Serratia pneumonia

Introduction to Serratia pneumonia Serratiapneumonia (Serratiapneumonia) is caused by Serratia infection, mostly acquired infections in hospitals. In recent years, the incidence rate has increased significantly, and drug-resistant strains have increased, and treatment is difficult. It has attracted widespread attention. basic knowledge The proportion of the disease: in the pneumonia, the incidence of the disease is about 0.05%-0.07% Susceptible people: no special people Mode of infection: respiratory transmission Complications: sepsis septic shock

The cause of Serratia pneumonia

(1) Causes of the disease

Serratia is a genus of Enterobacteriaceae. In 1896, Lehmann and Newmann first discovered Serratia plymuthica, which was called bacterium plymuthicca. It was attributed to Serratia after 1978 and is currently divided into 7 species: Serratia marcescens. ), Serratia liquefaciens, Serratia rubidaea, Serratia ficaria, Serratia odorifera, Serratia plymuthica and Serratia fonticola, of which Serratia marcescens is the main pathogen causing hospital-acquired infection.

With the application of DNA hybridization technology, Serratia proteamaculans, Serratia grimesii and Serratia liquefaciens, Serratia proteamaculflns are further divided into two biotypes: Serratia proteamaculanssubsp proteamaculans and Serratia proteamaculans subsp quinovora, Serratia grimesii and Serratia liquefaciens has been isolated from clinical specimens and is usually not clinically relevant. Both subtypes of Serratia proteamaculans are isolated from insects, soil, rodents, and plants, causing pneumonia. It has recently been discovered that Serratia odorifera can be further divided into two biotypes. : Serratia odorifera biogroup-1 and Serratia odorifera group-2, which can cause hospital-acquired infections, which have now been isolated from different clinical specimens of patients.

1. Morphology and staining Serratia are motivated and capable of movement. Some strains have capsules and flagella. Many strains produce pink or red pigments. The morphology of Serratia marcescens is generally smaller than other intestinal bacteria, and there is no capsule. For Gram-negative Brevibacterium, occasionally filamentous, (0.7 ~ 1.0) × 0.7cm size.

2. Culture and biochemical reaction Serratia strains are not required for growth medium, and can grow on nutrient agar, endo agar, MacConkey agar, blood agar plate, and the Serratia marcescens colony is round and slightly rough. It is viscous. When cultured at a temperature lower than 37 °C, flagella are more likely to develop and are aerobic or facultative anaerobic bacteria.

Serratia can ferment glucose, but only some strains produce small amounts of gas, do not ferment lactose, euphorbia, arabinose, raffinose and rhamnose, fermentable mannitol, salicin and sorbitol, contralateral The fermenting power of phytol and inositol is inconsistent, and no sputum is formed. Most of the strains are negative for methyl red reaction and grow in potassium cyanide medium. Most of the strains rapidly liquefy gelatin, a few are slow-reacting, with lysine and Ornithine decarboxylase, but does not form arginine double hydrolase and phenylalanine deaminase, does not use sodium malonate, can use citrate, VP reaction positive, on trisaccharide iron medium ( TSI) produces acid and does not produce gas, and can produce extracellular DNase, lipase.

Serratia produces red pigment. When cultured below 37 °C, pigment production tends to be more abundant, but the ability to produce pigment after multiple passages is weakened or even disappeared. In 1902, Kroft extracted the pigment and named it "spirin". (prodigiosin), so the sticky Serratia was formerly known as the bacterium, and it was not until 1960 that Rapoport and Hollen explained the chemical structure. The red pigment was dissolved in alcohol, ether, chloroform and other organic solvents, insoluble in water, and red The bacteriocin is a kind of lipopolysaccharide, which has been reported to have an increase in the number of white blood cells and an anti-inflammatory effect. The production of pigments and non-pigmented strains can cause disease, which can cause sepsis, urinary tract and respiratory infections, osteomyelitis and postoperative wound infection.

3. Antigen and subtype Serratia has a bacterial "O" antigen and flagella "H" antigen, and 15 O and 13 H species are known, for a total of 46 serotypes.

