OVERVIEW
Normally, anaerobic bacteria are present in the oral cavity, intestines, and vagina. If the symbiotic relationship between the normal anaerobic and aerobic flora is disrupted (e.g., by surgery or other trauma, poor blood supply, or tissue necrosis), anaerobic bacteria can invade the body and cause infections in a variety of ways. Aerobic and anaerobic bacteria can often be found at the same site, so the infection may be mixed, but is often overlooked clinically because of the special conditions required for anaerobic culture. In fact, anaerobes may be common pathogens in the pleural cavity and lungs, in the abdominal cavity, in gynecology, in the central nervous system, in upper respiratory tract infections, and in skin diseases and bacteremia.
Etiology
1. Types of pathogenic bacteria
The causative gram-positive anaerobic cocci are Streptococcus pepticus and Streptococcus pepticus, which are part of the normal flora of the oral cavity, upper respiratory tract, and large intestine. The major Gram-negative anaerobic bacilli are Anaplasma fragilis, Anaplasma melaninum, and Anaplasma clostridium. The group of Bacteroides fragilis is part of the normal colonic flora and includes the anaerobic pathogenic bacteria most frequently isolated from intra-abdominal infections.
2. Source of infection
Anaerobic infections are mostly characterized by endogenous sources. The rate of anaerobic infections in periodontitis and endodontitis is up to more than 96%; the mixed rate of anaerobic and aerobic infections in perianal, abdominal and pulmonary areas is up to more than 70%; the rate of anaerobic infections in pulmonary infections and lung abscess is up to more than 40%; and the pathogenic organisms are gram-negative anaerobic bacilli in the majority.
3.Susceptible people
People with low immunity, such as patients with cancer, bone marrow transplantation and patients in intensive care unit.
Symptoms
1. Clinical characteristics of anaerobic bacterial infection
(1) Infections of the skin, oral cavity, intestines and vagina, often with severe necrosis, abscesses, fasciitis or gangrene, and putrid, gaseous secretions.
(2) Infections secondary to malignant tumors, infective endocarditis, concomitant suppurative thrombophlebitis, and infections after human or animal bites, with typical clinical manifestations such as gas gangrene, actinomycosis, and lung abscess.
2.Clinical clues of anaerobic infection
Infections adjacent to mucosal surfaces with anaerobic flora, ischemia, tumors, penetrating trauma, foreign bodies, perforation of internal organs, diffuse gangrene involving skin, subcutaneous tissue, fascia and muscle, fecal odor of pus or infected tissue, abscess formation, gas in the tissues, septic thrombophlebitis, and ineffectiveness of treatment with antimicrobials without antianaerobic effect.
3. Types of anaerobic infections
(1) endogenous ① septicemia with oral mucosal damage may be carbon dioxide phagocytosis or oral ciliates septicemia; ② neutropenia with fever, vomiting, diarrhea and abdominal pain, may be neutropenic colitis, often accompanied by septicemia, often associated with Clostridium septicemia, the third Clostridium perfringens, or Clostridium perfringens and Gram-negative aerobic bacillus of mixed infections; ③ pelvis Most of the infections are actinomycetes or fungal infections; ④ pressure sore infections and septicemia with unknown invasion route, the causative organisms are often anaerobic bacteria of the group of fragile bacilli, and the latter enters the bloodstream from the pressure sore.
(2) exogenous ① catheter-related infections caused by non-anaerobic bacteria are more common, common anaerobic bacteria for the short rod seedling genus and Streptococcus pepticus; ② the causative organisms of wound infections in patients with bite wounds are often anaerobic bacteria and streptococci for oral parasites, the human bite is often erosive Aikenella, and animal bites are often Pasteurella spp.
Laboratory examination
1. Bacterial culture
All specimens should be examined by Gram staining and aerobic culture, and anaerobic culture should be examined after 48 to 72 hours of incubation using a special medium. It is possible that susceptibility information may not be available 1 week after the initial culture.
2. Specimen smear examination
When anaerobic culture is performed at the same time as smear microscopy, the information of anaerobic growth can be provided to the clinic at an early stage. If there is no bacterial growth in ordinary aerobic culture, but a large number of bacteria are seen in the direct smear, anaerobic infection can be considered; if there is only one kind of bacterial growth in ordinary culture, but two or more kinds of bacteria are seen in the direct smear, mixed infection can be considered.
3. Anaerobic bacteria drug sensitivity test
Anaerobic drug sensitivity test should be strict and confirmed by the National Clinical Laboratory Standards Steering Committee. However, if the bacterial species is known, the drug sensitivity can be predicted in advance, so many laboratories do not routinely conduct anaerobic drug sensitivity test.
