Anaerobic bacteria

Bacteria living under anaerobic conditions

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Anaerobic bacteria ） It is a kind of bacteria that grows better in anaerobic conditions than in aerobic environments, but cannot grow better in air (18% oxygen) and/or 10% carbon dioxide At concentration Solid medium Bacteria growing on the surface. Such bacteria lack integrity Metabolic enzyme Its energy metabolism is carried out by anaerobic fermentation. It can cause infection in different parts of the body, including appendicitis 、 cholecystitis 、 tympanitis , oral infection endocarditis 、 endometritis 、 brain abscess , myocardial necrosis osteomyelitis 、 peritonitis 、 empyema 、 Salpingitis , septic arthritis Liver abscess 、 nasosinusitis , intestinal surgery or wound infection after trauma pelvic infection as well as Bacteremia Etc.

Chinese name: Anaerobic bacteria
Foreign name: anaerobic bacteria

Introduction: It is a large group of specialized anaerobic
Features: Bacteria living under anaerobic conditions

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brief introduction

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Anaerobic bacteria are widely distributed in nature, humans and animals. non-spore-forming anaerobes It mainly exists in human and animal bodies, especially in the intestinal tract, oral cavity, upper respiratory tract, urinary tract, etc Facultative anaerobe They together form the normal flora of the body. Anaerobic bacteria usually have an absolute advantage in the normal flora. Under normal circumstances, the protection of flora is relatively balanced, such as long-term application Broad-spectrum antibiotic , hormones, immunosuppressants, etc., can lead to endogenous anaerobic infection in case of flora imbalance or body resistance decline.

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Anaerobic bacteria（ anaerobic bacteria ）It refers to bacteria living under anaerobic conditions. by Aerobic bacteria The corresponding words of. Among them, bacteria that cannot grow in the presence of oxygen are specially called Obligate anaerobe , such as clostridium Methanogen 、 Sulfate reducing bacteria And most Photosynthetic bacteria 。 On the contrary, bacteria that can grow and develop in both aerobic and anaerobic states are called facultative anaerobic bacteria 。 In addition to obtaining energy through fermentation and photosynthesis, some obligate anaerobes can use inorganic oxides such as sulfate as terminal electron receptors. It is believed that among the obligate anaerobic bacteria, those who obtain energy through fermentation generally lack cytochrome or hydrogen peroxide Enzymes and oxygen are harmful to growth due to lack of Superoxide Inhomogenizing enzyme and catalase, which can not decompose harmful superoxide or hydrogen peroxide produced by the action of flavin oxidase. When aerobic bacteria coexist in the soil, anaerobic bacteria can also be found in the place with permeable air. Among facultative anaerobes, many are like Escherichia coli In that way, in the presence of oxygen, the energy is obtained through respiration, and in the absence of oxygen, the energy is obtained through fermentation. But some, like lactic acid bacteria, obtain energy mainly through fermentation even if there is oxygen. Therefore, even facultative anaerobes include a variety of conditions from very good growth in aerobic conditions to very good growth in anaerobic conditions.

classification

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Anaerobes can be divided into three categories according to their tolerance to O ₂:

1. Anaerobic bacteria that are extremely sensitive to oxygen: the representative strain is Monomonas lunata, which has high requirements for anaerobic conditions. It is difficult to isolate it clinically because it will die after being exposed to air for 10 minutes.

2. Moderate anaerobic bacteria: representative bacteria are Bacteroides fragilis 、 Clostridium perfringens And other clinical isolates of common anaerobic bacteria. They can still be separated when exposed to air for 60~90 min or after the pus is extracted for 72 h.

3. Oxygen resistant anaerobic bacteria: the representative strain is clostridium histolyticum. This kind of bacteria can not use oxygen and grow well in anaerobic conditions, but not well in aerobic conditions.

According to the Gram staining method, anaerobic bacteria can be divided into two categories: Gram negative anaerobic bacteria and Gram positive anaerobic bacteria.

