Dermonecrotic toxin and tracheal cytotoxin, putative virulence factors of Bordetella avium

Characterization of Temperate LPS-Binding Bordetella avium Phages That Lack Superinfection Immunity

Bordetella avium causes a highly infectious upper respiratory tract disease in turkeys and other poultry with high economic losses. Considering the antimicrobial resistance crisis, bacteriophages (phages) may be an alternative approach for treating bacterial infections such as bordetellosis. Here, we describe seven B. avium phages, isolated from drinking water and feces from chicken and turkey farms. They showed strong bacteriolytic activity with a broad host range and used lipopolysaccharides (LPS) as a host receptor for their adsorption. All phages are myoviruses based on their structure observed by transmission electron microscopy. Genome sequence analyses revealed genome assembly sizes ranging from 39,087 to 43,144 bp. Their permutated genomes were organized colinearly, with a conserved module order, and were packed according to a predicted headful packing strategy. Notably, they contained genes encoding putative markers of lysogeny, indicative of temperate phages, despite their lytic phenotype. Further investigation revealed that the phages could indeed undergo a lysogenic life cycle with varying frequency. However, the lysogenic bacteria were still susceptible to superinfection with the same phages. This lack of stable superinfection immunity after lysogenization appears to be a characteristic feature of B. avium phages, which is favorable in terms of a potential therapeutic use of phages for the treatment of avian bordetellosis. IMPORTANCE To maintain the effectiveness of antibiotics over the long term, alternatives to treat infectious diseases are urgently needed. Therefore, phages have recently come back into focus as they can specifically infect and lyse bacteria and are naturally occurring. However, there is little information on phages that can infect pathogenic bacteria from animals, such as the causative agent of bordetellosis of poultry, B. avium. Therefore, in this study, B. avium phages were isolated and comprehensively characterized, including whole-genome analysis. Although phenotypically the phages were thought to undergo a lytic cycle, we demonstrated that they undergo a lysogenic phase, but that infection does not confer stable host superinfection immunity. These findings provide important information that could be relevant for potential biocontrol of avian bordetellosis by using phage therapy.

Prevalence, virulence attributes, and antibiogram of Bordetella avium isolated from turkeys in Egypt

Turkey coryza is a major respiratory disease caused by Bordetella avium (B. avium). It occurs in all ages of turkeys and is characterized by high morbidity and low mortality rates. The present study aimed firstly at determination of the prevalence rates of B. avium in turkeys reared in Egypt at different ages using various diagnostic methods including clinical examination, histopathology, enzyme-linked immunosorbent assay (ELISA), bacterial culture, and polymerase chain reaction (PCR). Using PCR, virulence-associated genes were detected in the confirmed B. avium isolates. Furthermore, the antibiotic resistance profiles of the confirmed B. avium isolates were examined. The achieved results indicated isolation and identification of B. avium infection at different ages of turkeys reared in Egypt. The overall PCR-confirmed prevalence rate of B. avium was 22.95%. The identified B. avium strains harbored virulence-associated genes responsible for colonization in the respiratory tract of turkeys including Bordetella virulence gene (100%), fimbriae (71.14%), and filamentous hemagglutinin (85.68%). The isolated B. avium strains showed multidrug resistance profiles. B. avium isolates were resistant to penicillin (92.82%), ceftiofur (85.68%), nalidixic acid (78.54%), and lincomycin (71.40%). The identified B. avium strains showed clear sensitivities to both gentamicin and neomycin, suggesting these as possible antimicrobial candidates for the control of B. avium infection in turkeys.

Role of Major Toxin Virulence Factors in Pertussis Infection and Disease Pathogenesis

Bordetella pertussis produces several toxins that affect host-pathogen interactions. Of these, the major toxins that contribute to pertussis infection and disease are pertussis toxin, adenylate cyclase toxin-hemolysin and tracheal cytotoxin. Pertussis toxin is a multi-subunit protein toxin that inhibits host G protein-coupled receptor signaling, causing a wide array of effects on the host. Adenylate cyclase toxin-hemolysin is a single polypeptide, containing an adenylate cyclase enzymatic domain coupled to a hemolysin domain, that primarily targets phagocytic cells to inhibit their antibacterial activities. Tracheal cytotoxin is a fragment of peptidoglycan released by B. pertussis that elicits damaging inflammatory responses in host cells. This chapter describes these three virulence factors of B. pertussis, summarizing background information and focusing on the role of each toxin in infection and disease pathogenesis, as well as their role in pertussis vaccination.

Biofilm formation and cellulose expression by Bordetella avium 197N, the causative agent of bordetellosis in birds and an opportunistic respiratory pathogen in humans

Although bacterial cellulose synthase (bcs) operons are widespread within the Proteobacteria phylum, subunits required for the partial-acetylation of the polymer appear to be restricted to a few γ-group soil, plant-associated and phytopathogenic pseudomonads, including Pseudomonas fluorescens SBW25 and several Pseudomonas syringae pathovars. However, a bcs operon with acetylation subunits has also been annotated in the unrelated β-group respiratory pathogen, Bordetella avium 197N. Our comparison of subunit protein sequences and GC content analyses confirms the close similarity between the B. avium 197N and pseudomonad operons and suggests that, in both cases, the cellulose synthase and acetylation subunits were acquired as a single unit. Using static liquid microcosms, we can confirm that B. avium 197N expresses low levels of cellulose in air-liquid interface biofilms and that biofilm strength and attachment levels could be increased by elevating c-di-GMP levels like the pseudomonads, but cellulose was not required for biofilm formation itself. The finding that B. avium 197N is capable of producing cellulose from a highly-conserved, but relatively uncommon bcs operon raises the question of what functional role this modified polymer plays during the infection of the upper respiratory tract or survival between hosts, and what environmental signals control its production.

