What Is an Anaerobic Infection?

Anaerobic bacteria are a group of bacteria that grow better under anaerobic conditions than in aerobic environments, but cannot grow on the surface of solid media in air (18% oxygen) and / or 10% carbon dioxide. This kind of bacteria lacks a complete metabolic enzyme system, and its energy metabolism is carried out by anaerobic fermentation. It can cause infections in different parts of the body, including appendicitis, cholecystitis, otitis media, oral infections, endocarditis, endometritis, brain abscesses, myocardial necrosis, osteomyelitis, peritonitis, empyema, salpingitis, septic joints Inflammation, liver abscess, sinusitis, wound infection after bowel surgery or trauma, pelvic inflammatory disease, and bacteremia. With the continuous improvement of culture technology, anaerobic bacteria can be isolated and identified in time, reports of anaerobic infections are increasing, and the importance of anaerobic bacteria in bacterial infectious diseases has been increasingly valued by clinicians. Elderly patients with cerebrovascular disease, patients with impaired consciousness, dysphagia, patients with chronic diseases, tumors, organ transplants, hematological diseases, and patients with long-term application of immunosuppressants and glucocorticoids are all susceptible to this disease.

Basic Information

English name: anaerobic infections
Visiting department: Infectious Diseases
Multiple groups: Elderly patients with cerebrovascular disease, patients with impaired consciousness, dysphagia, patients with chronic diseases, tumors, organ transplants, hematological diseases, and patients with long-term use of immunosuppressants and glucocorticoids

Common causes: Anaerobic bacteria

Causes of anaerobic infection

Anaerobic bacteria has no accepted exact definition. It is generally considered to be a group that can only grow under conditions of low oxygen partial pressure, and cannot be on the surface of solid medium in air with a carbon dioxide concentration of 10% (containing 18% oxygen). Growing bacteria. According to the degree of tolerance of anaerobic bacteria to oxygen, they can be divided into obligate anaerobic bacteria, facultative anaerobic bacteria and microaerobic anaerobic bacteria. The latter refers to a group of anaerobic bacteria that grows poorly or does not grow in an aerobic environment, but grows better in air with a carbon dioxide concentration of less than 10% or under anaerobic conditions. Anaerobic bacteria include spores and non-spores, the latter can also exist in vitro in the form of spores. Common pathogenic anaerobic bacteria causing infections: Gram-negative bacilli; Gram-positive cocci; Gram-negative cocci; Gram-positive Bacillus; Gram-positive non-bacillus.

Clinical manifestations of anaerobic infection

Central nervous system infection

Focal purulent infections, such as brain abscesses and subdural empyema, are often associated with anaerobic infections. Conversely, epidural empyema and meningitis caused by anaerobic bacteria are rare.

2. Septicemia and endocarditis

3. Respiratory system infection

Common upper respiratory infections and intrathoracic infections can cause diseases such as pneumonia, lung abscess, and necrotizing pneumonia.

4. Intraabdominal infection

The normal intestine contains a large number of anaerobic bacteria, and intra-abdominal infections are often related to intestinal flora contamination, so it has a high isolation rate of anaerobic bacteria, and is often a mixed infection of multiple bacteria. Can cause liver abscess, biliary infection, appendicitis, intestinal infection and so on.

5. Female reproductive tract and pelvic infections

Nearly all non-sexually transmitted female genital tract infections include anaerobic infections. Common pathogenic bacteria include Streptococcus digestive, Platts (especially Platts two and Przewia saccharolyticus), Bifidobacterium Clostridium (including Clostridium perfringens).

6. Urinary tract infection

Anaerobic urinary tract infections include urethritis, periurethritis, periurethral cellulitis, and abscesses (which can be associated with necrosis or multiple fistulas), urethritis (including necrotizing and emphysema), and prostatitis ( Occasionally necrotizing and purulent), Migrating kidney infections (often accompanied by pus with sepsis), Perirenal abscesses, pyelemia, retroperitoneal pus, nephrectomy wound infections, kidney transplant infections, purulent thrombotic renal veins Inflammation, bladder gangrene, perineal abscess or gangrene, gas gangrene in various parts of the urinary tract, testicular abscess, etc.