1. Gram negative anaerobes mainly include Bacteroides fragilis, Proctor, Porphyromonas and Clostridium.

2. Gram positive anaerobes include some anaerobic bacteria and cocci.

Anaerobes can be classified into two categories according to whether they produce spores:

1. Anaerobic Clostridium: Clostridium tetanus , Clostridium perfringens, Clostridium botulinum and Clostridium difficile, etc.

2. Non spore anaerobic bacteria: refers to a large category gram-positive Or Gram negative bacilli and cocci. For example: Bacteroides fragilis, Veroniella, digestive chain

Cocci, etc.

Important anaerobic bacteria

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1、 Bacillus

Clostridium（ clostridium ）

2、 Asporium

(I) Gram-positive cocci

one Gastrococcus （ peptococcus ）

two Digestive streptococcus （ peptostreptococcus ）

（2） Gram negative cocci

Veronica （ veillonella ）

（3） Gram negative non Bacillus

Class 1 Bacillus（ bacteroides ）

Clostridium（ fusobacterium ）

（4） Gram positive non Bacillus

one Bifidobacterium （ bifidobacterium ）

two Lactobacillus （ lactobacillus ）

Eubacterium（ eubacteriun ）

four Propionibacterium （ propionibacterium ）

Anaerobic infection

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ubiquitous

Anaerobes are human Normal flora It is a component of, which widely exists on the surface of the deep mucous membrane of the human skin and lumen. It occurs only when tissue ischemia, necrosis, or aerobic bacteria infection lead to the reduction of oxygen concentration in local tissue Anaerobic infection 。

Anti anaerobic bacteria drugs mainly include Nitroimidazole Class, including metronidazole and tinidazole Etc. It is widely used because it is cheap, has little side effects, and is not easy to produce bacterial resistance, among which metronidazole is used most, but bacterial resistance to metronidazole is also increasing. Anaerobic infection , use metronidazole or tinidazole 。

In the treatment of some infectious diseases, even if the use of advanced antibiotics is not effective, it may lead to Dysbacteriosis , aggravating the disease. This may be because we neglected the treatment of anaerobic bacteria.

Mostly mixed infection

As the intermediate product of metronidazole reduction is very sensitive to oxygen, it is easy to inactivate in aerobic environment, so it only plays a role in anaerobic bacteria. However, most anaerobic infections are mixed infections, that is, anaerobic bacteria and aerobic bacteria are mixed, and the two bacteria promote the growth of each other. Therefore, when treating anaerobic infections, drugs sensitive to aerobic bacteria and anaerobic bacteria must be used Cephalosporin Class B drugs are used together to improve the curative effect.

because Anaerobic bacteria culture Certain conditions and time are required, so doctors often make decisions on anti anaerobic treatment before obtaining experimental results. Because the common sites of infection are oral cavity, abdominal cavity, intestinal tract and pelvic cavity, when infectious diseases occur in these sites, anti anaerobic bacteria drugs are generally used for treatment. In addition, when the pus or exudate has a putrid odor or sweet taste, it indicates that the possibility of anaerobic infection is high.

Pathogenic bacteria of periodontitis

"There are many cavities in the oral cavity, which is conducive to bacterial growth." Beijing Chaoyang Hospital affiliated to Capital Medical University Dental Department Chen Shizhang, the director, said that the research showed that the proportion of gram negative anaerobes in adult periodontitis was about 75%.

In the treatment of stomatological inflammation, anti anaerobes are widely used. Mainly used in the following aspects: chronic Adult periodontitis Take metronidazole or tinidazole orally, and stop the drug after one week, and the efficacy can be maintained for 1-2 weeks; chronic periodontitis Acute attack, or serious infectious disease caused by anaerobic bacteria, such as anaerobic bacteria infection in the maxillofacial space Maxillary sinusitis And other antibiotics, intravenous drip for 3-5 days.

High bacteria in ileum and colon

The gastrointestinal tract is almost in a semi closed state, and the oxygen supply is poor, so anaerobic bacteria are easy to grow. Beijing Friendship Hospital affiliated to Capital Medical University General surgery Zhang Zhongtao The director said that most of the bacteria were sent into the lower intestine due to intestinal peristalsis, so the bacteria in the terminal ileum and colon were high, and 99.9% were anaerobic bacteria.