Pertussis: Microbiology, Disease, Treatment, and Prevention

Pertussis is a severe respiratory infection caused by Bordetella pertussis, and in 2008, pertussis was associated with an estimated 16 million cases and 195,000 deaths globally. Sizeable outbreaks of pertussis have been reported over the past 5 years, and disease reemergence has been the focus of international attention to develop a deeper understanding of pathogen virulence and genetic evolution of B. pertussis strains. During the past 20 years, the scientific community has recognized pertussis among adults as well as infants and children. Increased recognition that older children and adolescents are at risk for disease and may transmit B. pertussis to younger siblings has underscored the need to better understand the role of innate, humoral, and cell-mediated immunity, including the role of waning immunity. Although recognition of adult pertussis has increased in tandem with a better understanding of B. pertussis pathogenesis, pertussis in neonates and adults can manifest with atypical clinical presentations. Such disease patterns make pertussis recognition difficult and lead to delays in treatment. Ongoing research using newer tools for molecular analysis holds promise for improved understanding of pertussis epidemiology, bacterial pathogenesis, bioinformatics, and immunology. Together, these advances provide a foundation for the development of new-generation diagnostics, therapeutics, and vaccines.

Bordetella avium causes induction of apoptosis and nitric oxide synthase in turkey tracheal explant cultures

Bordetellosis is an upper respiratory disease of turkeys caused by Bordetella avium in which the bacteria attach specifically to ciliated respiratory epithelial cells. Little is known about the mechanisms of pathogenesis of this disease, which has a negative impact in the commercial turkey industry. In this study, we produced a novel explant organ culture system that was able to successfully reproduce pathogenesis of B. avium in vitro, using tracheal tissue derived from 26 day-old turkey embryos. Treatment of the explants with whole cells of B. avium virulent strain 197N and culture supernatant, but not lipopolysaccharide (LPS) or tracheal cytotoxin (TCT), specifically induced apoptosis in ciliated cells, as shown by annexin V and TUNEL staining. LPS and TCT are known virulence factors of Bordetella pertussis, the causative agent of whooping cough. Treatment with whole cells of B. avium and LPS specifically induced NO response in ciliated cells, shown by uNOS staining and diaphorase activity. The explant system is being used as a model to elucidate specific molecules responsible for the symptoms of bordetellosis.

The Bordetella avium BAV1965-1962 fimbrial locus is regulated by temperature and produces fimbriae involved in adherence to turkey tracheal tissue

Bordetella pertussis, Bordetella parapertussis, and Bordetella bronchiseptica cause respiratory tract disease in mammals, whereas Bordetella avium causes respiratory tract disease in avian hosts. While there are striking similarities between the diseases caused by the mammalian- and avian-adapted bordetellae, differences at the genetic level may account for their different host tropisms. Bacterial pathogens utilize the chaperone-usher pathway to assemble extracellular multisubunit structures (fimbriae) that play a role in virulence. Fimbriae of the mammalian bordetellae mediate attachment to the host respiratory epithelium. They are assembled by a single chaperone/usher system encoded by the fimbrial biogenesis operon fimA-D. B. avium contains a homologous fimbrial operon (BAV1965-1962), and we report here the functionality of this locus. Reverse transcription (RT)-PCR and quantitative PCR analyses demonstrated that transcription of the locus is regulated by temperature. By immuno-transmission electron microscopy (TEM), BAV1965-containing fimbriae were observed on bacteria grown at 37°C but not those grown at 22°C. A mutant in which BAV1965-1962 was deleted displayed significantly lower levels of adherence to turkey tracheal rings than the wild type. Thus, the BAV1965-1962 fimbrial locus is functional, its expression is regulated in response to temperature, and it produces fimbriae involved in adherence to host respiratory tract tissue.

Comparison of the genome sequence of the poultry pathogen Bordetella avium with those of B. bronchiseptica, B. pertussis, and B. parapertussis reveals extensive diversity in surface structures associated with host interaction

Bordetella avium is a pathogen of poultry and is phylogenetically distinct from Bordetella bronchiseptica, Bordetella pertussis, and Bordetella parapertussis, which are other species in the Bordetella genus that infect mammals. In order to understand the evolutionary relatedness of Bordetella species and further the understanding of pathogenesis, we obtained the complete genome sequence of B. avium strain 197N, a pathogenic strain that has been extensively studied. With 3,732,255 base pairs of DNA and 3,417 predicted coding sequences, it has the smallest genome and gene complement of the sequenced bordetellae. In this study, the presence or absence of previously reported virulence factors from B. avium was confirmed, and the genetic bases for growth characteristics were elucidated. Over 1,100 genes present in B. avium but not in B. bronchiseptica were identified, and most were predicted to encode surface or secreted proteins that are likely to define an organism adapted to the avian rather than the mammalian respiratory tracts. These include genes coding for the synthesis of a polysaccharide capsule, hemagglutinins, a type I secretion system adjacent to two very large genes for secreted proteins, and unique genes for both lipopolysaccharide and fimbrial biogenesis. Three apparently complete prophages are also present. The BvgAS virulence regulatory system appears to have polymorphisms at a poly(C) tract that is involved in phase variation in other bordetellae. A number of putative iron-regulated outer membrane proteins were predicted from the sequence, and this regulation was confirmed experimentally for five of these.

Molecular pathogenesis, epidemiology, and clinical manifestations of respiratory infections due to Bordetella pertussis and other Bordetella subspecies

Bordetella respiratory infections are common in people (B. pertussis) and in animals (B. bronchiseptica). During the last two decades, much has been learned about the virulence determinants, pathogenesis, and immunity of Bordetella. Clinically, the full spectrum of disease due to B. pertussis infection is now understood, and infections in adolescents and adults are recognized as the reservoir for cyclic outbreaks of disease. DTaP vaccines, which are less reactogenic than DTP vaccines, are now in general use in many developed countries, and it is expected that the expansion of their use to adolescents and adults will have a significant impact on reducing pertussis and perhaps decrease the circulation of B. pertussis. Future studies should seek to determine the cause of the unique cough which is associated with Bordetella respiratory infections. It is also hoped that data gathered from molecular Bordetella research will lead to a new generation of DTaP vaccines which provide greater efficacy than is provided by today's vaccines.

