The infectious dose is estimated to be between 10 and 100 cells. Indicator organisms are used to determine fecal contamination because detection of pathogens is more difficult, less efficient, and more expensive. Coliforms are defined as all aerobic and facultatively anaerobic, Gram negative, asporogenous rods able to ferment lactose with the production of acid and gas. Fecal coliforms are a division of coliforms that are considered to be of more recent fecal origin. Because of the prevalence of E. coli in the human and animal intestine, and in their resultant stools, the presence of E. coli in processed foods is generally considered to indicate pollution of direct or indirect fecal origin.
Colonies produce characteristic reactions on differential media.
Salmonella growth in liquid media has been observed between a w 0.999 and 0.945, although growth at an a w of 0.93 has been observed. Salmonella senftenberg 775W is one of the most heat-resistant strains known. Salmonellae do not compete well with naturally occurring microorganisms normally found associated with food. Growth of Salmonella has been shown to be inhibited by food spoilage organisms, other members of the Enterobacteriaceae, and the lactic acid-producing bacteria. The salmonellae are among the most ubiquitous microorganisms that cause bacterial diarrhea.