Pertactin contributes to shedding and transmission of Bordetella bronchiseptica.

Whooping cough is resurging in the United States despite high vaccine coverage. The rapid rise of Bordetella pertussis isolates lacking pertactin (PRN), a key vaccine antigen, has led to concerns about vaccine-driven evolution. Previous studies showed that pertactin can mediate binding to mammalian cells in vitro and act as an immunomodulatory factor in resisting neutrophil-mediated clearance. To further investigate the role of PRN in vivo, we examined the functions of pertactin in the context of a more naturally low dose inoculation experimental system using C3H/HeJ mice that is more sensitive to effects on colonization, growth and spread within the respiratory tract, as well as an experimental approach to measure shedding and transmission between hosts. A B. bronchiseptica pertactin deletion mutant was found to behave similarly to its wild-type (WT) parental strain in colonization of the nasal cavity, trachea, and lungs of mice. However, the pertactin-deficient strain was shed from the nares of mice in much lower numbers, resulting in a significantly lower rate of transmission between hosts. Histological examination of respiratory epithelia revealed that pertactin-deficient bacteria induced substantially less inflammation and mucus accumulation than the WT strain and in vitro assays verified the effect of PRN on the induction of TNF-α by murine macrophages. Interestingly, only WT B. bronchiseptica could be recovered from the spleen of infected mice and were further observed to be intracellular among isolated splenocytes, indicating that pertactin contributes to systemic dissemination involving intracellular survival. These results suggest that pertactin can mediate interactions with immune cells and augments inflammation that contributes to bacterial shedding and transmission between hosts. Understanding the relative contributions of various factors to inflammation, mucus production, shedding and transmission will guide novel strategies to interfere with the reemergence of pertussis.

A model of chronic, transmissible Otitis Media in mice.

Infection and inflammation of the middle ears that characterizes acute and chronic otitis media (OM), is a major reason for doctor visits and antibiotic prescription, particularly among children. Nasopharyngeal pathogens that are commonly associated with OM in humans do not naturally colonize the middle ears of rodents, and experimental models in most cases involve directly injecting large numbers of human pathogens into the middle ear bullae of rodents, where they induce a short-lived acute inflammation but fail to persist. Here we report that Bordetella pseudohinzii, a respiratory pathogen of mice, naturally, efficiently and rapidly ascends the eustachian tubes to colonize the middle ears, causing acute and chronic histopathological changes with progressive decrease in hearing acuity that closely mimics otitis media in humans. Laboratory mice experimentally inoculated intranasally with very low numbers of bacteria consistently have their middle ears colonized and subsequently transmit the bacterium to cage mates. Taking advantage of the specifically engineered and well characterized immune deficiencies available in mice we conducted experiments to uncover different roles of T and B cells in controlling bacterial numbers in the middle ear during chronic OM. The iconic mouse model provides significant advantages for elucidating aspects of host-pathogen interactions in otitis media that are currently not possible using other animal models. This natural model of otitis media permits the study of transmission between hosts, efficient early colonization of the respiratory tract, ascension of the eustachian tube, as well as colonization, pathogenesis and persistence in the middle ear. It also allows the combination of the powerful tools of mouse molecular immunology and bacterial genetics to determine the mechanistic basis for these important processes.

Integrated Signaling Pathways Mediate Bordetella Immunomodulation, Persistence, and Transmission.

The mammalian immune system includes a sophisticated array of antimicrobial mechanisms. However, successful pathogens have developed subversive strategies to detect, modulate, and/or evade immune control and clearance. Independent disciplines study host immunology and bacterial pathogenesis, but interkingdom signaling between bacteria and host during natural infection remains poorly understood. An efficient natural host infection system has revealed complex communication between Bordetella spp. and mice, identified novel regulatory mechanisms, and demonstrated that bordetellae can respond to microenvironment and inflammatory status cues. Understanding these bacterial signaling pathways and their complex network that allows precisely timed expression of numerous immunomodulatory factors will serve as a paradigm for other organisms lacking such a powerful experimental infection system. VIDEO ABSTRACT.

Bordetella bronchiseptica pneumonia: beware of the dog!