Unexpected similarities between Bordetella avium and other pathogenic Bordetellae

Bordetella avium causes an upper respiratory tract disease (bordetellosis) in avian species. Commercially raised turkeys are particularly susceptible. Like other pathogenic members of the genus Bordetella (B. pertussis and B. bronchiseptica) that infect mammals, B. avium binds preferentially to ciliated tracheal epithelial cells and produces similar signs of disease. These similarities prompted us to study bordetellosis in turkeys as a possible nonmammalian model for whooping cough, the exclusively human childhood disease caused by B. pertussis. One impediment to accepting such a host-pathogen model as relevant to the human situation is evidence suggesting that B. avium does not express a number of the factors known to be associated with virulence in the other two Bordetella species. Nevertheless, with signature-tagged mutagenesis, four avirulent mutants that had lesions in genes orthologous to those associated with virulence in B. pertussis and B. bronchiseptica (bvgS, fhaB, fhaC, and fimC) were identified. None of the four B. avium genes had been previously identified as encoding factors associated with virulence, and three of the insertions (in fhaB, bvgS, and fimC) were in genes or gene clusters inferred as being absent or incomplete in B. avium, based upon the lack of DNA sequence similarities in hybridization studies and/or the lack of immunological cross-reactivity of the putative products. We further found that the genotypic arrangements of most of the B. avium orthologues were very similar in all three Bordetella species. In vitro tests, including hemagglutination, tracheal ring binding, and serum sensitivity, helped further define the phenotypes conferred by the mutations. Our findings strengthen the connection between the causative agents and the pathogenesis of bordetellosis in all hosts and may help explain the striking similarities of the histopathologic characteristics of this upper airway disease in avian and mammalian species.

Use of bacteriophage Ba1 to identify properties associated with Bordetella avium virulence

Bordetella avium causes bordetellosis, an upper respiratory disease of birds. Commercially raised turkeys are particularly susceptible. We report here on the use of a recently described B. avium bacteriophage, Ba1, as a tool for investigating the effects of lysogeny and phage resistance on virulence. We found that lysogeny had no effect on any of the in vivo or in vitro measurements of virulence we employed. However, two-thirds (six of nine) spontaneous phage-resistant mutants of our virulent laboratory strain, 197N, were attenuated. Phage resistance was associated, in all cases, with an inability of the mutants to bind phage. Further tests of the mutants revealed that all had increased sensitivities to surfactants, and increased amounts of incomplete (O-antigen-deficient) lipopolysaccharide (LPS) compared to 197N. Hot phenol-water-extracted 197N LPS inactivated phage in a specific and dose-dependent manner. Acid hydrolysis and removal of lipid A had little effect upon the ability of isolated LPS to inactivate Ba1, suggesting that the core region and possibly the O antigen were required for phage binding. All of the mutants, with one exception, were significantly more sensitive to naive turkey serum and, without exception, significantly less able to bind to tracheal rings in vitro than 197N. Interestingly, the three phage-resistant mutants that remained virulent appeared to be O antigen deficient and were among the mutants that were the most serum sensitive and least able to bind turkey tracheal rings in vitro. This observation allowed us to conclude that even severe defects in tracheal ring binding and serum resistance manifested in vitro were not necessarily indicative of attenuation and that complete LPS may not be required for virulence.

Environmental sensing mechanisms in Bordetella

The success of a bacterial pathogen may depend on its ability to sense and respond to different environments. This is particularly true of those pathogens whose survival depends on adaptation to different niches both within and outside the host. Members of the genus Bordetella cause infections in humans, other animals and birds. Two closely related species, B. pertussis and B. bronchiseptica, cause respiratory disease and express a similar range of virulence factors during infection, but exhibit different host ranges and responses to environmental change. B. pertussis has no known reservoir other than humans and is assumed to be transmitted directly via aerosol droplets between hosts. B. bronchiseptica, on the other hand, has the potential to survive and grow in the natural environment. Comparison of the manner in which these two organisms respond to external signals has provided important insights into the co-ordinate regulation of gene expression as a response to a changing environment. During infection, both species produce a range of virulence factors whose expression is co-ordinated by two members of the two-component family of signal transduction proteins, the bvg (bordetella virulence gene) and ris (regulator of intracellular stress response) loci. When active, the bvg locus directs the activity of a number of virulence determinants in both species whose products, such as adhesins and toxins, establish colonization of the host by the bacteria, although each organism has evolved a slightly different strategy during pathogenesis. B. pertussis, the causative agent of whooping cough, promotes an acute disease and tends to be more virulent than B. bronchiseptica which generally causes chronic and persistent asymptomatic colonization of the respiratory tract. The recently identified ris locus appears to control the expression of factors important for intracellular survival of B. bronchiseptica, but a role for this regulatory locus in B. pertussis infection has not been established. Expression of the virulence determinants controlled by the bvg and ris loci is subject to modulation by different environmental signals, such as low temperature, which act through these two-component systems. Evidence indicates that, for B. bronchiseptica, bvg-controlled determinants expressed under modulating conditions, such as motility, facilitate adaptation and survival in environments outside the host. With B. pertussis, however, there is no apparent requirement for prolonged survival outside the host and this difference is reflected in the expression of different, as yet uncharacterized, determinants as a response to modulating signals. The nature of the gene products involved and their assumed role in the life cycle of B. pertussis remains to be determined. Thus, comparative analysis of these species provides an excellent model for understanding the genetic requirements for pathogenesis of respiratory infection and adaptation to changing environments, both within and outside the host.

Evolutionary trends in the genus Bordetella

The genus Bordetella comprises seven species with pathogenic potential for different host organisms. This article attempts to review our current knowledge about the systematics and evolution of this important group of pathogens, their relationship to environmental microorganisms and about molecular mechanisms of host adaptation.

