Gram staining reactionIt is an important character for bacteria classification and identification.It was founded by Danish physician Gram in 1884.Gram stainingGram stain can not only observe the morphology of bacteria, but also divide all bacteria into two categories: those with blue purple staining reaction are called gram-positive bacteria, which are represented by G+;Red (re dyeing color) in dyeing reaction is calledGram negative bacteria, denoted by G -.
Bacteria forGram stainingThe different reactions ofcell wallCaused by the difference in composition and structure.The thick cell wall of Gram positive bacteria (20-80nm) is mainly caused byPeptidoglycanIt is composed of phosphoteichoic acid and has only one layer of structure. Its main component is peptidoglycan, accounting for 50%~90% of the dry weight of cell wall.During dyeing, when treated with ethanol, the pore size in the reticular structure becomes smaller and the permeability decreases due to dehydrationcrystal violet-Iodine complex is retained in the cell and is not easy to decolorize, so it appears blue purple;The peptidoglycan content in the cell wall of gram-negative bacteria is low, while the lipid content is high. When treated with ethanol, the lipid material dissolves, and the permeability of the cell wall increases, making the crystal violet iodine complex easy to be extracted by ethanol and decolorized, and then stained with the re staining solution（Safranine）The color of[1]。
Structural characteristics
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Gram positive bacteriacell wallIt is thick, about 20~80nm.PeptidoglycanAbundant content, 15~50 layers, each layer is 1nm thick, accounting for aboutCell dry weight50~80%.In addition, there are a lot of special componentsPhosphoteichoic acid（teichoic acid）。Phosphotrichoic acid is composed ofRibol(ribitol) or glycerol residues are connected with each other via phosphoric acid double bond.Wall teichoic acid andMembrane teichoic acid(membrane teichoic acid), the former and n-acetyl of peptidoglycan in cell wallParietal acidConnection, membrane phosphoteichoic acid, also known asLipoteichoic acidLipteichoic acid is connected with the cell membrane, and the other end is free from the cell wall.Phosphotrichoic acid has strong antigenicityGram positive bacteriaImportant surface antigen of;In regulating ion passing throughMucopeptidePlay 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 humanscell surface, its function is similarFimbriae, which may be related to pathogenicity.In addition, some Gram positiveBacterial cellThere are also some specialSurface protein, such as protein a, all related to disease[2]。
Common Gram positive bacteria
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staphylococcus
1. Introduction
staphylococcusIt is widely distributed in air, water, soil and surface of objects, as well as in human and animal skin, mucosa, digestive tract, respiratory tract and mammary gland.According to its physiological characteristics and chemical compositionStaphylococcusDivided intoStaphylococcus aureus、Staphylococcus epidermidisandstaphylococcus saprophyticus 。The following Staphylococcus aureus is an example to introduce the main characteristics of pathogenic staphylococcus.
2. Form and structure
Staphylococcus is gram-positive coccus, with a diameter of 0.5~1.5 pm. It is named because it is usually arranged in a string of grapes.Staphylococcus aureus is usually arranged in a string shape on solid culture mediumLiquid mediumThey are often arranged in a double ball or short chain shape, and are easily mistaken for streptococcus.The fungus has no flagella, does not produce spores, and generally does not form a capsule.
3. Culture characteristics
Aerobic or facultative anaerobic.The nutritional requirements of this bacterium are not high, and it grows well on the ordinary medium. If blood or glucose is added, it grows more vigorously;stayBroth culture mediumIt grows evenly and turbidly.Form moist, smooth and raised round colonies on ordinary agar plates.The colony color varies according to the strain, showing gray white at first, then golden yellow, white or lemon color.Most pathogenicitystaphylococcusIt produces hemolysin and forms an obvious hemolytic ring on the blood agar plate, while non pathogenic staphylococcus does notHemolysisMost strains can decompose lactose, glucose, maltose and sucrose, and produce acid without gas.It can decompose mannitol to produce acid.Staphylococcus can produce contact enzyme. Staphylococcus aureus can also produce coagulase and thermostable nucleaseStaphylococcus aureusIt is different from other staphylococci.
4. Antigen structure and classification
staphylococcusThe structure of antigen is complex, including polysaccharide and protein antigens.The protein antigen is mainly A protein (SPA), which is the mostStaphylococcus aureusA common specific surface antigen is a single chain polypeptide that covalently binds to peptidoglycan.SPA can non-specific bind to Fc segment of almost all mammalian serum IgG molecules, and the combined IgG can still react specifically with the corresponding antigen. This property of SPA has been widely used in immunodiagnostic technology.Polysaccharide antigens can be used for staphylococcal typing[3]。
streptococcus
1. Introduction
StreptococcusThere are many kinds of bacteria, which are widely distributed in nature. Water, dust, human and animal upper respiratory tract, gastrointestinal tract, urogenital tract, etc. exist. Some are non pathogenic bacteria, some constitute normal flora of human and animals, and some can cause various suppurative diseases, pneumonia, mastitis, septicemia, etc.
2. Form and structure
Streptococci are spherical or ovoid, with a diameter of 0.6~1.0 μ m, often arranged in chains. The length of the chain is related to the strain and the growth environment. The composition of the cell varies from 4~8 to 20~30. The liquid culture is easy to form long chains, while the solid culture medium often presents short chains.The capsule of most streptococci can be seen in the young culture, and will disappear if the culture continues.No spores and flagella.Gram staining is positive.[3]
3. Culture characteristics
streptococcus
Most are facultative anaerobic, and a few are anaerobic bacteria.Pathogens have high nutritional requirements. They do not grow well in the ordinary medium, but grow well in the medium with blood, serum, glucose, etc.stayBlood agar plateSmall colonies with a diameter of 0.1~1.0mm, gray white, smooth surface and neat edges are formed on the surface.Most of the pathogenic strains have hemolytic abilityHemolysisIt can be divided into three categories: Type A, Type B and Type C.It grows in serum broth and appears uniform and turbid at first, and then settles at the bottom of the tube due to the formation of long chains of bacteria, and the supernatant is transparent.The bacteria of this genus can ferment glucose and sucrose, and the utilization ability of other sugars varies with different strains.Streptococcus has negative enzyme contact reaction, so it can be used withstaphylococcusMake a difference[3]。
