Virulence mechanisms of the family pasteurellaceae

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In many animals, the tonsil is an important site of colonization for a wide range of bacteria and viruses. In most cases, these organisms persist harmlessly. Some pathogenic species, however, can use the tonsil to enter the host and cause disease. Although there are 100's of papers describing the presence particular bacteria in mammalian tonsils, virtually nothing is known about how these organisms bind tonsil tissue. Our studies are focused on refining a porcine palatine tonsil explant model that can be using to study bacterial-tonsil interactions in the laboratory. With these tonsil "cultures" we will investigate the role of similar surface proteins of two closely related pathogens of swine, Actinobacillus suis and A. pleuropneumoniae (APP). APP can cause a very severe hemorrhagic pneumonia; A. suis causes a virtually indistinguishable pneumonia and can also invade the bloodstream causing conditions such as septicemia, arthritis, and meningitis. We hypothesize that these to organisms have very similar surface adhesins that they use to attach to the host, but small differences in these proteins allow these bacteria to bind to different sites in the tonsil and other tissues. In recent studies, we showed that the OmpA protein is needed for A. suis to bind to tonsil and brain cells, but nothing is known about the role of this protein in APP. Also, from genome sequence information, we know that very similar LamB proteins are present in both A. suis and APP and although this protein has been shown to be involved in attachment in other bacterial species, nothing is known about its role in Actinobacillus species. A. suis and APP also share so-called autotransporter proteins that have been reported to be important adhesins in other species. We plan to show the roles of these putative adhesins by creating mutant strains that lack these proteins and testing their ability to bind to tonsil explants and to lung and brain cell cultures. By learning how these bacteria bind to host tissues, these studies should help us to better understand and prevent the economically important diseases caused by A. suis and APP.