Bacillus hay

Bacillus subtilis is a kind of Bacillus. Single cell is 0.7 ~ 0.8× 2 ~ 3 microns, and the color is uniform. No capsule, no periflagella, you can exercise. Gram-positive bacteria, the spore is 0.6 ~ 0.9× 1.0 ~ 1.5 micron, oval to columnar, located in the center or slightly below the cell, and the cell does not swell after spore formation. The surface of colonies is rough and opaque, dirty white or yellowish, and wrinkles often form when they grow in liquid culture medium. Aerobic bacteria protein, various sugars and starch can be used to decompose tryptophan to form indole. Some strains are important producers of α -amylase and neutral protease; Some strains have strong nucleotide degrading enzyme system, so they are often used to cultivate new strains of nucleoside-producing bacteria or produce 5'- nucleotidase. It is widely used in genetic research, and the synthesis pathway and regulation mechanism of purine nucleotide of this strain are clearly studied Widely distributed in soil and decaying organic matter, it is easy to reproduce in the juice of hay, hence the name.

2. Escherichia coli

E. Escherichia coli is the representative bacterium of Escherichia coli. Generally speaking, it is not pathogenic, and it is a common bacteria in human and animal intestines, which can cause parenteral infection under certain conditions. Some serotype strains are highly pathogenic and cause diarrhea, which are collectively called pathogenic Escherichia coli.

I. Biological characteristics

Morphology and staining

The size is 0.4 ~ 0.7× 1 ~ 3um, without spores, and most strains have power. There are common fimbriae and sexual fimbriae, and some strains have polysaccharide coating and gram-negative bacilli.

(2) Cultivation characteristics

On blood agar plate, some strains produced β hemolysis. Smooth colonies with color and diameter of 2 ~ 3 mm are formed on differentiation medium or selective medium.

Biochemical reaction: most strains ferment lactose to produce acid and gas, and ferment glucose, malt cells, mannitol, wood gum sugar and Arabic gum to produce acid and gas. IMViC test is "+,+,-,-". It is a typical Escherichia coli.

(3) antigen structure

It is complicated, with four antigens: O, K, H and F. O antigen is lipopolysaccharide with 17 1 species, of which 162 is related to diarrhea, which is the basis of grouping. There are 103 kinds of K antigen, which are lipopolysaccharide antigens. Most of the newly isolated Escherichia coli from patients have K antigen, which has anti-phagocytosis and complement sterilization effects. According to the difference of heat resistance, K antigen can be divided into L, A and B, among which L and B are not heat-resistant, with a total of 60 kinds. There are at least five kinds of F antigens, which are related to the adhesion of E.coli. The serotypes of E.coli are expressed by O: K: H, such as O11:K58 (B4): H2.

(4) Resistance

This strain has stronger heat tolerance than other enterobacteria, and some bacteria still survive after 60 minutes at 55℃ or 60℃ 15 minutes. It can survive in natural water for weeks to months, and it can survive longer in low-temperature feces. Bile salt, bright green, etc. have inhibitory effect on Escherichia coli. Sensitive to sulfonamides, streptomycin and chloramphenicol. , but easy to resist, is obtained by plasmid transfer with r factor.

Second, pathogenicity.

(1) pathogenic substance

1. settlement factor, cf); Also known as adhesin, the pili of Escherichia coli. Pathogenic Escherichia coli should first adhere to the intestinal wall of the host to avoid being removed by intestinal peristalsis and intestinal secretions. CFAⅰⅰ and CTA ⅱ (settlement factor antigens ⅰ and ⅱ) are settlement factors that cause human diarrhea. Colonization factors have strong immunogenicity and can stimulate the body to produce specific antibodies.

2. Enterotoxin: an exotoxin released by enterotoxigenic Escherichia coli during its growth and reproduction, which can be divided into two types: heat-resistant and heat-labile.

