Shigella bacterium
"The # 1 Bacteria That Causes # 2"


Author: Bree Ann Mendoza
December 9, 2010


Shigella bacteria is one of the main causes of food poisoning. Shigella is the third most common pathogen transmitted through food. Just 10 of the microscopic bacteria found in the human body is enough to cause Shigellosis infection also known as food poisoning. Usually people get infected from fecal contamination in water or food. Symptoms of Shigellosis are abdominal discomfort, cramps, diarrhea, fever, and vomiting. The bacteria thrive in the human intestines. Though not all strains of the Shigella bacteria are harmful, some people do die as a result of the Shigella bacteria invading their body. It is simple to avoid the Shigella bacteria; simply washing your hands before handling food and after you use the restroom.


I was interested in researching Shigella because before and after meals, my mother would always make me wash my hands. I never understood why I had to wash up if my hands weren’t dirty. She always responded that it would help reduce the chances of getting food poisoning because we carry bacteria on our hands. I was interested in finding out how one actually gets infected with food poisoning and what causes it. I have found that through my research that there are simple precautionary methods one can take to avoid the uncomfortable infection.


Kiyoshi Shiga discovered Shigella in 1898. At the time, with 90,000 cases reported, Shigella was causing an epidemic. The Japanese microbiologist later named the genus after himself. (Marler, 2009) The classification of Shigella is as follows- Kingdom: Bacteria, Phylum: Proteobacteria, Class: Gammaproteobacteria, Order: Enterobacteriales, Family: Enterobacteriaceae, Genus: Shigella. (Wikipedia contributors, 2010)


Shigella bacteria:
Shigella is a gram-negative rod shaped bacteria that is not motile. Shigella is non-spore forming, urea hydrolysis negative, and is not a lactose fermenter. The bacteria is closely related to Escherichia coli and Salmonella. There are four different species of Shigella; S. boydii, S. dysenteriae, S. flexneri, and S. sonnei. S. sonnei, S. flexneri, and S. dysenteriae are the most common species that usually cause disease. (Todar, 2009)


Shigella bacteria can cause shigellosis and bacillary dysentery. (Case, Funke, Tortora, 2010)

Dysentery is when the intestines get inflamed and results in severe diarrhea that causes mucosa of the intestines to be damaged. As a result, the diarrhea usually contains blood and mucosa from the intestines. Because of the severe diarrhea, without treatment, people can die from dehydration. (Case, Funke, Tortora, 2010)

Shigellosis is a very infectious disease, also known as a type of food poisoning. Interestingly, Shigellosis is a disease only found in humans and primates. With less than 100 bacteria entering the body, one can be infected with Shigellosis. (Todar, 2009) Usually people are infected from fecal contamination in their food or water. (Arnold, 2009)

Shigellosis Symptoms:
  • cramps
  • abdominal pain
  • flatulence
  • diarrhea
  • vomiting
  • fever
(Centers for Disease Control and Prevention, 2009) digestive-system-23974146-ga.jpg

The Shigella bacteria thrive in the intestines. They usually invade the epithelial cells lining the intestines. (Arnold, 2009) "In order to thrive in the host, S. flexneri must adapt to environmental conditions in the gut and within the eukaryotic cytosol, including variability in the available carbon sources and other nutrients."(Gore, and Payne pg 4674-4682, 2010) Then, once the bacteria are in host cells, they cause it to produce inflammatory mediators. This helps them move around and divide more rapidly throughout neighboring epithelial cells. Mucosal abscesses are then formed as epithelial cells are killed by the infection. After being infected, symptoms usually start 12 to 50 hours later. Shigellosis infection should not last more than 5 to 7 days. (Arnold, 2009)
Diagnosis and Treatment:
People do not usually get diagnosed for the bacterial infection of Shigella in minor cases, but if they do, the doctor would obtain a sample of the infected person’s stool and test to see if it contained the Shigella bacteria and what strain. It’s best for doctors to find out which strain it is because they can then prescribe the best antibiotic to treat the infection.(Centers For Disease Control and Prevention, 2009) Some common antibiotics used to kill Shigella are Ampicillin, Trimethoprim/Sulfamethoxazole, Nalidixic Acid and the Fluoroquinolone, Ciprofloxacin. It is not necessary to take antibiotics, but it shortens the infection and stops the symptoms.(Todar, 2009)

