Microorganisms are present everywhere in the soil, in the water, in the air, on our bodies. Some are useful, like the organisms used to make yogurt, cheese, and sauerkraut. Some will cause food to spoil, making it look, taste, or smell bad. Most are harmless. But a few can make you sick.
Harmful bacteria can contaminate food at any point between the farm and the dinner plate.
Many of the organisms that cause food poisoning in people can also grow in the intestines of farm animals. So, harmful bacteria can easily contaminate animal products during processing. Although food poisoning organisms do not normally grow on fruits and vegetables, these products can become contaminated if they come in contact with animals or animal products. The environment is another potential source of contamination. For example, shellfish can pick up bacteria and other contaminants from the water they live in.