We report the case of a 35-year-old quadriplegic male with confirmed Bordetella bronchiseptica pneumonia, manifesting with acute hypoxic respiratory failure on a background of chronic hypercarbia requiring mechanical ventilation in intensive care.B. bronchiseptica are known to colonise the upper respiratory tracts of many mammals but are very rarely responsible for acute respiratory tract infections in humans.A review of the literature suggests preponderance for immunocompromised or immunoincompetent patients who have experienced environmental exposure to colonised animals. The disease pattern of B. bronchiseptica infection is non-uniform and while it is rarely described as a commensal or colonising organism, very few case reports describe severe respiratory infections.

An Extracellular Polysaccharide Locus Required for Transmission of Bordetella bronchiseptica.

Background: The lack of animal models to experimentally study how infectious agents transmit between hosts limits our understanding of what makes some pathogens so contagious. Methods: We recently developed a Bordetella bronchiseptica mouse model to study transmission and have used it to assess, for the first time, which of several well-studied "virulence factors" common to classical Bordetella species contribute to transmission. Results: Among 13 mutants screened, a mutant lacking an extracellular polysaccharide (EPS) locus consistently failed to transmit. The loss of EPS had no obvious effect on in vitro characteristics of growth, adherence, cytotoxicity, or serum resistance, though it profoundly reduced the ability of the mutant to colonize the lower respiratory tract of mice. While wild-type B. bronchiseptica was shed from colonized mice and efficiently transmitted to cage-mates, the mutant colonized less efficiently, shed at lower numbers, and consequently did not transmit to naive animals. Conclusions: These results have important implications for potential roles of polysaccharides in the pathogenesis and transmission of Bordetella species as well as other respiratory pathogens. Cases of pertussis (whooping cough) caused by Bordetella pertussis are on the rise, and understanding factors that contribute to their spread is critical to its control.

Bordetella bronchiseptica bloodstream infection in a renal transplant patient.

Bordetella bronchiseptica is a gram-negative coccobacillus that infects animals, but rarely affects humans. B. bronchiseptica has been reported to cause disease in immunocompromised hosts. We present a case of a 61-year-old man with a renal transplant who developed B. bronchiseptica bacteremia likely as a result of close contact between dogs and his skin cancer biopsy sites. The patient was successfully treated with 2 weeks of oral levofloxacin. This case alerts physicians to B. bronchiseptica as a cause of bacteremia in solid organ transplant patients with exposure to animals.

Bordetella bronchiseptica exploits the complex life cycle of Dictyostelium discoideum as an amplifying transmission vector.

Multiple lines of evidence suggest that Bordetella species have a significant life stage outside of the mammalian respiratory tract that has yet to be defined. The Bordetella virulence gene (BvgAS) two-component system, a paradigm for a global virulence regulon, controls the expression of many "virulence factors" expressed in the Bvg positive (Bvg+) phase that are necessary for successful respiratory tract infection. A similarly large set of highly conserved genes are expressed under Bvg negative (Bvg-) phase growth conditions; however, these appear to be primarily expressed outside of the host and are thus hypothesized to be important in an undefined extrahost reservoir. Here, we show that Bvg- phase genes are involved in the ability of Bordetella bronchiseptica to grow and disseminate via the complex life cycle of the amoeba Dictyostelium discoideum. Unlike bacteria that serve as an amoeba food source, B. bronchiseptica evades amoeba predation, survives within the amoeba for extended periods of time, incorporates itself into the amoeba sori, and disseminates along with the amoeba. Remarkably, B. bronchiseptica continues to be transferred with the amoeba for months, through multiple life cycles of amoebae grown on the lawns of other bacteria, thus demonstrating a stable relationship that allows B. bronchiseptica to expand and disperse geographically via the D. discoideum life cycle. Furthermore, B. bronchiseptica within the sori can efficiently infect mice, indicating that amoebae may represent an environmental vector within which pathogenic bordetellae expand and disseminate to encounter new mammalian hosts. These data identify amoebae as potential environmental reservoirs as well as amplifying and disseminating vectors for B. bronchiseptica and reveal an important role for the Bvg- phase in these interactions.