There is a concern with the Shigella bacteria becoming more resistant to the drugs, so with mild Shigellosis, doctors should not be prescribing antibiotics. Usually the infection clears up on its own within a week. It is important not to take antidiarrheals because your body is trying to rid itself of the Shigella bacteria naturally. It is also important to stay hydrated when infected with shigellosis, due to the dehydration from diarrhea.(Todar, 2009)


Hand_Washing_Sink-1.jpg Around 18,000 cases are reported of Shigellosis in the United States each year. Shigellosis is caused from the ingestion of contaminated stool with Shigella bacteria. Ingestion of feces is easier that one would think. Usually it is spread because of poor hand-washing habits and ingestion of contaminated foods. Shigella bacteria is commonly found in day care centers, nursing homes, and contaminated bodies of water. Swimming in water that has been polluted with sewage could cause Shigellosis in humans. Toddlers are more likely to become infected because they usually don't have as good sanitary habits and are around other children at daycare that may be infected. It is very important to wash your hands after using the restroom and before handling food in order to prevent yourself from becoming infected by Shigella bacteria. (WebMD, 2009)
Daycare Outbreak VIDEO!! Weapon?
Yes! Shigella was used on prisoners of war during World War II by the Japanese in Mancheria. Also more recently, in 1997 an angry employee of a medical center stole some of the Shigella bacteria and contaminated staff breakfast treats. Many of the workers were infected with Shigellosis after the eating the contaminated treats; some were even hospitalized. Shigella is an effective biological weapon because it is highly infectious and has no vaccine against it. (Pike, 2007)
Literature Cited:
Arnold, Paul. "The Facts About Shigella Bacteria." Bright Hub. Bright Hub Inc., 30 Oct 2009. Web. 7 Nov 2010. <

Case, Christine, Berdell Funke, and Gerard Tortora. Microbiology An Introduction. 10th. San Francisco, CA: Pearson Benjamin Cummings, 2010. 710-12. Print.

Gore, Aja, and Shelley Payne. "CsrA and Cra Influence Shigella flexneri Pathogenesis." American Society for Microbiology. 78.11 (2010): 4674-4682. Print.

"Health Department Cautions Day Cares Of Shigellosis Outbreak." YouTube. Web. 11 Nov 2010. <>.

Marler, Bill. "Shigella Food Poisoning." About Shigella. OutBreak, Inc., 2009. Web. 13 Nov 2010. <>.

Pike, John. "Shigellosis - Biological Weapons." Global Security. Global Securit, 23 Oct 2007. Web. 7 Nov 2010. <>.

"Shigellosis." Centers For Disease Control and Prevention. Centers for Disease Control and Prevention, 16 Nov 2009. Web. 15 Nov 2010. <>.

"Shigellosis-Topic Overview." WebMD. WebMD LLC, 23 Feb 2009. Web. 7 Nov 2010. <>.

Todar, Kenneth. "Shigella and Shigellosis." Todar's Online Textbook of Bacteriology. Kenneth Todar, 2009. Web. 11 Nov 2010. <>.

Wikipedia contributors. "Dysentery." Wikipedia, The Free Encyclopedia. Wikipedia, The Free Encyclopedia, 30 Nov. 2010. Web. 7 Dec. 2010.<>

Wikipedia contributors. "Shigella." Wikipedia, The Free Encyclopedia. Wikipedia, The Free Encyclopedia, 30 Nov. 2010. Web. 7 Dec. 2010.<>