Enterobacteriaceae
Enterobacteriaceae are widely distributed and have a large host range, and are parasitic or symbiotic, epiphytic, and saprophytic in humans, animals, and plants, and can also live in soil or water, and are closely related to humans. Enterobacteriaceae bacteria are easy to culture and reproduce quickly (under suitable conditions every 20-30 minutes can proliferate 1 generation). Some species such as E. coli are important materials for the study of genetics and molecular biology.
Enterobacteriaceae include non-budding, periphytic flagellated or non-flagellated Gram-staining negative straight bacilli. It is a chemo-energetic organic nutrition, both respiratory and fermentation metabolism; it can obtain energy by oxidizing many simple organic compounds or fermenting sugars, organic acids or polyols; most species can grow on inorganic nitrogen medium containing a carbon source;
Some species need some kind of amino acids or water-soluble vitamins when growing; in addition to individual serotypes, contact enzymes are positive, oxidase negative; in addition to a few species in the genus Owenia, all reduce nitrate to nitrite; DNA (deoxyribonucleic acid) in the G + C (guanine and cytosine) gram molecular content of 39-59%.
Classification basis
Fermentation reaction and serum reaction are important bases for the classification of Enterobacteriaceae bacteria. There are two main pathways for the fermentation of sugars: one is to metabolize the main end products as mixed organic acids, including succinic acid, lactic acid, acetic acid and formic acid; the other metabolizes the main end products as neutral solvents, including ethanol and butanediol. In the former pathway, if there is formic acid dehydrogenase, the bacteria ferment sugars to produce considerable amounts of carbon dioxide and hydrogen in a ratio of 1:1.
The latter pathway produces carbon dioxide in the formation of butanediol, and the ratio of carbon dioxide to hydrogen is greater than 1. The detection of the fermentation pathway and the ability to utilize certain sugars for fermentation is an important basis for the division of the Enterobacteriaceae into clades and genera.
Taxonomic system
Since 1937, when Rahn proposed the establishment of Enterobacteriaceae, the range of the included genera has changed several times. Generally, the family is divided into 5 families and 12 genera, and the main identifying characteristics of each family and genus are shown in the following table.
Main distinguishing features
Clades and genera G + C gram molecular % optimum growth temperature fermentation products power to lactose fermentation from sugar gas production Remarks
1.Eichiaceae tribe
①Eichia genus 50-53 37℃ mixed acid + + + + enteric pathogens
②Edwardsella spp. 50-53 37℃ mixed acid + – + enteric pathogens
Citrobacter spp. 50-53 37℃ mixed acid + + + + enteric pathogens
④Salmonella spp. 50-53 37℃ mixed acid + – + enteric pathogens
⑤ Shigella spp. 50-53 37℃ mixed acid – mostly negative – enteric pathogens
2.Klebsiella family
①Klebsiella spp. 52-59 37℃ Neutral solvent – ± + respiratory pathogens, red pigment producing
② Enterobacteriaceae 52-59 37℃ neutral solvent + + + + respiratory pathogens, red pigment production
③Havnibacter spp. 52-59 37℃ Neutral solvent + + (late) + respiratory pathogens, red pigment production
④Salesella 52-59 37℃ neutral solvent + ± (late) ± respiratory pathogens, red pigment production
3.Amoeba family
①Amoeba spp. 39-42 37℃ mixed acid and neutral solvent + – +
4.Yersinia pestis
Yersinia spp. 45-47 30-37°C mixed acid ± mostly negative (late) – rodent and human pathogenic bacteria
5.Owen’s family
①Owenella spp. 50-58 27-30°C mixed acid and neutral solvent + – ± plant pathogenic bacteria +: positive; ±: mostly positive; -: negative [1] common species
Escherichia coli
①Esherichia spp.: including five species, namely Escherichia coli, Escherichia cockroach, Escherichia fergusonii, Escherichia hermannii, and Escherichia wounderi. The GC ratio of bacterial DNA of this genus is 48% to 52%. The most common clinical species is Escherichia coli. Escherichia coli is commonly known as Escherichia coli, and most strains are normal flora of the human and animal intestines. Pathogenicity: mainly invasiveness, endotoxin, enterotoxin and other pathogenic factors cause various inflammatory diseases (such as cholecystitis, urinary tract infection, pneumonia, neonatal meningitis, wound infection, bacteremia and diarrhea, etc.). Endotoxin can also cause fever, shock, DIC, etc.
② Salmonella spp.: body size (0.6 ~ 0.9) microns × (1 ~ 3) microns, no spores, generally no pods, except for chicken dysentery Salmonella and chicken typhoid Salmonella, most of the circumference of the flagellum. Salmonella bacteria through the animal’s digestive tract infectious disease, collectively known as salmonellosis. Disease type typhoid and paratyphoid (collectively called enteric fever), food poisoning, septicemia, can also cause chronic enteritis.
Shigella spp.: The genus is the causative agent of human bacteriophage dysentery, commonly known as dysentery bacilli. Bacterial body size (0.5 ~ 0.7) microns × (2 ~ 3) microns, no spores, no flagella, no pods, some strains of bacteria have hairs, aerobic or partly anaerobic, can grow on ordinary media.
④ Klebsiella spp.: short and thick, no flagellum, with pods, bacterium size (0.3 ~ 1.5) microns × (0.6 ~ 6.0) microns, single, in pairs or short chain arrangement, partly anaerobic, nutrient requirements are not high, in solid medium to form a characteristic mucus-like colonies. Present in nature such as soil, water, cereals and in the respiratory tract of humans or animals. When the immunity of the muscle is reduced, it can cause a variety of infections. There are three species of Klebsiella pneumoniae, Klebsiella odorata and Klebsiella nasalis sclerotiorum.
⑤ Serratia spp.: can produce non-water-soluble yellow, purple and red pigments. Generally present in soil, water, plants, animals and human intestinal and respiratory tracts. There are mucoid Serratia, Serratia liquefaciens, and Serratia crimsonis. The slimy Serratia, also known as Listeria monocytogenes, is the smallest of the bacteria, surrounded by flagella, can move, no pods, no budding spores, about half of the strains can produce red Listeria monocytogenes. Because the bacteria are small and pigmented, often used to check the quality of the filter.
(6) Anaplasma genus: is a class of no bacterium, no pods, circumferential flagella, active, both ends of the blunt round small rod bacteria. Bacterial size (0.4 ~ 0.6) microns × (1.0 ~ 3.0) microns, part-time anaerobic, water, soil, gutter and a variety of rotten animals and plants in the most, they are conditionally pathogenic bacteria, in special circumstances can make people sick.
(7) Yersinia genus: oval, short bacilli. Bacterial body size (0.5 to 1.0) microns × (1.0 to 2.0) microns. No bacterium, no pods, part-time anaerobic. The genus has three species of Mycobacterium plague, Mycobacterium pseudotuberculosis and Mycobacterium enterocolitica. Mycobacterium plague is the causative agent of plague. Plague is often prevalent in rodents before it is prevalent in the population. After human plague, it can be spread in humans through human fleas or the respiratory tract (pulmonary type).