|Casey, Thomas - Retired ARS Employee|
Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 3/27/2019
Publication Date: N/A
Technical Abstract: Shiga toxin-producing E. coli (STEC) can cause bloody diarrhea and serious extraintestinal sequelae in humans. Sixty-four percent of all human STEC infections are caused by non-O157 serotypes of which six are most commonly implicated in disease and declared as food adulterants by the USDA. These six non-O157 STEC serotypes, commonly referred to as the ‘Big Six’, include, O26, O111, O145, O103, O121 and O45. Cattle are the primary reservoirs for STEC, including O157 and non-O157 serotypes. Recently we reported that STEC serotype O157 cultured in vitro in rumen fluid from dairy cattle on a maintenance diet (high in fiber), expresses proteins involved primarily in survival rather than virulence (BMC Microbiol. 2014; 14:48). This observation was corroborated in a related study evaluating three additional O157 strains in rumen fluid from animals on different diets including the maintenance diet, both in vitro and in vivo. The O157 strains also exhibited distinct in vitro but shared in vivo growth patterns that grouped them apart from a control non-STEC E. coli. In the present study, we evaluated responses of the ‘Big Six’ STEC serotypes under similar growth conditions as the O157 strains: (i) in vitro in rumen fluid from cattle on the maintenance (high fiber, low protein) or the lactation (low fiber, high protein) diets, at 39 degree C for 48 h under anaerobic conditions, and (ii) in vivo for 48 h within the rumen fistula of cattle on the same diets using a method that allows reuse of animals. On the maintenance diet, the ruminal pH ranged from 6.27 - 8.0, with total volatile fatty acids (VFA) concentrations of 86 -182 muM/ml and on the lactation diet the ruminal pH ranged from 5.0 – 6.4, with total VFA of 148 - 219 muM/ml. Each non-O157 STEC serotype demonstrated different growth patterns in these rumen fluids, in both the in vitro and in vivo assays. A greater reduction in viable STEC counts was observed in rumen fluid from cattle fed the lactation diet in the in vitro assay compared to the in vivo assay. Thus, in vitro experiments with rumen fluid do not seem to mimic the environment of the rumen in a live animal. The protocol we have standardized provides a valuable option for studying bacteria directly in the rumen of cattle without the need for euthanasia of the animal at the end of study. We are presently analyzing the proteomes of the STEC isolates recovered from the in vitro and in vivo assays. This will provide insights into the adaptive mechanisms used by STEC to survive the cattle rumen which in turn could be used to design effective anti-colonization therapies.