Chemical inhibition of the thyroid gland and its effects on E. coli O157:H7 fecal shedding patterns in sheep
Year: 2005
Type: dissertation
Abstract: Due to the seasonal nature of E. coli O157:H7 shedding and of hormone\nproduction by the thyroid gland, two studies were initiated to determine whether\nchemical inhibition of the thyroid gland influences fecal shedding of Escherichia coli \nO157:H7. Twenty-four crossbred sheep (68.6 kg BW) were randomly assigned to pen\nand either 0.0 mg/kg BW PTU or 20 mg/kg BW PTU for 5, 11, or 14 days. Sheep were\nexperimentally infected (d 0) with E. coli O157:H7 11 days prior to PTU treatment.\nFecal and serum samples were collected for bacterial enumeration and for analysis of T3\nand T4, respectively. Sheep were humanely euthanized and tissue and content samples\nwere collected from the rumen, ileum, colon and rectum. Detection of E. coli O157:H7\nincreased toward the terminal end of the GI tract. In the treatment group, serum T3\nlevels decreased to an overall lower level than the control group. A correlation was seen\nbetween T3 levels and daily O157:H7 bacterial shedding (P=0.003; r=0.37). In\nexperiment 2, 12 growing lambs (41.04 kg BW) were exposed to either 0.0 mg/kg BW\nPTU or 40 mg/kg BW PTU for 21 days. Fecal samples were collected for analysis of\ngeneric E. coli and body weights were recorded on days 0, 7, 14, and 21. Feed intake\nwas recorded throughout the experiment. Animals were experimentally infected with E. \ncoli O157:H7 on day 15. Sheep were humanely euthanized on day 21 and GI tract tissue and content was collected from the rumen, ilium, colon and rectum. A date by treatment\ninteraction was observed for T4 (P=0.0016) and hormone levels decreased in treated\nanimals. Thyroxine and E. coli O157:H7 display a multivariate treatment (P=0.0005)\nand date effect (P=0.0174) but no significant interaction. Triiodothyronine and E. coli \nO157:H7 shedding have a slight date trend (P=0.065) but no significant treatment or\ntreatment by date interaction. Generally, the treatment group shed genreric E. coli at\nhigher levels throughout the study period with slightly more than a log count difference\nbetween groups at the last collection point (control = 3.8 CFU/gram of feces (log10);\ntreatment = 4.9 CFU/gram of feces (log10)). Results from these experiments suggest that\ncorrelations exist between both E. coli O157:H7 and generic E. coli shedding in sheep.
Author: S.B. Schroeder
Language: English
Subfield: Microbiology
Field: Immunology and Microbiology
Domain: Life Sciences
Open Access status: green
OpenAlex ID: W2309961713