Enterobacter belongs to Enterobacteriaceae, and there are many kinds. According to biochemical reaction, antigen structure, nucleic acid hybridization and sequence analysis, there are currently 44 genera of Enterobacteriaceae. There are 10 genera related to medicine, including 25 strains of Escherichia, Shigella, Salmonella, Klebsiella, Proteus, Morgan, Citrobacter, Enterobacter, Serratia and Yersinia. Most of them are normal flora in the intestine, but when the host immunity decreases or bacteria move out of the intestine, they can become conditional pathogens and cause diseases. Only a few are pathogenic bacteria, such as Shigella, Salmonella typhi and a few Escherichia coli.
Enterobacter has the following biological characteristics:
1. Morphological and structural similarity is (0.3~ 1.0)×( 1~6)? M medium-sized Gram-negative bacilli, with round ends and no spores, most of them have flagella and fimbriae, and a few have capsules.
2. Aerobic or facultative anaerobic bacteria have low culture requirements and grow well on ordinary agar plates, forming smooth and moist medium-sized colonies; Some bacteria can appear hemolysis ring on blood agar plate, and grow evenly and turbid in liquid culture.
3. This active biochemical reaction can decompose various sugars and protein, which is often used to identify bacteria and strains. Lactose fermentation test is of great significance in the preliminary identification of intestinal pathogenic bacteria and non-pathogenic bacteria. Pathogenic bacteria generally do not decompose lactose, while most non-pathogenic bacteria can decompose lactose.
4. The complex antigen structure mainly includes bacterial (O) antigen, flagella (H) antigen and capsule (K) antigen or envelope antigen. Others have fimbriae antigens. (1)O antigen: It exists in the lipopolysaccharide (LPS) layer of the cell wall and has genus and species specificity. Its specificity depends on the arrangement of sugar residues in polysaccharide chain with repeated structure at the end of LPS molecule. O antigen is heat-resistant and will not be destroyed at 100℃. Most colonies of newly isolated strains from patients are smooth (S) type. After repeated subculture and preservation in artificial culture medium, LPS lost its external O-specific side chain, and the colony became rough (R) type, which was called S-R type variation. The virulence of R strain was obviously lower than that of S strain. (2)H antigen: It exists in flagellin. Not heat resistant, it will be destroyed at 60℃ for 30 minutes. The specificity of H antigen depends on the arrangement order and spatial structure of amino acids in polypeptide chain. After the bacteria lose flagella, the movement disappears; Exposure to O antigen at the same time is called H-O mutation. (3) Envelope or envelope antigen: located at the periphery of O antigen, which can prevent O agglutination. The ingredient is polysaccharide, but it can be destroyed at 60℃ for 30 minutes. What is important is the Vi antigen of Salmonella typhi and the K antigen of Escherichia coli.
5. The reason why the resistance is not strong is that there are no spores and the resistance to physical and chemical factors is not strong. Generally, it dies after heating at 60℃ for 30 minutes, which is easy to be killed by general disinfectants. Chlorine is usually used to disinfect drinking water. Bile salt, bright green, etc. Can selectively inhibit non-pathogenic bacteria such as Escherichia coli, and can prepare enterobacteria selective culture medium to separate enteropathogenic bacteria.
6. The mutable Enterobacteriaceae bacteria are easy to produce mutant strains. In addition to spontaneous mutation, because they are in the same close contact with each other, genetic material can be transferred through transduction, conjugation or lysogenic transformation, thus enabling recipient bacteria to acquire new characters and lead to mutation. The most common changes are drug resistance transfer, toxin production and biochemical reaction characteristics. It is of great significance in pathogenicity, bacteriological diagnosis, treatment and prevention.