E.coli
overviwe E. coli is a Gram negative rod-shaped bacterium that is commonly found in the lower intestine of warm-blooded organisms. Most E. coli strains are harmless, but some, such as serotype O157:H7, can cause serious food poisoning in humans, and are occasionally responsible for product recalls.the harmless strains are part of the normal flora of the gut, and can benefit their hosts by producing vitamin K2, and by preventing the establishment of pathogenic bacteria within the intestine.the worst type of E. coli, known as E. coli O157:H7, causes bloody diarrhea and can sometimes cause kidney failure and even death.
overview Domain: Bacteria Kingdom: Bacteria Phylum: Proteobacteria Class: Gamma Proteobacteria Order: Enterobacteriales Family: Enterobacteriaceae Genus: Escherichia Species: Escherichia coli (E. coli)
Discoverer Escherichia coli was discovered by Theodor Escherich in 1885 after isolating it from the feces of a newborn. At first it was described as Bacterium coli commune, but then it was later named Escherichia coli (named for Escherich... who would've thought?). It wasn't until 1935, however, that it was found that E. coli was the cause of diarrhea in newborns!
Features: 1. Gram-negative (G-) bacterium with an outer membrane composed primarily of lipopolysaccharides 2.rod-shaped facultatively anaerobic G- bacterium. 3. motile via peritrichous flagella that grows well at 37oC, is Oxidase negative, Catalase positive, and reduces nitrates. 4.mostly opportunistic flora that are enteric (colonize in the intestinal tract of mammals). 5.ferments lactose, possesses lysine decarboxylase, is Vogus-Proskauer negative, produces indole, doesn't grow on nitrate, and doesn't produce H2S.
dark, with a metallic green sheen Features of bacterial colony
Tree of life
Metabolism a heterotrophic organism: main source of carbon comes from glucose molecules ingested by its host organism. This is then broken down into useable carbon by means of central metabolism, which consists of three steps: 1. Embden-Meyerhof-Parnas (EMP) Pathway: converts glucose to pyruvate 2. Tricarboxylic Acid (TCA) cycle: oxidizes Acetyl CoA to CO2 3. Pentose Phosphate Cycle (PPP): oxidizes glucose to CO2
classification standard: 1. serological characterisitics 2. virulence properties
1ETEC Name: Enterotoxigenic E. coli (ETEC) Hosts: causative agent of diarrhea (without fever) in humans, pigs, sheep, goats, cattle, dogs, and horses Description: ETEC uses fimbrial adhesins (projections from the bacterial cell surface) to bind enterocyte cells in the small intestine. ETEC can produce two proteinaceous enterotoxins: the larger of the two proteins, LT enterotoxin, is similar to cholera toxin in structure and function. the smaller protein, ST enterotoxin causes cgmp accumulation in the target cells and a subsequent secretion of fluid and electrolytes into the intestinal lumen. ETEC strains are non-invasive, and they do not leave the intestinal lumen. ETEC is the leading bacterial cause of diarrhea in children in the developing world, as well as the most common cause of traveler's diarrhea. Each year, ETEC causes more than 200 million cases of diarrhea and 380,000 deaths, mostly in children in developing countries.
2. EPEC Name: Enteropathogenic E. coli (EPEC) Hosts: causative agent of diarrhea in humans, rabbits, dogs, cats and horses Description: Like ETEC, EPEC also causes diarrhea, but the molecular mechanisms of colonization and etiology are different. EPEC lack fimbriae, ST and LT toxins, but they utilize an adhesin known as intimin to bind host intestinal cells. This virotype has an array of virulence factors that are similar to those found in Shigella, and may possess a shiga toxin. Adherence to the intestinal mucosa causes a rearrangement of actin in the host cell, causing significant deformation. EPEC cells are moderately invasive (i.e. they enter host cells) and elicit an inflammatory response. Changes in intestinal cell ultrastructure due to "attachment and effacement" is likely the prime cause of diarrhea in those afflicted with EPEC.
