Distinct tissue localization and transcriptional profiles of Shiga toxin-producing Escherichia coli with and without the locus of enterocyte effacement at the bovine recto-anal junction

Authors: MENDEZ, DIEGO - Universidad De Chile; CARTAJENA, JOSE - Universidad De Chile; FLORES, JACQUELINE - Universidad De Chile; QUINTANILLA, FERNANDA - Universidad De Chile; TOLEDO, JORGE - University Of Aysén; CRUZ, PABLO - Universidad De Chile; DORNER, JESSICA - Universidad De Chile; ESCOBAR, BEATRIZ - Universidad De Chile; RIOS, MARIA - Universidad De Chile; LAVANDEROS, CRISTOBAL - Universidad De Chile; FERRER, VICENTE - Universidad De Chile; ROJAS, PAZ - Chilean Meat Processing And Refrigeration Association (CHILEMEAT); LUNA, DANIELA - Universidad De Chile; LAPIERRE, LISETTE - Universidad De Chile; Kudva, Indira; MARTINEZ, VICTOR - Universidad De Chile; GALARCE, NICOLAS - Universidad De Chile

Submitted to: International Journal of Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/21/2026
Publication Date: 8/29/2026
Citation: Mendez, D., Cartajena, J.T., Flores, J., Quintanilla, F., Toledo, J., Cruz, P., Dorner, J., Escobar, B., Rios, M.P., Lavanderos, C., Ferrer, V., Rojas, P., Luna, D., Lapierre, L., Kudva, I.T., Martinez, V., Galarce, N. 2026. Distinct tissue localization and transcriptional profiles of Shiga toxin-producing Escherichia coli with and without the locus of enterocyte effacement at the bovine recto-anal junction. International Journal of Microbiology. 2026. Article 2576911. https://doi.org/10.1155/ijm/2576911.
DOI: https://doi.org/10.1155/ijm/2576911

Interpretive Summary: Cattle are the main source of the foodborne, human-disease causing bacteria called the Shiga toxin-producing Escherichia coli (STEC). STEC infections cost U.S. consumers billions annually due to illness, productivity losses, and economic losses through recalls of contaminated foods. Reducing STEC at the source would reduce STEC transmission to the American consumer and decrease food recalls. STEC are found attached to cattle intestinal cells and our goal has been to study the role of bacterial proteins called adhesins in STEC attachment to guide methods to remove or reduce STEC in the animal. Also, with the 2025 U.S. trade expansion with Chile to include import of raw beef trimmings for production of ground beef and hamburgers in addition to premium muscle cuts, total Chilean beef exported to the U.S. is projected to increase to 24,000 metric tons in 2026, thereby setting a need to collaboratively study the prevalence, strain types, and virulence patterns of STEC in Chilean cattle for reduction of the foodborne pathogen to enhance food safety of the meat imported for the American consumer. In this study, STEC isolated from cattle were evaluated for traits that influence STEC attachment, including binding properties to intestinal tissues, expression of genes involved in STEC attachment (adhesins), and biofilm formation (a characteristic of attachment strength and bacterial persistence). Collectively, our findings demonstrate that attachment to the intestinal cells is strongly dependent on the STEC serotype and is influenced by the structural complexity of the host tissue. Given the critical role of cellular attachment for long-term carriage and shedding, these insights provide a basis for developing pre-harvest control tools aimed at disrupting early adhesion, including anti-adhesion strategies and vaccine candidates to reduce STEC in cattle for ensuring a safer food supply for the American consumer, a USDA priority.

Technical Abstract: Shiga toxin-producing Escherichia coli (STEC) colonizes the bovine recto-anal junction (RAJ), a key site supporting long-term bacterial persistence and contributing to carcass contamination and human infection. However, the early adhesion mechanisms used by diverse STEC lineages remain insufficiently characterized, particularly for LEE-negative serotypes. This study aimed to investigate strain-dependent adhesion traits in bovine and human STEC using complementary phenotypic, ex vivo, and transcriptional approaches. Seventy-one bovine isolates and two human clinical strains were first characterized for curli, cellulose, and biofilm production. Most isolates produced curli and formed weak biofilms, while one strain (O130:H11) was the only cellulose-producing and strong biofilm-forming isolate. Four representative serotypes (O157:H7, O26:H11, O113:H21, O130:H11) were selected for functional assays. All adhered to primary recto-anal junction squamous epithelial (RSE) cells, with O157:H7 displaying the most clustered pattern. In RAJ explants, adhesion was confirmed for all strains, but LEE-positive serotypes (O157:H7 and O26:H11) localized deeper within the stratified epithelium, whereas LEE-negative strains remained confined to superficial layers. Gene expression analysis revealed serotype/strain-specific transcriptional responses to the RAJ environment. LEE-positive strains upregulated eae and pgaA, while LEE-negative strains showed distinct expression for iha, saa, csgD, pgaA, and fliC, indicating that adhesion-related pathways are host tissue and strain dependent. Overall, these findings demonstrate clear serotype-dependent differences in early STEC colonization strategies. The combined use of cell culture, explant models, and transcriptional profiling provides a comprehensive understanding of RAJ adhesion and supports the development of targeted pre-harvest interventions to reduce STEC carriage in cattle within a One Health framework.