Discovery, purification, and characterization of a temperate transducing bacteriophage for Bordetella avium

We discovered and characterized a temperate transducing bacteriophage (Ba1) for the avian respiratory pathogen Bordetella avium. Ba1 was initially identified along with one other phage (Ba2) following screening of four strains of B. avium for lysogeny. Of the two phage, only Ba1 showed the ability to transduce via an allelic replacement mechanism and was studied further. With regard to host range, Ba1 grew on six of nine clinical isolates of B. avium but failed to grow on any tested strains of Bordetella bronchiseptica, Bordetella hinzii, Bordetella pertussis, or Bordetella parapertussis. Ba1 was purified by CsCl gradient centrifugation and was found to have an icosahedral head that contained a linear genome of approximately 46.5 kb (contour length) of double-stranded DNA and a contractile, sheathed tail. Ba1 readily lysogenized our laboratory B. avium strain (197N), and the prophage state was stable for at least 25 generations in the absence of external infection. DNA hybridization studies indicated the prophage was integrated at a preferred site on both the host and phage replicons. Ba1 transduced five distinctly different insertion mutations, suggesting that transduction was generalized. Transduction frequencies ranged from approximately 2 x 10(-7) to 1 x 10(-8) transductants/PFU depending upon the marker being transduced. UV irradiation of transducing lysates markedly improved transduction frequency and reduced the number of transductants that were lysogenized during the transduction process. Ba1 may prove to be a useful genetic tool for studying B. avium virulence factors.

A role for lipopolysaccharide in turkey tracheal colonization by Bordetella avium as demonstrated in vivo and in vitro

We isolated two insertion mutants of Bordetella avium that exhibited a peculiar clumped-growth phenotype and found them to be attenuated in turkey tracheal colonization. The mutants contained transposon insertions in homologues of the wlbA and wlbL genes of Bordetella pertussis. The wlb genetic locus of B. pertussis has been previously described as containing 12 genes involved in lipopolysaccharide (LPS) biosynthesis. Polyacrylamide gel analysis of LPS from B. avium wlbA and wlbL insertion mutants confirmed an alteration in the LPS profile. Subsequent cloning and complementation of the wlbA and wlbL mutants in trans with a recombinant plasmid containing the homologous wlb locus from B. avium eliminated the clumped-growth phenotype and restored the LPS profile to that of wild-type B. avium. Also, a parental level of tracheal colonization was restored to both mutants by the recombinant plasmid. Interestingly, complementation of the wlbA and wlbL mutants with a recombinant plasmid containing the heterologous wlb locus from B. pertussis, B. bronchiseptica, or Bordetella parapertussis eliminated the clumped-growth phenotype and resulted in a change in the LPS profile, although not to that of wild-type B. avium. The mutants also acquired resistance to a newly identified B. avium-specific bacteriophage, Ba1. Complementation of both wlbA and wlbL mutants with the homologous wlb locus of B. avium, but not the heterologous B. pertussis locus, restored sensitivity to Ba1. Complementation of the wlbL mutant, but not the wlbA mutant, with the heterologous wlb locus of Bordetella bronchiseptica or B. parapertussis restored partial sensitivity to Ba1. Comparisons of the LPS profile and phage sensitivity of the mutants upon complementation by wlb loci from the heterologous species and by B. avium suggested that phage sensitivity required the presence of O-antigen. At the mechanistic level, both mutants showed a dramatic decrease in serum resistance and a decrease in binding to turkey tracheal rings in vitro. In the case of serum resistance, complementation of both mutants with the homologous wlb locus of B. avium restored serum resistance to wild-type levels. However, in the case of epithelial cell binding, only complementation of the wlbA mutant completely restored binding to wild-type levels (binding was only partially restored in the wlbL mutant). This is the first characterization of LPS mutants of B. avium at the genetic level and the first report of virulence changes by both in vivo and in vitro measurements.

Bordetella avium virulence measured in vivo and in vitro

Bordetella avium causes an upper-respiratory-tract disease called bordetellosis in birds. Bordetellosis shares many of the clinical and histopathological features of disease caused in mammals by Bordetella pertussis and Bordetella bronchiseptica. In this study we determined several parameters of infection in the domestic turkey, Meleagris galapavo, and compared these in vivo findings with an in vitro measure of adherence using turkey tracheal rings. In the in vivo experiments, we determined the effects of age, group size, infection duration, and interindividual spread of B. avium. Also, the effect of host genetic background on susceptibility was tested in the five major commercial turkey lines by infecting each with the parental B. avium strain and three B. avium insertion mutants. The mutant strains lacked either motility, the ability to agglutinate guinea pig erythrocytes, or the ability to produce dermonecrotic toxin. The susceptibilities of 1-day-old and 1-week-old turkeys to B. avium were the same, and challenge group size (5, 8, or 10 birds) had no effect upon the 50% infectious dose. Two weeks between inoculation and tracheal culture was optimal, since an avirulent mutant (unable to produce dermonecrotic toxin) persisted for a shorter time. Communicability of the B. avium parental strain between confined birds was modest, but a nonmotile mutant was less able to spread between birds. There were no host-associated differences in susceptibility to the parental strain and the three B. avium mutant strains just mentioned: in all turkey lines tested, the dermonecrotic toxin- and hemagglutination-negative mutants were avirulent whereas the nonmotile mutants showed no loss of virulence. Interestingly, the ability of a strain to cause disease in vivo correlated completely with its ability to adhere to ciliated tracheal cells in vitro.

