Escherichia coli (scientific name:Escherichia coli）, also calledEscherichia coli。yesEnterobacteriaceaeEscherichiaIt was discovered by German Austrian pediatrician Theodor Escherichy in 1885.Escherichia coli is mainly parasitic in the large intestine of humans and animals, accounting for about 1% of intestinal bacteria.
Escherichia coli is a kind of gram-negative, facultative anaerobic, rod-shaped, rod-shaped, Escherichia coli bacteria with blunt ends, mobility, and no spores. It is common in the warm blooded organisms in the lower part of the small intestine.[5]
E. coli is conditionally inducedgermsUnder certain conditions, it can cause gastrointestinal tract infection or urethra and other local tissues and organs infection in humans and many animals.[1]
In 1885, Theodor Escherich, a German Austrian pediatrician, tried to find outcholeraHe isolated this organism from the feces of healthy people because it exists incolon(colon), it is initially named“Bacterium coli commune”。[6]
Note:prokaryoteAccording to its shape and mobility, Ernst Haeckel classified it into a few genera in the early stage of classification. At that time, Ernst Haeckel had already classified bacteria in the Monera.
In the case of bacteria（Bacterium）After revision, Migula reclassified it as“Bacillus coli”Later, Aldo Castellani and Albert John Chalmers reclassified it as a newly created genus of Escherichia（Escherichia）, with the inflectional ending of the name of its original discoverer, and often withE. colia sign.[11]
Escherichia coli（Escherichia）Enterobacteriaceae, butEnterobacteriaceaeThe scientific name of is not "Escherichiaceae", but "Enterobacteriaceae".[16]
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Escherichia coli is a short bacterium with round ends, which mostly exists alone or in pairs.
Escherichia coli is a kind of gram-negative, facultative anaerobic, rod-shaped, rod-shaped, Escherichia coli bacteria with blunt ends, mobility, and no spores. It is common in the warm blooded organisms in the lower part of the small intestine.[5]Most strains of Escherichia coli are harmless. The harmless strains are normal resident bacteria in the animal intestines, which can produce vitamin K and prevent the growth of other pathogenic bacteria in the intestines, and are beneficial to the human body.However, a small part of them cause diseases under certain conditions. Some serotypes (EPEC, ETEC, etc.) of E. coli can cause serious food poisoning in their hosts, and occasionally lead to food contamination incidents of product recalls. This is mainly caused by specific fimbriae antigens, pathogenic toxins, and other infections. In addition to gastrointestinal tract infections, it can also causeurinary-tract infection, arthritis, meningitis, and septicemia[1]。
Escherichia coli is often spread to the environment through fecal discharge. They will breed in fresh feces and oxygen rich environment for about 3 days, and then the number of bacteria will decline.[15]
This kind of bacteria can easily and cheaply grow and cultivate in the laboratory environment, and is widely used as a host for gene replication and expression in biological experiments.[12-13]Escherichia coli is also a chemotrophic type, and its chemical composition must be determined by the medium containing carbon source and energy.Escherichia coli is the most widely studied prokaryotic model organism, and also an important species in biotechnology and microbiology. In most work of recombinant DNA, it is a host organism.Under favorable conditions, replication takes only 20 minutes[14]。
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According to pathogenicity
According to the internationally recognized classification, there are mainly six kinds of Escherichia coli, namely Enteropathogenic Escherichia coli, which can cause gastrointestinal tract infectionE. coli, EPEC), enterotoxigenic Escherichia coli (enterotoxigenicE. coli, ETEC), enteroinvasive Escherichia coliE. coli, EIEC), enterohemorrhagic Escherichia coliE. coli, EHEC), enteroaggregative Escherichia coliE. coli, EAEC), as well as intestinal Shiga like toxin producing Escherichia coli (ESIES) with certain invasiveness found in recent years, and uropathic Escherichia coli that can cause urinary tract infectionE. coli, UPEC), and the newly named Intestinal Agglomerative Adhesive Escherichia coli (EAggEC)[1][17]。
According to hemolysis
Escherichia coli
According to the infection characteristics of Escherichia coli, whether it can produce hemolysin and whether it has hemolytic ability, Escherichia coli can be divided into two categories: hemolytic Escherichia coli and non hemolytic Escherichia coli[1]。
According to enterotoxin production
