Adherence ofBordetella bronchisepticaandPasteurella multocidato swine nasal ciliated epithelial cellsin vitro

Pasteurella multocida: from zoonosis to cellular microbiology

In a world where most emerging and reemerging infectious diseases are zoonotic in nature and our contacts with both domestic and wild animals abound, there is growing awareness of the potential for human acquisition of animal diseases. Like other Pasteurellaceae, Pasteurella species are highly prevalent among animal populations, where they are often found as part of the normal microbiota of the oral, nasopharyngeal, and upper respiratory tracts. Many Pasteurella species are opportunistic pathogens that can cause endemic disease and are associated increasingly with epizootic outbreaks. Zoonotic transmission to humans usually occurs through animal bites or contact with nasal secretions, with P. multocida being the most prevalent isolate observed in human infections. Here we review recent comparative genomics and molecular pathogenesis studies that have advanced our understanding of the multiple virulence mechanisms employed by Pasteurella species to establish acute and chronic infections. We also summarize efforts being explored to enhance our ability to rapidly and accurately identify and distinguish among clinical isolates and to control pasteurellosis by improved development of new vaccines and treatment regimens.

Functional BvgAS virulence control system in Bordetella bronchiseptica is necessary for induction of Ca2+ transients in ciliated tracheal epithelial cells

To study initial Bordetella bronchiseptica-tracheal epithelial cell interactions, we coincubated B. bronchiseptica with rabbit tracheal explant cultures and assayed bacterial adherence and host cell Ca(2+) signaling. Wild-type B. bronchiseptica (RB50) preferentially adhered to cilia and induced ciliated host cell Ca(2+) transients within 2 min of coincubation, whereas coincubation with an avirulent strain (RB57) resulted in limited binding and Ca(2+) signaling. The described cell system allows for assessment of initial B. bronchiseptica-host cell interactions that can contribute to pathogenicity or to host cell defense.

Early colonization of the rat upper respiratory tract by temperature modulated Bordetella bronchiseptica

The ability of nonmodulated Bvg+ phase cultures, temperature modulated Bvg- phase cultures, and a Bvg- phase-locked mutant of Bordetella bronchiseptica to colonize the rat upper respiratory tract was investigated. Initially, greater numbers of the temperature modulated Bvg- phase bacteria adhered to the nasal cavity of the rats. The temperature modulated Bvg- phase bacteria appeared to be quickly cleared to levels lower than the Bvg+ phase bacteria by 4 h after inoculation and stayed lower until 48 h after inoculation when colonization levels were equal to the Bvg+ phase bacteria. The level of colonization with the Bvg- phase-locked mutant of B. bronchiseptica was lower than both the nonmodulated Bvg+ phase and temperature modulated Bvg- phase cultures and declined over time during the experiment. These findings suggest that there may be increased adherence from an environmental phase to ensure bacteria survive initial clearance mechanisms until the switch to the Bvg+ phase occurs.

A highly adherent phenotype associated with virulent Bvg+-phase swine isolates of Bordetella bronchiseptica grown under modulating conditions

The ability of Bvg(-)-phase and Bvg(+)-phase Bordetella bronchiseptica swine isolates, grown under modulating or nonmodulating conditions, to adhere to swine ciliated nasal epithelial cells was determined. When virulent strains were cultivated at 37 degrees C in the Bvg+ phase, numerous adherent bacteria (approximately eight per cell, depending on the strain used) were observed. However, when such strains were grown under modulating conditions (23 degrees C), a significant increase in the level of attachment was seen, suggesting that B. bronchiseptica produces a Bvg-repressed adhesin under these conditions. bvg mutant strains, including an isogenic bvgS mutant, adhered minimally. Western blots indicated that two putative B. bronchiseptica adhesins, filamentous hemagglutinin and pertactin, were not detectable in cultures displaying the highly adherent phenotype. Several proteins apparent in Western blots obtained by using bacterial extracts enriched in outer membrane proteins derived from B. bronchiseptica grown at 23 degrees C were not present in similar extracts prepared from an isogenic bvgS mutant grown at 23 degrees C or from the parent strain grown at 37 degrees C. Adherence of bacteria cultivated at 23 degrees C was almost completely abolished by pretreatment of organisms at 60 degrees C; adherence was reduced by 57% when bacteria were pretreated with pronase E. Temperature shift experiments revealed that the heightened level of adhesion that occurs following growth at 23 degrees C was maintained for up to 18 h when bacteria were subsequently incubated at 37 degrees C. We propose that a Bvg-repressed adhesin, expressed only by modulated bvg+ strains of B. bronchiseptica, may play a key role in the initial colonization of naturally infected swine.

