Shirley Tsai
Period 1
Salmonella
For this cell project,we chose to make the model on Salmonella.
Salmonella is a genus of rod-shaped, Gram-negative bacteria. There are only two species of Salmonella, Salmonella bongori and Salmonella enterica, of which there are around six subspecies and innumerable serovars. The genus belongs to the same family as Escherichia, which includes the species E.coli. Salmonellae are found worldwide in both cold-blooded and warm-blooded animals, and in the environment. They cause illnesses such as typhoid fever, paratyphoid fever, and food poisoning.
Salmonella are non-spore-forming, predominantly motile enterobacteria with diameters around 0.7 to 1.5 µm, lengths from 2 to 5 µm, and peritrichous flagella (flagella that are all around the cell body). They are chemoorganotrophs, obtaining their energy from oxidation and reduction reactions using organic sources, and are facultative anaerobes.
Infection with nontyphoidal serovars of Salmonella will generally result in food poisoning. Infection usually occurs when a person ingests foods that contain a high concentration of the bacteria. Infants and young children are much more susceptible to infection, easily achieved by ingesting a small number of bacteria. In infants, infection through inhalation of bacteria-laden dust is possible.
The organism enters through the digestive tract and must be ingested in large numbers to cause disease in healthy adults. An infectious process can only begin after living salmonellae reach the gastrointestinal tract. Some of the microorganisms are killed in the stomach, while the surviving salmonellae enter the small intestine and multiply in tissues (localized form). Gastric acidity is responsible for the destruction of the majority of ingested bacteria, however Salmonella has evolved a degree of tolerance to acidic environments that allows a subset of ingested bacteria to survive. Bacterial colonies may also become trapped in mucus produced in the oesophagus. By the end of the incubation period, the nearby cells are poisoned by endotoxins released from the dead salmonellae. The local response to the endotoxins is enteritis and gastrointestinal disorder.
Salmonella can also be detected and subtyped using PCR from extracted salmonella DNA, various methods are available to extract salmonella DNA from target samples.Mathematical models of salmonella growth kinetics have been developed for chicken, pork, tomatoes, and melons. Salmonella reproduce asexually with a cell division rate of 20 to 40 minutes under optimal conditions.
Salmonella lead predominantly host-associated lifestyles, however the bacteria were found to be able to persist in a bathroom setting for weeks following contamination, and are frequently isolated from water sources, which act as bacterial reservoirs and may help to facilitate transmission between hosts. The bacteria are not destroyed by freezing, but UV light and heat accelerate their demise—they perish after being heated to 55 °C (131 °F) for 90 min, or to 60 °C (140 °F) for 12 min.To protect against Salmonella infection, heating food for at least ten minutes at 75 °C (167 °F) is recommended, so the center of the food reaches this temperature.
The bacteria of Salmonella can be found in the digestive tracts of humans and animals, such as birds and reptiles. "Unusual serotypes of Salmonella have been associated with the direct or indirect contact with reptiles (for example, lizards, snakes turtles, and iguanas)." Food and water can also be contaminated with the bacteria by coming in contact with the feces of infected people or animals.
