Gram negative bacteria

Bacterial category

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Gram negative bacteria are a large group of bacteria. In order to classify bacteria, people often use a staining method, that is, first smear bacteria on the slide, use crystal violet for initial dyeing, add iodine solution, use alcohol for decolorization, and finally use dilute fuchsin for re dyeing. After a series of treatments, the purple bacteria are Gram positive bacteria , such as Lactobacillus 、 Bacillus tetanus , Streptococcus staphylococcus All belong to this type; On the contrary, some bacteria are red after the above treatment Gram negative bacteria , such as Shigella 、 Meningococcus Etc. This method was first discovered and used by Danish physician Gram, hence the name.

Chinese name: Gram negative bacteria
Foreign name: Gram-negative bacteria

Substantive: A large group of bacteria
Discipline: biology
Identification method: Gram staining reaction

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Gram negative bacteria Gram staining reaction Red bacteria. stay Gram staining In the experiment, we first added Gentian violet (crystal violet), and then add another compound dye, usually using Safranine (safranin) or fuchsine, so that all Gram negative bacteria Dye red or pink. Through this test, we can distinguish two types cell wall Bacteria with different structures. Gram positive bacteria The color of gentian violet will appear in the decolorization solution after reaction.

Both positive and negative bacteria bacillus and cocci 。 staphylococcus 、 Escherichia coli 、 Pseudomonas aeruginosa It is the most common pathogenic bacteria in clinic. Staphylococcus belongs to gram-positive cocci and Escherichia coli belongs to gram-negative bacteria Enterobacteriaceae In addition to Escherichia coli, the most common clinical enterobacteriaceae bacteria are Proteus 、 Salmonella 、 Klebsiella ； Pseudomonas aeruginosa Pseudomonas , for Non fermenting bacteria , is a common drug-resistant gram-negative bacterium in clinic^[1] 。

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Gram negative bacilli

Flagellate

yes Fimbriae Hewei Capsule , no sporulation

Obligate aerobic bacteria

Legionella pneumophila cause Legionellosis Most of them are popular in summer and autumn, and the death rate can reach 15% if they are not properly treated.

Gram staining reaction

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Gram negative bacteria

Gram staining reaction It is an important character for bacteria classification and identification. It was founded in 1884 by Denmark It was founded by physician Gram. Gram staining Gram stain can not only observe the morphology of bacteria, but also divide all bacteria into two categories: those with blue and purple staining reactions are called Gram positive bacteria , represented by G+; Red (re dyeing color) in dyeing reaction is called Gram negative bacteria , denoted by G -.

Bacteria react differently to Gram staining because they cell wall Caused by the difference in composition and structure. The cell wall of Gram positive bacteria is mainly composed of Peptidoglycan Formed Reticular structure During the dyeing process, when treated with ethanol, the pore size in the reticular structure becomes smaller and the permeability decreases due to dehydration crystal violet -Iodine complex is retained in the cell and is not easy to decolorize, so it appears blue purple; The content of peptidoglycan in the cell wall of Gram negative bacteria is low, without Phosphoteichoic acid The network structure formed by the peptide bridge, peptide tail and disaccharide in the cell wall is relatively loose, while the content of lipid is high. When treated with ethanol, the lipid is dissolved, and the permeability of the cell wall is increased, 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^[2] 。

Common types

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Gram positive bacteria: Staphylococcus aureus 、 streptococcus 、 enterococcus Listeria, etc

Gram negative bacilli ： Klebsiella , Escherichia coli, Pseudomonas aeruginosa Haemophilus influenzae Salmonella, etc

therapeutic method

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Gram negative bacteria

Mainly various antibiotics. However, due to increasingly serious drug resistance, many antibiotics have lost their former glory, such as penicillin Etc. And for gram-negative bacteria, improper use of antibiotics will aggravate the development of the disease. Because the polysaccharide of gram-negative bacteria has an outer membrane, which is composed of specific polysaccharide, Core polysaccharide And lipid A. Lipid A is the toxic part and main component of endotoxin. If antibiotics are used indiscriminately, specific polysaccharide and core polysaccharide will be destroyed, which will expose lipid A, release endotoxin and aggravate the disease. Many doctors are also misusing antibiotics, and patients should go to regular hospitals for treatment and medication.