7. Bone and joint infections

Anaerobic osteomyelitis is relatively rare. Anaerobic osteomyelitis is divided into two types: actinomycete and non-actinomycete. Actinomyelitis osteomyelitis is mainly found in the jaw and spine, followed by ribs and skull. , Long bones, short bones, etc., may be accompanied by mixed infections of other anaerobic and aerobic bacteria, mostly caused by direct spread of nearby infections (such as periodontal infection, sinusitis, trauma or malignant tumor infection), infection The process is usually subacute or chronic. There are typical lumps in the crotch or neck, and there are sinuses that often pus and discharge "sulfur granules". Most of them involve large joints, which are knee, hip, elbow, sternlock, Shoulders, shoulders, etc.

8. Skin and soft tissue infections

There are often rancid secretions, gas production, extensive tissue necrosis, and tend to extend to the subcutaneous tissue and fascial surface to form sinus. Most of them are caused by the cooperation of aerobic and anaerobic bacteria. Some anaerobic bacteria can cause the following special Clinical syndrome: progressive bacterial synergistic infectious gangrene; synergistic necrotizing cellulitis; chronic sinus ulcers; necrotizing fasciitis; anaerobic streptococcal myositis; clostridial Muscle necrosis (gas gangrene); mouth and cheek infections.

Anaerobic infection test

1. Isolation and identification of anaerobic bacteria

Routine identification of anaerobic bacteria includes colony morphology, hemolysis, pigmentation, presence or absence of fluorescence upon UV irradiation, colony smears, staining and microscopy, biochemical reactions, motility, and virulence tests; of which the sugar fermentation test is basic For biochemical reactions, the test tube method is routinely used, and the amount of culture medium is large and takes a long time. At present, a small, rapid, and commercial identification system has been developed.

2. Gas chromatography analysis

Including analysis of bacterial metabolites and cellular components.

(1) Gas chromatographic analysis of anaerobic bacteria metabolites One of the characteristics of anaerobic bacteria is the production of various volatile and non-volatile short-chain fatty acids and alcohol products during metabolism, and fatty acids produced by different bacteria and species Different types and quantities of alcohols can be identified by gas chromatography.

(2) Gas chromatographic analysis of anaerobic cell components Saponification of bacterial cells to release fatty acids, followed by methanol methylation and gas chromatography analysis, the identification results are objective and repeatable.

3. Immunological examination and other

Fluorescent antibody technology (both direct and indirect) can successfully identify various anaerobic bacteria (such as bacillus, Clostridium, Clostridium, Corynebacterium, etc.). In clinical anaerobic infections, pathogenic bacteria are vulnerable Bacillus is most common.

Anaerobic infection diagnosis

Comprehensive clinical and bacteriological examination can consider the diagnosis of this disease.

1. Some clinical features suggest

(1) Any infection on mucosal surfaces where colonies of anaerobic bacteria can colonize, vagina and oropharynx.

(2) The secretion has a typical rancid odor, but those who do not have this odor cannot be ruled out, because half of the cases may not have this odor.

(3) There is severe tissue necrosis, abscess, fasciitis or gangrene.

(4) There is gas in the diseased tissue or exudate.

(5) Infective endocarditis with negative blood (aerobic) culture results.

(6) Infection secondary to malignant tumors (especially the colon, uterus and lungs) or other diseases that cause tissue destruction.

(7) Infections that occur after application of aminoglycosides and -lactam antibiotics.

(8) Accompanied by purulent thrombophlebitis.

(9) Infection secondary to human or animal bites.

(10) Bloody exudate is black. Under ultraviolet light, it can emit red fluorescence (P. melanogenesis or Porphyromonas infection).

(11) Sulfur particles are present in the secretion (actinomyces infection).

(12) Some clinical manifestations suggesting anaerobic infection. Such as septic abortion, aspiration pneumonia, infections after bowel surgery.

(13) Typical clinical manifestations (such as gas gangrene, actinomycosis, and lung abscess, etc.).