The effects of Bordetella avium infection on elastin and collagen content of turkey trachea and aorta

Turkey poults were inoculated at hatch with the "W" isolate of Bordetella avium. At 17 d of age, serum copper levels and ceruloplasmin activities were determined. The trachea and aorta were analyzed for collagen and elastin content in an attempt to relate these structural proteins to the clinical observations of tracheal ring distortion and cardiac dysfunction associated with bordetellosis. Serum copper levels and ceruloplasmin activity were elevated in the B. avium-infected poults and indicated enzyme activity sufficient for elastin and collagen cross-link formation. In the infected poults, crude elastin content was increased significantly (0.67% infected vs 0.59% control) in the trachea but not in the aorta (13.12% infected vs 12.68% control). However, collagen content in infected poults (69.7 hydroxyproline residues per 1,000 amino acid residues) was decreased in the trachea compared to the controls (97 hydroxyproline residues per 1,000 amino acid residues), whereas collagen and elastin cross-links (HLNL, hydroxy-lysinohydroxy-norleucine, moles per mole of collagen per 300 residues hydroxyproline) were increased in the trachea of infected poults (2.85 in infected vs 1.80 in control) and also increased (DHLNL, dihydroxy-lysinohydroxy-norleucine, moles/mole of collagen/300 residues hydroxyproline) in the aorta (0.49 in infected vs 0.39 in control) of infected poults. The differences in collagen and elastin content, in association with differences in the cross-linking, appeared to be the cause of tracheal collapse that is characteristic of B. avium infection and also may have an adverse influence on cardiovascular function.

Iron starvation of Bordetella avium stimulates expression of five outer membrane proteins and regulates a gene involved in acquiring iron from serum

Iron starvation of Bordetella avium induced expression of five outer membrane proteins with apparent molecular masses of 95, 92, 91.5, 84, and 51 kDa. Iron-responsive outer membrane proteins (FeRPs) of similar sizes were detected in six of six strains of B. avium, suggesting that the five FeRPs are common constituents of the outer membrane of most, if not all, strains of B. avium. Iron-regulated genes of B. avium were targeted for mutagenesis with the transposon TnphoA. Two mutants with iron-responsive alkaline phosphatase activities were isolated from the transposon library. The transposon insertion did not alter the iron-regulated expression of the five FeRPs in mutant Pho-6. The mutant Pho-20 exhibited a loss in expression of the 95-kDa FeRP and the 84-kDa FeRP. Both Pho-6 and Pho-20 were able to use free iron as a nutrient source. However, Pho-20 was severely compromised in its ability to use iron present in turkey serum. The data indicated that the mutation in Pho-20 affected expression of one or more components of an uptake machinery that is involved in acquisition of iron from organic ferricomplexes.

Molecular characterization of two Bordetella bronchiseptica strains isolated from children with coughs

During a surveillance program associated with the Italian clinical trial for the evaluation of new acellular pertussis vaccines, two bacterial isolates were obtained in cultures of samples from immunocompetent infants who had episodes of cough. Both clinical isolates were identified as Bordetella bronchiseptica by biochemical criteria, although both strains agglutinated with antisera specific for Bordetella parapertussis, suggesting that the strains exhibited some characteristics of both B. bronchiseptica and B. parapertussis. Both children from whom these strains were isolated exhibited an increase in serum antibody titer to pertussis toxin (PT), a protein that is produced by Bordetella pertussis but that is not thought to be produced by B. bronchiseptica. We therefore examined whether the clinical isolates were capable of producing PT. Neither strain produced PT under laboratory conditions, although both strains appeared to contain a portion of the ptx region that encodes the structural subunits of PT. In order to determine whether the ptx genes may encode functional proteins, we inserted an active promoter directly upstream of the ptx region of one of these strains. Biologically active PT was produced, suggesting that this strain contains the genetic information necessary to encode an active PT molecule. Sequence analysis of the ptx promoter region of both strains indicated that, while they shared homology with the B. bronchiseptica ATCC 4617 sequence, they contained certain sequence motifs that are characteristic of B. parapertussis and certain motifs that are characteristic of B. pertussis. Taken together, these findings suggest that variant strains of B. bronchiseptica exist and might be capable of causing significant illness in humans.

Characterization of the dermonecrotic toxin in members of the genus Bordetella

All members of the genus Bordetella and Pasteurella multocida (a gram-negative bacillus genetically unrelated to Bordetella spp., yet often sharing the same ecological niche) produce a dermonecrotic toxin (DNT). The amount of toxin produced and the time required for appearance of the lesions are identical for Bordetella pertussis, B. parapertussis, and B. bronchiseptica but different for P. multocida and B. avium. DNT has been reported to act by promoting vasoconstriction; however, vasoactive compounds (verapamil, prazosin, hydralazine, tolazoline, or isoxsuprine) are able to reverse the action of the toxin only slightly. Vasoconstrictors (atropine, serotonin, epinephrine, or endothelin) did not produce DNT-like lesions. We have characterized a region of DNA essential for DNT expression. We have determined by Southern analysis that the restriction map of the DNT gene is nearly identical in B. pertussis, B. parapertussis, and B. bronchiseptica, but the sequences are not present in toxigenic B. avium and P. multocida strains. A gentamicin resistance-origin of transfer cassette cloned into a 1.8-kb NotI-BamHI fragment results in constructs which can be mobilized and recombined into the Bordetella chromosome, rendering the resultant B. pertussis, B. parapertussis, and B. bronchiseptica strains negative for DNT. A 5-kb BamHI-ApaI fragment from the B. pertussis chromosome was sequenced and revealed homology to the Escherichia coli CNF1 (cytotoxic necrotizing factor 1) toxin.

Epithelial autotoxicity of nitric oxide: role in the respiratory cytopathology of pertussis

Bordetella pertussis releases a specific peptidoglycan fragment known as tracheal cytotoxin (TCT) that reproduces the respiratory epithelial cytopathology of whooping cough (pertussis). In vitro, TCT inhibits DNA synthesis in hamster trachea epithelial cells and causes specific destruction of ciliated cells in explants of human and hamster respiratory epithelium. We have recently demonstrated that TCT triggers production of intracellular interleukin 1 by respiratory epithelial cells, and this cytokine may act as an intermediate signal in the generation of TCT toxicity. Here we report the identification of a subsequent critical step in this pathway: induction of nitric oxide synthesis in the respiratory epithelium. The toxic effects of nitric oxide are consistent with spectroscopic evidence of the formation of iron-dinitrosyl-dithiolate complexes in TCT-treated cells. Aconitase, with its iron-sulfur center, is one expected target of nitric oxide, and TCT inhibited 80% of the activity of this enzyme in respiratory epithelial cells. The deleterious effects of TCT and interleukin 1 were dramatically attenuated by the nitric oxide synthase inhibitors NG-monomethyl-L-arginine and aminoguanidine. These results indicate that nitric oxide mediates the toxicity of TCT for the respiratory epithelium, thus implicating a central role for nitric oxide in the pathogenesis of pertussis.

