Salmonella facts for kids
Quick facts for kids Salmonella |
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| Color-enhanced scanning electron micrograph showing Salmonella Typhimurium (red) invading cultured human cells | |
Scientific classification  |
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| Unrecognized taxon (fix): | Enterobacterales |
| Family: | Enterobacteriaceae |
| Genus: | Salmonella Lignières, 1900 |
| Species and subspecies | |
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Salmonella is a type of bacteria that looks like tiny rods. These bacteria are very small, usually between 0.7 and 1.5 micrometers wide and 2 to 5 micrometers long. They can move around using tiny whip-like tails called flagella.
Salmonella gets its energy from chemical reactions and can live with or without oxygen. They are often found inside living things, like humans and animals. Some types of Salmonella can make people sick.
Most Salmonella infections happen when people eat food or drink water that has been touched by animal or human waste. For example, if a food worker doesn't wash their hands properly.
Salmonella types are split into two main groups: typhoidal and nontyphoidal. Nontyphoidal types usually come from animals and cause salmonellosis, which is a kind of food poisoning. This often affects only the stomach and intestines and usually gets better without medicine.
However, in some places, like parts of Africa, nontyphoidal Salmonella can cause more serious infections that need antibiotics. Typhoidal types, like those that cause typhoid fever, spread only from person to person. These can be very dangerous and need urgent medical care.
Contents
- What is Salmonella?
- How Salmonella Was Discovered
- How Scientists Identify Salmonella Types
- How Salmonella Grows and Survives
- Different Names for Salmonella Types
- How Salmonella Causes Illness
- Typhoidal Salmonella Infection
- Tracking Salmonella Around the World
- How Salmonella Infects the Body
- Salmonella and the Immune System
- How Salmonella Adapts to Hosts
- Studying Salmonella
- Salmonella from the Past
- See also
What is Salmonella?
Salmonella is a group of bacteria that belongs to the family called Enterobacteriaceae. There are two main species: Salmonella bongori and Salmonella enterica. S. enterica is the most common one and has over 2,600 different types, called serotypes.
The name Salmonella comes from Daniel Elmer Salmon, an American animal doctor who lived from 1850 to 1914.
How Salmonella Was Discovered
The first time Salmonella was seen was in 1880 by Karl Eberth. He saw it in the bodies of people who had typhoid fever. A few years later, in 1884, Georg Theodor Gaffky was able to grow the bacteria in a lab.
In 1885, a scientist named Theobald Smith found a type of Salmonella that was later called Salmonella enterica. He was working for the U.S. Department of Agriculture, which was led by Daniel Elmer Salmon. They first thought this bacteria caused a pig disease, so they called it "Hog-cholerabacillus." The name Salmonella was suggested in 1900 by Joseph Leon Lignières to honor Daniel Elmer Salmon.
In the late 1930s, an Australian scientist named Nancy Atkinson set up a special lab to identify different types of Salmonella. She discovered many new types, including Salmonella Adelaide in 1943.
How Scientists Identify Salmonella Types
Scientists use a method called serotyping to identify different types of Salmonella. This involves mixing the bacteria with special liquids called antibodies. This helps them understand how risky a certain type might be.
For example, a study in 2014 found that a type called S. reading was common in young turkeys. But it didn't cause many illnesses in humans. Identifying the type can also help find the source of an infection, like if a certain food caused an outbreak.
Newer methods, like molecular serotyping, use DNA to identify Salmonella types much faster.
How Salmonella Grows and Survives
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Most types of Salmonella produce a gas called hydrogen sulfide. Scientists can easily detect this gas when they grow the bacteria in special dishes. Salmonella can also be found and identified using DNA tests.
Salmonella can multiply very quickly, dividing into new cells about every 40 minutes. They can live in bathrooms for weeks after contamination. They are also often found in water sources, which helps them spread between animals and people.
These bacteria are very tough. They can survive for years in dry places and foods. Freezing doesn't kill them, but heat and UV light can. They die if heated to 55°C (131°F) for 90 minutes, or 60°C (140°F) for 12 minutes. However, in foods with high fat and liquid, like peanut butter, they can survive even higher temperatures. To be safe, food should be heated to an internal temperature of 75°C (167°F).
Salmonella lives in the guts of humans and animals, especially reptiles. If you touch a reptile or amphibian, Salmonella on their skin can transfer to you. Food and water can also get contaminated if they come into contact with waste from infected people or animals.
Different Names for Salmonella Types
At first, each Salmonella type was named based on the illness it caused, like Salmonella typhi-murium (mouse typhoid fever). Later, new types were named after the place where they were found.
Now, scientists believe there are only two main species: S. enterica and S. bongori. The many different types are called "serotypes" or "serovars" and are grouped under these two species. For example, Salmonella enterica serovar Typhimurium is often shortened to Salmonella Typhimurium.
How Salmonella Causes Illness
Salmonella can get inside different types of cells in the body, including those lining the intestines and immune cells. Most infections happen when people eat food or water contaminated with animal or human waste.
Salmonella types are divided into two main groups based on how they cause illness:
- Nontyphoidal Salmonella: These are more common and usually cause stomach problems. They can infect many animals and can spread between animals and humans.
- Typhoidal Salmonella: These include Salmonella Typhi and Salmonella Paratyphi. They are mostly found in humans and do not usually infect other animals.