4. Inducing factors Serratia pneumonia occurred in hospitalized patients with the original underlying diseases. A11en et al observed 135 cases of Serratia marcescens infection in Temple University Hospital, and 89% of cases were related to decreased host resistance, which can lead to immunity Functional impairment may be the cause of infection, such as various serious diseases, malignant tumors, leukemia, diabetes, cirrhosis, heart failure, chronic bronchitis, pulmonary heart disease, uremia and burns; long-term abuse of steroids, immunity Inhibitors, impaired systemic immune function; partial invasive examination and treatment, such as major surgery, indwelling catheter, venous cannula, blood and peritoneal dialysis; respiratory treatment measures, such as tracheal intubation, tracheotomy, mechanical Ventilation, nebulization, etc. can directly inhale Serratia into the lungs. In addition, long-term use of broad-spectrum antibiotics and narcotics addicts makes Serratia easy to colonize the respiratory tract, leading to the possibility of infection, especially in newborns. , the elderly and pregnant women.

(two) pathogenesis

Serratia is a conditional pathogen. It is known that Serratia can cause disease in rabbits, horses, buffaloes and deer. Under experimental conditions, rats, cats, guinea pigs, hamsters, sea turtles and dogs can be sick. The results showed that the LD50 was 1.5×1062.6×107, and the LD50 was 4.7×1055.3×107 after adding mucin. The mucin appeared to enhance the virulence. The endotoxin produced by Serratia can cause the body to occur. Pathophysiological changes, necrosis of lung tissue, and platelet aggregation, increased fragility, so that the circulating platelets are drastically reduced, resulting in bleeding of various organs, sometimes affecting the production of DIC by blood coagulation factors, and severely inhibiting the hematopoietic function of bone marrow. In addition, the sticky sand The hemolysin, protease and hemosiderin macrophage produced by the bacterium also play an important role in the pathogenesis. Pulmonary edema and hemorrhage occur after inoculation of protease in guinea pigs or mice. These symptoms are similar to those of human pneumonia. The immune serum of protease can protect animals, such as protease into the rabbit cornea, the cornea produces inflammation and necrosis, and the protease has a destructive effect on the immune function of the body. There is an 1-egg in the human body. The white enzyme inhibitor enhances the killing ability of macrophages, and the protease produced by Serratia marcescens can degrade the 1-protease inhibitor. When the Serratia enters the lung, several proteases such as lecithinase can be produced. , protease, chitinase, cause phagocytic infiltration and tissue destruction, weaken and destroy the body's immune function, causing primary or secondary Serratia pneumonia.

Serratia pneumonia prevention

Prevention: Active treatment of primary disease, enhance the body's resistance, strict disinfection system and aseptic operation, strengthen nursing for susceptible patients, isolate and treat infected and infected patients, prevent cross-infection, strictly control antibiotics, corticosteroids Application indications.

Serratia pneumonia complications Complications sepsis septic shock

Often bacteremic pneumonia, such as sepsis, pleurisy, empyema, septic shock, renal failure and other complications, such as treatment, often worsened, and the corresponding complications.

Symptoms of Serratia pneumonia Common symptoms Leukocytosis, dyspnea, chills, chest pain, snoring, snoring, shortness of breath, high heat shock

Symptom

Similar to general acute bacterial pneumonia, mainly characterized by fever, chills, cough, hemoptysis or pseudo-blood or jaundice, difficulty breathing, chest pain, but secondary sand for hospital acquired infections and original lung infections Lei-bacteria pneumonia, the symptoms are not typical, can cover the symptoms of pneumonia due to the primary disease symptoms, while fever, cough, cough and jaundice are the symptoms of the primary disease, but this time patients often have increased disease, respiratory failure, heart failure or Sudden high fever, increased cough and purulent sputum.

2. Signs

Both lungs can smell dry and wet voices. When the lungs or lungs are solid, there may be corresponding lung segments. The lobes of the lungs are enhanced, turbid, audible and bronchial breath sounds. Critically ill patients may have shortness of breath. Bun and shock, etc.

Serratia pneumonia examination

1. routine inspection

(1) Peripheral blood shows an increase in white blood cells and neutrophils, and platelets can be reduced.

(2) sputum examination routine smear Gram staining, a large number of Gram-negative bacilli can be seen.

(3) severe cases often have hypoxemia, some patients may be associated with hypercapnia, may have varying degrees of acid-base imbalance.

(4) Some patients may have renal failure, BUN, Cr increased.

