Browsing by Author "Alexander, Trevor W."

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    Bacterial Respiratory Microbiota and its Role in Respiratory Health in Beef Cattle
    (2020-08-12) McMullen, Christopher A.; Orsel, Karin; Timsit, Edouard; van der Meer, Frank; Alexander, Trevor W.
    Bovine respiratory disease (BRD) is one of the most significant diseases facing the North American beef industry. Mounting concern over the role mass medication with antibiotics in beef production may play in antimicrobial resistance has elevated pressure on the industry to develop novel techniques and approaches for controlling BRD. This includes approaches that involve modulation of the bovine respiratory tract microbiota. The overall aim of this thesis was to investigate the role of respiratory bacterial microbiota in respiratory health and disease in beef cattle. Four studies were designed to assess different features of the respiratory microbiota using a targeted amplicon (16S rRNA gene) sequencing approach. In the first study, the bacterial microbiotas present along the entire cattle respiratory tract were described to determine which upper respiratory tract niches may contribute the most to the composition of the lung microbiota. In the second study, evolution of the nasopharyngeal bacterial microbiota of beef calves was characterized from the time of spring processing to a targeted 40 days after arrival at the feedlot. In the third study, nasopharyngeal bacterial microbiotas of beef feedlot calves raised without the use of antimicrobials that were either healthy or diagnosed with BRD were characterized and compared. In the fourth study, the progression of the nasopharyngeal and tracheal bacterial microbiotas of beef calves during the development of BRD were described. The findings of all studies were summarized and discussed. Although the nasopharynx was confirmed to likely be the most important location that should be targeted in bovine respiratory microbiota research, it appears the role of the respiratory bacterial microbiota in cattle health and disease is more complex than originally anticipated. Indeed, no common patterns of change in community composition over time, including over large periods of time and during the development of clinical BRD, were observed. These findings may affect how we research the role of the bovine microbiota in respiratory health, as well as how we design and implement novel methods for controlling, preventing, and diagnosing BRD in beef cattle.
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    Characterization of the hoof bacterial communities in feedlot cattle affected with digital dermatitis, foot rot or both using a surface swab technique
    (2024-01-22) Wong, Nicholas S. T.; Malmuthge, Nilusha; Gellatly, Désirée; Nordi, Wiolene M.; Alexander, Trevor W.; Ortega Polo, Rodrigo; Janzen, Eugene; Schwartzkopf-Genswein, Karen; Jelinski, Murray
    Abstract Background Lameness is defined as altered or abnormal gait due to dysfunction of the locomotor system, and is a health issue of feedlot cattle, having major economic, labour, and welfare implications. Digital dermatitis (DD—a lesion of the plantar surface of the foot) and foot rot (FR—affects the interdigital cleft) are common infectious causes of lameness in feedlots. These hoof lesions can occur alone or in combination (DD + FR) in the same hoof. A total of 208 hoof swabs were collected from three commercial feedlots located in southern Alberta. Every lesion sample was matched with a corresponding control skin sample taken from a healthy contralateral foot. Control skin samples were also collected from cattle with no lesion on any feet. Bacterial communities of three types of hoof lesions (DD, DD + FR, FR) and healthy skin were profiled using 16S amplicon sequencing. Results Alpha diversity analysis revealed a lower bacterial diversity on DD and FR lesions compared to control skin. Beta diversity analysis showed that bacterial communities of DD, FR, and DD + FR lesions were distinct from those of the control skin. While the impact of feedlot was minimal, lesion type contributed to 22% of the variation observed among bacterial communities (PERMANOVA-R = 0.22, P < 0.01). Compared to the corresponding control skin, there were 11, 12, and 3 differentially abundant (DA) bacterial genera in DD, DD + FR, and FR lesions, respectively. Conclusions The bacterial community description of a DD + FR lesion is a novel finding. Not only did lesions lead to altered bacterial communities when compared to healthy skin, but the composition of those communities also differed depending on the hoof lesion. The 16S amplicon sequencing of surface swabs has significant value as a research tool in separating different hoof lesions and can provide additional insights to the polybacterial etiology of DD and FR in feedlot cattle.
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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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    Effects of transportation to and commingling at an auction market on the bacterial communities of the respiratory tract of beef cattle
    (2018-07-12) Stroebel, Christina Maria; Timsit, Édouard; Alexander, Trevor W.; De Buck, Jeroen M.; Janzen, Eugene D.