Chromosomal DNA from both flagellate and non-flagellate Bordetella species contains sequences homologous to the Salmonella H1 flagellin gene

The genus Bordetella contains four species: two are non-motile, the human pathogens B. pertussis and B. parapertussis; and two are motile, the broad host-range mammalian pathogen B. bronchiseptica, and the avian pathogen B. avium. The motility of the latter two species is due to peritrichous flagella. Here we show that strains of all four species contain DNA sequences homologous to flagellin genes. Two types of gene probe were hybridised to Bordetella chromosomal DNa in Southern blots: the structural gene for H1 flagellin of Salmonella typhimurium and an oligonucleotide derived from the conserved N-terminal amino acid sequences of various flagellin proteins. ClaI-digested DNa from all four Bordetella species hybridised with both probes in Southern blots, although each species gave a characteristic pattern of hybridisation. This indicates that the non-motile B. pertussis and B. parapertussis species contain non-expressed flagellin genes.

Bordetella pertussis tracheal cytotoxin and other muramyl peptides: distinct structure-activity relationships for respiratory epithelial cytopathology

Tracheal cytotoxin (TCT) is a disaccharide-tetrapeptide released by Bordetella pertussis, the causative agent of pertussis (whooping cough). We have previously determined the structure of TCT to be GlcNAc-1,6-anhydro-MurNAc-L-Ala-gamma-D-Glu-meso-A2pm-D-Ala, where MurNAc = N-acetylmuramic acid and A2pm = diaminopimelic acid. Purified TCT reproduces the respiratory cytopathology observed during pertussis, including ciliostasis and extrusion of ciliated cells. We have tested structural analogs of TCT for their ability to reproduce native TCT toxicity in explanted hamster tracheal tissue and hamster trachea epithelial (HTE) cell cultures. Other investigators have evaluated many of these analogs, which are muramyl or desmuramyl peptides, for muramyl peptide activities such as immunopotentiation, induction of slow-wave sleep, and pyrogenicity. Four desmuramyl peptides were produced in our laboratory from B. pertussis peptidoglycan or by chemical synthesis, including unusual peptides containing alpha-aminopimelic acid in place of A2pm. Based on the relative ability of compounds to inhibit DNA synthesis in HTE cells, truncated analogs lacking A2pm entirely or lacking only the side-chain amine or carboxyl group of A2pm were less active than TCT by a factor of at least 1000. All active analogs included a native or near-native peptide moiety, independent of the presence, absence, or substitution of the sugar moiety. We conclude that the structural requirements for TCT toxicity differ considerably from those for most other muramyl peptide activities, in that the disaccharide moiety is irrelevant for toxicity and both the free amino and carboxyl groups of the A2pm side chain are required for activity.

Cloning and sequencing of a gene encoding a 21-kilodalton outer membrane protein from Bordetella avium and expression of the gene in Salmonella typhimurium

Three gene libraries of Bordetella avium 197 DNA were prepared in Escherichia coli LE392 by using the cosmid vectors pCP13 and pYA2329, a derivative of pCP13 specifying spectinomycin resistance. The cosmid libraries were screened with convalescent-phase anti-B. avium turkey sera and polyclonal rabbit antisera against B. avium 197 outer membrane proteins. One E. coli recombinant clone produced a 56-kDa protein which reacted with convalescent-phase serum from a turkey infected with B. avium 197. In addition, five E. coli recombinant clones were identified which produced B. avium outer membrane proteins with molecular masses of 21, 38, 40, 43, and 48 kDa. At least one of these E. coli clones, which encoded the 21-kDa protein, reacted with both convalescent-phase turkey sera and antibody against B. avium 197 outer membrane proteins. The gene for the 21-kDa outer membrane protein was localized by Tn5seq1 mutagenesis, and the nucleotide sequence was determined by dideoxy sequencing. DNA sequence analysis of the 21-kDa protein revealed an open reading frame of 582 bases that resulted in a predicted protein of 194 amino acids. Comparison of the predicted amino acid sequence of the gene encoding the 21-kDa outer membrane protein with protein sequences in the National Biomedical Research Foundation protein sequence data base indicated significant homology to the OmpA proteins of Shigella dysenteriae, Enterobacter aerogenes, E. coli, and Salmonella typhimurium and to Neisseria gonorrhoeae outer membrane protein III, Haemophilus influenzae protein P6, and Pseudomonas aeruginosa porin protein F. The gene (ompA) encoding the B. avium 21-kDa protein hybridized with 4.1-kb DNA fragments from EcoRI-digested, chromosomal DNA of Bordetella pertussis and Bordetella bronchiseptica and with 6.0- and 3.2-kb DNA fragments from EcoRI-digested, chromosomal DNA of B. avium and B. avium-like DNA, respectively. A 6.75-kb DNA fragment encoding the B. avium 21-kDa protein was subcloned into the Asd+ vector pYA292, and the construct was introduced into the avirulent delta cya delta crp delta asd S. typhimurium chi 3987 for oral immunization of birds. The gene encoding the 21-kDa protein was expressed equivalently in B. avium 197, delta asd E. coli chi 6097, and S. typhimurium chi 3987 and was localized primarily in the cytoplasmic membrane and outer membrane. In preliminary studies on oral inoculation of turkey poults with S. typhimurium chi 3987 expressing the gene encoding the B. avium 21-kDa protein, it was determined that a single dose of the recombinant Salmonella vaccine failed to elicit serum antibodies against the 21-kDa protein and challenge with wild-type B. avium 197 resulted in colonization of the trachea and thymus with B. avium 197.

