Browsing by Author "Amat, Samat"

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    Development of Intranasal Bacterial Therapeutics to Mitigate the Bovine Respiratory Pathogen Mannheimia haemolytica
    (2019-11) Amat, Samat; van der Meer, Frank; Alexander, Trevor W.; Buret, Andre G.; De Buck, Jeroen M.; McAllister, Tim
    The emergence of multidrug-resistant pathogens associated with bovine respiratory disease (BRD) presents a significant challenge to the beef industry, as antibiotic administration is commonly used to prevent and control BRD in commercial feedlot cattle in North America. Thus, developing antibiotic alternatives such as bacterial therapeutics (BTs) to mitigate BRD is needed. Recent studies suggest that the nasopharyngeal (NP) microbiota, particularly lactic acid-producing bacteria (LAB), are important to bovine respiratory health and may be a source of BTs for the inhibition of BRD pathogens. The research presented in this thesis aimed to develop intranasal BTs to mitigate the BRD pathogen Mannheimia haemolytica and promote NP microbiota stability in feedlot cattle. Results from Study 1 showed that commercial probiotic bacteria were able to inhibit M. haemolytica growth and its adherence to epithelial cells. Study 2 revealed that the NP microbial community structure and relative abundance of LAB families underwent significant changes when cattle transported from the farm to an auction market, then to feedlot. Many of the LAB families were inversely correlated with the BRD-associated Pasteurellaceae family, and isolates from Lactobacillaceae, Streptococcaceae and Enterococcaceae families inhibited growth of M. haemolytica in vitro. This study provided evidence of potential antagonistic competition taking place between LAB and BRD-associated pathogens within the respiratory tract. Following these studies, using a targeted approach based on criteria evaluating M. haemolytica inhibition, adherence to turbinate cells, and immunomodulation, 6 Lactobacillus strains from an initial group of 178 bacterial isolates originating from nasopharynx of cattle were identified as the best BT candidates (Study 3). Intranasal inoculation of these BTs reduced colonization by M. haemolytica and induced modulation of respiratory microbiota in dairy calves experimentally challenged with M. haemolytica (Study 4). Finally, the longitudinal effects of intranasally administered BTs on the NP microbiota and the prevalence of BRD pathogens including Mannheimia were evaluated in post-weaned beef calves (Study 5). A single dose of intranasal BTs induced longitudinal modulation of the NP microbiota while showing no adverse effects on animal health and growth performance. With further characterization of inoculant dose and time of inoculation, the BTs may have potential for application as an antimicrobial alternative for mitigation of M. haemolytica in beef cattle.
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    Erratum to: The nasopharyngeal microbiota of beef cattle before and after transport to a feedlot
    (2017-04-20) Holman, Devin B; Timsit, Edouard; Amat, Samat; Abbott, D. W; Buret, Andre G; Alexander, Trevor W
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    The nasopharyngeal microbiota of beef cattle before and after transport to a feedlot
    (2017-03-22) Holman, Devin B; Timsit, Edouard; Amat, Samat; Abbott, D. W; Buret, Andre G; Alexander, Trevor W
    Abstract Background The nasopharyngeal (NP) microbiota plays an important role in bovine health, comprising a rich and diverse microbial community. The nasopharynx is also the niche for potentially pathogenic agents which are associated with bovine respiratory disease (BRD), a serious and costly illness in feedlot cattle. We used 14 beef heifers from a closed and disease-free herd to assess the dynamics of the NP microbiota of cattle that are transported to a feedlot. Cattle were sampled prior to transport to the feedlot (day 0) and at days 2, 7, and 14. Results The structure of the NP microbiota changed significantly over the course of the study, with the largest shift occurring between day 0 (prior to transport) and day 2 (Pā€‰<ā€‰0.001). Phylogenetic diversity and richness increased following feedlot placement (day 2; Pā€‰<ā€‰0.05). The genera Pasteurella, Bacillus, and Proteus were enriched at day 0, Streptococcus and Acinetobacter at day 2, Bifidobacterium at day 7, and Mycoplasma at day 14. The functional potential of the NP microbiota was assessed using PICRUSt, revealing that replication and repair, as well as translation pathways, were more relatively abundant in day 14 samples. These differences were driven mostly by Mycoplasma. Although eight cattle were culture-positive for the BRD-associated bacterium Pasteurella multocida at one or more sampling times, none were culture-positive for Mannheimia haemolytica or Histophilus somni. Conclusions This study investigated the effect that feedlot placement has on the NP microbiota of beef cattle over a 14-d period. Within two days of transport to the feedlot, the NP microbiota changed significantly, increasing in both phylogenetic diversity and richness. These results demonstrate that there is an abrupt shift in the NP microbiota of cattle after transportation to a feedlot. This may have importance for understanding why cattle are most susceptible to BRD after feedlot placement.