Opportunistic Pulmonary Bordetella hinzii Infection after Avian Exposure.

We report 2 cases of pulmonary Bordetella hinzii infection in immunodeficient patients. One of these rare cases demonstrated the potential transmission of the bacteria from an avian reservoir through occupational exposure and its persistence in humans. We establish bacteriologic management of these infections and suggest therapeutic options if needed.

Toll-like receptor 4 limits transmission of Bordetella bronchiseptica.

Transmission of pathogens has been notoriously difficult to study under laboratory conditions leaving knowledge gaps regarding how bacterial factors and host immune components affect the spread of infections between hosts. We describe the development of a mouse model of transmission of a natural pathogen, Bordetella bronchiseptica, and its use to assess the impact of host immune functions. Although B. bronchiseptica transmits poorly between wild-type mice and mice lacking other immune components, it transmits efficiently between mice deficient in Toll-Like Receptor 4 (TLR4). TLR4-mutant mice were more susceptible to initial colonization, and poorly controlled pathogen growth and shedding. Heavy neutrophil infiltration distinguished TLR4-deficient responses, and neutrophil depletion did not affect respiratory CFU load, but decreased bacterial shedding. The effect of TLR4 response on transmission may explain the extensive variation in TLR4 agonist potency observed among closely related subspecies of Bordetella. This transmission model will enable mechanistic studies of how pathogens spread from one host to another, the defining feature of infectious disease.

Enzymatic modification of lipid A by ArnT protects Bordetella bronchiseptica against cationic peptides and is required for transmission.

Pathogen transmission cycles require many steps: initial colonization, growth and persistence, shedding, and transmission to new hosts. Alterations in the membrane components of the bacteria, including lipid A, the membrane anchor of lipopolysaccharide, could affect any of these steps via its structural role protecting bacteria from host innate immune defenses, including antimicrobial peptides and signaling through Toll-like receptor 4 (TLR4). To date, lipid A has been shown to affect only the within-host dynamics of infection, not the between-host dynamics of transmission. Here, we investigate the effects of lipid A modification in a mouse infection and transmission model. Disruption of the Bordetella bronchiseptica locus (BB4268) revealed that ArnT is required for addition of glucosamine (GlcN) to B. bronchiseptica lipid A. ArnT modification of lipid A did not change its TLR4 agonist activity in J774 cells, but deleting arnT decreased resistance to killing by cationic antimicrobial peptides, such as polymyxin B and ß-defensins. In the standard infection model, mutation of arnT did not affect B. bronchiseptica colonization, growth, persistence throughout the respiratory tract, recruitment of neutrophils to the nasal cavity, or shedding of the pathogen. However, the number of bacteria necessary to colonize a host (50% infective dose [ID50]) was 5-fold higher for the arnT mutant. Furthermore, the arnT mutant was defective in transmission between hosts. These results reveal novel functions of the ArnT lipid A modification and highlight the sensitivity of low-dose infections and transmission experiments for illuminating aspects of infectious diseases between hosts. Factors such as ArnT can have important effects on the burden of disease and are potential targets for interventions that can interrupt transmission.

Different effects of whole-cell and acellular vaccines on Bordetella transmission.

BACKGROUND: Vaccine development has largely focused on the ability of vaccines to reduce disease in individual hosts, with less attention to assessing the vaccine's effects on transmission between hosts. Current acellular vaccines against Bordetella pertussis are effective in preventing severe disease but have little effect on less severe coughing illness that can mediate transmission. METHODS: Using mice that are natural host's of Bordetella bronchiseptica, we determined the effects of vaccination on shedding and transmission of this pathogen. RESULTS: Vaccination with heat-killed whole-cell B. bronchiseptica or B. pertussis inhibited shedding of B. bronchiseptica. Differences in neutrophil and B-cell recruitment distinguished sham-vaccine from whole-cell-----vaccine responses and correlated with shedding output. Both B and T cells were essential for vaccine-induced control of shedding. Adoptive transfer of antibodies was able to limit shedding, while depletion of CD4(+) T cells led to increased shedding in vaccinated mice. Finally, whole-cell vaccination was able to prevent transmission, but an acellular vaccine that effectively controls disease failed to control shedding and transmission. CONCLUSIONS: Our results highlight discrepancies between whole-cell and acellular vaccination that could contribute to the increased incidence of B. pertussis infection since the transition to the use of acellular vaccination.

