Foodborne illness bacteria have a fecal reservoir
A majority of the foodborne illness bacteria have a fecal reservoir. [read genera]. This makes perfect sense, since many cause gastroenteritis as an infection in the small intestines. 2 Cholera, a lethal diarrheal disease historically killed millions each year, especially during endemics. Robert Koch himself traveled to India during one such endemic to isolate the bacterial cause of the disease. In 1884, after over a year of work he was convinced the organism was Vibrio cholera. The organism proved difficult to culture. 3 Just a year later, Escherichia coli, originally known as Bacterium coli, was identified in 1885 by the German pediatrician, Theodor Escherich. He noted that it was widely distributed in the intestine of humans and warm‐blooded animals. In 1892, Shardinger proposed the use of E. coli as an indicator of fecal contamination. This was based on the premise that E. coli is abundant in human and animal feces and not usually found in other niches. Furthermore, since E. coli could be easily detected by its ability to ferment lactose, it was easier to isolate than known gastrointestinal pathogens, especially Vibrio. 4 The presence of E. coli in food or water became accepted as indicative of recent fecal contamination. Although the concept of using E. coli as an indicator of fecal presence, it was complicated in the lab, due to the presence of other bacteria including Citrobacter, Klebsiella and Enterobacter that can also ferment lactose. As a result, the term “coliform” was coined to describe this entire group of enteric bacteria. Coliform is not a taxonomic classification but simply a definition of this group of bacteria. In 1914, the U.S. Public Health Service adopted the enumeration of coliforms as a more convenient standard of sanitary significance. 5 Coliforms are defined as rod‐shaped gram‐negative non‐spore forming bacteria that ferment lactose with the production of acid and gas when incubated at 35‐37°C. The table indicates the many media that have been created over the years to culture and enumerate coliforms. Most will permit growth in 24 hours and a few require 48 hour incubations. We’ll work with the yellow highlighted media in lab. 6 Although coliforms were easy to detect, their association with fecal contamination was questionable because some coliforms are found naturally in environmental samples. This led to the introduction of the fecal coliforms as an indicator of contamination. Fecal coliforms were first defined based on the works of Eijkman. They are a subset of total coliforms that grow and ferments lactose at 44.5 to 45.5°C. Fecal coliform analyses are done at 45.5°C for food testing. Water, shellfish and shellfish harvest water analyses use 44.5°C. The photo depicts a filtered water sample placed over mFC medium. The petri dish was incubated at 45.5°C for 24 hours. The blue colonies […]
