Gram positive bacteria

Bacterial name

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synonym Gram positive bacteria (Firmicutes) generally refers to gram-positive bacteria

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Gram positive bacteria and Gram negative bacteria Is using Gram staining come identify The two main types of bacteria. majority Pyogenic coccus They belong to gram-positive bacteria, which can produce exotoxin to cause disease, and most of them Intestinal bacteria More of Gram negative bacteria They produce endotoxin, which makes people sick.

Chinese scientific name: Gram positive bacteria
circles: Bacterial kingdom
door: Firmicutes

Outline: Bacillus
order: Lactobacteriales
Genus: Pyogenic coccus
Common species: Streptococcus, anthrax, etc

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▪ Infiltration theory
five Related research

brief introduction

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Gram positive bacteria

There are many kinds of bacteria in nature. How to identify and classify these bacteria and choose effective drugs for treatment is a very important issue.

1884 Gram staining The invention is used for morphological observation and classification of bacteria according to Gram staining reaction Bacteria can be mainly divided into two categories: G positive (G+) and G negative (G -). After the former is dyed, the bacterial cells still retain the blue purple of the primary crystal violet, while after the latter is dyed, the bacterial cells first remove the color of the primary crystal violet, and take on the red of complex saffron or sand yellow.

Cell morphology and structure

The basic structure of cells includes cell wall and Protoplast Two parts. Protoplast Located in the cell wall, including the cell membrane（ Cell plasma membrane ）Cytoplasm, nucleoplasm and inclusions. In addition, cells also contain some special structures, mainly Capsule 、 Spore 、 Flagellum and Fimbriae 4 kinds.

1. Cell wall

Gram staining The mechanism of Gram positive bacteria The structure and composition of cell wall are different from those of negative bacteria. See the following table for specific comparison:

Furthermore, the cell wall of Gram positive bacteria is mainly composed of peptidoglycan and acidic polysaccharide including phosphoteichoic acid, cell surface The overall negative charge is partly due to the negative charge of phosphoteichoic acid. At the same time, phosphoteichoic acid endows Gram positive bacteria with specific surface antigen.

In general, the difference in cell wall structure leads to the difference in dye absorption and also leads to many physiological characteristics.

2. Non cell wall structure

nature		Gram positive bacteria	Gram negative bacteria
nature		Gram positive bacteria	Inner wall layer	Outer parietal layer
structure	Thickness (nm)	20~80	2~3	eight
	arrangement	monolayer	multi-storey
	Peptidoglycan relationship	Multilayer, 75% subunit cross-linking, tight and firm network	Single layer, 30% subunit cross-linking, loose network
	Relationship with cell membrane	Not compact	close together
form	Peptidoglycan	40%~90% of cell dry weight	5%~10%	nothing
	Phosphopolyesters	Yes or No	nothing	nothing
	Polysaccharide	yes	nothing	nothing
	protein	Yes or No	nothing	yes
	lipopolysaccharide	nothing	yes	11%~22%

In the non cell wall structure, the main difference between gram-positive bacteria and negative bacteria is whether there are spores, flagella and sex pili.

Spore is a stage in the development of some bacteria, which forms a special structure due to the concentration and agglutination of cytoplasm and nucleoplasm under certain environmental conditions. Gram negative bacteria There are no spore forming strains in Gram positive bacteria sure.

In addition, there are differences in flagella and sex pili. Flagella and sex pili are appendages. The slender, wavy appendages protruding from the surface of some bacteria are called flagella. (Gu Xiasheng, Hu Hongying, Wen Xianghua, Wang Hui, et al. Water Treatment Biology. Beijing: China Construction Industry Press, 2010. P16) Gram positive bacteria basically have two rings on their flagellum, and Gram negative bacteria basically have four rings. (Zhao Kaihong, Environmental Microbiology, Wuhan: Huazhong University of Science and Technology (2009. P30) sex fimbriae are only found in Gram negative bacteria They participate in the mating process between cells called conjugation.

Physiological characteristics

The following is a comparison of the physiological characteristics of Gram positive bacteria and Gram negative bacteria. In essence, the difference between the two is mainly determined by the difference in cell structure.

project	Gram positive bacteria	Gram negative bacteria
Resistance to mechanical forces	strong	weak
Cell wall anti lysozyme	Weak (sensitive)	Strong (insensitive)*
Parapenicillin, sulfanilamide	sensitive	Insensitivity*
Parastreptomycin, chloramphenicol, tetracycline	Insensitivity	sensitive
Antibacterial effect on basic dyes	strong	Weak*
Para anion detergent	sensitive	Insensitivity*
Sodium p-azide	sensitive	Insensitivity
For drying	Strong resistance	Weak resistance

*Lipopolysaccharide at the outermost layer of cell wall blocks the entry of lysozyme, antibiotics, dyes, detergents and other large molecules

Common gram-positive bacteria

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Gram positive bacteria

Common gram-positive bacteria are: staphylococcus （Staphylococcus）、 streptococcus (Streptococcus), pneumonia Diplococcus 、 Bacillus anthracis 、 Diphtheria 、 Bacillus tetanus Etc; common Gram negative bacteria yes Shigella 、 Typhoid bacillus 、 Proteus , and Vibrio cholerae Etc.

