When e coli is become pathogenic?

Escherichia coli (E. coli) becomes pathogenic when it acquires specific virulence factors, such as toxins or adhesins, that enable it to cause disease. Pathogenic strains, like Enterohemorrhagic E. coli (EHEC) or Enterotoxigenic E. coli (ETEC), can lead to severe gastrointestinal illnesses or systemic infections. These strains often arise from genetic mutations or horizontal gene transfer, allowing them to exploit host environments or evade immune responses. Contaminated food or water is a common transmission route for these harmful strains.