Work

Orchestrating infection: the impact of RyfA and TimR sRNAs on stress resistance and virulence in avian pathogenic Escherichia coli in chickens

Year: 2026

Type: article

Abstract: ABSTRACT Avian pathogenic Escherichia coli (APEC) strains collectively represent a subpathotype of extraintestinal pathogenic E. coli (ExPEC) and are associated with substantial economic losses to the poultry industry, amounting to hundreds of millions of dollars worldwide. While chickens are the primary host, APEC strains also pose a zoonotic threat through cross-host transmission via contaminated meat or eggs. Supporting this, APEC shares numerous virulence factors and genetic features with uropathogenic E. coli (UPEC), another well-characterized ExPEC subpathotype. RyfA, a small regulatory RNA (sRNA), has been identified in UPEC as an essential regulator in stress resistance and virulence. However, its role in APEC, as well as that of another sRNA, TimR, located in the same genomic region, remains unclear. In this study, ryfA deletion in the APEC O1:K1 strain CH138 significantly reduced virulence in both single-strain and competitive co-infection models in chickens. Loss of ryfA decreased type 1 fimbria production (pili) in vitro , increased sensitivity to osmotic and oxidative stress, and impaired APEC internalization and survival within macrophages. In contrast, CH138 Δ timR and ΔΔ ryfA-timR mutants exhibited phenotypes similar to the wild-type strain. These findings suggest RyfA is required for stress adaptation in APEC strain CH138, likely contributing to virulence and survival during infection. The absence of additive effects in the double mutant suggests that attenuation of the ryfA mutant is intrinsically linked to effects caused by TimR in the absence of RyfA. Elucidating the regulatory interplay between RyfA and TimR will advance understanding of APEC pathogenesis and may highlight conserved sRNA targets for novel therapeutic approaches. IMPORTANCE Avian pathogenic Escherichia coli (APEC) strains cause colibacillosis in poultry, leading to significant financial losses and representing a potential zoonotic reservoir. Understanding how APEC persists in the host and withstands environmental stress is crucial for animal and public health. We identify the small regulatory RNA (sRNA), RyfA, as a key determinant of APEC virulence. Loss of RyfA impairs stress resistance, reduces type 1 fimbriae, limits survival in macrophages, and attenuates infection in chickens. By contrast, loss of the adjacent sRNA TimR had no discernible phenotypic effects compared to the wild-type parent. Interestingly, the combined loss of both ryfA-timR abrogated any phenotypic effects on virulence or stress resistance, suggesting the potential interplay between these sRNAs in gene regulation. These results demonstrate the critical role of RyfA for APEC pathogenesis and suggest that conserved sRNA-mediated regulatory pathways could provide future targets for prevention or treatment to improve poultry health and food safety.

Source: Applied and Environmental Microbiology

DOI: 10.1128/aem.02000-25

Authors: Carole Anamalé, Hicham Bessaiah, Evelyne Ng Kwan Lim, Sébastien Houle, Éric Massé, Charles M. Dozois

Institutions: Institut National de la Recherche Scientifique, Centre Armand-Frappier Santé Biotechnologie, Université de Montréal, Université de Sherbrooke

Language: English

Topic: Escherichia coli research studies

Subfield: Microbiology

Field: Immunology and Microbiology

Domain: Life Sciences

SDG: Good health and well-being

Open Access status: diamond

Funders: Mitacs, Canadian Institutes of Health Research, Natural Sciences and Engineering Research Council of Canada