2. Pathogen examination

(1) Blood culture: Because Serratia pneumonia is often bacteremia, if you can seize the opportunity to take blood, you can find the growth of Serratia, and the blood culture positive rate of blood-borne Serratia pneumoniae is high.

(2) sputum bacterial culture: This method is simple and convenient, and the patient is easy to accept, but it is easily contaminated by the upper respiratory tract colony. Therefore, the specimen is required to be from the deep part of the lung, and is first cleaned and homogenized quantitatively and then sent to culture. To improve accuracy.

(3) Direct collection of lower respiratory secretions: direct use of lower respiratory secretions can reduce the pollution of upper respiratory flora, the results are more accurate, but traumatic, require certain conditions, clinically according to the advantages and disadvantages of various methods And the hospital conditions and the skill level of the operator use one of the following methods, especially for patients with acquired Serratia pneumonia in the hospital, the commonly used inspection methods are:

1 Insert a sterile thin plastic catheter through the ring-shaped membrane puncture and aspirate the secretions of the lower respiratory tract. Because the nasopharyngeal cavity is not used, the contamination of the pharyngeal bacteria is reduced, but it is traumatic.

2 Under the chest X-ray positioning, the lung tissue and secretions infiltrated by the lung inflammation through the chest wall puncture, completely avoiding the upper respiratory tract pollution, but the traumatic, bleeding and pneumothorax and other complications can reach 20% .

3 The secretion of secretions by fiberoptic bronchoscopy is a safer method of examination, but requires certain equipment, and the operator must have a certain level of technology.

(4) Other body fluid culture: Mid-stage urinary bacterial culture, bone marrow bacterial culture, and pleural effusion culture can be found in Serratia growth.

Through the above various body fluid cultures, the positive result of Serratia can be obtained. For the guidance treatment, the susceptibility test should be added when the bacteria are cultured, and other bacteria can be cultured simultaneously for the mixed infection.

Chest X-ray findings: enhanced lung texture, characterized by focal patchy bronchopneumonia, diffuse patchy lung infiltration, mostly in the middle and lower lung fields, lobular or small nodular lung infiltration, lobes or Separation of the lung segment, there may be a small abscess <1cm in diameter, there may be pleural thickening, pleural effusion.

Diagnosis and identification of Serratia pneumonia

Diagnostic criteria

Clinically, there are fever, chills, cough, sputum, blood stasis or false hemoptysis, chest pain, wet snoring or bronchial breath sounds in both lower lungs, chest bronchial pneumonia or diffuse infiltration, and small abscess There are a large number of Gram-negative bacilli in the sputum smear, peripheral blood leukocytes and neutrophils, especially for those over 50 years old, or those who use hormones, immunosuppressive agents, aerosol inhalation and mechanical ventilation, should consider this The disease may be, but sometimes the clinical manifestations of Serratia pneumonia are not typical, especially on the basis of severe primary disease.

Therefore, in the process of primary disease, high fever, coughing a lot of purulent phlegm or white sticky sputum, new infiltrating shadow on the chest radiograph or enlargement of the original lesion, peripheral leukocytosis, sputum smear showing a large number of Gram-negative bacilli, should also consider This case may be pneumonia, should be checked several times, blood or pleural effusion and other cultures, if necessary, direct access to lower respiratory secretion culture, where two or more times in a row of sputum culture of Serratia; or sputum and blood or Serratia is cultured in pleural effusion; or Serratia is cultured directly in the lower respiratory tract secretions and contaminated; or sputum culture and post-mortem autopsy are isolated from the lungs, combined with the above clinical manifestations and chest X-ray results Can be diagnosed, can not rely on a single sputum cultivation of Serratia growth and treatment of this disease, because it may be the upper respiratory tract colonization, so the diagnosis of Serratia pneumonia should be based on clinical manifestations, chest X-ray and pathogenic results.

Differential diagnosis

The onset conditions, clinical manifestations and X-ray findings of Serratia pneumonia are similar to those of other Gram-negative bacilli pneumonia, such as Klebsiella pneumonia, Pseudomonas aeruginosa pneumonia, Proteus pneumonia, P. citrate pneumonia, Morgan Morgan Bacterial pneumonia is often difficult to distinguish clinically. Especially in hospital-acquired infections, there are no typical clinical manifestations. Therefore, it is necessary to check the blood and pleural effusions several times to facilitate the difference between them.

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