Final answer:
E. coli, or Escherichia coli, is a type of bacteria that is a normal resident of the human gut but can also cause disease outbreaks when virulent strains produce toxins.
Step-by-step explanation:
E. coli, or Escherichia coli, is a type of bacteria. It is a commonly studied prokaryotic organism that resides in the human gut and plays a role in maintaining a healthy intestinal flora, aiding in the absorption of vitamin K and other nutrients. Despite its beneficial presence, certain strains of E. coli can become pathogenic and lead to serious illnesses, such as diarrhea and urinary tract infections, by producing toxins like Shiga toxin. Unlike viruses, fungi, or protozoa, bacteria like E. coli are characterized by the lack of a true nucleus and membrane-bound organelles, and they reproduce through a process called binary fission.