Enterobacteriaceae Bacteria of 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. The bacterium is a chemotrophic organic nutrition, both respiratory and fermentative metabolism; can obtain energy by oxidizing a variety of simple organic compounds or fermenting sugars, organic acids or polyols; most species can grow on inorganic nitrogen medium containing a carbon source; some species require some amino acids or water-soluble vitamins for growth; except for individual serotypes, contact enzymes are positive and oxidase negative; except for a few species in the genus Owenella, all Reduced nitrate to nitrite; DNA (deoxyribonucleic acid) in the G + C (guanine and cytosine) gram molecular content of 39 to 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 a considerable amount 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 fermentation pathways and the ability to use certain sugars to ferment is an important basis for the division of 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 distinguishing features of each family and genus are shown in the following table. Main identifying characteristics Clade and genus G + C gram molecular % optimum growth temperature fermentation product power to lactose fermentation from sugar gas production Remarks 1, Escherichia colony ① Escherichia genus 50-5337 ℃ mixed acid ++ + enteric pathogens ② Edwardsiella genus 50-5337 ℃ mixed acid +- + enteric pathogens ③ Citrobacter genus 50-5337 ℃ mixed acid ++ + enteric pathogens ④ Salmonella genus 50- 5337℃ mixed acid +-+ intestinal pathogens ⑤ Shigella spp. 50-5337℃ mixed acid – mostly negative – intestinal pathogens 2, Klebsiella spp. ① Klebsiella spp. 52-5937℃ neutral solvent -±++ respiratory pathogens, red pigment production ② Enterobacter spp. 52-5937℃ neutral solvent +++ respiratory pathogens, red pigment production ③ Hafniella spp. 52-5937℃ neutral solvent ++(late)+ respiratory pathogens, red pigment production ④ Salmonella spp. 52-5937°C neutral solvent +±(late)± respiratory pathogens, red pigment production 3, Aspergillus spp. ① Aspergillus spp. 39-4237°C mixed acid and neutral solvent +-+ 4, Yersinia spp. ① Yersinia spp. 45-4730-37°C mixed acid ± mostly negative (late)- rodent and human pathogenic bacteria 5 , Owen’s family ①Owen’s genus 50-5827-30°C mixed acid and neutral solvent +-± plant pathogenic bacteria +: positive; ±: mostly positive; -: negative [1] common species Escherichia coli ①Eicheria genus: including five species, namely Escherichia coli, Escherichia cockroach, Escherichia fergusonii, Escherichia hermanni and Escherichia wound. The GC ratio of bacterial DNA of this genus is 48%. 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, bacteraemia 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 flagella, 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 mucilaginous Serratia, Serratia liquefaciens, and Serratia crimsonis. The slimy Serratia marcescens, 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. 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).