Shigella: Difference between revisions

Revision as of 04:09, 29 April 2009

A Microbial Biorealm page on the genus Shigella

Shigella bacteria in a stool sample. Image in public domain; found in Wikipedia.

Classification:

Higher order taxa:

Bacteria (domain), Proteobacteria (phylum), Gammaproteobacteria (class), Enterobacteriales (order), Enterobacteriaceae (family), Shigella (genus)

Species:

Shigella dysenteriae, S. flexneri, S. boydii, and S. sonnei

Background Information:

History

Shigella organisms are a group of gram-negative pathogens, which were initially recognized as the causal agents of shigellosis (also known as bacillary dysentery) in the 1890s and became an official genus in the 1950s. Each species has their own “niche”, which represents what the species main function or area is. S. dysenteriae serotype 1 causes deadly epidemics mainly in developing countries, S boydii is restricted to the Indian subcontinent, and S. flexneri and S. sonnei are prevalent in developing and developed countries, respectively. S. flexneri is also responsible for the worldwide endemic form of bacillary dysentery.

Description

Shigella is a non spore-forming gram-negative bacterium which aids in the facilitation of intracellular pathogens. It is able to survive the proteases and acids of the intestinal tract, which allows the bacteria to infect in very small amounts, down to as few as 10 bacteria being necessary.

Genome structure

The four different 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.

Life Cycle

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.

File:Shigellalifecycle.jpg

Life cycle of Shigella bacteria; courtesy of Samuel Baron, Graduate School of Biomedical Sciences at UTMB.

Metabolism

Shigella pathogens use a mixed acid fermentation pathway to metabolize substrates. Products of this anaerobic pathway include ethanol, acetic acid, lactic acid, succinic acid, formic acid, and carbon dioxide.

Pathology

Transmission

Fecal-oral transmission is the main path of shigella infection. Other modes of transmission include ingestion of contaminated food or water, contact with infected objects, or sexual contact. Outbreaks of shigella infection are common in places where sanitation is poor.

Frequency

Worldwide, there are approximately 165 million cases of shigella infection and 1 million shigella-related deaths annually, with 98% of those cases occurring in third world or developing nations. Of the various strains of shigella, S. sonnei is the cause of 78% of infections. S. flexneri and S. boydii are responsible for most of the remaining 22% of cases. The occurrence of S. dysenteriae is rare in developed countries, where sanitation conditions are satisfactory, but account for 30% of cases in under-developed areas. The majorities of infections are reported during the summer season and occur mostly in teenagers and adolescents under the age of 15, hypothetically due to poor hygiene techniques. It is difficult to have an extremely accurate gauge of the actual number of cases that occur, since 90-95% of shigella infections are typically asymptomatic and thus unreported.

Current Research

High Prevalence of Antimicrobial Resistance among Shigella Isolates in the United States Tested by the National Antimicrobial Resistance Monitoring System from 1999 to 2002, Sivapalasingam, S., Nelson, J. M., Joyce, K., Hoekstra, M., Angulo, F. J., and Mintz, E. D. This information on shigella's resistance to various antibiotics will help in treating shigellosis. Click this hyperlink for the full text of this article.

References

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>.

Sivapalasingam, S. "High Prevalence of Antimicrobial Resistance among Shigella Isolates in the United States Tested by the National Antimicrobial Resistance Monitoring System from 1999 to 2002." PubMed Central. New York, NY: NYU School of Medicine, 2006. 17 Nov. 2006 <http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pubmed&pubmedid=16377666#N0x84ceb98.0x92357c0#N0x84ceb98.0x92357c0>.

Sureshbabu, Jaya, and Poothirikovil Venugopalan. "Shigella Infection." EMedicine From WebMD. 12 Sept. 2006. WebMD. 10 Nov. 2006 <http://www.emedicine.com/ped/topic2085.htm>.

Toebe, Carol. "Microbial Metabolism." CCSF. City College of San Francisco. 17 Nov. 2006 <http://cloud.ccsf.edu/Departments/Biology/ctoebe/metab.htm>.

Edited by Deidre DeSilva, Kayleigh Erazmus, and Megan Harney under Dr. Kirk Bartholomew of Sacred Heart University, Fairfield, CT.