4. Bacterial staining
Anaerobic infections may be considered if a Gram stain of pus from the site of infection shows mixed polymorphic flora. Since it is difficult to detect bacilli on Gram stain, the characteristic variable filamentous bacilli must be carefully observed. If a Gram stain of material taken from the site of infection shows a mixed flora and the culture of visibly necrotic tissue shows only α-hemolytic streptococci or a single aerobic bacterium such as Escherichia coli, or even no bacterial growth, consideration should be given to the fact that the specimen may have been transported or cultured with an inappropriate bacteriologic technique.
Diagnosis.
Anaerobic bacteria have a universal nature of infection and may cause infections in various parts, organs and tissues of the body, such as neonatal aspiration pneumonia, brain abscess, lung abscess, bacteremia, sinusitis and peritonitis.
The diagnosis of mixed anaerobic infections can be considered by combining certain features of clinical and bacteriologic examination.
Differential diagnosis
1. Mixed anaerobic infections
Mixed anaerobic infections are mainly differentiated from aerobic infections by bacterial culture. If there is only one type of bacterial growth in common culture, but two or more types of bacteria can be seen in direct smear, the patient can be considered as mixed infection.
2. Anaerobic infection
Most of them are endogenous. Anaerobic bacteria are conditionally pathogenic, and must be invaded and infected when systemic or local resistance is reduced. The identification of anaerobic bacteria can use API 20A, VITEK-ANI, MICRO-01D, gas-liquid chromatography and other equipment identification. Most laboratories use the agar dilution method recommended by the National Committee for Clinical Laboratory Standardization (NCCLS) for drug sensitivity testing of anaerobic bacteria.
Complications
1. Complications of bacteremia
May cause fever, chills and critical illness, shock, diffuse intravascular coagulation may occur in Clostridium difficile septicemia.
2. Lung infection
It can be complicated with aspiration pneumonia and lung abscess.
3. Intestinal infection
Intestinal perforation and peritonitis may occur.
4. Gynecological infection
It can be complicated by sepsis, shock, renal failure, and severe myocardial abscess.
5. Other
Such as brain abscess, sinusitis and thrombophlebitis. Serious cases can lead to death.
Treatment
1. Antibacterial drug treatment
Combined use of anti-anaerobic and aerobic drugs is very necessary. Due to the different drug resistance spectrum of anaerobic bacteria in different regions and different hospitals, the empirical use of drugs should be based on the drug sensitivity spectrum of the region and the laboratory to select drugs. In order to improve the efficacy and reduce the toxic side effects of antimicrobial drugs, it is best to select drug therapy according to the drug sensitivity test.
(1) Anti-anaerobic drugs Mainly nitroimidazoles, including metronidazole, tinidazole, ornidazole and so on. Because of the low price, small side effects, not easy to produce bacterial resistance, so widely used, of which metronidazole is used most. Treatment of anaerobic infections, must be used for aerobic bacteria and anaerobic bacteria sensitive drugs, the above drugs are generally used in combination with cephalosporins, can improve the efficacy.
Metronidazole is effective against clindamycin-resistant Mycobacterium fragilis and may avoid clindamycin-associated pseudomembranous colitis, and no clinical consequences have been seen regarding the potential mutagenic effects of this drug, Cefoxitin and cefotetan have a broad antimicrobial coverage against anaerobes. The combination of metronidazole, carbapenems and beta-lactams/beta-lactamases have shown good antibacterial effects in in vitro tests. All of these drugs, except metronidazole, can be used alone as they also have good antimicrobial activity against aerobic bacteria. The side effects of anti-anaerobic drugs are mainly gastrointestinal reactions such as nausea, vomiting, headache and dizziness.
(2) Other antibacterial drugs such as penicillin, chloramphenicol, clindamycin, cephalosporins, carbapenems, moxifloxacin, etc., also have anti-anaerobic effects. However, the antibacterial spectrum of these drugs is relatively broad, which can easily lead to bacterial dysbiosis, fungal infections and so on.
2.Drainage surgery treatment
(1) Treatment of deep anaerobic infections should include drainage of pus and surgical removal of inactivated tissue. Antimicrobial drugs with surgery can help control bacteremia, reduce secondary or migratory septic complications, and prevent local spread of infection around the surgical site.
(2) Mixed infections Certain strains of bacteria are resistant to antimicrobial drugs, and antimicrobial therapy can still be effective, especially when adequate drainage is given. Management of anaerobic bacteria in mixed infections reduces the number of bacteria in the wound and also reduces the number of abscesses that form. Abscess inactivated tissue, foreign bodies, and necrotic tissue must be removed.
Prevention
1. In vitro anaerobic bacterial prophylaxis
Early and aggressive treatment of limited infections with necessary surgical exploration, drainage, and removal of foreign bodies and necrotic tissue. A single dose of antimicrobial drug should be given prophylactically before debridement surgery, and then continue to give antimicrobial drugs for 24 hours after surgery, which can reduce the rate of postoperative infection to 4%~8%.
2. Normal anaerobic flora in the body
Chronic lesions such as chronic otitis media, sinusitis, mastoiditis should be treated aggressively to prevent intracranial anaerobic infections.