Agencies and their function in preventing food contamination and food poisoning?

Which government agencies are involved with food safety will depend upon the laws and regulations that apply to the part of the world in which you live.

In the United States, on the Federal level the main players for food in interstate commerce are the U.S. Department of Agriculture (most meat products) and the Food & Drug Administration (everything else that USDA doesn't cover). Then you have state and local health departments to cover where the Federal agencies don't. Occasionally, there will be overlap.

The government agencies perform inspections of food companies during which policies and procedures are observed as well as the condition of the physical structure. They might collect product samples and/or take swabs of the equipment or of the surrounding environment. Deficiencies are pointed out to management, who is expected to correct the problems.

Even though the various agencies might regulate the food industry, it is still the business's responsibility to have programs in place to consistently produce safe food.