Molecular Microbiology Research, 2025, Vol.15, No.1, 18-27 http://microbescipublisher.com/index.php/mmr 18 Research Perspective Open Access E. coli Pathogenesis: From Commensal to Pathogenic Strains Chunyang Zhan Hainan Institute of Biotechnology, Haikou, 570206, Hainan, China Corresponding email: chunyang.zhan@cuixi.org Molecular Microbiology Research, 2025, Vol.15, No.1 doi: 10.5376/mmr.2025.15.0003 Received: 06 Nov., 2024 Accepted: 18 Jan., 2025 Published: 06 Feb., 2025 Copyright © 2025 Zhan, This is an open access article published under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Preferred citation for this article: Zhan C.Y., 2025, E. coli pathogenesis: from commensal to pathogenic strains, Molecular Microbiology Research, 15(1): 18-27 (doi: 10.5376/mmr.2025.15.0003). Abstract Escherichia coli (E. coli) is a versatile bacterium that exists as a harmless commensal in the intestines of humans and animals but can transition into a pathogenic state, causing a variety of diseases. This study explores the mechanisms by which E. coli shifts from a commensal organism to a pathogen, focusing on four primary mechanisms of pathogenesis: quorum sensing, secretion systems, genetic variation, and virulence factors. Quorum sensing allows E. coli to regulate virulence factor expression in response to cell density, enhancing its pathogenic potential. The Type VI Secretion System (T6SS) is a nanomachine that injects toxic effector proteins into target cells, playing a crucial role in bacterial competition and virulence. Genetic variations, such as mutations in the FimH adhesin, can increase E. coli's ability to bind to host tissues, thereby enhancing its virulence. Additionally, E. coli can acquire virulence factors through horizontal gene transfer, enabling it to cause a wide range of diseases. Understanding these mechanisms is essential for developing new strategies to combat E. coli infections. Keywords Quorum sensing; Type VI secretion; System genetic; Variation virulence factors; Pathogenesis 1 Introduction Escherichia coli (E. coli) is a common bacteria that usually lives in the human intestine. It plays an important role in our intestines, can help us maintain the balance of microbial organisms in the intestines, and also participate in some physiological processes. Most E. coli are actually harmless, coexisting peacefully with our bodies and maintaining a stable gut together (Tenaillon et al., 2010; Escribano-Vázquez et al., 2019; Martinson and Walk, 2020). However, E. coli has a "good side" and a "bad side". Some strains were originally symbiotic, but in some cases they became pathogenic bacteria. These pathogenic bacteria can cause many diseases, some occur in the intestine, such as gastroenteritis, and some occur elsewhere, such as urinary tract infection, neonatal meningitis, and even sepsis (Escribano-Vázquez et al., 2019; Denamur et al., 2020; Geurtsen et al., 2022). These strains are harmful because they acquire certain "virulence factors". These genes are not produced by themselves, but are “learned” from elsewhere through plasmids, transposons or bacteriophages (Geurtsen et al., 2022; Tawfick et al., 2022). The goal of this study is to introduce how E. coli turns from a "good bacteria" to a "bad bacteria". We will see what genetic changes or environmental factors contribute to this transformation and will also explain how these pathogenic bacteria cause infection. In addition, we will also analyze the prevalence characteristics of different types of pathogenic E. coli. Through these contents, we hope that everyone can have a clearer understanding of the dual characteristics of these bacteria and their health effects. Finally, we will also talk about the current practices in monitoring, preventing and treating E. coli infections, and explain why research in this area needs to be further deepened. 2 Biology and Ecology of E. coli 2.1 General characteristics of E. coli as a species Escherichia coli is a slender bacteria that belongs to the Gram-negative bacteria and also belongs to the Enterobacteriaceae. It can survive in an aerobic or oxygen-free environment, so it is called "familiar anaerobic bacteria". Most of this bacteria exist in the intestines of humans and other warm-blooded animals. They are part of
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