In terms of treatment, most gram-positive bacteria are penicillin Sensitive（ Mycobacterium tuberculosis Not sensitive to penicillin); Gram negative bacteria are not sensitive to penicillin (but Neisseria In Epidemic meningitis Diplococcus and Diplococcus gonorrhoeae Sensitive to penicillin), while sensitive to penicillin streptomycin 、 chloramphenicol Etc. Therefore, it is of great significance to first distinguish between gram-positive bacteria and negative bacteria in the selection of antibiotics.

Structural characteristics

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Cell wall of gram-positive bacteria

Gram positive bacteria cell wall It is thick, about 20~80nm. Peptidoglycan Abundant content, 15~50 layers, each layer is 1nm thick, accounting for about Cell dry weight 50~80%. In addition, there are a lot of special components Phosphoteichoic acid (teichoic acid)。 Phosphotrichoic acid is composed of Ribol (ribitol) or glycerol residues are connected with each other via phosphoric acid double bond. Wall teichoic acid and Membrane teichoic acid (membrane teichoic acid), the former and n-acetyl of peptidoglycan in cell wall Parietal acid Connection, membrane phosphoteichoic acid, also known as Lipoteichoic acid Lipteichoic acid is connected with the cell membrane, and the other end is free from the cell wall. Phosphotrichoic acid has strong antigenicity and is an important surface antigen of Gram positive bacteria; In regulating ion passing through Mucopeptide Play a role in the layer; It may also be related to the activity of some enzymes; Phosphotrichoic acid of some bacteria, which can adhere to humans cell surface , its function is similar Fimbriae , which may be related to pathogenicity. In addition, some Gram positive Bacterial cell There are also some special Surface protein , such as protein a, are all related to pathogenesis.

Schematic diagram of G+bacteria cell wall

Gram positive bacteria and Gram negative bacteria Of cell wall The structure is significantly different, resulting in Bacteroid In terms of staining, antigenicity, toxicity susceptibility And so on.

Gram staining The result of depends on Bacterial cell wall The structure, i.e. Gram staining principle, is as follows: G+bacteria: cell wall thickness, peptidoglycan network molecules form a permeability barrier. When ethanol decolorizes, peptidoglycan dehydrates and pore barrier shrinks, so it remains crystal violet -Iodine complex is on the cell membrane. It is purple.

G - bacteria: peptidoglycan layer is thin, cross-linking is loose, alcohol decolorization cannot make its structure shrink, its fat content is high, alcohol dissolves the fat, the gap is enlarged, and crystal violet iodine complex is dissolved cell wall It turns red after sand yellow double dyeing. The cell wall thickness of Gram positive bacteria is about 20-80nm, with 15-50 layers of peptidoglycan Lamella , containing 20-40% phosphoteichoic acid. Gram negative bacteria The cell wall is about 10nm thick, only 2-3 layers of peptidoglycan, in addition, lipopolysaccharide Bacterial adventitia and Lipoprotein 。

G-bacterial cell wall diagram

Actinomycetes (Actinomycete) is another large group of gram-positive bacteria Guanine (G) And cytosine (C) Actinomycetes are called high G+C gram-positive bacteria, while chlamydia are called low G+C gram-positive bacteria. If the second membrane of the cell is derived, these two types of Gram positive bacteria may be branches of the bacterial base, otherwise they may form relatively close relationships Monophyletic group 。 They are considered to be the ancestors of archaea and eukaryotes, because they lack the second membrane and have some biochemical similarities, such as containing sterols. In addition, although Deinococcus Thermus like bacteria are structurally similar Gram negative bacteria , but it can also be dyed gram-positive

Theory of principle

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Gram staining At present, there are three views on the principle: Isoelectric point theory 、 Chemical theory and Infiltration theory 。

Isoelectric point theory

Gram-positive Isoelectric point In pH2-3, it is lower than the negative bacteria (pH4-5). In addition, iodine is a weak oxidant, which can reduce the isoelectric point of gram-positive bacteria, causing the difference between the isoelectric points of the two types of bacteria to expand. Therefore, the binding power of positive bacteria and alkaline dyes is stronger than that of negative bacteria.

Chemical theory

Iodine solution in bacteria body and crystal violet Combined with bacteria Ribonucleic acid Magnesium salt protein complex, which is not easy to be acetone alcohol Take off Gram staining Positive. because Gram negative bacteria Lack of magnesium salt of ribonucleic acid, so the intake of the combination of iodine and crystal violet is small and not firm, which is easy to be decolorized by acetone alcohol Gram staining negative 。

Infiltration theory

Ethanol makes the positive bacteria sticky Peptide polysaccharide Dehydration cell wall The gap is narrowed, the permeability is reduced, and the dye iodine complex is retained in the bacteria, which is purple. Negative bacteria Mucopeptide Less, the cell wall changes little, and the permeability is not affected. The dye iodine complex in the cell is easy to penetrate, lose purple, and become red again.

Related research

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On August 22, 2023, Markus Weingarth of the University of Utrecht in the Netherlands and Tanja Schneider of the University of Bonn in Germany jointly published a research paper entitled "An antibiotic from an uncultured bacterium binds to an immune target" online in Cell, which found an antibiotic clovibactin isolated from uncultured soil bacteria, It can effectively kill drug-resistant gram-positive bacterial pathogens without producing detectable drug resistance.

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