(1) Heat-resistant enterotoxin (LT): unstable to heat and inactivated after 30 minutes at 65℃. Protein has high molecular weight and immunogenicity. It consists of two subunits, A and B. A is further divided into A 1 and A2, where A 1 is the active site of toxin. After B subunit binds to GM 1 ganglioside receptor on intestinal epithelial cell membrane, A subunit crosses the cell membrane and interacts with adenylate cyclase to convert intracellular ATP into cAMP. When cAMP rises, it leads to excessive secretion of small intestinal juice, which exceeds the absorption capacity of the intestine and leads to diarrhea. The immunogenicity of LT is similar to that of Vibrio cholerae enterotoxin, and their antiserum is cross-neutralized.

(2) Heat-stable enterotoxin (ST): it is stable to heat, and will not be destroyed after 20 minutes at100℃, with small molecular weight and weak immunogenicity. ST can activate guanylate cyclase in intestinal epithelial cells, increase cGMP in cells, change the movement of fluid in jejunum, and cause intestinal effusion and diarrhea. ST has no common antigenic relationship with cholera toxin.

Some enterotoxigenic Escherichia coli strains produce only one enterotoxin, namely LT or ST; Others can have both. Some pathogenic Escherichia coli can also produce vero toxin.

3. Others: Lipoid A of cell wall lipopolysaccharide is toxic, and O- specific polysaccharide can resist the host defense barrier. K antigen of Escherichia coli has phagocytosis.

(2) Diseases caused by

1. Parenteral infection: mostly endogenous infection, mainly urinary tract infection, such as urethritis, cystitis, pyelonephritis, ascending urinary tract infection, etc., more common in married women. It can also cause peritonitis, cholecystitis and appendicitis. Escherichia coli can invade the blood and cause septicemia in infants, the elderly, the infirm, patients with chronic wasting diseases and patients with extensive burns. Premature infants, especially newborns within 30 days after birth, are prone to E.coli meningitis.

2. Acute diarrhea: Some serotypes of Escherichia coli can cause human diarrhea. According to different pathogenesis, it can be divided into four types.

(1) Enterotoxigenic Escherichia coli (ETEC): causes diarrhea in infants and tourists, ranging from watery diarrhea to cholera-like symptoms. Diarrhea is often self-limited, and it usually heals in 2 ~ 3 days. Malnutrition can last for weeks or recur. The pathogenic factors are LT or ST, or both. Some strains have colonization factors, such as O6: K 15: H 16, O25: K7: H42. The identification of ETEC mainly determines the enterotoxin of Escherichia coli, and its serotype has certain reference significance.

(2) Enteropathogenic Escherichia coli (EPEC) is the main pathogen of infantile diarrhea, which is highly contagious and can be fatal in severe cases; Adults are rare. After bacteria invade the intestine, they mainly reproduce in the duodenum, jejunum and upper ileum. Slice specimens showed that bacteria adhered to villi, which led to the destruction of brush border, villi atrophy, disordered arrangement of epithelial cells and impaired function, leading to severe diarrhea. EPEC does not produce LT or St, and it is reported that EPEC can produce an enterotoxin encoded by phage, which is called VT toxin, because it is toxic to Vero cells (green monkey kidney passage cell). VT toxin is similar to Shigella toxin in structure and function, and has neurotoxicity, cytotoxicity and enterotoxicity. EPEC can be identified according to clinical manifestations and serotypes.

Most strains of EIEC have no motivity, and their biochemical reaction and antigen structure are similar to those of Shigella dysenteriae, which should be paid attention to. EIEC can cause keratitis in guinea pigs, which is helpful to distinguish EIEC in clinic.

(4) Enterohemorrhagic Escherichia coli (EHEC): It can cause sporadic or fulminant hemorrhagic colitis and produce Shiga toxin-like cytotoxin. The main bacterial types of EHCO are O 157: H7, and there are also O26 and O ⅲ.

Table 9-2 Escherichia coli causing acute diarrhea

In addition, enteroadhesive Escherichia coli (EAEC) can also cause diarrhea, but its pathogenesis and serotype are still unknown. EAEC does not invade intestinal epithelial cells, does not produce LT or ST, and has no VT toxin. Its uniqueness lies in its ability to adhere to Hep-2 cells (human laryngeal epithelial cell cancer cell line), so it is also called Hep-2 cell adhesive Escherichia coli.

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