Growth dynamics and protein-expression of non-O157 Shiga toxin producing Escherichia coli O26, O111 and O145 in the bovine rumen

Authors: Kudva, Indira; TRACHSEL, JULIAN - Retired ARS Employee; BIERNBAUM, ERIKA - Oak Ridge Institute For Science And Education (ORISE)

Submitted to: PLOS ONE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/18/2025
Publication Date: N/A
Citation: N/A

Interpretive Summary: Cattle are asymptomatic carriers of Shiga toxin-producing Escherichia coli (STEC) that can cause disease in humans after consumption of contaminated products. STEC comprise different serogroups identified by the different outer membrane (O) antigens, of which STEC O157 and the ‘Big 6’ STEC O26. O111. O145, O103, O121, O45, are often associated with human illness. The rumen is the first gastrointestinal (GIT) compartment encountered by STEC in cattle where the bacteria need to survive ruminations, varying pH, fatty acids, and other micro-organisms to be able to colonize rest of the intestine. To better understand this STEC survival process, we developed a reusable animal model system that allows for introduction and recovery of the same test bacteria from cattle rumens without contaminating the GIT. Using this model system, we evaluated three bacteria belonging to the STEC serogroups, O26, O111 and O145, along with a non-disease causing, commensal E. coli as the control, in the rumen of cattle fed the lactation or maintenance diets. Interestingly, STEC O26, O111 and O145 demonstrated survival patterns similar to each other and to the control commensal E. coli but different from STEC O157. The growth of STEC O26, O111, and O145 was suppressed in rumen fluid especially from animals fed the lactation diet. Like STEC O157, STEC O26, O111, and O145 mainly expressed proteins supporting ruminal adaptation with variations. The observed differences between STEC O157 and non-O157 serogroups support the need to explore survival and protein expression of different STEC within the host to identify common conditions/ targets that may have broad application in STEC control in cattle.

Technical Abstract: To adapt to the ruminal environment, Shiga toxin-producing Escherichia coli (STEC) O157:H7 (O157) expresses proteins involved in survival rather than virulence. Additionally, STEC O157 strains exhibit distinct in vitro but shared in vivo survival patterns in rumen fluids that sets them apart from non-STEC, commensal E. coli. To determine if similar responses would be observed with other STEC, we evaluated three non-O157 STEC serotypes, O26:H11, O111:H8 and O145:NM, along with a non-STEC E. coli, under the growth conditions used for STEC O157: (i) anaerobically, in vitro, in rumen fluid from cattle on a lactation (low fiber, high protein) or maintenance (high fiber, low protein) diet, at 39 oC for 48 hr, and (ii) in vivo for 48 hr within the rumen of cattle on the same diets using a non-terminal, rumen-fistulated animal model that allows for introduction of bacteria without ruminal contamination. On the lactation diet, the ruminal pH was acidic ranging from 5.2 - 6.0, and the total volatile fatty acids (VFA) concentration, 141 - 230 µM/ml. On the maintenance diet, the ruminal fluid pH was close to neutral ranging from 6.0 - 7.0, with a total VFA of 87 - 190 µM/ml. Unlike STEC O157, the three non-O157 STEC demonstrated survival patterns similar to each other and the control non-STEC E. coli. A greater reduction in viable STEC counts was observed in vitro in rumen fluid from cattle fed the lactation diet than in vivo, corroborating previous reports that in vitro conditions cannot mimic those observed in vivo. Like STEC O157, the non-O157 STEC mainly expressed proteins supporting ruminal adaptation although not all proteins matched those expressed by STEC O157, and included the virulence protein, intimin. Explorative studies such as this could provide insights into common conditions/ targets that may have application in broader STEC control in cattle.