Salmonella: Symptoms of Food Poisoning Caused By Salmonella

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  • 0:06 The Vegetarian Solution
  • 2:15 Salmonella
  • 4:01 Salmonellosis
  • 5:38 Diagnosis and Treatment
  • 7:36 Lesson Summary
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Lesson Transcript
Instructor: Angela Hartsock

Angela has taught college Microbiology and has a doctoral degree in Microbiology.

There is a very good reason for not eating raw cookie dough, despite how delicious it is. In this lesson, we will look at Salmonella, a bacterium often found in the dough's raw eggs, which can cause a serious case of foodborne illness.

The Vegetarian 'Solution'

I was doing some background research for this lesson and happened on a website article discussing foodborne illness caused by the bacteria Salmonella. Lots of readers were making comments on the article, and as you can imagine, the comments got pretty interesting. There were people cracking jokes, some of which were pretty funny, but not appropriate here. Other posts were busy refuting the accuracy of the information presented. And, of course, just to prove I am giving a good representation of the comments, there was one post trying to sell me generic pharmaceuticals at rock bottom prices.

But, one post in particular caught my eye. The reader claimed that if you want to avoid foodborne illness, you must become a vegetarian. At first, this might sound like a reasonable idea. Most of the bacteria that cause foodborne illness originate from the animals you are eating. We are constantly reminded not to eat raw or undercooked meats, raw eggs and unpasteurized milk. Switching to a vegetarian diet would seem to eliminate this threat. So, is this anonymous poster onto something? Let's take a quick look at the data.

On the Centers for Disease Control and Prevention website, they have a list of 49 selected Salmonella outbreak investigations since 2006. I took a minute and crunched the numbers. There were 12 investigations into contaminated meats, like chicken, eggs and ground beef. This represents about a quarter of the total. About another quarter were investigations into live animal sources, like pet shop turtles, frogs and live chickens. But nearly half, 21 cases, identified a non-animal based product as the source of the outbreak. This includes alfalfa sprouts, peanut butter, pine nuts and cantaloupe.

The take-home message here is that simply avoiding animal products won't keep you safe. The vegetables on your table may be more dangerous, simply because people are less careful with them than they are with their meats. So keep this in mind as we take a closer look at the bacteria Salmonella.


Salmonella is a genus of gram-negative, facultative aerobic, rod-shaped bacteria normally found in the gut of animals. Gram-negative refers to Salmonella having a cell wall with a thin peptidoglycan layer and an outer membrane, making these cells appear red in the classic Gram stain. Being a facultative aerobe, Salmonella can grow with or without oxygen. In fact, Salmonella normally lives in the anaerobic small and large intestines of animals, including mammals, birds and reptiles. It is then passed out of the intestines and can be found in feces, and is normally present in sewage.

Food products can become contaminated by fecal material, spreading the bacteria to consumers. This contamination can be from the food animal itself, from fertilizers sprayed on food crops or from food handlers. Raw poultry, raw eggs, unpasteurized dairy products and contaminated raw vegetables are frequent sources of exposure.

The bacteria can also be found on the surfaces of live animals, especially reptiles and birds. Who hasn't heard the horror stories about little kids getting Salmonella from putting turtles in their mouths? This might sound like a joke, but it has happened. Simply handling these reptiles, then eating without washing your hands can also lead to infection.

The species of Salmonella most often responsible for foodborne illness is S. enterica. Within this species, there are around 1,400 subspecies, also called serotypes. Within these serotypes, S. enterica serovar Typhimurium is the most common cause of illness, even though almost all are pathogenic to humans.


Salmonellosis is the term used to describe any symptoms caused by a foodborne infection by the bacteria Salmonella. In a food infection, the symptoms are caused by actively growing bacteria in the body. A person must consume a very large dose of Salmonella for symptoms to occur, often millions of cells. The bacteria pass through the stomach and begin to colonize the walls of the small and large intestine. The Salmonella bacteria inject a cocktail of proteins and toxins into the intestinal cells, which forces the cell to engulf the bacteria.

Once inside, the Salmonella cells release more toxins that cause a rush of fluid into the intestines and stimulates inflammation and a host immune response. One of the toxins released by growing and dying Salmonella is endotoxin, which consists of lipopolysaccharides, a major component of the outer membrane of gram-negative bacteria. The release of endotoxin during cell growth and death contributes to the fever and inflammation associated with Salmonellosis.

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