Derivation of a physical map of the chromosome of Bordetella pertussis Tohama I

We have used pulsed-field gel electrophoresis to derive a restriction map of the chromosome of Bordetella pertussis for the enzymes XbaI, SpeI, PacI, and PmeI, which cleave 25, 16, 2, and 1 times, respectively. The apparent size of the genome is 3,750 kb. The positions of genes for major virulence determinants in the vir regulon and of some housekeeping genes were determined. Apart from the previously known linkage of the vir and fha loci, no significant linkage of virulence genes was demonstrated.

Heat-labile toxin from Bordetella parapertussis induces contraction of smooth muscle cells in culture

The ability of Bordetella heat-labile toxin (HLT) to contract various types of cells in culture was examined. HLT from B. parapertussis induced contraction of cultured smooth muscle cells from trachea, intestine, uterus and vas deferens as well as from aorta. The time required for contraction decreased as the dose of B. parapertussis HLT increased from 3 to 100 MID/ml. Upon exposure of cells to concentrations of toxin greater than 100 MID/ml, at least 2 hr was required for contraction. HLT from B. parapertussis did not affect cultured cardiac or skeletal muscle cells within 8 hr after the exposure to HLT (100 MID/ml). No effect on other types of primary culture cells or established cells such as Chinese hamster ovary (CHO) cells has been described. These data indicate that the primary target cells for HLT might be smooth muscle cells.

Characterization of the outer membrane proteins of Bordetella avium

The outer membrane proteins of Bordetella avium were examined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Sarkosyl-insoluble outer membrane protein-enriched profiles from 50 virulent B. avium isolates, containing major 21,000- and 37,000-molecular-weight proteins (21K and 37K proteins, respectively) and at least 13 less intensely stained proteins with molecular weights ranging from 13,500 to 143,000, were very similar. The 21K, 27K, 31K, and 37K outer membrane proteins were shown to be associated noncovalently with the underlying peptidoglycan layer. It was necessary to treat cell envelopes with 2% sodium dodecyl sulfate and at temperatures in excess of 60 degrees C for 15 min to release these proteins. Exposure of proteins on the cell surface of B. avium was assessed by labeling with 125I followed by electrophoresis. As many as 13 bands were present in profiles from labeled whole cells. Of the surface-labeled bands, eight corresponded to bands in a radiolabeled outer membrane preparation. The outer membrane protein profile of B. avium was compared with profiles from other Bordetella spp., including 20 B. avium-like and 16 B. bronchiseptica strains isolated from turkeys. The outer membrane protein profile of B. avium was distinctly different from those of the other bordetella. The effect of variations in the growth medium on the expression of outer membrane proteins of B. avium was examined. Expression of 22K, 26K, 56K, and 73K proteins was decreased or eliminated by addition of 50 mM MgSO4 to the medium.

The bvgAS locus negatively controls motility and synthesis of flagella in Bordetella bronchiseptica

The products of the bvgAS locus coordinately regulate the expression of Bordetella virulence factors in response to environmental conditions. We have identified a phenotype in Bordetella bronchiseptica that is negatively controlled by bvg. Environmental signals which decrease (modulate) the expression of bvg-activated genes lead to flagellum production and motility in B. bronchiseptica. Wild-type (Bvg+) strains are motile and produce peritrichous flagella only in the presence of modulating signals, whereas Bvg- (delta bvgAS or delta bvgS) strains are motile in the absence of modulators. The bvgS-C3 mutation, which confers signal insensitivity and constitutive activation of positively controlled loci, eliminates the induction of motility and production of flagellar organelles. The response to environmental signals is conserved in a diverse set of clinical isolates of both B. bronchiseptica and B. avium, another motile Bordetella species; however, nicotinic acid induced motility only in B. bronchiseptica. Purification of flagellar filaments from B. bronchiseptica strains by differential centrifugation followed by CsCl equilibrium density gradient centrifugation revealed two classes of flagellins of Mr 35,000 and 40,000. A survey of clinical isolates identified only these two flagellin isotypes, and coexpression of the two forms was not detected in any strain. All B. avium strains tested expressed a 42,000-Mr flagellin. Amino acid sequence analysis of the two B. bronchiseptica flagellins revealed 100% identity in the N-terminal region and 80% identity with Salmonella typhimurium flagellin. Monoclonal antibody 15D8, which recognizes a conserved epitope in flagellins in members of the family Enterobacteriaceae, cross-reacted with flagellins from B. bronchiseptica and B. avium. Our results highlight the biphasic nature of the B. bronchiseptica bvg regulon and provide a preliminary characterization of the Bvg-regulated motility phenotype.

Isolation and characterization of Bordetella avium phase variants

Two spontaneous phase variants of Bordetella avium were isolated at a frequency of 2 x 10(-4) by colony immunoblot assay of B. avium with antibody against B. avium dermonecrotic toxin. The two phase variants, designated GOBL309 and GOBL312, lack dermonecrotic toxin and four outer membrane proteins with molecular masses of 93, 48, 38, and 27 kDa but retain the ability to agglutinate guinea pig erythrocytes. The proteins which are not expressed by GOBL309 and GOBL312 correspond to five proteins which are phenotypically modulated in B. avium by growth in the presence of nicotinic acid or MgSO4. Growth of the phase variants in supplemented Stainer-Scholte media containing nicotinamide did not alter expression of these five proteins. Intranasal inoculation of the spontaneous phase variants into 3-day-old turkeys and reisolation of B. avium at 2 weeks postinoculation resulted in the recovery of B. avium which had the wild-type phenotype, colonized the turkey tracheas, and produced the four outer membrane proteins and dermonecrotic toxin. Hybridization of B. avium and B. avium-like chromosomal DNA with internal portions of the Bordetella pertussis virulence regulatory genes, bvgA and bvgS, revealed that B. avium and B. avium-like isolates contain 5.3- and 5.7-kb DNA fragments, respectively, which are homologous to bvgS. B. avium and B. avium-like chromosomal DNA failed to hybridize to B. pertussis bvgA.