Nontyphoidal Salmonella Infection
Infection with nontyphoidal Salmonella usually causes food poisoning. This happens when a person eats food with a lot of the bacteria. Babies and young children can get sick from even a small number of bacteria.
The bacteria enter through the mouth and travel to the stomach. Many are killed by stomach acid, but some survive and reach the small intestine. There, they multiply and release toxins that make the person sick, causing stomach upset and diarrhea.
There are about 2,000 known types of nontyphoidal Salmonella. They cause millions of illnesses in the United States each year. Babies, older people, and those with weak immune systems are at higher risk for severe illness.
While in many countries these types cause stomach issues, in parts of Africa, they can cause serious bloodstream infections. These infections are very dangerous and can lead to death in a high percentage of cases.
How Salmonella Spreads
It's hard to know exactly how many Salmonella infections happen because many cases go undiagnosed. One study estimated that about 93.8 million cases of stomach flu each year are due to Salmonella. About 155,000 deaths are also estimated from these infections.
Children under 4 are much more likely to get Salmonella infections in some countries. People who are most at risk include children, pregnant women, older people, and those with weak immune systems.
Many foods can carry Salmonella, including chicken, pork, some vegetables, sprouts, and even processed foods like chicken nuggets.
To prevent Salmonella infections, organizations like the FDA and the United States Department of Agriculture create rules and inspect food. They have plans to reduce Salmonella in food. The Centers for Disease Control and Prevention also teaches people how to handle raw foods safely. In Europe, the European Food Safety Authority has also worked to reduce Salmonella in poultry, which has cut infections by half.
Recently, a Salmonella outbreak was linked to chocolate.
Typhoidal Salmonella Infection
Typhoid fever is caused by specific Salmonella types, like Salmonella Typhi, that only infect humans. In severe cases, these bacteria can travel from the intestines into the blood and spread to organs like the liver, spleen, and kidneys.
When this happens, the bacteria release toxins that can damage blood vessels and affect the body's temperature control. This can lead to severe dehydration, low blood pressure, and a dangerous condition called septic shock. These serious forms of the disease need intensive medical care.
Tracking Salmonella Around the World
In Germany, all food-borne infections must be reported. The number of recorded Salmonella cases there dropped from about 200,000 in 1990 to about 13,000 in 2016.
In the United States, about 1.2 million Salmonella infections are estimated to happen each year. The World Health Organization estimated that in 2000, over 21 million cases of typhoid fever occurred worldwide, leading to over 216,000 deaths.
How Salmonella Infects the Body
Salmonella bacteria have different ways of causing infection depending on whether they are typhoidal or nontyphoidal types. Both types must first get past the protective lining of the intestines. Once inside, they use different methods to cause illness.
To cause an infection, Salmonella goes through several steps:
- Approach: They move towards the cells lining the intestine.
- Adhesion: They stick to a host cell using special bacterial parts.
- Invasion: They enter the host cell.
- Replication: They can multiply inside the host cell.
- Spread: They can spread to other organs through the blood, or go back to the intestine.
- Re-invasion: They can cause a new infection in other parts of the body.
Nontyphoidal Salmonella often enters special cells in the intestine, causing inflammation and diarrhea. They can also break down the connections between intestinal cells, which makes diarrhea worse.
Typhoidal Salmonella can enter immune cells and use them to travel throughout the body. This is a more hidden way to spread and means fewer typhoidal bacteria are needed to cause a serious infection.
Salmonella uses special systems to inject proteins into host cells. These proteins help the bacteria get inside cells and survive. They also help cause inflammation and diarrhea.
Salmonella and the Immune System
Salmonella is known to cause problems like back pain. It can show up in different ways: as a stomach infection, typhoid fever, bloodstream infection, local infection (like in joints or bones), or a long-term carrier state. Initial symptoms often include fever and weakness.
A study in 2018 showed that Salmonella can mess with specific parts of the body's immune system, making it harder for the body to fight off the infection.
How Salmonella Adapts to Hosts
Some types of Salmonella, like Typhimurium, can infect many different animals, including humans. Other types, like Typhi, mostly infect only humans. Salmonella adapts to its hosts by changing its genetic material.
For example, some Salmonella types can lose the genes that make their flagella (tails). This helps them hide from the host's immune system, which might target the flagella.
Scientists believe Salmonella has evolved by gaining genetic information from other bacteria. This has helped them become so many different types.
Studying Salmonella
Scientists often study nontyphoidal Salmonella types, like S. enterica serovar Typhimurium, to learn about typhoid types. This is safer for researchers, but it has limits because some things, like specific toxins, can only be studied in the actual typhoid bacteria.
Salmonella has been very important in developing tools for studying bacteria. For example, a special virus called phage P22 was found in S. Typhimurium. This virus helps scientists change bacterial genes easily. This led to a better understanding of how bacteria work.
These studies also led to the Ames test, a simple way to check if chemicals can cause cancer. Scientists are also looking at using phages (viruses that infect bacteria) as a natural way to control Salmonella in food.
Salmonella from the Past
Scientists have found S. enterica DNA in human remains up to 6,500 years old in Europe and Asia. This shows that Salmonella infections were widespread long ago. It also suggests that the development of farming might have played a role in how these bacteria evolved.
DNA from colonial Mexico also suggests that S. enterica caused a major epidemic in the 16th century called cocoliztli.
See also