3. EIEC Name: Enteroinvasive E. coli (EIEC) Hosts: found only in humans Description: EIEC infection causes a syndrome that is identical to Shigellosis, with profuse diarrhea and high fever.
4.EHEC Name: Enterohemorrhagic E. coli (EHEC) Hosts: found in humans, cattle, and goats Description: The most famous member of this virotype is strain O157:H7, which causes bloody diarrhea and no fever. EHEC can cause hemolytic-uremic syndrome and sudden kidney failure. It uses bacterial fimbriae for attachment (E. coli common pilus, ECP), is moderately invasive and possesses a phage-encoded Shiga toxin that can elicit an intense inflammatory response.
5. EAEC Name: Enteroaggregative E. coli (EAEC) Hosts: found only in humans Description: So named because they have fimbriae which aggregate tissue culture cells, EAEC bind to the intestinal mucosa to cause watery diarrhea without fever. EAEC are noninvasive. They produce a hemolysin and an ST enterotoxin similar to that of ETEC.
role in biology 1.engineering bacteria Advantages: long history of laboratory culture and ease of manipulation Application: play an important role in modern biological engineering and industrial microbiology. 1. a very versatile host for the production of heterologous proteins,researchers can introduce genes into the microbes using plasmids, allowing for the mass production of proteins in industrial fermentation processes. 2.Genetic systems have also been developed which allow the production of recombinant proteins using E. coli.e.g.the manipulation of E. coli to produce human insulin. 3.Modified E. coli have been used in vaccine development, bioremediation, and production of immobilised enzymes.
2.model organism E. coli is frequently used as a model organism in microbiology studies. Cultivated strains (e.g. E. coli K12) are well-adapted to the laboratory environment, and, unlike wild type strains, have lost their ability to thrive in the intestine. Many lab strains lose their ability to form biofilms.these features protect wild type strains from antibodies and other chemical attacks, but require a large expenditure of energy and material resources.
Reproduction asexual reproduction:cellular division ( This is the most prevalent form of reproduction for E. coli. ) The individual bacterium begins this process by elongation of the cell, followed by almost exact replication of the genome so there are two identical copies. Mutations and mistakes may happen during genetic replication, but normally these occur in small numbers and don't have a large effect on the bacterium. A septum is formed, and the cell equally divides the cellula components and one copy of the parental genome gets placed in each side of the cell. The cell divides, leaving two copies of the original bacterium called daughter cells.
evolvement 1. horizontal gene transfer 2.mutation
Where can we find E.coli? The primary habitat of Escherichia coli is in the gastrointestinal (GI) tract of humans and many of the warm blooded animals.
Relationship with our human being There are many bacteria that can be found in the human body, and most of them are strict anaerobes. However, E. coli is the most abundant facultatively anaerobic microorganism that is found in the GI tract of humans and mammals. The average human GI tract contains upwards of 1 kg (~2.21 lb) of bacteria, and approximately 0.1-1% of these are E. coli. In fact, these bacteria appear in the body just a few hours after birth. Don't let this scare you, because most of these E. coli bacteria are harmless opportunistic organisms. The E. coli actually forms a mutualistic relationship with its host. The bacteria normally adhere to the mucus or the epithelium on the wall of the intestines (which is critical, otherwise most E. coli will not grow in that particular area), and a single strain can last for months or years
Pathogenicity If someone has eaten foods contained E. coli O157:H7, he would become very ill and be in need of medical attention. Unfortunately, there is more than one pathogenic strain of E. coli.there are over 700 serotypes of E. coli. These are based on three different antigens: 1.the O antigen which is derived from the cell wall, 2.the H antigen which is derived from flagella that are used for motility 3.the K antigen which is derived from a polysaccharide capsule that is secreted. Most of these specific strains can be further divided into three more categories based on how they infect the human body: Urinary Tract Infections (UTI), Neonatal Meningitis, and Intestinal Diseases (gastroenteritis).
