These bacteria encase themselves in a protein coat, forming a spore. Spores can withstand heating and freezing processes. These bacteria are called spore formers. The Clostridiums and Bacillus bacteria are considered to be spore formers. Home canned goods and Honey are examples of food products known to occasionally be infected with spores.
Anaerobic bacteria thrive in environments with limited amounts of oxygen or no oxygen present.
Aerobic bacteria require oxygen for growth. Facultative bacteria are those that can grow with or without oxygen. Unfortunately, most of the bacteria implicated in foodborne illness are facultative in varying degrees. Salmonella, Shigella, Staphylococcus aureus, and Bacillus cereus are generally considered to be facultative bacteria.