding hemagglutinin adhesin (HBHA) required for extrapulmonary dissemination and a laminin-binding protein (LBP) involved in cytoadherence through laminin recognition. These adhesins bear posttranslational modifications that are not present when the proteins are produced in a recombinant (r) form in Escherichia coli. Mass spectrometry analysis of HBHA revealed that the posttranslational modifications are borne by the C-terminal moiety, which comprises the heparin-binding domain made of repeated lysine-rich motifs. Amino acid sequencing showed that these modifications consist of mono- and dimethyllysines within these motifs. The methyllysine-containing repeats were recognized by mAb 4057D2 and were also detected in LBP, which is equally recognized by mAb 4057D2. This Ab does not recognize the recombinant forms of these proteins. However, when rHBHA and rLBP were subjected to NaBH(4) and formalin treatment to induce lysine methylation, reactivity with mAb 4057D2 was recovered. Methylated rHBHA displayed enhanced resistance to proteolysis compared with rHBHA, as previously observed for native HBHA. S-adenosylmethionine-dependent HBHA methyltransferase activity was detected in the cell-wall fractions of M. bovis bacillus Calmette–Guérin and of Mycobacterium smegmatis, a species that produces LBP but naturally lacks hbhA, suggesting that the same enzyme(s) methylate(s) both LBP and HBHA. This hypothesis was confirmed by the fact that HBHA produced by recombinant M. smegmatis was also methylated. These results show that mycobacteria use enzymatic methylation of lysines to ensure greater stability of their adhesins