A porcine model for the evaluation of virulence of Bordetella bronchiseptica

Studies of virulence factors of Bordetella bronchiseptica require a suitable system. Such a system was devised in colostrum-deprived, caesarean-derived pigs, aged 7 d. In two different experiments, pigs (n = 11) were inoculated intranasally with 10(6) colony-forming units of the virulent strain 4609. In the same way, further pigs (n = 11) were inoculated with a strain (B133) of unknown virulence. No significant differences between 4609 and B133 colonization were seen. However, colonization of the turbinates was significantly higher than that of the trachea, lung and tonsil, and a significantly higher degree of colonization was present at 11 d post-inoculation (PI) than at 15 days. Moderate turbinate atrophy was present by 11 d PI, and peribronchiolar fibrosis was present at 15 days. Immunocytochemical methods showed that all pigs had bacterial antigen in the ciliated cells of the turbinates and trachea, and in the lung; some pigs also had antigen in the bronchi. Bacterial antigen was present in some bronchioles and within the cytoplasm of pulmonary macrophages and neutrophils. This model should prove useful for comparing strains of B. bronchiseptica and isogenic mutants deficient in putative virulence factors.

bvg Repression of alcaligin synthesis in Bordetella bronchiseptica is associated with phylogenetic lineage

Recent studies have shown that Bordetella bronchiseptica utilizes a siderophore-mediated transport system for acquisition of iron from the host iron-binding proteins lactoferrin and transferrin. We recently identified the B. bronchiseptica siderophore as alcaligin, which is also produced by B. pertussis. Alcaligin production by B. bronchiseptica is repressed by exogenous iron, a phenotype of other microbes that produce siderophores. In this study, we report that alcaligin production by B. bronchiseptica RB50 and GP1SN was repressed by the Bordetella global virulence regulator, bvg, in addition to being Fe repressed. Modulation of bvg locus expression with 50 mM MgSO4 or inactivation of bvg by deletion allowed strain RB50 to produce alcaligin. In modulated organisms, siderophore production remained Fe repressed. These observations contrasted with our previous data indicating that alcaligin production by B. bronchiseptica MBORD846 and B. pertussis was repressed by Fe but bvg independent. Despite bvg repression of alcaligin production, strain RB50 was still able to acquire Fe from purified alcaligin, suggesting that expression of the bacterial alcaligin receptor was not repressed by bvg. We tested 114 B. bronchiseptica strains and found that bvg repression of alcaligin production was strongly associated with Bordetella phylogenetic lineage and with host species from which the organisms were isolated.

Experimental model of atrophic rhinitis in gnotobiotic pigs

To study the pathogenesis of atrophic rhinitis, gnotobiotic pigs (n = 6) were inoculated intranasally with a sterile sonicate of a toxigenic strain of Bordetella bronchiseptica (0.16 mg of protein per ml) at 5 days of age, and they were then inoculated intranasally with 1 ml (5,250 CFU/ml) of a live, toxigenic strain of Pasteurella multocida at 7 days of age. Pigs were necropsied at 2, 5, 9, 14, 21, and 28 days postinoculation; those pigs necropsied after 5 days had developed turbinate atrophy. Other gnotobiotic pigs received the following inoculation protocols: (i) a sterile sonicate of a nontoxigenic strain of B. bronchiseptica (0.2 mg of protein per ml), followed by toxigenic P. multocida (n = 4); (ii) toxigenic P. multocida alone (n = 7); (iii) diluent (sterile tryptose broth) (n = 2); (iv) the sterile sonicate of toxigenic B. bronchiseptica alone (n = 2); or (v) the sterile sonicate of a nontoxigenic strain of B. bronchiseptica alone (n = 2). Turbinate atrophy did not occur in the latter groups except for one pig inoculated with only toxigenic P. multocida. These studies show that turbinate atrophy occurs in pigs given the toxigenic B. bronchiseptica sonicate and then given live, toxigenic P. multocida. This experimental regimen is a useful model for (i) studying the pathogenesis of atrophic rhinitis and (ii) testing vaccine strategies.