RESUMO
The development and growth of animals coincide with the establishment and maturation of their microbiotas. To evaluate the respiratory and fecal microbiotas of beef calves from birth to weaning, a total of 30 pregnant cows, and their calves at birth, were enrolled in this study. Deep nasal swabs and feces were collected from calves longitudinally, starting on the day of birth and ending on the day of weaning. Nasopharyngeal, vaginal, and fecal samples were also collected from cows, and the microbiotas of all samples were analyzed. The fecal microbiota of calves was enriched with Lactobacillus during the first 8 weeks of life, before being displaced by genera associated with fiber digestion, and then increasing in diversity across time. In contrast, the diversity of calf respiratory microbiota generally decreased with age. At birth, the calf and cow nasal microbiotas were highly similar, indicating colonization from dam contact. This was supported by microbial source-tracking analysis. The structure of the calf nasal microbiota remained similar to that of the cows, until weaning, when it diverged. The changes were driven by a decrease in Lactobacillus and an increase in genera typically associated with bovine respiratory disease, including Mannheimia, Pasteurella, and Mycoplasma. These three genera colonized calves early in life, though Mannheimia was initially transferred from the cow reproductive tract. Path analysis was used to model the interrelationships of calf respiratory and fecal microbiotas. It was observed that respiratory Lactobacillus and fecal Oscillospiraceae UCG-005 negatively affected the abundance of Mannheimia or Pasteurella.IMPORTANCEIn beef cattle production, bovine respiratory disease (BRD) accounts for most of the feedlot morbidities and mortalities. Metaphylaxis is a common management tool to mitigate BRD, however its use has led to increased antimicrobial resistance. Novel methods to mitigate BRD are needed, including microbiota-based strategies. However, information on the respiratory bacteria of beef calves prior to weaning was limited. In this study, it was shown that the microbiota of cows influenced the initial composition of both respiratory and fecal microbiotas in calves. While colonization of the respiratory tract of calves by BRD-associated genera occurred early in life, their relative abundances increased at weaning, and were negatively correlated with respiratory and gut bacteria. Thus, microbiotas of both the respiratory and gastrointestinal tracts have important roles in antagonism of respiratory pathogens and are potential targets for enhancing calf respiratory health. Modulation may be most beneficial, if done prior to weaning, before opportunistic pathogens establish colonization.
RESUMO
BACKGROUND: Mannheimia haemolytica is a bovine respiratory pathogen commonly associated with bacterial bronchopneumonia. Current vaccine strategies have shown variable efficacy in feedlot cattle, and therefore novel vaccines are needed. Bacillus subtilis spores have been investigated as a mucosal vaccine platform, due to their ability to bind and present antigens to the mucosa and act as an adjuvant. The aim of this study was to develop two spore-based mucosal vaccines targeting M. haemolytica and evaluate their immunogenicity in mice. METHODS: Two antigen constructs composed of cholera toxin B subunit, M. haemolytica leukotoxin, and either the M. haemolytica outer membrane protein PlpE (MhCP1) or GS60 (MhCP2) were synthesized, purified and then bound to spores as vaccines. In two separate mice trials, the spore-bound vaccines (Spore-MhCP1 and Spore-MhCP2) were administered to mice through intranasal and intragastric routes, while free antigens were administered intranasally and intramuscularly. Unbound spores were also evaluated intranasally. Antigen-specific serum IgG and mucosal IgA from bronchoalveolar lavage, feces, and saliva were measured after vaccination. Mice sera from all treatment groups were assessed for their bactericidal activity against M. haemolytica. RESULTS: In both mice experiments, intramuscular immunization induced the strongest serum IgG antibody response. However, the intranasal administration of Spore-MhCP1 and Spore-MhCP2 elicited the greatest secretory IgA-specific response against leukotoxin, PlpE, and GS60 in bronchoalveolar lavage, saliva, and feces (p < 0.05). Compared to the intranasal administration of free antigen, spore-bound antigen groups showed greater bactericidal activity against M. haemolytica (p < 0.05). CONCLUSIONS: Since intranasally delivered Spore-MhCP1 and Spore-MhCP2 elicited both systemic and mucosal immune responses in mice, these vaccines may have potential to mitigate lung infection in cattle by restricting M. haemolytica colonization and proliferation in the respiratory tract. The efficacy of these mucosal spore-based vaccines merits further assessment against M. haemolytica in cattle.
