What organism commonly causes food poisoning?

Answer 1

The most common bacterial microorganism to cause food poisoning is by far Escherichia coli - E. coli. Other common bacterial pathogens that cause food poisoning are Salmonella, Campylobacter and Listeria. Common viruses that cause food poisoning are Noroviruses, Rotaviruses and Enteroviruses. In some classifications, Hepatitis A and Hepatitis E viruses are considered to be causes of food poisoning, although they have much longer incubation periods and affect organs outside stomach and intestines.

To be complete, it is worth going slightly outside the scope of the question and mention another common cause of food poisoning: toxins (although, they are not organisms - they are biologically active organic and inorganic compounds).