2. Bacteriological examination suggests the possibility of anaerobic infection

(1) The colonies seen in Gram staining or culture of exudate have morphological characteristics.

(2) Purulent specimens have no bacterial growth in conventional culture (bacterial growth can be found in sodium thioglycollate broth or deep in agar), and bacteria can be seen in Gram staining.

(3) Gram-negative bacilli grow in the medium containing kanamycin and vancomycin.

(4) A large amount of gas is generated during the cultivation process, and there is a foul smell.

(5) There are typical colonies (such as Clostridium nucleus and Clostridium perfringens) on the anaerobic agar plate; the newly-produced melanin-producing colonies show red fluorescence under ultraviolet light.

(6) Gas chromatography analysis showed volatile fatty acids specific to anaerobic bacteria.

3. Suggest possible anaerobic infection types

(1) Patients with leukemia undergoing chemotherapy, if the symptoms of sepsis with oral mucosal damage, may be carbon dioxide phagocytosis or oral ciliated sepsis.

(2) Those with neutropenia, fever, vomiting, diarrhea, and abdominal pain may be neutropenic colitis, often accompanied by sepsis, which is common in Clostridium septicum, Clostridium tertiary, or Mixed infection of Clostridium perfringens and Gram-negative microaerobic bacteria.

(3) When pelvic infection occurs in women who place IUDs, actinomycetes or Eubacteria are more common.

(4) When lung infection appears in the sagging lung lobe, especially those with periodontal disease, recent history of anesthesia or history of inhalation, it may be aspiration pneumonia.

(5) For those who develop pressure ulcer infection and septicemia with unknown invasion path, the pathogenic bacteria are often anaerobic bacteria of the fragile bacillus group, and the latter enters the blood from the pressure ulcer.

(6) Non-anaerobic bacteria are more common in catheter-associated infections, and the common anaerobic bacteria are Corynebacterium Brevibacterium and Streptococcus pneumoniae.

(7) The pathogenic bacteria of wound infections in bite patients are usually oral anaerobic bacteria and streptococcus. Those who are bitten by humans are usually infected by E. coli, and those who are bitten by animals are usually Pasteurella.

Anaerobic infection treatment

The principle of treatment is to establish an environment that is not conducive to the growth and reproduction of anaerobic bacteria (including surgical treatment) and antibacterial treatment. For a few anaerobic infections of exotoxin producing bacteria, such as tetanus and botulinum food poisoning, antitoxin should be applied at the same time. Patients with severe infections should be strengthened with supportive therapy, transfusion of plasma or whole blood as appropriate, and actively treat the primary disease.

1. Destroy the anaerobic environment

Including drainage and drainage of local lesions, removal of necrotic tissue or ineffective cavity, decompression of markedly swollen tissues with gas formation, and removal of coexisting malignancies, foreign bodies, obstructions, and thrombus. To control the spread of infection and reduce toxemia, amputation and hysterectomy are performed when necessary. However, liver abscesses, brain abscesses without obvious cystic wall, and fallopian tube abscesses may not be treated for incision and drainage. Superficial anaerobic infections can be locally washed with hydrogen peroxide solution. Hyperbaric oxygen therapy is suitable for cases of gas gangrene.

2. Antibacterial treatment

metronidazole; clindamycin and lincomycin; chloramphenicol; -lactam antibiotics; macrolides; vancomycin and norvancomycin.

3. Other treatments

Support and symptomatic treatment including maintenance of water, electrolyte balance, blood transfusion, correction of shock, pain relief, treatment of renal failure, and fixation of affected limbs are also important. In the presence of thrombophlebitis or DIC, there are indications for the use of anticoagulants such as heparin. When intravascular hemolysis is caused by post-abortion infection or sepsis caused by Clostridium perfringens, transfusion therapy can be applied. When tetanus or Clostridium botulinum is infected, toxins are an important pathogenic factor. At this time, the application of antitoxins is particularly important. In addition, oxygen can be given, including local application of 3% hydrogen peroxide solution and systemic administration. Hypertensive oxygen chamber treatment can be considered for severe patients.