Salmonella are non-fastidious as they can multiply under various environmental conditions outside the living hosts. They do not require sodium chloride for growth, but can grow in the presence of 0.4 to 4%.
Salmonella is spread by the fecal-oral route and can be transmitted by
•food and water,
•by direct animal contact, and
•rarely from person-to-person.
They are carried asymptomatically in the intestines or gall bladder of many animals, and are continuously or intermittently shed in the feces. These bacteria are also shed in the feces of animals and humans that are ill. In addition, Salmonella spp. can be carried latently in the mesenteric lymph nodes or tonsils; these bacteria are not shed, but can become reactivated after stress or immunosuppression.
The main reservoirs for human infection are poultry, cattle, sheep and pigs. Infection in animals is maintained by recycling slaughterhouse waste as animal feed, fecal oral spread and fecal contamination of hatching eggs. Transmission occurs when organisms, introduced into the kitchen in poultry carcasses, meat or unpasteurized milk, multiply in food owing to inadequate cooking, cross-contamination of cooked foods and inadequate storage. Person-to-person spread is common in institutions such as hospitals.
When Salmonella bacteria are ingested, they pass through a person’s stomach and colonize the small and large intestine. There, the bacteria invade the intestinal mucosa and proliferate. The bacteria can invade the lymphoid tissues of the gastrointestinal tract and spread to the bloodstream.
Transmission
of salmonella