Transmission of Bordetella holmesii during pertussis outbreak, Japan.

We describe the epidemiology of a pertussis outbreak in Japan in 2010-2011 and Bordetella holmesii transmission. Six patients were infected; 4 patients were students and a teacher at the same junior high school. Epidemiologic links were found between 5 patients. B. holmesii may have been transmitted from person to person.

Bordetella bronchiseptica in a paediatric cystic fibrosis patient: possible transmission from a household cat.

Bordetella bronchiseptica is a zoonotic respiratory pathogen commonly found in domesticated farm and companion animals, including dogs and cats. Here, we report isolation of B. bronchiseptica from a sputum sample of a cystic fibrosis patient recently exposed to a kitten with an acute respiratory illness. Genetic characterization of the isolate and comparison with other isolates of human or feline origin strongly suggest that the kitten was the source of infection.

Phenotypic modulation of the virulent Bvg phase is not required for pathogenesis and transmission of Bordetella bronchiseptica in swine.

The majority of virulence gene expression in Bordetella is regulated by a two-component sensory transduction system encoded by the bvg locus. In response to environmental cues, the BvgAS regulatory system controls expression of a spectrum of phenotypic phases, transitioning between a virulent (Bvg(+)) phase and a nonvirulent (Bvg(-)) phase, a process referred to as phenotypic modulation. We hypothesized that the ability of Bordetella bronchiseptica to undergo phenotypic modulation is required at one or more points during the infectious cycle in swine. To investigate the Bvg phase-dependent contribution to pathogenesis of B. bronchiseptica in swine, we constructed a series of isogenic mutants in a virulent B. bronchiseptica swine isolate and compared each mutant to the wild-type isolate for its ability to colonize and cause disease. We additionally tested whether a BvgAS system capable of modulation is required for direct or indirect transmission. The Bvg(-) phase-locked mutant was never recovered from any respiratory tract site at any time point examined. An intermediate phase-locked mutant (Bvg(i)) was found in numbers lower than the wild type at all respiratory tract sites and time points examined and caused limited to no disease. In contrast, colonization of the respiratory tract and disease caused by the Bvg(+) phase-locked mutant and the wild-type strain were indistinguishable. The Bvg(+) phase-locked mutant transmitted to naïve pigs by both direct and indirect contact with efficiency equal to that of the wild-type isolate. These results indicate that while full activation of the BvgAS regulatory system is required for colonization and severe disease, it is not deleterious to direct and indirect transmission. Overall, our results demonstrate that the Bvg(+) phase is sufficient for respiratory infection and host-to-host transmission of B. bronchiseptica in swine.

Kitten-transmitted Bordetella bronchiseptica infection in a patient receiving temozolomide for glioblastoma.

Bordetella bronchiseptica is a gram negative coccobacillus that can be transmitted from domestic animals and cause severe infections in immunocompromised patients. A 56-year-old man with a left parietal glioblastoma was treated with resection, radiation and concomitant and adjuvant temozolomide chemotherapy. He received bevacizumab for progression, and dose dense metronomic temozolomide was added for additional progression. He developed chronic cough and was diagnosed with B. bronchiseptica infection. This is the first reported case of B. bronchiseptica infection in a patient receiving temozolomide. The infection was likely acquired from an infected kitten. Patients receiving temozolomide should be counseled on the risks of acquiring zoonotic infections, including B. bronchiseptica, from their pets.

Seasonal breeding drives the incidence of a chronic bacterial infection in a free-living herbivore population.

