Bordetella bronchiseptica is a respiratory animal pathogen that can infect almost all mammals except two-legged primates, and colonize the upper respiratory tract for the duration of the animal's life. It can have an agricultural impact on livestock as they can cause chronic rhinitis in pigs when co-infected with Pasteurella multocida. Common pet species are also prone to B. bonchiseptica causing veterinary diseases such kennel coughs in dogs, snuffles in rabbits (P. multocida co-infection), and respiratory infections in cats.
B. bronchiseptica is a close relative to human pathogens B. pertussis and B. parapertussis which cause whooping cough. Comparative genomics of the three species revealed almost identical sets of virulence factors, and they are regulated by a two-component system BvgAS. Thus, B. bronchiseptica being less fastidious to grow than B. pertussis, is a useful model organism to study the relationship between biofilms and infection. Whooping cough in modern times is classified as a re-emerging infectious disease, as reports of failed vaccination are gradually increasing to endemic heights in some parts of the developed world. It is long thought that B. pertussis may be asymptomatically carried in some percentage of our population, and they may be colonizing the nasal cavity as biofilms as B. bronchiseptica does in infected animals.
Bordetella species regulate most of their virulence factors through BvgAS. BvgAS can switch the expression patterns of Bordetella from virulent (Bvg+ phase), intermediate (Bvgi phase), and avirulent (Bvg- phase) profiles. Biofilms are formed most prominently in Bvgi phase, in part due to the high expression level of adhesin filamentous haemagglutinin (FHA).
Polysaccharide compositions of Bordetella biofilms
Carbohydrate composition analyses showed that B. bronchiseptica is capable of synthesizing xylosyl polymers, which is has previously never been shown by bacterial species. Biochemical pathways for this is completely uncharacterized as known mammalian and plant pathways do not appear to be encoded on Bordetella genomes. We are in the process of establishing a genetic screen to uncover the genes and gene products involved to carry out xylose biosynthesis. Our more recent carbohydrate analyses have indicated that other oligosaccharides previously undetected may be involved. We are in the process of phenotypic characterizations.
B. bronchiseptica as a biofilm pathogen model organism
Despite intensive work done on serious biofilm pathogens such as Pseudomonas aeruginosa and Staphylococcus aureus, effective in vivo biofilm infection models remain poor or non-existent for many species in question. Animal models often do not manifest comparable pathologies and many of the commonly used experimentation systems are highly artificial and limited. B. bronchiseptica forms microscopically visible biofilms in long-term infections of murine nasal cavities. Mice are natural hosts to B. bronchiseptica, and therefore not an infection model, but rather a direct infection system capable of experimental manipulations. B. bronchiseptica therefore has the potential to be an ideal system to study biofilm formation at the host-pathogen interface without having to consider drawbacks that other model infection systems may have. Using this experimental system, we were able to determine a three-dimensional map of where B. bronchiseptica forms biofilms within the nasal cavity. We are expanding this as a tool for studying biofilm pathogenesis and its relationship with long-term chronicity, as well as in-depth investigation of the interaction with the host immune system of the nasal mucosa.