1. Urinary Tract Infections 90% of UTI's are caused by Uropathogenic E. coli (UPEC). This is caused by E. coli colonizing in the feces and/or the perineal region, and then somehow ascending to the urethra (the urinary tract) and finally the bladder causing inflammation. The bacteria are able to adhere and aggregate to the urethra and the bladder by use of fimbriae. The movement of E. coli can occur during sexual intercourse, wiping back to front after using the restroom, among other ways, and are more common in females.
2. Neonatal Meningitis Neonatal Meningitis (inflammation of the meninges), which affects 1/2000 infants, is caused by E. coli strains invading the either the nasopharynx or the GI tract, absorbed into the bloodstream, and then the blood carries the bacteria to the meninges. This is treated by antibiotic therapy, most often with ampicillin. This can be fatal if untreated.
3.GI infections Intestinal mucosa-associated E. coli are observed in increased numbers in the inflammatory bowel diseases, Crohn's disease and ulcerative colitis. Invasive strains of E. coli exist in high numbers in the inflamed tissue, and the number of bacteria in the inflamed regions correlates to the severity of the bowel inflammation
Epidemiology Transmission. of pathogenic E. coli : via fecal-oral transmission Common routes of transmission include: 1.unhygienic food preparation 2.farm contamination due to manure fertilization, 3.irrigation of crops with contaminated greywater or raw sewage 4.feral pigs on cropland 5. direct consumption of sewage-contaminated water. Shiga toxin-producing E. coli (STEC), specifically serotype O157:H7, have also been transmitted by flies as well as direct contact with farm animals, petting zoo animals,and airborne particles found in animal-rearing environments. Dairy and beef cattle are primary reservoirs of E. coli O157:H7, and they can carry it asymptomatically and shed it in their feces.food products associated with E. coli outbreaks include raw ground beef, raw seed sprouts or spinach, raw milk, unpasteurized juice, unpasteurized cheese and foods contaminated by infected food workers via fecal-oral route. [
prevention by cooking food properly, preventing cross-contamination, instituting barriers such as gloves for food workers, instituting health care policies so food industry employees seek treatment when they are ill, pasteurization of juice or dairy products and proper hand washing requirements.
Vaccines Researchers have actively been working to develop safe, effective vaccines to lower the worldwide incidence of E. coli infection. 1. In March 2006, a vaccine eliciting an immune response against the E. coli O157:H7 O-specific polysaccharide conjugated to recombinant exotoxin A of Pseudomonas aeruginosa was reported to be safe in children two to five years old. Previous work had already indicated that it was safe for adults.a phase III clinical trial to verify the large-scale efficacy of the treatment is planned. 2.In 2006 Fort Dodge Animal Health (Wyeth) introduced an effective live attenuated vaccine to control airsacculitis and peritonitis in chickens. The vaccine is a genetically modified avirulent vaccine that has demonstrated protection against O78 and untypeable strains. 3.In January 2007 the Canadian bio-pharmaceutical company Bioniche announced it has developed a cattle vaccine which reduces the number of O157:H7 shed in manure by a factor of 1000, to about 1000 pathogenic bacteria per gram of manure. 4.In April 2009 a Michigan State University researcher announced that he has developed a working vaccine for a strain of E. coli.
Antibody and Resistance Bacterial infections are usually treated with antibiotics. However, the antibiotic sensitivities of different strains of E. coli vary widely. As Gram-negative organisms, E. coli are resistant to many antibiotics that are effective against Gram-positive organisms. Antibiotics which may be used to treat E. coli infection include amoxicillin as well as other semisynthetic penicillins.antibiotic resistance is a growing problem. Some of this is due to overuse of antibiotics in humans, but some of it is probably due to the use of antibiotics as growth promoters in food of animals Resistance to beta-lactam antibiotics has become a particular problem in recent decades, as strains of bacteria that produce extendedspectrum beta-lactamases have become more common. These betalactamase enzymes make many, if not all, of the penicillins and cephalosporins ineffective as therapy. Extended-spectrum betalactamase producing E. coli are highly resistant to an array of antibiotics and infections by these strains is difficult to treat. In many instances, only two oral antibiotics and a very limited group of intravenous antibiotics remain effective.