Understanding seasonal changes in age-related incidence of infections can be revealing for disentangling how host heterogeneities affect transmission and how to control the spread of infections between social groups. Seasonal forcing has been well documented in human childhood diseases but the mechanisms responsible for age-related transmission in free-living and socially structured animal populations are still poorly known. Here we studied the seasonal dynamics of Bordetella bronchiseptica in a free-living rabbit population over 5 years and discuss the possible mechanisms of infection. This bacterium has been isolated in livestock and wildlife where it causes respiratory infections that rapidly spread between individuals and persist as subclinical infections. Sera were collected from rabbits sampled monthly and examined using an ELISA. Findings revealed that B. bronchiseptica circulates in the rabbit population with annual prevalence ranging between 88% and 97%. Both seroprevalence and antibody optical density index exhibited 1-year cycles, indicating that disease outbreaks were seasonal and suggesting that long-lasting antibody protection was transient. Intra-annual dynamics showed a strong seasonal signature associated with the recruitment of naive offspring during the breeding period. Infection appeared to be mainly driven by mother-to-litter contacts rather than by interactions with other members of the community. By age 2 months, 65% of the kittens were seropositive.

Identifying the age cohort responsible for transmission in a natural outbreak of Bordetella bronchiseptica.

Identifying the major routes of disease transmission and reservoirs of infection are needed to increase our understanding of disease dynamics and improve disease control. Despite this, transmission events are rarely observed directly. Here we had the unique opportunity to study natural transmission of Bordetella bronchiseptica--a directly transmitted respiratory pathogen with a wide mammalian host range, including sporadic infection of humans--within a commercial rabbitry to evaluate the relative effects of sex and age on the transmission dynamics therein. We did this by developing an a priori set of hypotheses outlining how natural B. bronchiseptica infections may be transmitted between rabbits. We discriminated between these hypotheses by using force-of-infection estimates coupled with random effects binomial regression analysis of B. bronchiseptica age-prevalence data from within our rabbit population. Force-of-infection analysis allowed us to quantify the apparent prevalence of B. bronchiseptica while correcting for age structure. To determine whether transmission is largely within social groups (in this case litter), or from an external group, we used random-effect binomial regression to evaluate the importance of social mixing in disease spread. Between these two approaches our results support young weanlings--as opposed to, for example, breeder or maternal cohorts--as the age cohort primarily responsible for B. bronchiseptica transmission. Thus age-prevalence data, which is relatively easy to gather in clinical or agricultural settings, can be used to evaluate contact patterns and infer the likely age-cohort responsible for transmission of directly transmitted infections. These insights shed light on the dynamics of disease spread and allow an assessment to be made of the best methods for effective long-term disease control.

Immune regulation of a chronic bacteria infection and consequences for pathogen transmission.

BACKGROUND: The role of host immunity has been recognized as not only playing a fundamental role in the interaction between the host and pathogen but also in influencing host infectiousness and the ability to shed pathogens. Despite the interest in this area of study, and the development of theoretical work on the immuno-epidemiology of infections, little is known about the immunological processes that influence pathogen shedding patterns. RESULTS: We used the respiratory bacterium Bordetella bronchiseptica and its common natural host, the rabbit, to examine the intensity and duration of oro-nasal bacteria shedding in relation to changes in the level of serum antibodies, blood cells, cytokine expression and number of bacteria colonies in the respiratory tract. Findings show that infected rabbits shed B. bronchiseptica by contact up to 4.5 months post infection. Shedding was positively affected by number of bacteria in the nasal cavity (CFU/g) but negatively influenced by serum IgG, which also contributed to the initial reduction of bacteria in the nasal cavity. Three main patterns of shedding were identified: i- bacteria were shed intermittently (46% of individuals), ii- bacteria shedding fell with the progression of the infection (31%) and iii- individuals never shed bacteria despite being infected (23%). Differences in the initial number of bacteria shed between the first two groups were associated with differences in the level of serum antibodies and white blood cells. These results suggest that the immunological conditions at the early stage of the infection may play a role in modulating the long term dynamics of B. bronchiseptica shedding. CONCLUSIONS: We propose that IgG influences the threshold of bacteria in the oro-nasal cavity which then affects the intensity and duration of individual shedding. In addition, we suggest that a threshold level of infection is required for shedding, below this value individuals never shed bacteria despite being infected. The mechanisms regulating these interactions are still obscure and more studies are needed to understand the persistence of bacteria in the upper respiratory tract and the processes controlling the intensity and duration of shedding.