@@ Line 4: / Line 4: @@
-methyllobacillius flagellatus\
+==Classification:==
+===Higher order taxa:===
-==Background Information==
+	Bacteria (domain), Proteobacteria (phylum), Gammaproteobacteria (class), Enterobacteriales (order), Enterobacteriaceae (family), Shigella (genus)
+===Species:===
+	''Shigella dysenteriae, S. flexneri, S. boydii'', and ''S. sonnei''
+==Background Information:==
 ===History===
-Shigella organisms are a group of gram-negative pathogens, which were initially recognized as the causal agents of shigellosis (also known as bacillary dysentery) in the 1890s.  Shigella became an official genus in the 1950s, consisting of four species: ''S. dysenteriae'', ''S. flexneri'', ''S. boydii'', and ''S. sonnei''.  Each of these species have their own responsibilities.  ''S. dysenteriae'' serotype 1 causes deadly epidemics, ''S boydii'' is restricted to the Indian subcontinent, and ''S. flexneri'' and ''S. sonnei'' are prevalent in developing and developed countries, respectively. ''S. flexneri'', an enteroinvasive gram-negative bacterium, is responsible for the worldwide endemic form of bacillary dysentery.
+Shigella organisms are a group of gram-negative pathogens, which were initially recognized as the causal agents of shigellosis (also known as bacillary dysentery) in the 1890s and became an official genus in the 1950s. Each species has their own “niche”, which represents what the species main function or area is.  ''S. dysenteriae'' serotype 1 causes deadly epidemics mainly in developing countries, ''S boydii'' is restricted to the Indian subcontinent, and ''S. flexneri'' and ''S. sonnei'' are prevalent in developing and developed countries, respectively. ''S. flexneri'' is also responsible for the worldwide endemic form of bacillary dysentery.
 ===Description===
-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.
+Shigella is a non spore-forming gram-negative bacterium which aids in the facilitation of intracellular pathogens.  It is able to survive the proteases and acids of the intestinal tract, which allows the bacteria to infect in very small amounts, down to as few as 10 bacteria being necessary.
 ==Genome structure==
-The four different 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.
+The four different 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.
-==Structure and Life Functions==
+==Life Cycle==
+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.
-===Cell Structure===
+[[image:shigellalifecycle.jpg|center|thumb|750px|[[help:contents|Life cycle of Shigella bacteria; courtesy of Samuel Baron, Graduate School of Biomedical Sciences at UTMB.]]]]
-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.
-===Life Cycle===
-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.
-[[image:shigellalifecycle.jpg|center|thumb|750px|[[help:contents|Life cycle of Shigella bacteria; courtesy of Samuel Baron, Graduate School of Biomedical Sciences at UTMB.]]]]
+==Metabolism==
+Shigella pathogens use a mixed acid fermentation pathway to metabolize substrates. Products of this anaerobic pathway include ethanol, acetic acid, lactic acid, succinic acid, formic acid, and carbon dioxide.
-===Metabolism===
-Shigella pathogens use a mixed acid fermentation pathway to metabolize substrates. Products of this anaerobic  pathway include ethanol, acetic acid, lactic acid, succinic acid, formic acid, and CO2.
 ==Pathology==
 ===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.
+Fecal-oral transmission is the main path of shigella infection.  Other modes of transmission include ingestion of contaminated food or water, contact with infected objects, or sexual contact. Outbreaks of shigella 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 infection and 1 million shigella-related deaths annually, with 98% of those cases occurring in third world or developing nations.  Of the various strains of shigella, ''S. sonnei'' is the cause of 78% of infections.  ''S. flexneri'' and ''S. boydii'' are responsible for most of the remaining 22% of cases. The occurrence of ''S. dysenteriae'' is rare in developed countries, where sanitation conditions are satisfactory, but account for 30% of cases in under-developed areas.  The majorities of infections are reported during the summer season and occur mostly in teenagers and adolescents under the age of 15, hypothetically due to poor hygiene techniques. It is difficult to have an extremely accurate gauge of the actual number of cases that occur, since 90-95% of shigella infections are typically asymptomatic and thus unreported.
-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==
+High Prevalence of Antimicrobial Resistance among Shigella Isolates in the United States Tested by the National Antimicrobial Resistance Monitoring System from 1999 to 2002, Sivapalasingam, S., Nelson, J. M., Joyce, K., Hoekstra, M., Angulo, F. J., and Mintz, E. D.  This information on shigella's resistance to various antibiotics will help in treating shigellosis.  [http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pubmed&pubmedid=16377666#N0x84ceb98.0x902c5f0#N0x84ceb98.0x902c5f0 Click this hyperlink for the full text of this article.]
-High Prevalence of Antimicrobial Resistance among Shigella Isolates in the United States Tested by the National Antimicrobial Resistance Monitoring System from 1999 to 2002, Sivapalasingam, S., Nelson, J. M., Joyce, K., Hoekstra, M., Angulo, F. J., and Mintz, E. D.
--This information on shigella's resistance to various antibiotics will help in treating shigellosis.  [http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pubmed&pubmedid=16377666#N0x84ceb98.0x902c5f0#N0x84ceb98.0x902c5f0 Click this hyperlink for the full text of this article.]
 ==References==