According to the ability of E. coli to produce enterotoxin during infection, E. coli can be divided into two categories: enterotoxigenic E. coli and non enterotoxigenic E. coli.Enterotoxigenic Escherichia coli is any of theInfectious diarrheaIdentification of enterotoxigenic Escherichia coli is mainly to determine the type of enterotoxin secreted by the isolated Escherichia coli.In addition, according to the ability of Escherichia coli to produce enterotoxin and its sensitivity to different enterotoxins, Escherichia coli can also be classified as enterotoxin type[1]。
Biological characteristics
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Physical and chemical properties
Escherichia coli is a short bacterium with blunt round ends and gram negative.Sometimes, due to different environments, individual bacteria appear similar to ball shaped or filament shaped;Escherichia coli mostly exists in a single or two forms, but does not arrange in a long chain shape;MostEscherichia coli strainIt has capsule or microcapsule structure, but can not form spores;Most Escherichia coli strains grow fimbriae, some of which are host specific fimbriae that have adhesive effects on the host and other tissues or cells[1]。
Biochemical characteristics
The biochemical metabolism of Escherichia coli is very active.Escherichia coli can ferment glucose to produce acid and gas. Some strains do not produce gas. Escherichia coli can ferment many kinds of bacteriacarbohydrateVarious organic acid salts can also be used.Among the commonly used biochemical characteristics of E. coli, methyl red test is positive, indole production and lactose fermentation are positive (some strains are negative), vitamin culture test is negative, urease and citrate utilization are negative (very few strains are positive), nitrate reduction test is positive, oxidase is negative, and oxidation fermentation test is F type[1]。
Pathogenic properties
For humans and many animals, pathogenic Escherichia coli often tends to have certain host specificity, and strains that have pathogenic effects on humans often rarely cause animal infection, and vice versa. According to this, pathogenic Escherichia coli can be roughly divided into two types: human pathogenic Escherichia coli and animal pathogenic Escherichia coli.The diarrhea causing Escherichia coli in animals has been clearly characterized by strains similar to ETEC.UPEC is one of the most common pathogenic Escherichia coli that can cause urinary tract infection in humans.Urethral infection rarely exists independently in animalsColibacillosisInfection symptoms in[1]。
Epidemiological characteristics
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regional distribution
The occurrence and epidemic infection of Escherichia coli are distributed worldwide, but the prevalence of Escherichia coli still has certain regional distribution characteristics.These regional distribution characteristics areE. coli infectionThe most obvious is that it is related to the economic conditions and social health conditions among regions[1]。
Susceptible host
Animal colibacillosis can occur in a variety of domestic animals, poultry, breeding economic animals, other terrestrial animals and some aquatic animals, of which pigs and chickens are the most susceptible, and the harm is very serious[1]。
Onset season
The seasonal onset characteristics of E. coli infection among animal populations are not very obvious.It can occur in all seasons of the year in pigs, but as long as it occurs from the farrowing stage to the weaning stage, it is related to the susceptible age of pigs.Calves and lambs usually occur in winter and spring.Escherichia coli infection of other animals occurs all year round, and the seasonality is not obvious[1]。
Source of infection and route of transmission
The main source of infection of human colibacillosis is that a large number of colibacillosis pathogens are discharged into the body in the feces of patients with gastrointestinal infection.The transmission of Escherichia coli among people is mostly through the fecal oral route, which can cause the sporadic or epidemic of colibacillosis under certain conditions[1]。
test method
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Rapid and accurate detection of escherichia coli in food has become a problem that people often pay attention to.The following describes the detection method and analysis of Escherichia coli in food[2]。
Fermentation
This method is mainly to culture Escherichia coli on the medium at 44.5 ℃, which contains fluorescent substrate and needs to be cultured for 24h.Then release the fluorescent substrate by usingGlucuronic acidTo make the medium fluoresce under ultraviolet light.In this way, the colony in the original sample can also be statistically estimated.The main steps include fermentationIsolation culture, secondary fermentation, microscope observation, etc[2]。