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Severe pneumonia patients are often accompanied by basic diseases, often with poor prognosis and high mortality. Anti infection is crucial for their treatment. This study found that the main causes of severe pneumonia are pathogenic bacteria Gram negative bacteria, accounting for 74.8%, of which Pseudomonas aeruginosa In the first place, it can be seen in Table 2 that the bacteria except cefepime (25.0%), Piperacillin triazobactam （27.8%）， Ceftazidime （27.8%）， Imipenem （30.5%）， ciprofloxacin (33.3%), and other drugs are severely resistant. Pseudomonas aeruginosa can develop resistance through a variety of mechanisms, including the modification of enzymes, Membrane porin Loss, target change and reverse pump action, it is also believed that the bacterial surface can produce biofilm, and Macrolides Medically inhibited Alginate So as to enhance the penetration of antibiotics to Pseudomonas aeruginosa. and Fluoroquinolone Class A is considered to be the best antibiotic for biofilm permeability. It is noteworthy that, Pseudomonas aeruginosa It can be in the state of carrying bacteria for a long time. During the diagnosis and treatment of severe pneumonia, there were 2 cases Tracheal intubation The patient, sputum samples aspirated from trachea and lung lavage fluid were all pseudomonas aeruginosa for multiple cultures. However, according to the drug sensitivity test results, the clinical symptoms of the patient did not improve after regular use of anti pseudomonas aeruginosa drugs, and the sputum culture was still pseudomonas aeruginosa for reexamination. Therefore, it is believed that even if the patient was repeatedly cultured Pseudomonas aeruginosa However, the therapists should still comprehensively judge whether the bacteria is in the carrier state or infection state according to the clinical conditions of patients and the changes of sputum, which is also of great significance to reduce the resistance rate of Pseudomonas aeruginosa to various antibiotics.

Acinetobacter baumannii A total of 16 strains were isolated. Except for imipenem and amikacin, the drug resistance rate to other antibiotics was as high as 43.8%~93.8%, which was related to the complex and changeable drug resistance mechanism. In addition, the bacteria had strong vitality, which was easy to cause an outbreak of infection. Imipenem is the first choice for treatment, and can be used in combination if necessary Aminoglycosides Drugs. and enzyme inhibitor Sulbactam Yes Acinetobacter It has unique antibacterial activity, so a composite preparation containing sulbactam can be selected for treatment.

This study found that, Escherichia coli ， Enterobacteriaceae ， klebsiella pneumoniae The highest detection rate of ESBLs was 55.6%, 40.0% and 25.0%, respectively. Imipenem had the highest antibacterial activity against these three bacteria, Piperacillin - Triazobactam and Cefepime For ESBLs producing bacteria, different ESBLs have different effects on three generations cephalosporin With different activities, some ESBLs can endow bacteria with amide A high level of resistance to antibiotics, but only slightly increased resistance, and Cefotaxime Ceftazidime and ceftazidime are the best substrates for recognizing different ESBLs. Imipenem is the first choice for treating ESBLs bacteria.

Stenotrophomonas maltophilia It is also a common multiple drug resistance cause of severe pneumonia germs In this monitoring, except for levofloxacin (33.3%), other antibiotics were severely resistant. Because of its low permeability of outer membrane and the presence of inducible B-lactams L2 and L1, it was highly resistant to B-lactams, aminoglycosides and carbapenems. Therefore, the infection of this bacterium has become a difficult problem in clinical treatment, Compound sulfamethoxazole and Ticarcillin - Clavulic acid It's therapy Stenotrophomonas maltophilia infection The most effective medicine.

In recent years, due to Broad-spectrum antibiotic The widespread use of gram-negative bacteria such as Pseudomonas aeruginosa ， klebsiella pneumoniae and Acinetobacter baumannii The infection of pathogenic bacteria Severe drug resistance is one of the main reasons for the difficulty in treatment and high mortality of severe pneumonia. In the treatment of severe pneumonia, it is advisable to adopt the strategy of antibiotic step-down therapy. The antimicrobial spectrum should cover all pathogenic bacteria as far as possible, and empirically, imipenem, piperacillin tazobactam and cefepime are preferred enzyme inhibitor The third generation cephalosporins and new quinolones of bacteriology After the results, according to the drug sensitivity results and clinical conditions, the targeted antibiotics and step-down treatment were used. At the same time, we must pay attention to the detection of ESBLs, strengthen monitoring and management, and prevent the spread and outbreak of ESBLs strains.

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