Escherichia coli - from Normal Intestinal Bacteria to Lethal Microbes Escherichia coli as a Common Gut Commensal

<jats:p>Introduction Escherichia coli (E. coli) is a ubiquitous gram-negative bacterium that exists as a commensal organism essential for gut health and as a significant human pathogen. While commensal strains play critical roles in nutrient metabolism, vitamin synthesis, colonisation resistance, and modulation of host immunity, pathogenic lineages are responsible for severe enteric and systemic infections. This dual nature underscores the importance of distinguishing between ecological and clinical roles, particularly in low-resource settings, where sanitation and antimicrobial stewardship are often inadequate. Methodology This review synthesises recent international and Nigerian studies identified through systematic searches of PubMed, Google Scholar, and African Journals Online, with an emphasis on diarrheagenic and extraintestinal pathogenic E. coli. Diarrheagenic strains, including enteropathogenic, enterotoxigenic, enterohaemorrhagic, enteroinvasive, enteroaggregative, and diffusely adherent variants, are associated with childhood diarrhoea, foodborne outbreaks, and toxin-mediated complications. Extraintestinal strains, particularly uropathogenic and neonatal meningitis-associated lineages, are the major causes of urinary tract infections, neonatal sepsis, and meningitis. Together, these pathogenic groups represent a substantial global and regional health burden. Results A critical concern emerging from the literature is the increasing prevalence of antimicrobial resistance, with extended-spectrum β-lactamase-producing isolates reported in many Nigerian hospitals. Resistance to fluoroquinolones and other critical drug classes further complicates treatment, increasing mortality risk and healthcare costs. The convergence of commensal and pathogenic roles with increasing resistance highlights the need for integrated interventions that strengthen water, sanitation, and hygiene infrastructure, improve food safety, enhance prevention and control, and promote rational antimicrobial use. Conclusion Escherichia coli exemplifies a dual public health challenge that demands a balanced strategy aimed at preserving its beneficial role within the microbiota while curbing its pathogenic and resistant variants.</jats:p>