This chapter discusses bacteria and their mode of transmission. Both of them play important roles in the potential for a given parasite to become an emerging infection in humans. Two closely related species of bacillus have been found in both humans and wild animals: Bacillus anthracis and Bacillus cereus. Bacillus cereus is closely related to Bacillus anthrax, but poses less of a threat. Similar to B. anthracis, B. cereus is a spore-forming soil bacterium, but it is quite ubiquitous in the environment and can also occur in water. It is an opportunistic infection most commonly associated with food poisoning, sometimes referred to as "fried rice syndrome" with typical symptoms being diarrhea from bacterial toxins. Brucella species have been identified in cattle, pigs, goats, dogs, and marine mammals. The CDC has classified Brucella as a category B biological weapon (second highest priority) due to its ease of dissemination.