9:00 am - 10:00 am
A graduate exam seminar is a presentation of the student’s final research project for their degree.
This is an ALES MSc Final Exam Seminar by Maximo Lange. This seminar is open to the general public to attend.
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Conference ID: 580065845
Thesis Topic: Development and use of a gnotobiotic murine model for beef cattle to evaluate competitive exclusion of Escherichia coli O157:H7 using commensal Escherichia coli strains, and to ascertain the impact of physiological stress on the host-bacteria interaction
MSc with Drs. Richard Uwiera, Douglas Inglis, and Trina Uwiera.
Enterohemorrhagic Escherichia coli (EHEC) serotype O157:H7 is an important foodborne pathogen, and cattle are considered the primary reservoir of this bacterium. Research was undertaken to ascertain factors that regulate competitive exclusion of E. coli O157:H7. A gnotobiotic (GB) murine model for cattle was used to study host-microbiota interactions. For years, isolators have been used to rear germ-free (GF) and GB mice. However, isolators can be costly and the segregation of treatments within the same isolator is problematic. Recently, methodologies for housing GF mice in specially designed individually ventilated cages (IVCs) operated under barrier mode (outward directional airflow) have been developed; however this equipment can be expensive and their operation in barrier mode for research involving GF mice and pathogens is not permissible under modern biosafety and biosecurity regulations. Methods were developed to house GF mice in a commercially available conventional IVC system operated under containment mode (inward directional airflow). Moreover, the methods developed ensured that the GF or GB status of mice was maintained for at least 4 weeks with weekly handling. The use of a common IVC infrastructure with the application of operational procedures could be used to study E. coli O157:H7 in defined microbiota mice with each IVC treated as an experimental unit.
Currently there are no proven and effective methods of eliminating EHEC from cattle reservoirs and the impact of colonization resistance on EHEC in cattle is poorly understood. Using GB mice, a representative cattle EHEC infection model was developed to elucidate key aspects of the host-pathogen-microbiota interaction, and investigate competitive colonization between 20 phylogenetically-distinct commensal E. coli (EC) strains isolated from cattle and EHEC. Commensal strains were grown together or separately. Stress has been suggested as an important factor in intestinal tract colonization by EHEC in cattle, but this has not been experimentally investigated. To induce a physiological stress response, mice were administered the stress hormone corticosterone (CORT) in drinking water.
The EHEC strain FRIK 2001 was selected to colonize the intestinal tract of GB mice to mimic colonization of EHEC within the bovine gut. FRIK 2001 effectively colonized the gut with good bacterial densities and neither symptoms of disease nor metabolomic differences in kidney at 5 days post treatment were observed when compared to the other EHEC strains. Twenty bovine commensal strains of EC decreased EHEC densities in the cecum, proximal colon, and distal colon. These EC were equally effective at reducing growth of EHEC when grown before administration to GF mice individually or in combination. Moreover, histopathologic changes and expression of the pro-inflammatory cytokines, tumor necrosis factor alpha (Tnfα) and Keratinocyte-derived chemokine (Kc) were reduced in the distal colon of mice inoculated with commensal EC strains. A difference in mice behavior between the CORT– and CORT+ treatments was observed in the open field test for mean velocity and total distance travelled. Stress induced by CORT treatment, however, did not enhance FRIK 2001 colonization nor influence the efficacy of competitive exclusion of the bacterium.
Colonization of the intestinal tract of GF mice by a bovine isolated EHEC strain mimicked colonization of EHEC in cattle. The presence of commensal EC strains effectively reduced intestinal colonization and ameliorated disease, particularly within the distal colon, the main intestinal tract colonization site of EHEC in cattle. Notably, physiological stress did not potentiate enteric colonization nor intestinal disease incited by EHEC.