Filter membrane method
The main process of this method: add about 10mL of sterile water into the filter, and then add some sterile water to clean the inner wall of the filter, and then filter. Put the filter membrane in M-FC medium, without bubbles between the two, and then seal it. The storage temperature is 44.5 ℃, and the storage time is about 24h, until the coliform bacteria become blue or blue-green.Then record the data, estimate the number of bacteria in each unit of aqueous solution, and then convert the quantity of Escherichia coli[2]。
Plate counting method
Escherichia coli growing in culture medium
Use a sterile straw to suck 1mL of dilution sample, which is similar to the fermentation of lactose bile salt, and then put it into a sterile culture dish. Add 10mL of CDLJJD color developing medium at 45 ℃, and mix the solution in the culture dish evenly. You can quickly rotate the culture dish and add about 5mL after the solution is solidified[3]Then shake the medium quickly so that it can evenly cover the surface of the plate. After it has solidified, turn over the medium, incubate it at 37 ℃ for about 24h, and then observe the changes in its shape, color, etc.In addition, two dilution media are set in parallel. The step is to dilute the sample first. After dilution, the microorganism can be dispersed into a single cell, and then culture under certain environmental conditions until it grows into colonies. Then calculate the number of Escherichia coli through dilution and sample number[2]。
Immunomagnetic bead method
The main principle of this separation technology is to use magnetic beads as a carrier and antibody to combine antibody and magnetic beads, and then complete mechanical movement through magnetic technology to isolate Escherichia coli.Compared with other methods of isolating bacteria, this method has certain advantages. This technology can improve the detection success rate of pathogenic vibrio in samples, and the immune magnetic bead technology can treat different microorganisms in different strains, thus greatly improving the detection efficiency[2]。
Automatic instrument detection method
It mainly uses the immune automatic analyzer, which was produced and used in 1970.With the development and progress of science and technology, automatic instrument detection technology is widely used, and it is very convenient to operate, which can save a lot of time, and its degree of interference is small, which can save human and material investment, and can also improve the accuracy of detection.In the current development process, automatic enzyme immunoassay system is widely used[2]。
ATP bioluminescence method
In recent years, bioluminescence technology has been widely used in the development process. It is a relatively fast technology to detect microorganisms.In active cells, ATP is a common energy metabolism product, which can provide energy needed in the process of cell physiological activities.Moreover, the technology can maintain a certain content in the organism within a certain range.The detection technology of Escherichia coli in food can adopt the method of fluorescence, because the reason for the bioluminescence is the role of luciferase, which produces the luminous effect.The substance is from the body of fireflies in North America and can catalyze the oxidation of fluorescein. However, the substance is unstable and can rapidly decompose fluorescence.In addition, the process of obtaining the results of the detection technology is very fast, and the equipment is convenient to carry, which is very suitable for on-site detection[2]。
high-temperature sterilization
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Common bacterial propagules such as pathogenic Escherichia coli, typhoid bacillus, Vibrio cholerae, etc., which can cause diarrhea, need 5-10 minutes for hot water at 80 ℃, and 2-5 minutes for boiling water to kill。[4]
Biological value
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Escherichia coli is one of the most studied bacteria in modern biologyModel organismIts genome sequence has been completely determined.The conclusion obtained in Escherichia coli by molecular biological method can be used for the study of other organisms.In addition, in bioengineering, Escherichia coli is widely used as a host for gene replication and expression.[12-13]
Pathogenic event
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In 1996, an outbreak of E. coli food poisoning occurred in Weshaw, Scotland, resulting in 21 deaths[10]。This death toll isEpidemic situation of H4 type Escherichia coli in 2011Exceeded. This event is related to organic fenugreek sprouts, resulting in 53 deaths[7-9]。
