Bordetella pertussis causes pertussis, a respiratory disease that is most severe for infants. Vaccination was introduced in the 1950s, and in recent years, a resurgence of disease was observed worldwide, with significant mortality in infants. Possible causes for this include the switch from whole-cell vaccines (WCVs) to less effective acellular vaccines (ACVs), waning immunity, and pathogen adaptation. Pathogen adaptation is suggested by antigenic divergence between vaccine strains and circulating strains and by the emergence of strains with increased pertussis toxin production. We applied comparative genomics to a worldwide collection of 343 B. pertussis strains isolated between 1920 and 2010. The global phylogeny showed two deep branches; the largest of these contained 98% of all strains, and its expansion correlated temporally with the first descriptions of pertussis outbreaks in Europe in the 16th century. We found little evidence of recent geographical clustering of the strains within this lineage, suggesting rapid strain flow between countries. We observed that changes in genes encoding proteins implicated in protective immunity that are included in ACVs occurred after the introduction of WCVs but before the switch to ACVs. Furthermore, our analyses consistently suggested that virulence-associated genes and genes coding for surface-exposed proteins were involved in adaptation. However, many of the putative adaptive loci identified have a physiological role, and further studies of these loci may reveal less obvious ways in which B. pertussis and the host interact. This work provides insight into ways in which pathogens may adapt to vaccination and suggests ways to improve pertussis vaccines.

Background: Halophilic prokaryotes are adapted to thrive in extreme conditions of salinity. Identification and analysis of distinct macromolecular characteristics of halophiles provide insight into the factors responsible for their adaptation to high-salt environments. The current report presents an extensive and systematic comparative analysis of genome and proteome composition of halophilic and non-halophilic microorganisms, with a view to identify such macromolecular signatures of haloadaptation.

SummaryThe BvgAS signal transduction system in Bordetella spp. mediates a transition between infectious (Bvg þ ) and non-infectious (Bvg ¹ ) phases by sensing environmental conditions and regulating gene expression. Using differential display, arbitrary-primed polymerase chain reaction (PCR), we identified a gene expressed in the Bvg þ phase of Bordetella bronchiseptica that shows a high degree of sequence similarity to a locus involved in providing energy for type III secretion in pathogenic Gram-negative bacteria (yscN in Yersinia spp.). We determined that the expression of this homologue in B. bronchiseptica (

SummaryBordetella bronchiseptica establishes respiratory tract infections in laboratory animals with high efficiency. Colonization persists for the life of the animal and infection is usually asymptomatic in immunocompetent hosts. We hypothesize that this reflects a balance between immunostimulatory events associated with infection and immunomodulatory events mediated by the bacteria. We have identified 15 loci that are part of a type III secretion apparatus in B. bronchiseptica and three secreted proteins. The functions of the type III secretion system were investigated by comparing the phenotypes of wild-type bacteria with two strains that are defective in type III secretion using in vivo and in vitro infection models. Type III secretion mutants were defective in long-term colonization of the trachea in immunocompetent mice. The mutants also elicited higher titres of anti-Bordetella antibodies upon infection compared with wild-type bacteria. Type III secretion mutants also showed increased lethal virulence in immunodeficient SCID-beige mice. These observations suggest that type III-secreted products of B. bronchiseptica interact with components of both innate and adaptive immune systems of the host. B. bronchiseptica induced apoptosis in macrophages in vitro and inflammatory cells in vivo and type III secretion was required for this process. Infection of an epithelial cell line with high numbers of wild type, but not type III deficient B. bronchiseptica resulted in rapid aggregation of NF-kB into large complexes in the cytoplasm. NF-kB aggregation was dependent on type III secretion and aggregated NF-kB did not respond to TNFa activation, suggesting B. bronchiseptica may modulate host immunity by inactivating NF-kB. Based on these in vivo and in vitro results, we hypothesize that the Bordetella type III secretion system functions to modulate host immune responses during infection.

The persistence of Bordetella pertussis and B. parapertussis within vaccinated populations and the reemergence of associated disease highlight the need to better understand protective immunity. The present study examined host immunity to bordetellae and addressed potential concerns about the mouse model by using a comparative approach including the closely related mouse pathogen B. bronchiseptica. As previously observed with B. pertussis, all three organisms persisted throughout the respiratory tracts of B-cell-deficient mice, indicating that B cells are required for bacterial clearance. However, adoptively transferred antibodies rapidly cleared B. bronchiseptica but not human pathogens. These results obtained with the mouse model are consistent with human clinical observations, including the lack of correlation between antibody titers and protection, as well as the limited efficacy of intravenous immunoglobulin treatments against human disease. Together, this evidence suggests that the mouse model accurately reflects substantial differences between immunities to these organisms. Although both B. pertussis and B. parapertussis are more closely related to B. bronchiseptica than they are to each other, they share the ability to resist rapid clearance from the lower respiratory tract by adoptively transferred antibodies, an adaptation that correlates with their emergence as human pathogens that circulate within vaccinated populations.Bordetella bronchiseptica, B. pertussis, and B. parapertussis are closely related gram-negative respiratory pathogens that have recently been reclassified as subspecies (12, 16). B. pertussis and B. parapertussis appear to have diverged independently from a B. bronchiseptica-like progenitor and are highly infectious pathogens that primarily infect humans, causing the acute and severe disease pertussis or whooping cough (5, 6). In contrast, B. bronchiseptica infects a wide range of mammals (4), typically asymptomatically, and persists in the upper respiratory tract indefinitely (4). The basis for the interspecies differences in host range and severity of disease is not known, but these differences may be related to differences between bacterial subspecies or host differences in physiology or immune response to Bordetella infection.Little is known definitively about the normal human immune response to Bordetella infection because it has generally been studied in individuals who were previously vaccinated (10). In the murine model, B cells are necessary to eliminate B. pertussis, suggesting that antibodies have a critical role in clearance (9). Although the importance of antibodies in immunity to other bacterial respiratory pathogens, such as Haemophilus influenzae and Pasteurella multocida, are well documented (10) and Bordetella-specific antibodies are generated in response to vaccination or infection (15), anti-Bordetella titers do not correlate well with protection in large clinical trials (3). In contrast to natural immunity following an infection, vaccination provides little, if any...