Review: Microbial endocrinology: intersection of microbiology and neurobiology matters to swine health from infection to behavior.

From birth to slaughter, pigs are in constant interaction with microorganisms. Exposure of the skin, gastrointestinal and respiratory tracts, and other systems allows microorganisms to affect the developmental trajectory and function of porcine physiology as well as impact behavior. These routes of communication are bi-directional, allowing the swine host to likewise influence microbial survival, function and community composition. Microbial endocrinology is the study of the bi-directional dialogue between host and microbe. Indeed, the landmark discovery of host neuroendocrine systems as hubs of host-microbe communication revealed neurochemicals act as an inter-kingdom evolutionary-based language between microorganism and host. Several such neurochemicals are stress catecholamines, which have been shown to drastically increase host susceptibility to infection and augment virulence of important swine pathogens, including Clostridium perfringens. Catecholamines, the production of which increase in response to stress, reach the epithelium of multiple tissues, including the gastrointestinal tract and lung, where they initiate diverse responses by members of the microbiome as well as transient microorganisms, including pathogens and opportunistic pathogens. Multiple laboratories have confirmed the evolutionary role of microbial endocrinology in infectious disease pathogenesis extending from animals to even plants. More recent investigations have now shown that microbial endocrinology also plays a role in animal behavior through the microbiota-gut-brain axis. As stress and disease are ever-present, intersecting concerns during each stage of swine production, novel strategies utilizing a microbial endocrinology-based approach will likely prove invaluable to the swine industry.

Altered Schaedler flora mice: A defined microbiota animal model to study the microbiota-gut-brain axis.

Despite considerable attention, the mechanisms by which the microbiota affect brain function and host behaviour via the gut-brain axis remain undefined. Identifying microbe-specific pathways that influence neuronal function and bi-directional communication between the gut microbiota and the host central nervous system is challenging due to the extreme microbial diversity in the gut of conventionally-reared mice. Herein, we describe the use of the altered Schaedler flora (ASF) mouse model as an alternative to conventionally-reared and germ-free animals. Colonized with only 8 bacterial species, use of ASF mice greatly simplifies the examination of microbiota-host interactions. We assessed the extent to which behaviour differed between mice with a limited consortium of bacteria compared with a complex, conventional microbiota. The elevated plus maze and open-field assays were utilized to assess murine behaviour. Histological analysis of ileum and colon was performed to evaluate intestinal morphology, and 16 s rRNA gene taxonomic profiling was performed to determine host-stress induced changes in fecal microbial communities. Behavioural and serum corticosterone differences were observed between ASF and conventionally-reared mice, while no differences were found between the intestinal morphology of these two groups. The stress of the behavioural tests induced significant changes in the ASF fecal microbial community but not in that of the conventionally-reared mice. In contrast to the conventionally-reared mice, the results indicated that the ASF mice displayed a marked anxiogenic-like behaviour. These data indicate that ASF mice represent a unique model to elucidate mechanisms governing microbiota-gut-brain communication affecting behaviour.