Salmonella is an opportunistic bacterium. Known for its effects on health, it can cause serious foodborne illnesses. All Salmonella strains are potentially pathogenic in humans. They exist in the environment, plants and animals.
Salmonella is a genus of rod-shaped bacteria. It belongs to the Enterobacteriaceae family and is best known for causing salmonellosis or salmonella food poisoning.
A large family of bacteria, its two main species are Salmonella enterica and S. bongori. Over 2,500 serotypes or groupings are identified, each with unique traits.
Severity of the infection varies. Influencing factors include bacterial strain, amount of bacteria ingested and response of the host's immune system.
Some strains, like Salmonella enterica serovar Typhi, the cause of typhoid fever, are highly virulent and cause severe illness. Other strains might cause symptoms like gastroenteritis (stomach flu).
Salmonella can be found in various environments. It’s common in intestinal tracts of many animals. Like E. coli, Salmonella is continuously released into the environment from infected humans, livestock, pets and wildlife.
From there, it enters soil, water and plants. It's found in compost. An opportunistic organism, it thrives where conditions are favorable. It can live in both land and water environments.
Soil is a long-term reservoir for Salmonella. In pig manure, salmonella bacteria remain a minimum of 21 days. Originating from poultry droppings they can live in soil as long as a year.
Salmonella bacteria get nutrients from organic matter. In the environment, they eat sugars, amino acids and other compounds in decaying matter. In intestines of animals or humans, it uses nutrients from digested food.
While Salmonella can occur naturally in the intestinal tracts of many animals without causing illness, it's not a natural inhabitant of humans. Its presence indicates infection, even if symptoms are mild or absent.
Once ingested, Salmonella must survive the toxic acidity of the stomach to reach more alkaline conditions in the small intestine. Not all succeed, but if it does, it multiplies and invades intestinal cells.
The invasion triggers an inflammatory response in the host. Salmonella can enter the bloodstream, causing systemic infection.
Salmonella has the endotoxin Lipopolysaccharide (LPS) in its membrane. When bacteria die and break down, LPS is released. This further stimulates the host's immune system and contributes to inflammation and fever.
Salmonella uses sophisticated secretion systems, such as the Type III secretion system, to inject effector proteins directly into host cells. These proteins manipulate the host cell's internal machinery.
This causes changes in cell structure and function. The changes promote bacterial uptake, survival, and replication within the host cell. Salmonella can also attach to surfaces in the food industry and form biofilms.
A biofilm is an organized group cells attached to a surface and each other with the glue of Extracellular Polymeric Substances (EPS). It protects the bacteria, modifies their habitat and increases resistance to antibiotics.
Salmonella infection in humans most often occurs through consumption of contaminated food or water. Common sources include:
Raw or undercooked meat, poultry, and eggs: These products can be contaminated during slaughter or processing and if not cooked sufficiently, Salmonella can survive.
Unpasteurized milk and dairy products: Pasteurization kills Salmonella, so unpasteurized products pose a risk.
Raw fruits and vegetables: These can become contaminated through contact with contaminated water or animal feces.
Cross-contamination: Salmonella from raw foods can easily spread to other foods through contaminated surfaces, cutting boards, and utensils.
Contact with animals: Handling reptiles, poultry, and other animals can lead to Salmonella exposure.
Common symptoms of Salmonella infection include diarrhea, abdominal cramps, fever, nausea and vomiting. Symptoms appear 6-72 hours after infection and last for 4-7 days.
In severe cases, Salmonella can spread from the intestines to the bloodstream and other organs. The best way to prevent Salmonella infection is to use and enforce good food safety habits.
Basic Food Safety
Cook foods thoroughly, especially meat, poultry, and eggs. Internal temperature of meat should reach 74°C (165°F).
Wash hands frequently with soap and water, especially before preparing food, after handling raw meat or poultry, other animals like reptiles, and after using the bathroom.
Prevent cross-contamination by using separate cutting boards and utensils for raw and cooked foods.
Refrigerate perishable foods promptly.
Avoid unpasteurized milk and dairy products.
Wash raw fruits and vegetables thoroughly.
Most Salmonella infections are self-limiting and resolve within a few days. Treatment focuses on managing symptoms and preventing dehydration.
Drinking plenty of fluids is important. In severe cases, or when the infection spreads beyond the intestines, antibiotics may be necessary.
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