Inhibition of heat-labile toxin from Bordetella parapertussis by fatty acids

The ability of heat-labile toxin (HLT) from Bordetella parapertussis to induce skin lesions in guinea pigs was found to be inhibited by lipids isolated from skin layers of adult mice, which are refractory to the lesion-inducing activity of HLT. These lipids were identified as linoleic and oleic acids. Other long-chain unsaturated fatty acids were also found to inhibit HLT; however, fatty alcohols, neutral lipids, phospholipids, cholesterol, prostaglandin, and leukotriene had no measurable effects on HLT action. The data presented in this report indicate that the ability of HLT to induce skin lesions in animals may depend, at least in part, on the free fatty acid content of the skin layer.

Development of a cell culture assay for Bordetella parapertussis heat-labile toxin

A cell culture assay for heat-labile toxin isolated from Bordetella parapertussis has been developed. In this assay, the ability of heat-labile toxin to induce contraction of vascular smooth muscle cells is measured. The method allows for detection of as little as 0.6 ng/ml of the toxin. The results obtained from this in vitro assay correlated well with those obtained with in vivo assays indicating that the cell culture assay may be a useful alternative to animal assays.

Isolation and characterization of the recA gene of Bordetella pertussis

This report describes the detection and cloning of the Bordetella pertussis recA gene. Escherichia coli clones having recombinant plasmids containing the B. pertussis recA gene were isolated by complementing an E. coli RecA- mutant's inability to survive in the presence of methylmethanesulphonate (MMS). This gene was shown to complement the deficiency of E. coli RecA- strains to tolerate the DNA-damaging effects of both a chemical agent and ultraviolet light (u.v.). Deletion mapping experiments localized the gene to a 2.5 kb StuI-EcoRI fragment, and expression of the gene in E. coli resulted in the production of a 40 kD protein. These data strongly suggest that a region of the B. pertussis chromosome that encodes RecA-like activity has been isolated and cloned.

Effects of exogenous agents on the action of Bordetella parapertussis heat-labile toxin on guinea pig skin

Injection of sonic extracts of Bordetella parapertussis into the shaved backs of guinea pigs produced hemorrhagic necrosis, which previously has been attributed to the action of heat-labile toxin. As heat-labile toxin was purified from this crude mixture, its ability to induce hemorrhagic lesions decreased significantly. However, ischemic lesions were apparent after injection of the purified toxin. These lesions, while not hemorrhagic in nature, were marked by erythema surrounded by a region in which the ischemia was apparent. Exogenous agents were found to alter the nature of the skin lesion induced by heat-labile toxin. The lipid A portion of endotoxin in combination with heat-labile toxin caused hemorrhagic lesions surrounded by a ring of ischemia, whereas bovine serum albumin increased the area of erythema. While the nature of lesions induced by heat-labile toxin was affected by exogenous agents, the diameter of ischemia produced by the toxin was found to be independent of the presence of these agents and was linear with toxin dose. These results indicate that induction of hemorrhagic necrosis may not be a reliable indicator of heat-labile toxin activity. Instead, measurement of the ischemic lesion produced by heat-labile toxin may be a useful assay for the toxin.

Tryptophan 2,3-dioxygenase activity in turkey poults infected with Bordetella avium

1. Liver tryptophan 2,3-dioxygenase (TPO) activity was depressed significantly by the Bordetella avium infection localized in the trachea of the turkey poult. 2. Tryptophan, given orally, induced a significant increase in TPO activity in both control and infected poults. 3. Hydrocortisone induced TPO activity in the turkey in a dose dependent manner.

Biological activities and chemical composition of purified tracheal cytotoxin of Bordetella pertussis

Specific destruction of ciliated epithelial cells lining the large airways is the primary respiratory tract cytopathology associated with human Bordetella pertussis infections. We have purified a single low-molecular-weight glycopeptide, tracheal cytotoxin (TCT), that appears to cause this pathology. By using a combination of solid-phase extraction and reversed-phase high-pressure liquid chromatography, about 700 nmol of biologically active peptide can be isolated from 1 liter of B. pertussis culture supernatant (approximately 60% yield). TCT at concentrations of 1 microM destroyed the ciliated cell population when incubated with respiratory epithelium in vitro. This concentration of TCT is similar to the concentrations found in the culture supernatant of growing B. pertussis. Purified TCT also inhibited DNA synthesis of hamster trachea epithelial cells in a quantitative, dose-dependent fashion. Endotoxin was not detected in the purified material, and neither B. pertussis nor Escherichia coli endotoxin could duplicate the biological activities of TCT. Amino acid and amino sugar analyses of purified TCT revealed the presence of glucosamine, muramic acid, alanine, glutamic acid, and diaminopimelic acid in molar ratios of 1:1:2:1:1. This suggests that TCT, the released ciliostatic principle of B. pertussis, is a disaccharide tetrapeptide subunit of peptidoglycan.

Electron microscopic observations on ciliated epithelium of tracheal organ cultures infected with Bordetella bronchiseptica

Using mouse tracheal organ cultures, the pathogenic effect of Bordetella bronchiseptica to epithelial cells was studied by electron microscopy. The ultrastructure of epithelial cells in uninfected tracheal rings was preserved well for longer than 3 days. In mouse tracheal rings infected with graded doses (3 x 10(5) to 10(7) CFU/ml) of phase I B. bronchiseptica, the colonization in the interciliary spaces of ciliated epithelial cells was observed after a 20-hr infection period. The infected tracheal rings showed swelling of nonciliated cells as well as ciliated cells, rupture of cell membrane of cilia, swelling and disappearance of cilia, and atrophic cytomorphosis of epithelial cells. The severity of these changes occurred depending on the infection doses. These changes were essentially similar to those observed previously in the tracheal epithelia of the B. bronchiseptica-infected mice. The usefulness of this in vitro model was suggested for studying the pathogenesis of Bordetella infection.