When performing rectal and colon surgery, it is easy to break the intestinal tube or need to be cut off surgically, so the anaerobic bacteria in it can enter the abdominal cavity. In order to prevent infection, metronidazole drugs are generally taken orally one day before such operations to prevent infection, and three days of rest should be continued after the operation.

For contaminated surgical procedures, such as various intestinal tube ruptures Emergency operation There is a great possibility that the anaerobic bacteria in the intestines can infect the abdominal cavity. Therefore, during the operation, metronidazole liquid can be poured into the abdominal cavity for soaking and washing.

Susceptible to pelvic infection

"Metronidazole was first used in gynecology Trichomonas vaginalis It is also called Metronidazole Later, it was found that this drug also has a very good anti anaerobic effect. " Beijing Maternity Hospital Affiliated to Capital Medical University Chen Suwen The deputy chief physician said that because the pelvic tissue is close to the rectum and anus, it is easy to be infected with anaerobic bacteria; The pelvic anatomy is deep, the environment is relatively closed and oxygen free, and anaerobic bacteria are easy to reproduce. In this special environment, almost most women Genital tract infection Anaerobic infection is not excluded, so anti anaerobic drugs are widely used in gynecological anti infection treatment, including pelvic infection and colpitis 。

When vaginitis is treated, it is generally taken orally with local medication, and 7 days is a course of treatment; pelvic infection It is often combined with other antibiotics for intravenous drip, and 7-10 days is a course of treatment.

Metronidazole may cause Fetal malformation It is better not to use suppositories in the first three months of pregnancy and during lactation, but vaginal suppositories are relatively safe.

Director Duan finally said that anti anaerobic bacteria Side effects of drugs , mainly digestive tract reaction, such as nausea and vomiting; There may be extrapyramidal reactions , such as headache and dizziness; No obvious liver renal function Damage, relatively safe.

Other antibiotics, such as penicillin 、 chloramphenicol 、 Clindamycin , cephalosporins Taineng It also has the function of anti anaerobic bacteria. But these drugs Antibacterial spectrum It is relatively wide and easy to lead to dysbacteriosis, mold infection, etc., so it is not specially used for the treatment of anaerobic infection.

Infection indications

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1. A large amount of gas is produced locally in the infected tissue, causing tissue swelling and necrosis, and there are twirling sounds under the skin - Gas gangrene Infection caused by clostridium flora.

2. Infections that occur near mucous membranes - most anaerobic bacteria in the body are parasitic in the organs with cavities.

3. After deep trauma, human and animal bites Secondary infection 。 It can reduce tissue oxygen tension or Eh.

4. The secretion has malodor, or is dark red, and emits red fluorescence under ultraviolet light (Prevotella melanogenes and Ultraviolet glycolytic bacteria); There are sulfur particles in the secretion or pus (actinomycete infection).

5. There are bacteria on the smear of the specimen (especially bacteria with uneven staining, light coloring and polymorphous morphology), while the conventional aerobic bacteria culture is negative; Or bacteria growing deep in liquid and semi-solid medium.

6. Long term use Aminoglycosides Cases of ineffective antibiotic treatment-- Aminoglycoside antibiotics are ineffective against anaerobic bacteria.

7. Have a recent history of abortion, or infection after gastrointestinal surgery; Puncture or various Endoscopy 。

Infection conditions

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1. Tissue hypoxia or reduction of redox potential is an important condition for the growth and reproduction of anaerobic bacteria. Obstruction of local tissue blood supply: Vascular injury , tumor compression, burns Arteriosclerosis , tissue edema, necrosis, foreign bodies. Large area trauma and stab injury can reduce tissue oxygen tension or Eh.

2. Decreased immune function: receiving immunosuppressants Antimetabolic drug Radiotherapy and chemical drug treatment; long-term Chronic consumptive disease (diabetes chronic hepatitis , kidney disease, etc.); Gastrointestinal, urogenital surgery; The elderly and premature infants.

