Microorganisms

Four types of pathogens can contaminate food and cause foodborne illness:
Bacteria, Viruses, Parasites and Fungi.

What Bacteria Need to Grow
Most bacteria need FAT TOM – nutrients, acidity, time, temperature, oxygen (some bacteria need oxygen to grow, while others grow when oxygen isn’t there) and moisture.
Moisture:
aw = water activity; the amount of moisture available in food for bacterial growth
aw scale ranges from 0.0 to 1.0
Water has a water activity of 1.0

The FDA has identified three types of bacteria that cause severe illness and are highly contagious:
Salmonella Typhi
Shigella spp.
Enterohemorrhagic and shiga toxin-producing Escherichia coli

The FDA has identified two viruses that are highly contagious
and can cause severe illness:
Hepatitis A
Norovirus
Source:
Shellfish
Feces and water contaminated with feces
Food handlers diagnosed with an illness from hepatitis A or Norovirus must not work in an operation while they are sick.

Parasites
Require a host to live and reproduce
Source:
Seafood, wild game, and food processed with contaminated water, such as produce
Prevention:
Purchase food from approved, reputable suppliers

Fungi
Yeasts, molds, and mushrooms: