Senile anaerobic bacterial pneumonia

　　1. Etiology

　　Anaerobic bacteria are a type of bacteria that can only grow and reproduce under anaerobic or low oxidation-reduction potential conditions. According to their sensitivity to oxygen, anaerobic bacteria can be broadly divided into obligate anaerobes, microaerophiles, and aerotolerant bacteria. By convention, anaerobic bacteria refer to obligate anaerobes, which must grow under conditions with significantly reduced oxygen partial pressure, and can be further divided into facultative anaerobes, microaerophiles, and obligate anaerobes. The so-called anaerobic pneumonia in clinical practice mainly refers to pulmonary infections caused by obligate anaerobes. Obligate anaerobes can only survive or grow under anaerobic or conditions with oxygen partial pressure lower than that of the normal atmosphere, and can be further divided into extreme anaerobes, moderate anaerobes, and oxygen-tolerant anaerobes.

　　1. Extreme anaerobic bacteria:These anaerobic bacteria are extremely sensitive to oxygen. They die within 10 minutes when exposed to the air at an oxygen concentration of 0.5% or less. Due to the difficulty in isolation in clinical laboratories, their pathogenic conditions are currently unknown.

　　2. Moderate anaerobic bacteria:These anaerobic bacteria can grow at oxygen concentrations of 2% to 8%, and can still be isolated after being exposed to the air for 60 to 90 minutes. Common anaerobic bacteria causing pulmonary infections, such as Bacteroides fragilis and Clostridium perfringens, all belong to this category, which is the most common type of anaerobic bacteria in clinical practice.

　　3. Oxygen-tolerant anaerobic bacteria:These anaerobic bacteria grow best under anaerobic conditions and poorly under aerobic conditions. The second species of Clostridium and Clostridium histolyticum belong to this category.

　　Among the common anaerobic bacteria causing pulmonary infections are:

　　(1) Gram-negative anaerobic bacilli: Common bacteria causing pulmonary anaerobic infections. Literature reports indicate that in aspiration pneumonia, necrotizing pneumonia, lung abscess, and empyema, Gram-negative anaerobic bacilli were isolated and accounted for approximately 53.67%, 56.45%, 50.87%, and 39.29% respectively, among which the Bacteroides genus ranked first, followed by the Fusobacterium genus.

　　①Bacteroides: Gram-negative, non-spore-forming bacilli. Some strains have capsules or flagella. Obligate anaerobic. They can utilize intermediate metabolic products of sugars and proteins. The type strain is Bacteroides fragilis. The bacterial body is short rod-shaped, with uneven staining, with the middle stained lightly or not at all, making the bacterial body appear vesicular. Both ends are round and heavily stained. On solid culture media, they are irregular, with varying lengths. If the culture conditions change slightly, such as insufficient anaerobic conditions, malnutrition, or accumulation of acidic products, the bacterial bodies may show polymorphism. The most common Bacteroides causing pulmonary infections are Bacteroides fragilis and Bacteroides melaninogenicus.

　　②Fusobacterium: It may be a Gram-negative, non-spore-forming, obligate anaerobic bacterium without flagella, capable of utilizing sugars and peptones. The type strain is Fusobacterium nucleatum, which is centrally expanded, pointed at both ends, contains Gram-positive granules of varying lengths, and has a relatively regular shape. The bacilli are paired, with the tips facing each other. The Fusobacterium species that cause pulmonary infections are most commonly Fusobacterium nucleatum and Fusobacterium necrophorum.

　　(2) Gram-positive anaerobic cocci: Gram-positive anaerobic cocci are second only to Gram-negative anaerobic bacilli in pulmonary infections. Literature reports indicate that they account for about 1/4～1/3 of the aforementioned pulmonary infections, with Peptostreptococcus and Peptococcus being the most common.

　　①Peptostreptococcus: Peptostreptococcus has a smaller body, 0.5～0.6mm in diameter, arranged in pairs or chains, forming needle-point-sized colonies with a diameter of 1mm, which are circular, smooth, convex, grayish white, opaque, and non-hemolytic. It is the most common Gram-positive anaerobic cocci in pulmonary infections.

　　②Peptococcus: The bodies of Peptococcus are circular, with a diameter of 0.3～1.3mm, arranged in pairs, short chains, or in clusters. Growth is slow, and small colonies are formed after 2～4 days of culture, making it a common bacterium in pulmonary anaerobic infections.

　　(3) Gram-negative anaerobic cocci: Veillonella, a Gram-negative anaerobic cocci, is also a pathogen of pulmonary anaerobic infections, accounting for about 3.7% of pulmonary anaerobic infections. The bacterium has a small body, 0.3～0.6mm in diameter, sometimes forming short chains, and is Gram-positive in the early stage of culture, but becomes Gram-negative overnight.

　　(4) Gram-positive anaerobic bacilli: Gram-positive anaerobic bacilli account for about 1/5 of anaerobic pulmonary infections, among which Eubacterium, Propionibacterium, and Clostridium are the most common.

　　①Eubacterium: Eubacterium is a Gram-positive, non-spore-forming bacillus with regular morphology, with a size of (0.6～1)mm×(2～4)mm. It often arranges in single, double, or short chains. Gram-positive colonies are small, round, flat, semi-transparent, gray, and non-hemolytic. The type strain is Eubacterium adhaerens. It accounts for about 1/4 of pulmonary Gram-positive bacillary infections.

　　②Propionibacterium: Propionibacterium is a Gram-positive, non-spore-forming, pleomorphic bacillus. It is straight or slightly curved, rod-shaped, with a size of (0.5～0.8)mm×(1～5)mm, unevenly stained. Arranged in X, Y, V, and reticulated patterns. Without a capsule and without flagella. The colonies are small, circular, grayish or other colors, and opaque. The type strain is Propionibacterium freudenreichii. It is also a common bacterium in pulmonary infections.

　　③Clostridium: The middle part of the bacillus is enlarged in a spindle shape, with Clostridium butyricum as the type strain. The shape of the bacillus is straight or slightly curved, with constant length or width, ends are pointed or rounded, arranged in single, double, short chains or various forms.

　　Old age is an important factor in the onset of the disease, often with a history of poor oral hygiene, periodontitis, craniocerebral injury, cerebrovascular disease, epilepsy, alcoholism, and general anesthesia. In addition, underlying diseases such as bronchial stenosis, bronchial neoplasms, obstructive pneumonia, bronchiectasis, and pulmonary embolism are also prone to trigger anaerobic bacterial infection.

　　Second, pathogenesis

　　The entry of anaerobic bacteria into the lungs does not necessarily lead to infectious lesions. Pulmonary anaerobic bacterial infection is also the result of the mutual competition between microorganisms and the body. The body's defense ability is the main factor determining whether infection occurs, and the pathogenic process of anaerobic bacteria plays an important role in causing infection.

　　1. Decreased defense ability of the body

　　(1) Decreased systemic immune function: In some patients with chronic diseases, such as diabetes, liver cirrhosis, and terminal stage renal disease, in addition to being prone to ordinary bacterial infection, it is also prone to anaerobic bacterial infection. Tumor patients receiving radiotherapy and chemotherapy, organ transplant recipients, and patients with connective tissue diseases receiving antimetabolite drugs, patients with blood diseases receiving corticosteroid hormone treatment, and chronic alcoholism can all lead to serious immune function decline, which is prone to anaerobic bacterial infection.

　　(2) Local defense ability disorder: includes three aspects, such as the reduction of the barrier function of local mucosa, the reduction of the redox potential of local tissues, and the damage to the vitality of phagocytes and杀菌 systems. The reduction of the barrier function of local mucosa is more common in pulmonary diseases such as bronchiectasis, bronchogenic lung cancer, and chronic obstructive pulmonary disease. The damage not only favors the invasion of anaerobic bacteria but also favors the reproduction and spread of bacteria. The reduction of the redox potential is often caused by local vascular diseases, shock, edema, trauma, surgery, cancer, and the growth of aerobic bacteria. In normal circumstances, although anaerobic bacteria can enter the lower respiratory tract, due to the normal blood supply of respiratory mucosal tissues and the maintenance of 150mV redox potential, it is not conducive to their growth. However, when the redox potential is reduced to below 150mV due to the aforementioned reasons, anaerobic bacteria can enter the tissue for growth and reproduction. The vitality of phagocytes and杀菌 systems is often reduced in the presence of hypoxia, ischemia, acidosis, and bacterial metabolites, which also favors the growth and reproduction of anaerobic bacteria.

　　2. Pathogenic effects of bacteria

　　Attachment and adhesion: the first step in the process of anaerobic bacterial infection. Different genera of anaerobic bacteria, relying on certain special structures of their own, attach to the surface of target cells through different mechanisms. For example, Bacteroides fragilis mainly uses pili and spores to adhere to mucosal epithelial cells, Fusobacterium nucleatum attaches to target cell receptors containing galactose through a mechanism mediated by plant hemagglutinin and arginine, and Bacteroides gingivalis and others use proteases to hydrolyze immunoglobulins and complement, reducing the blockage of bacterial surface receptors by immunoglobulins and complement components.

　　If the mucosal epithelial structure is intact, most anaerobic bacteria cannot directly invade the tissue except for fusiformis, but when the integrity of the mucosa is damaged, anaerobic bacteria attached to target cells dissolve mucosal epithelial cells into the tissue by relying on their own proteases and phospholipase C.

　　(3) Growth and reproduction: Whether bacteria can form an infection focus locally after entering the tissue depends on local metabolism, bacterial nutrition, and the bacteria's resistance to the host's defense mechanisms. If the tissue is due to ischemia and hypoxia, the degradation of carbohydrates and the activation and release of proteases increase, on the one hand, reducing the local pH and redox potential, and on the other hand, providing abundant nutrients for anaerobic bacteria to promote their growth and reproduction locally. In addition, bacteria entering the tissue can also produce many substances to resist the host's defense mechanisms. For example, in addition to producing spores to protect itself from being engulfed by phagocytes, Bacteroides fragilis can also produce some soluble substances such as succinate and other short-chain fatty acids to inhibit the chemotaxis, phagocytosis, and killing of polymorphonuclear leukocytes and macrophages. Many anaerobic bacteria can also produce substances to inhibit and destroy the host's humoral immunity. For example, the lipopolysaccharide of Bacteroides fragilis can weaken the opsonizing effect of complement, and the proteolytic enzymes produced by Bacteroides melaninogenicus can degrade complement and immunoglobulins, etc.

　　(4) Tissue damage: Anaerobic bacteria produce toxins, enzymes, and soluble substances during the infection process, which not only act at each stage but also directly damage the structure of tissues and cells. For example, the alpha toxin produced by Clostridium perfringens can dissolve red blood cells and tissue cells, causing hemolysis and tissue necrosis. Heparinase produced by Bacteroides fragilis decomposes heparin, promotes coagulation, and may lead to thrombophlebitis. Collagenase produced by Bacteroides melaninogenicus destroys connective tissue. Bacteroides produce hyaluronidase, neuraminidase, DNAase, etc., which are all related to pathogenicity and the spread of infection.

　　Complications are common, most of which are related to the existing various underlying diseases, including: shock, sepsis, septicemia, arrhythmia, electrolyte and water metabolism disorders, acid-base imbalance, respiratory failure, heart failure, multiple organ dysfunction syndrome, etc. After the occurrence of complications, the condition is severe, progresses rapidly, and the mortality rate is high. Elderly patients often do not have chest pain but only present with progressive worsening of dyspnea. Due to the poor baseline pulmonary function in elderly patients, even with little lung collapse, they may present with severe symptoms and require timely rescue.

　　1. Typical manifestations

　　1. Inhalational pneumonia:Patients all have a history of primary disease and aspiration, with an acute onset, sudden aversion to cold and high fever, body temperature reaching above 39℃, accompanied by cough, expectoration of mucus or purulent sputum. Although the production of malodorous sputum is a characteristic of anaerobic bacterial infection, literature reports that only 37.8% of the disease presents with malodorous sputum. Therefore, the absence of malodor in purulent sputum does not exclude the possibility of anaerobic bacterial infection. Inflammation involving the pleura can cause chest pain. With the expansion of the lesion range, progressive dyspnea may occur. In severe cases of intoxication, symptoms such as nausea, vomiting, abdominal distension, and diarrhea may be accompanied. Signs: Smaller lesions may not show any abnormal signs, while larger lesions may show cyanosis, flaring of the nostrils, and dyspnea. Lung auscultation may present with dull or flat sounds, with reduced respiratory sounds, and sometimes rales may be heard.

　　2. Necrotizing pneumonia:The characteristics of this disease are the formation of many abscesses and necrosis with diameters less than 2 cm. In severe cases, rapid spread can cause large areas of necrosis and sloughing of the lung parenchyma, even forming lung abscesses. About 75% of patients have a history of aspiration. The condition of the patients is severe, with a body temperature as high as 40℃, severe cough, a large amount of sputum, and 61% of patients cough up foul-smelling sputum. When there is lung abscess, a large amount of purulent, foul-smelling sputum is coughed up, up to several hundred milliliters per day. The patients have shortness of breath, cyanosis, and most lung examinations show dullness, weakened respiratory sounds, and a high mortality rate. Chronic lung abscess patients have chronic cough, purulent sputum, recurrent hemoptysis, often presenting with anemia and emaciation, and chronic consumptive states. Physical examination shows that the affected side of the chest is slightly sunken, percussion is dull, respiratory sounds are reduced, and hemoptysis is rare. Most physical signs are negative.

　　3. Empyema:The onset is slow, and symptoms are usually not obvious until 1 to several weeks after the onset, with a high fever that can reach 40℃, a long fever period, and half of the cases show significant weight loss. If it is secondary to lung abscess, coughing is marked, with a large amount of purulent sputum. If it is directly spread from an abscess under the diaphragm, there is dry cough and marked chest pain. The secretions of empyema are purulent, foul-smelling, thick, forming many small abscess cavities, which are difficult to extract.

　　2. Atypical manifestations

　　The onset is insidious, the symptoms are often atypical, and there is usually no fever, cough, sputum, or chest pain. Common symptoms include: increased respiratory rate, tachypnea, and general malaise, weight loss, decreased appetite, fatigue, acute confusion, and depression, among other systemic toxic symptoms. Sudden deterioration of underlying diseases or slow recovery from the disease may also occur, such as the recurrence or exacerbation of heart failure during treatment, and a few patients have prominent gastrointestinal symptoms, often manifested as nausea, vomiting, abdominal pain, diarrhea, anorexia, and dyspepsia, which occur concurrently with respiratory symptoms. Physical examination: typical consolidation signs are rare, half of the patients have no rales in the lungs, 1/4 of the patients have no abnormal auscultation in the lungs, and even if rales are heard, they are easily confused with chronic bronchitis and heart failure.

　　The pulmonary infections caused by anaerobic bacteria in the elderly have the following characteristics:

　　1. Most have primary diseases and triggering factors;

　　2. The course of the disease can be acute or chronic;

　　3. Sputum and pleural effusion have a foul smell;

　　4. The infected lesions have a tendency to necrosis;

　　5. The onset is insidious, and the symptoms are atypical;

　　6. The direct smear of the specimen shows a large number of bacteria, while the ordinary bacterial culture is negative;

　　7. There are many complications and a high mortality rate.

　　1. Tier 3 prevention

　　1. Tier 1 prevention:Elderly people are more prone to pneumonia due to the aging and degeneration of the lungs and changes in local anatomical structures. Anaerobic pneumonia is mostly contracted through aspiration, belonging to endogenous infection, so elderly people should be strengthened in care.

　　(1) Elderly patients with stroke, brain atrophy, and long-term bedridden patients who cannot take care of themselves, have difficulty swallowing, and have water coughing. This requires nursing staff to be particularly careful during meals, and the head of the bed should be appropriately elevated. When visible aspiration is found, immediate and rapid positional drainage or aspiration should be performed to clear the contents in the airway, and a fiberoptic bronchoscope may be used if necessary to remove food residue in the large airway, in order to avoid blocking the bronchus and triggering anaerobic pneumonia;

　　(2) Pay attention to keeping warm during sudden changes in temperature, prevent colds, and reduce the chance of pneumonia;

　　(3) Elderly people should drink less alcohol to reduce the chance of aspiration;

　　(4) Actively treat tonsillitis and acute abdominal conditions such as appendicitis perforation and other purulent infections to reduce the occurrence of pulmonary anaerobic infections.

　　2. Tier 2 prevention:Elderly pneumonia often has an insidious onset and is often not easily discovered. If the patient's health condition deteriorates, there is a decrease in appetite, anorexia, fatigue, urinary incontinence, acute confusion, or the sudden deterioration of underlying diseases, or the recovery is slow, attention should be paid to atypical changes in pneumonia. Immediate medical treatment should be sought, a detailed physical examination should be conducted, and an 'X' ray examination should be performed to check for sputum bacteria, in order to discover pneumonia early and treat it promptly.

　　3. Tier 3 prevention:Since anaerobic pneumonia is not caused by a single bacterium but often by mixed infections, effective antibiotics for anaerobic bacteria should be used at the same time, and other antibiotics should be used according to the results of drug sensitivity tests. After the condition improves, without fever, cough, and sputum disappearance, the X-ray results should be observed, and the medication should be stopped after the X-ray shadow basically disappears to reduce the possibility of evolving into chronic pneumonia and causing lung function damage.

　　2. Risk factors and preventive measures

　　1. Risk factors for elderly patients with anaerobic pneumonia include: smoking can reduce the defense function of the airways, increasing the chance of pneumonia; poor oral hygiene, difficulty swallowing, coughing, long-term bed rest, and coma are common causes of aspiration pneumonia; surgical procedures and anesthesia in the throat are common causes of iatrogenic anaerobic pneumonia; acute tonsillitis and purulent appendicitis can spread hematogenously to the lungs, forming anaerobic infections.

　　2. Intervention measures include: maintaining oral hygiene, strengthening oral care, treating caries, gingivitis, and tonsillitis in a timely manner. Patients who are bedridden for a long time, have difficulty swallowing, or cough should be observed to prevent the reflux of gastric juice into the trachea. Eating should be done carefully, with the body position adjusted, and food should be eaten slowly. More liquid food can be consumed, and nasogastric feeding can be used if necessary.

　　1. Peripheral blood picture

　　The blood leukocyte count and neutrophils are significantly increased, with a total count of up to (20～30)×10^9/L; neutrophils account for more than 80％～90％. In patients with chronic onset, the total leukocyte count may not change significantly, but there may be varying degrees of anemia.

　　二、纤维支气管镜检查

　　The double lumen bronchoscope can also be used to take samples for bacterial culture, attract pus, and inject antibiotics into the lesion site to promote bronchial drainage and healing of the abscess cavity, and help to find the underlying lesion.

　　Three. Bacteriological examination

　　1. Anaerobic culture

　　It is the most reliable diagnostic basis. Since the sputum coughed out is contaminated by normal anaerobic flora in the oropharynx, special attention should be paid to the collection of specimens. Currently, the following methods are commonly used:

　　(1) Cricothyroid membrane puncture: This method is a measure taken to reduce contamination from the oropharynx and is quite valuable when detecting pulmonary anaerobic bacterial infections, but is not suitable for patients with ongoing tracheal intubation.

　　(2) Spleen-lung puncture: Literature reports that the detection rate of bacteria reaches 84%.

　　(3) Double lumen bronchoscope technique: This method uses double-layer polytetrafluoroethylene tubes and polyethylene ethyl alcohol plugs in front of the tubes to prevent brush contamination. Under the direct vision of the bronchoscope, the brush is inserted into the lesion segment of the trachea, and the specimen is brushed for culture. Literature reports that the sensitivity of this method reaches 70%.

　　(4) Immunoenzyme histochemical method: Using this method to check for Clostridium perfringens and 8 other species of clostridia, 8 species of facultative anaerobic bacteria, and aerobic bacteria for 10 times, the results are negative for all bacteria except Clostridium perfringens. By diluting the specimen to 2,500 bacteria per milliliter, a large amount of purulent, foul-smelling sputum can be coughed out, which can be detected daily up to several hundred milliliters. A stable positive result can be obtained with 5,000 bacteria per milliliter, therefore, this method is highly specific and sensitive, simple and rapid, and results can be obtained in 2 to 3 hours, which is valuable for early diagnosis.

　　2. Nucleic acid probes

　　It has the advantages of specificity and high sensitivity, not affected by sample placement and oxygen exposure, and is suitable for the detection of anaerobic bacteria with strong pathogenicity, difficult cultivation, and slow growth. Due to the complex and time-consuming process of extracting DNA samples from specimens, radioactive contamination, short shelf life, and insufficient sensitivity, it has not been widely used in clinical practice. In recent years, non-radioactive nucleic acid probe technologies with no radiation hazards, long shelf life, and simple detection procedures have been developed, such as biotin nucleic acid probes, immunoribonucleic acid probes, and chemical probe methods, etc.

　　3. Polymerase Chain Reaction (PCR)

　　Using a specific sequence on a certain DNA strand of anaerobic bacteria as a template, complementary sequences are synthesized using primers, and after dozens of cycles, the DNA quantity is amplified to millions of times, improving the sensitivity of detection. Currently, anaerobic bacteria such as Clostridium difficile, Clostridium gingivalis, and Clostridium actinomycetum are detected using PCR in foreign countries.

　　Imaging manifestation

　　1. Inhalation pneumonia, the lesion sites are mostly located in the posterior superior or inferior lobe of the right lobe, showing large, dense, and blurred inflammatory shadows uniformly distributed along the pulmonary segments, with unclear edges. They are often unifocal segmental distributions, but can also be multifocal, resembling small splinter-like shadows, usually located at the periphery of the lung, close to the pleura. Similar to common pneumonia, after 1 to 2 weeks, tissue necrosis occurs, forming abscesses, leading to necrotizing pneumonia.

　　2. Necrotizing pneumonia is mainly manifested by the rapid formation of cavities in the dense shadow of lung segments, with the diameter

　　3. The manifestations of acute lung abscess are the rapid formation of cavities in the dense shadow of lung segments, with the cavities being round, the inner walls smooth, and liquid-gas levels visible inside. With proper treatment, the consolidation shadows and cavities gradually decrease, disappear, or leave cord-like shadows.

　　4. The X-ray findings of chronic lung abscess are variable, with thick walls of the abscess cavity, irregular inner walls, different sizes and shapes of cavities, sometimes with liquid levels, surrounded by fibrous cord shadows, and varying degrees of lobar contraction. Those who recover and improve have about half with secondary bronchiectasis.

　　5. The blood-borne disseminated type is characterized by multiple scattered small patchy inflammatory shadows or spherical lesions with relatively regular edges in the marginal areas of one or both lungs. Pus cavities and liquid levels can be seen within them.

　　The manifestations of empyema vary with the amount of pus, with a large dense shadow appearing on the affected side of the chest. If empyema with pneumothorax is present, a liquid level can be seen.

　　What kind of food is good for elderly patients with anaerobic bacterial pneumonia

　　It is advisable to eat light and more vegetables and fruits, reasonably match the diet, pay attention to dietary hygiene and ensure adequate nutrition. Avoid smoking, drinking, and spicy foods.

　　1. Treatment

　　1. Control of infection

　　The absorption, distribution, metabolism, and excretion rates of drugs in the elderly change significantly. Diabetic patients have unstable absorption of intramuscularly injected drugs, and elderly patients with lack of gastric acid and changes in gastrointestinal function have unstable absorption of oral drugs. Therefore, intravenous administration is recommended for elderly patients with pneumonia. The renal function of patients over 50 years old gradually declines, and the serum creatinine level is not sufficient to reflect the extent of renal function damage. Aging, smoking, drug intake, diet, and health are all factors that have a significant impact on the metabolism of drugs in the elderly. The clearance rate of drugs with high intravascular clearance decreases due to the reduction in visceral blood flow in the elderly. These factors should be considered before selecting antibiotics. The selection of anti-anaerobic drugs should be based on the results of bacterial culture and sensitivity testing. However, since pulmonary anaerobic bacterial infections are often mixed infections, anaerobic bacteria often coexist with facultative anaerobic bacteria or aerobic bacteria and grow slowly. The isolation of pathogenic anaerobic bacteria and the sensitivity test are often delayed. Therefore, drugs with strong antibacterial activity, low toxicity, and pharmacokinetic characteristics should be selected according to the analysis of the most likely pathogenic bacteria causing the infection. The duration of antibacterial therapy is generally 8 to 12 weeks, until clinical symptoms completely disappear, X-rays show that the inflammatory lesions and abscess cavities are completely resolved, and only cord-like fibrous shadows remain.

　　(1) Penicillin class: Penicillin has a strong effect on anaerobic cocci, gas-forming clostridia, and other anaerobic bacteria, but has a weak effect on Bacteroides fragilis and a few fusiform bacteria. However, some people have found that in mixed pulmonary infections, even if Bacteroides fragilis is present, penicillin can still cure the infection, possibly because after other bacteria are eliminated, the body's defense mechanism can clear Bacteroides fragilis. In general, penicillin is the first-line drug for all anaerobic bacterial infections (except Bacteroides fragilis). The dose should be higher, with the maximum dose up to 20 million U/d, administered by intravenous infusion in divided doses.

　　① Carbenicillin (carbenicillin): At high doses, it has a stronger effect on Bacteroides fragilis than penicillin G, with higher blood drug concentrations and better clinical efficacy. The usual dose is 5 to 20g per day, 1 to 2 times per day, and can reach up to 20 to 40g per day in severe infections.

　　② Pipersillin (pipercillin): Its antibacterial activity is stronger than that of carbenicillin, and it has antibacterial activity against Gram-positive anaerobic bacteria and Bacteroides fragilis, with high blood drug concentrations. It has no accumulation effect in mild to moderate renal impairment. The recommended dose for adults is 4 to 8g per day, and can be doubled in severe infections, administered in 4 divided doses.

　　③ Ticarcillin (carboxythiazole cephalosporin): Its antibacterial activity is similar to that of carbenicillin, but the concentration in pleural effusion and sputum is lower. The recommended dose for adults is 2 to 4g per day, 1 to 2 times per day, and can reach up to 10 to 20g per day in severe infections, administered by intravenous injection in 2 to 3 divided doses.

　　④ Moxifloxacin (benzimidazole cephalosporin): It is resistant to beta-lactamase and has antibacterial activity against most anaerobic bacteria. Its effect on Bacteroides fragilis is similar to that of pipercillin, but stronger than that of carbenicillin. The recommended dose for adults is 12 to 16g per day, administered by intravenous injection in 3 to 4 divided doses.

　　⑤ Nafcillin: It has antibacterial activity against most anaerobic bacteria, but Bacteroides fragilis is resistant to this drug. The usual dose is 1 to 2g per day, and can reach up to 4g in severe infections, administered by intramuscular or intravenous injection in 2 to 3 divided doses.

　　⑥ Apalcillin: It has certain antibacterial activity against anaerobic cocci and Bacteroides species. It has high concentrations in sputum and pleural effusion. The effective rate for respiratory system infections is 89.4%. The recommended dose is 2 to 4g per day, administered by intravenous or intramuscular injection in 2 to 4 divided doses, and can be increased to 8g per day in severe cases.

　　⑦ Lactamycin: It forms ampicillin (ampicillin) after entering the body. It has strong antibacterial activity against Peptostreptococcus species. After absorption, it has a high concentration in sputum and is mainly used for mild Peptostreptococcus infections, 250mg per dose, 2 to 3 times per day.

　　(2) Cephalosporins: The first-generation cephalosporins (except cefazolin) have weaker antibacterial activity against anaerobic bacteria than penicillin G. Therefore, there is no need to elaborate further. The second-generation cephalosporins effective against anaerobic bacteria include:

　　Cefoxitin: It is resistant to beta-lactamase and has a good effect on most anaerobic bacteria, including Peptostreptococcus, Streptococcus, Clostridium botulinum, and Bacteroides species. After intravenous administration, it reaches a high concentration in pleural effusion quickly. Foreign scholars advocate using this drug as the first-line treatment for anaerobic infections. The recommended dose for adults is 4 to 10g per day, administered by intramuscular or intravenous injection in 3 to 4 divided doses.

　　Cefminox: It has strong activity against Bacteroides species. However, its concentration in sputum is low. The usual dose for adults is 2g per day, taken in two divided doses, and can reach up to 6g per day in sepsis, taken in 3 to 4 divided doses.

　　Cefamandole: It has strong activity against most anaerobic bacteria. The clinical effective rate and bacterial clearance rate for anaerobic infections are both over 90%, with a clinical cure rate of 89.8%. The recommended dose for adults is 2 to 8g per day, with a maximum of up to 12g, administered by intramuscular or intravenous injection in 3 to 4 divided doses.

　　(3) Chloramphenicol: Currently, it is often used for severe anaerobic bacterial infections of unknown etiology with definite efficacy. Most anaerobic bacteria are sensitive to it, except for a few Clostridium perfringens. A group of foreign reports showed that 60 anaerobic bacteria were sensitive to the drug at a concentration of 12.5μg/ml in drug sensitivity tests. When the serum concentration is 3.1 to 12.5mg/ml, it has antibacterial activity against 100% of Bacteroides fragilis. Therefore, some people believe that for Bacteroides fragilis resistant to penicillin, chloramphenicol should be the first choice. However, there have been some reports of failure in clinical treatment despite in vitro sensitivity testing.

　　(4) Lincomycin and Clindamycin (chloro lincomycin): These two drugs are particularly suitable for patients allergic to penicillin G. Lincomycin has a strong antibacterial effect on Bacteroides fragilis, but its effect on Clostridium perfringens and Fusobacterium is weaker. Clindamycin (chloro lincomycin) has a stronger effect on various anaerobic bacteria than lincomycin. More than 97% of anaerobic strains are sensitive to a concentration of 3.1mg/ml of clindamycin (chloro lincomycin), which can be achieved through oral administration. Therefore, it has significant efficacy for the vast majority of anaerobic bacterial infections. However, a small number of Streptococcus species, variably fusiform bacteria, and Clostridium are resistant to it. If it can be used in combination with penicillin G, it can make up for its shortcomings. It is used for severe pulmonary anaerobic bacterial infections and empyema. The usual dose for adults is 600 to 900mg, taken every 8 hours.

　　(5) Imidazoles: Including metronidazole and tinidazole, etc. Clinically, metronidazole is effective against most anaerobic bacteria and has bactericidal activity against Bacteroides fragilis. At a concentration of ≤8mg/ml, it can inhibit 95% of Bacteroides fragilis and almost 100% of Melaninogenic bacteria; at a concentration of ≤1mg/ml, it can inhibit all Fusobacterium, and has inhibitory effects on Clostridium perfringens, anaerobic cocci are highly sensitive to it, but it cannot counteract aerobic and facultative anaerobic bacteria. These blood drug concentrations can be achieved after intravenous injection, intramuscular injection, or oral administration of 500mg. Therefore, in recent years, it has been applied in China for severe anaerobic bacterial infections such as necrotizing pneumonia, empyema, and sepsis.

　　Tinidazole (metronidazole sulfoxide imidazole) is an imidazole antibacterial drug with high activity against anaerobic bacteria and Trichomonas vaginalis. It has stronger activity against Bacteroides fragilis, Fusobacterium, and other Bacteroides than metronidazole, but slightly weaker antibacterial activity against Clostridium perfringens. It is suitable for various infections caused by anaerobic bacteria. Dosage: oral initial dose of 2g, followed by 0.5 to 1g daily, taken twice, intravenous infusion of 800mg per time, once a day.

　　(6) Macrolides: Including erythromycin, josamycin, erythromycin, and roxithromycin (rosamicin), which have inhibitory effects on most anaerobic cocci. Especially, they have antibacterial activity against Staphylococcus aureus and Streptococcus species.

　　①Erythromycin: When the blood concentration is greater than 0.8mg/ml, 40% to 50% of Bacteroides fragilis, Fusobacterium, Clostridium perfringens, and Staphylococcus aureus can be inhibited. This concentration can be achieved when taking oral medication. The blood concentration can reach 3.1mg/ml with the usual intravenous dose, which can inhibit 90% of Bacteroides fragilis and 100% of Clostridium perfringens. However, recent reports indicate an increase in drug-resistant strains and the risk of phlebitis with intravenous administration, limiting its use.

　　② Josamycin: It has a strong effect on obligate anaerobic bacteria, among which the effect on Enterococcus is significantly better than that of Clindamycin, and the inhibitory effect on Bacteroides fragilis is similar to that of Metronidazole and Clindamycin. However, it has poor effects on Veillonella, Clostridium sporogenes, and Clostridium fusiforme are resistant to this drug. After oral administration, the concentration in sputum is high. Oral: adults 0.8 to 1.2g per day, divided into 3 to 4 doses.

　　③ Gital霉素 (Rothamycin): It has a stronger effect on anaerobic cocci than Josamycin. After oral administration, it is absorbed and has high concentrations in sputum and saliva, almost not reaching amniotic fluid and infant blood. The usual dose is 200mg, three times a day.

　　(7) Fluoroquinolones: Oxygen floxacin, Ciprofloxacin, Lomefloxacin, Floxacin (Difloxacin), and Tofloxacin, etc., in fluoroquinolones, have antibacterial effects against anaerobic bacteria.

　　① Ciprofloxacin, Ofloxacin (Floxacin): It has poor efficacy against Bacteroides fragilis, but moderate sensitivity to other Bacteroides. It also has antibacterial activity against Peptostreptococcus and Streptococcus. The dosage is 250mg of Ciprofloxacin, twice a day, by mouth, or 100 to 200mg, twice a day, by intravenous infusion, and 200mg of Ofloxacin, three times a day.

　　② Lomefloxacin (Roflomycin): It has 2 to 3 times stronger antibacterial activity against anaerobic bacteria than Ofloxacin (Floxacin) and Ciprofloxacin (Ciprofloxacin). It is suitable for acute and chronic infections caused by anaerobic bacteria. The usual dose is 100 to 200mg, 2 to 3 times a day, by mouth.

　　③ Floxacin (Difloxacin): It has similar activity against anaerobic bacteria to Chloramphenicol and is characterized by strong antibacterial activity. The antibacterial activity of Multifloxacin against anaerobic bacteria is stronger than that of Ciprofloxacin.

　　(8) Imipenem (Imipenem): It is a new type of atypical β-lactam antibiotic. It has similar activity against Gram-positive anaerobic bacteria and Clostridium sporogenes to Clindamycin (Clindamycin) and Metronidazole, and stronger antibacterial activity against Bacteroides fragilis than other antibiotics. After intravenous infusion, the lungs are one of the organs with the highest concentration, followed by sputum. It has a significant therapeutic effect on bacterial pneumonia, lung suppurative diseases, chronic respiratory tract diseases, and suppurative pleurisy caused by anaerobic bacteria. The usual dose is 1g, twice a day, by intravenous infusion or intramuscular injection.

　　Patients who start treatment in the inhalation pneumonia stage show effective antiseptic treatment, with the effect visible within 3 to 4 days and fever subsiding within 7 to 10 days. If high fever persists after 7 to 10 days of treatment, fiberoptic bronchoscopy should be performed to clarify the cause and perform drainage. If this is still ineffective, other diagnoses should be considered and other antibiotics should be used. If空洞性损害 occurs, it often takes several months to absorb and close. If the diameter of the cavity is greater than 6cm, it is difficult to close, and symptoms are often only relieved after 8 weeks of treatment. If empyema occurs, even with effective drainage, it takes an average of 29 days to subside fever.

　　2. Optimal anti-inflammatory treatment plan

　　(1) Outpatient acquired infections, the first choice for inflammation with anaerobic bacteria as the main pathogen is metronidazole, 0.2g twice a day intravenous drip, or tinidazole 0.4g, 2 times/d, intravenous drip.

　　(2) Mixed infections can be treated with clindamycin (chlorocephalosporin) 0.6g, 1-2 times/d, or piperacillin 2.0g, 3-4 times/d, intravenous drip.

　　(3) Severe patients can use cefoxitin 2.0g, 2-4 times/d, intravenous drip, and metronidazole or tinidazole can be added intravenously if necessary. To achieve a broader spectrum of coverage of pathogenic bacteria, imipenem (imipenem) 0.5g, 2-4 times/d, intravenous drip can be used.

　　3. Clearing sputum

　　(1) Sputum drainage: If the patient has a specific infected site, the affected side can be placed in a higher position, and the bronchus opening for drainage is below, and coughing sputum by patting the back. Long-term bedridden patients should frequently turn over and cough sputum on their sides. Patients with bulbar palsy can undergo sputum aspiration treatment. When sputum is abundant and cannot be coughed out, tracheal intubation or bronchoscope aspiration treatment can be performed.

　　(2) Mucolytic drugs: Ammonium chloride, bromhexine, acetylcysteine, and other drugs can be taken orally.

　　(3) Supportive treatment: Provide adequate protein, calories, and vitamins, encourage patients to drink more water, and determine the amount and type of intravenous fluid according to the condition, keeping the specific gravity at 1.020 is desirable. Generally, all patients should be given oxygen, and if the condition is severe, PaCl2

　　II. Prognosis

　　The prognosis of anaerobic bacterial lung infection depends on the patient's overall condition, the type of infection, and whether the treatment is timely. Old age, systemic failure, necrotizing pneumonia, and bronchial obstruction are poor prognostic factors. Generally, the prognosis of community-acquired anaerobic bacterial pneumonia is good. Patients with hospital-acquired anaerobic bacterial pneumonia often have underlying diseases and often develop Gram-negative bacterial infections, so the prognosis is poor, and the mortality rate can reach 5% to 12%.