3. Long term use of broad-spectrum antibiotics: Aminoglycoside antibiotics 、 cephalosporin Etc. These two kinds of antibiotics are ineffective against anaerobic bacteria, and destroy the relationship between various microbial species in the normal flora.

4. The development of surgery, puncture, various endoscopic examinations and invasive surgical techniques can all lead to changes in the location of bacterial colonization.

5. Synergy between bacteria: Anaerobic bacteria are mostly mixed with aerobic bacteria and facultative anaerobes to infect, which shows that one bacterium provides growth conditions, growth factors or nutrients for another bacterium.

Anaerobic treatment

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Expansion and drainage of anaerobic infections are often accompanied by extensive Tissue necrosis , must be completely removed, because necrotic tissue can reduce local Eh It is conducive to the reproduction of anaerobic bacteria, which is a prerequisite for the treatment of anaerobic infection. Clostridium perfringens Myositis (gas gangrene) causes extensive muscle necrosis, which must also be removed, and even amputation is required for severe cases. Necrotizing fasciitis It is a rare anaerobic infection. Fascia and skin often have extensive necrosis. If it is not completely removed, it is often difficult to control the spread of infection and cause death.

Antibiotic therapy

Antibiotics must be sensitive to anaerobic bacteria. Anaerobic bacteria Aminoglycosides Antibiotics often Drug resistance 。 Most anaerobic bacteria, except Bacteroides fragilis External, all right Penicillin G sensitive. The antibacterial spectrum of lincomycin is similar to that of penicillin G penicillin anaphylaxis Is optional. Chloramphenicol is effective for almost all anaerobic bacteria, including Bacteroides fragilis, but its disadvantages are Myelosuppression Risk. Anaerobic bacteria tetracycline 、 erythromycin It is different from chloramphenicol in sensitivity, and rapidly produces resistance during treatment, Clindamycin The curative effect on anaerobic infection is better than Lincomycin , but it, like lincomycin, sometimes causes fatal pseudomembrane colitis 。 Among antibacterial drugs, metronidazole is the first one with the best efficacy, which is effective for all anaerobic bacteria, including Bacteroides fragilis. Sharp Et al. (1977) found that the efficacy of metronidazole was better than that of clindamycin and lincomycin. The drug was cheap, and there were no serious complications even if it was used for a long time. Metronidazole can not only be taken orally (500mg, three times a day) and enema (1~2g each time), but also has been given intravenously recently, 0.5% to 100ml, intravenous drip 2-3 times a day. The role of oral metronidazole and intravenous metronidazole in the preparation of colon surgery proves that both methods can effectively reduce the infection rate 。

As mentioned earlier, there is a synergistic effect between anaerobic bacteria and aerobic bacteria, so drugs sensitive to aerobic bacteria and anaerobic bacteria must be used respectively when treating anaerobic infections. Cefoxitin （ Cefoxitin ）It is effective against bacteroides, but its efficacy is not as good as that of clindamycin, chloramphenicol or metronidazole. Cefmondo is a new cephalosporin for intravenous use. It has a wide antibacterial spectrum and is effective against both gram-positive and gram-negative aerobic and anaerobic bacteria.

Third generation cephalosporins such as cefadroximide（ Moxalactam ）、 cefoperazone （ Cefoperazone ）And Cefotaxime （ Cefotaxime ）It is effective for aerobic bacteria and anaerobic bacteria, and has strong bactericidal power for all anaerobic bacteria.

Hyperbaric oxygen therapy

Hyperbaric oxygen can improve the oxygen tension of tissues and inhibit the reproduction of anaerobic bacteria. This therapy is spindle shaped Bacillus As an important aspect of infection treatment, many people doubt the value of non spore anaerobic infection.

hydrogen peroxide

Hydrogen peroxide is an effective drug for treating wounds infected by anaerobic bacteria. The new oxygen released by hydrogen peroxide can kill anaerobic bacteria. Zinc peroxide Paste can be used to treat some anaerobic infections, especially Meleney Ulcer.

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