is the name of a genus
, named after the scientist Dr. Daniel Salmon
, who discovered them. The various species
bacteria have between 95% to 99% of their DNA identical. The most common strains
are the main serovar
s of Salmonella enterica
, though there are over 1800 known serovars of Salmonella
. Currently, several projects
are in progress
of various strains of Salmonella
, especially the ones stated below.
The bacteria is anaerobic, and possesses three major antigens. The H antigen (or flagellar antigen) may occur in either or both of two seperate forms, known as "phase 1" and "phase 2", and bacteria tend to change between them. The O antigen (or somatic antigen) occurs on the surface of the outer membrane, determined by specific sugar sequences on the surface. The Vi antigen is found on only a few serovars, such as S. Typhi.
- Salmonella enterica serovar Typhi, which is also known as Salmonella Typhi, and may be abbreviated to S. Typhi.
This strain is responsible for Typhoid Fever. It is not common in first-world nations, but is still very common in many underdeveloped nations. It has only been found to infect humans, and is spread through swallowing infected water, or washing food in infected water.
- Salmonella enterica serovar Typhimurium, which is also known as Salmonella Typhimurium, or S. Typhimurium.
This strain causes a typhoid-like sickness in mice. It can also infect humans, but is less severe than S. Typhi - it can be very harmful, though, when it infects a person with a weak or compromised immune system. It was once the most common cause of food poisoning, but not in the last twenty years. Causes diarrhea, abdominal cramps, vomiting, and nausea, lasting about a week.
- Salmonella enterica serovar Enteritidis, or Salmonella Enteritidis or S. Enteritidis).
In the last twenty years, it has surpassed S. Typhimurium as the most common cause of food poisoning. The symptoms are similar, however, it readily infects chickens, speading easily among them, usually without visible signs of disease. The large industrial chicken farms common today are likely helping spread this strain.
When Salmonella is ingested, it travels through the digestive system to the intestines, where it attaches itself to the intestinal walls. Then it begins to produce proteins that allow it to pass through the intestinal wall. Most of the bacteria ingested don't manage to attach and penetrate properly, and are flushed through the body. Those that do, first infect the epithelium, and them multiply and head to the liver or spleen, where they take hold. The body's immune system has trouble fighting Salmonella, due to a number of evolved mechanisms.
Salmonella infection is often called Salmonellosis. Infections usually last 5-7 days, and cause diarrhea, cramps, and fever. It can be identified as the cause by doing a test on a person's stool. Treatment is usually not necessary, as the body can fight it off, but may be treated with antibiotics. Reiter's syndrome is a rare long-term effect from infection, resulting in joint pain, irritation of the eyes, and pain during urination. It is difficult to treat, and shows no correlation to whether or not treating with antibiotics has been done.
Salmonella is most often found in chicken and eggs, though the chances of infected eggs are often overstated - estimates are that infected chickens only produce 1 in 1000 eggs that also contain Salmonella. Other foods can also host it, but are much less common. There are also slight chances of catching it from an infected pet, if a person is not careful or not aware. Many pets do not even show symptoms other than diarrhea.
In the labs where work is being done with Salmonella, the bacteria are cultured in a special mixture. This mixture involves yeast extract, as it is high in nutrients, tryptone, a broken down form of casein which provides the amino acids not present in the extract, and table salt, as Salmonella prefer a salt-rich environment, but most other bacteria don't. When the bacteria are stored in this mixture at a temperature of 98 degrees F, the bacteria divide approximately every 20 minutes. Salmonella can even survive without the presence of oxygen, but they grow very slowly.
Preventing Salmonella infection can, for the most part, be accomplished by a few simple steps. Make sure that all food is properly cooked, especially those involving meat or eggs. Wash all surfaces and utensils that come in contact with raw foods, and wash your hands well after touching those foods. Make sure not to bring cooked food in contact with juices, utensils, or dishes that came from or touched raw food.
Recently, an increased risk of receiving Salmonella from reptiles has been observed. The risk is not high, but persons handling reptiles or their cages should wash their hands well afterwards. Persons at higher risk, such as young children, should avoid reptiles, and they should not be kept around areas with young children, such as child care facilities and classrooms, and a reptile should be removed from a household that is expecting a new child.
About 40,000 cases of infection are reported each year in the United States, leading to about 1,000 deaths. There may be as many as four times as many cases, and it is more common in the summer than in winter.
NRAAC, Recommendations for Preventing Transmission of Salmonella from Reptiles to Humans, http://www.nraac.org/salmonella.html
CDC, Division of Bacterian and Mycotic Diseases, Salmonellosis Information, http://www.cdc.gov/ncidod/dbmd/diseaseinfo/salmonellosis_g.htm
Medmicro Chapter 21, Salmonella, http://gsbs.utmb.edu/microbook/ch021.htm