    Commingling at auction markets is considered a major predisposing factor for bacterial bronchopneumonia (BP) in beef cattle. However, the effects of commingling on the respiratory tract bacterial communities is largely unknown. Therefore, the objective of the thesis was to study the effects of transportation to and commingling at an auction market on the nasopharyngeal and tracheal bacterial communities of recently weaned calves using culture-dependent and independent methods. Two groups of 30 Angus-cross heifers were studied from weaning at the ranches of origin to 28 d after arrival at a feedlot. For each group, half the heifers were either transported directly to a feedlot after weaning (RANC) or transported to and commingled at an auction market for 24 hrs before being placed in a feedlot (AUCT). Heifers from both groups received vaccines against major respiratory viruses and a parenteral injection of a long acting macrolide (tildipirosin) at on-arrival processing (d2). Deep nasal swabs (DNS) and trans-tracheal aspirates (TTA) were collected at weaning (d0) and at on-arrival processing at the feedlot (d2). Deep nasal swab sampling only was then repeated 7 days (d9) and 28 days (d30) after arrival. Bacterial culture and 16S rRNA sequencing did not reveal difference in the nasopharyngeal and tracheal bacterial communities between RANC and AUCT at any sampling days. However, both time after arrival and feedlot where calves were placed affected diversity and composition of the nasopharyngeal bacterial communities. In both groups, there was a reduction in bacterial diversity and a large increase in Mycoplasma after feedlot placement, especially seven days after on-arrival processing. Furthermore, we observed the horizontal transmission of a multi-resistant strain of Pasteurella multocida among calves at d9 and d30 in one of the two groups of heifers. Based on these findings, we concluded that transportation to and commingling at an auction market for 24 hrs did not significantly influence the composition and diversity of the nasopharyngeal and tracheal bacterial communities of recently weaned calves.
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    In vitro and ex vivo metabolism of chemically diverse fructans by bovine rumen Bifidobacterium and Lactobacillus species
    (2024-09-09) King, Marissa L.; Xing, Xiaohui; Reintjes, Greta; Klassen, Leeann; Low, Kristin E.; Alexander, Trevor W.; Waldner, Matthew; Patel, Trushar R.; Wade Abbott, D.
    Abstract Background Inulin and inulin-derived fructooligosaccharides (FOS) are well-known prebiotics for use in companion animals and livestock. The mechanisms by which FOS contribute to health has not been fully established. Further, the fine chemistry of fructan structures from diverse sources, such as graminan-type fructans found in cereal crops, has not been fully elucidated. New methods to study fructan structure and microbial responses to these complex carbohydrates will be key for evaluating the prebiotic potency of cereal fructans found in cattle feeds. As the rumen microbiome composition is closely associated with their metabolic traits, such as feed utilization and waste production, prebiotics and probiotics represent promising additives to shift the microbial community toward a more productive state. Results Within this study, inulin, levan, and graminan-type fructans from winter wheat, spring wheat, and barley were used to assess the capacity of rumen-derived Bifidobacterium boum, Bifidobacterium merycicum, and Lactobacillus vitulinus to metabolize diverse fructans. Graminan-type fructans were purified and structurally characterized from the stems and kernels of each plant. All three bacterial species grew on FOS, inulin, and cereal crop fructans in pure cultures. L. vitulinus was the only species that could metabolize levan, albeit its growth was delayed. Fluorescently labelled polysaccharides (FLAPS) were used to demonstrate interactions with Gram-positive bacteria and confirm fructan metabolism at the single-cell level; these results were in agreement with the individual growth profiles of each species. The prebiotic potential of inulin was further investigated within naïve rumen microbial communities, where increased relative abundance of Bifidobacterium and Lactobacillus species occurred in a dose-dependent and temporal-related manner. This was supported by in situ analysis of rumen microbiota from cattle fed inulin. FLAPS probe derived from inulin and fluorescent in situ hybridization using taxon-specific probes confirmed that inulin interacts with Bifidobacteria and Lactobacilli at the single-cell level. Conclusion This research revealed that rumen-derived Bifidobacteria and Lactobacilli vary in their metabolism of structurally diverse fructans, and that inulin has limited prebiotic potential in the rumen. This knowledge establishes new methods for evaluating the prebiotic potential of fructans from diverse plant sources as prebiotic candidates for use in ruminants and other animals.