Shigella
A Microbial Biorealm page on the genus Shigella
Classification
Higher order taxa
Bacteria; Proteobacteria; Gammaproteobacteria; Enterobacteriales; Enterobacteriaceae
Species
Shigella boydii; S. dysenteriae; S. flexneri; S. sonnei
Description and significance
Shigiella is a non spore forming gram negative bacteria that aids in the facilitation of intracellular pathogens. It is able to survive the proteases and acids of the intestinal tract and infections to hosts can be caused from a very low dose. As little as 10 to 100 bacteria are needed to cause infection.
Genome structure
The four difference species of Shigella vary greatly in the genomic structure. The largest species S. sonnei contains 4,825,265 base pairs. S. flexneri contains 4,607,203 base pairs, S. boydii contains 4,519,823 base pairs and the smallest species S. dysenteriae contains 4,369, 232 base pairs.
Cell structure and metabolism
Interesting features of cell structure; how it gains energy; what important molecules it produces.
The Shigella life cycle begins with penetration of colonic mucosa. This results in degradation of the epithelium and acute inflammatory colitis in the lamina propria. This causes leakage of blood, inflammation in the colon, and mucus into the intestinal lumen.
Ecology
Habitat; symbiosis; contributions to the environment.
Pathology
How does this organism cause disease? Human, animal, plant hosts? Virulence factors, as well as patient symptoms.
Transmission: Fecal-oral transmission is the main path of Shigellosis infection however other modes of transmission include ingestion of contaminated food or water, contact with a contaminated inanimate object, and sexual contact. Outbreaks of Shigellosis infection are common in places where sanitation is poor.
Frequency: Shigella spp. Infects around 450,000 individuals just in the United States yearly, and of those 450,000 cases approximately 6,000 infected people require hospitalization to treat the aliment. Of the various strains of shigella, S sonnei is the cause of 78% of infections, and S flexneri, and S boydii combined are responsible for the rest of the remaining 22% of cases. The occurrence of S dysenteriae is rare in the United States, it is however more common in developing countries with poor sanitary conditions, and water purification systems. Worldwide there are approximately 165 million cases of shigella annually, with 98% of those cases occurring in third world, developing nations. In those developing nations shigella was responsible for 1 million deaths. Unlike in the United States there are a fair amount of cases especially those resulting in death are due to the infection of S dysenteriae it accounts for 30% of infections. Developing countries are some 20 times more likely to develop a case of shigella then more developed countries. In developed countries the number of fatal cases is around 1%, and in countries of the Far and Middle East the fatality is more along the lines of 20% of cases result in death. The majority of cases of shigella are reported in the summer months. The majority of shigella cases occur in children 15 years old and under accounting for 50% of reported cases. This is most like due to poor personal hygiene and hand washing technique, or lack there of. It is difficult to have an extremely accurate gauge of the actual number of cases that occur because 90-95% of shigella infections are typically asymptomatic so they may go unnoticed, and thus unreported.
Current Research
Enter summarries of the most rescent research here--at least three required
References
Edited by Deidre DeSilva, Kayleigh Erazmus, and Megan Harney under Dr. Kirk Bartholomew of Sacred Heart University, Fairfield, CT.
Hale, Thomas L. Genetic Basis of Virulence in Shigella Species. Dept. of Enteric Infections, Walter Reed Amry Institute of Research. Washington, D. C.: American Society for Microbiology, 1991. 206-224. 10 Nov. 2006 <http://mmbr.asm.org/cgi/reprint/55/2/206.pdf>.
Hale, Thomas L., and Gerald T. Keusch. "Shigella." GSBS At UTMB. The Graduate School of Biomedical Sciences at UTMB. 10 Nov. 2006 <http://www.gsbs.utmb.edu/microbook/ch022.htm>.
Sureshbabu, Jaya, and Poothirikovil Venugopalan. "Shigella Infection." EMedicine From WebMD. 12 Sept. 2006. WebMD. 10 Nov. 2006 <http://www.emedicine.com/ped/topic2085.htm>.
