P. aeruginosa is a representative strain of Pseudomonas, widely distributed in nature and human body. Its important condition in the external environment is humid environment; it is a conditional pathogen, mainly causing hospitals. Internal infection.
1. Bacterial properties
(1) morphologically staining Gram-negative bacilli, the cells are in the shape of bulbs or filaments, varying in length; single, double or short chain arrangement; no spores, capsules, single flagella at one end, active movement, Clinical isolates often have pili.
(2) Cultivation of characteristic aerobic bacteria, some strains can grow in facultative anaerobic environment, low nutritional requirements, good growth on common medium, growth temperature range of 25 ° C ~ 42 ° C, optimal growth The temperature is 35 ° C, 4 ° C does not grow and 42 ° C growth is one of the identification points of the bacteria.
In the blood plate, MacConkey plate can form five different forms of colonies: 1 typical type, the colonies are gray-green, the size is different, flat and moist, the edges are irregular, umbrella-like stretching, the surface often shows metallic luster; 2 Coliform-like, colony rounded, gray-white translucent, like Escherichia coli colony; 3 mucus type, colony smooth convex, mucus-like; 4 pygmy type, small, dull translucent colonies; 5 rough The colony has a convex central shape with a flat edge and a rough surface. The transparent hemolysis ring is often seen on the blood plate, and has the smell of ginger; it grows turbid in the liquid medium, and the surface can form a bacterial membrane. On the SS agar plate, the bacteria are cultured for 24 hours to form smaller colorless translucent colonies, generally It is not easy to distinguish from Salmonella and Shigella colonies, but the center of the colonies is brownish green after 48 hours. Pseudomonas aeruginosa can produce a variety of pigments when grown on ordinary agar plates, mainly pyocyanin (a characteristic pigment of Pseudomonas aeruginosa) and pyocyanin (fluorescein), the former being blue-green. About 80% to 90% of Pseudomonas aeruginosa isolated from clinical specimens produce pyocyanin and pyocyanin.
(3) Biochemical reaction oxidase positive, on the OF medium, can be oxidized by glucose, xylose acid production, arginine double hydrolase positive, acetamidase positive, liquefied gelatin, using citrate, reducing nitrate Nitrogen is produced and helium is negative.
(4) Antigen structure Pseudomonas aeruginosa has a bacterial (O) antigen, a flagellar (H) antigen, a mucus (S) antigen, and a pili antigen. O antigen has two components: one is an outer membrane protein, which is a protective antigen, which is highly immunological and genus specific; the other is lipopolysaccharide (LPS), which is type-specific and can be used for bacterial typing.
(5) Resistance Pseudomonas aeruginosa is more resistant to external factors than other non-spore bacteria and can survive for a long time in a humid environment. It is resistant to dryness and ultraviolet rays, but it is not strong against heat. Clinical isolates are not sensitive to various antibiotics.
2. Clinical significance
Pseudomonas aeruginosa can be isolated from many sterile vessels and solutions in hospitals. Commonly used aqueous solutions include wash water, disinfectant and liquid drugs. Common invasive pathways for pulmonary infections caused by Pseudomonas aeruginosa in hospitals are aerosol inhalation, oxygen inhalation, various invasive examinations and treatments, such as fiberoptic bronchoscopy, catheters, biliary tract, postoperative drainage, etc., destroying the body. Skin or mucosal barrier, often caused by the invasion of the bacteria.
Severe Pseudomonas aeruginosa infections often occur in patients with local tissue damage or reduced resistance, such as burn patients, various cancer patients and patients with broad-spectrum antibiotics, hormones, antineoplastic agents and immunosuppressive agents; premature birth, congenital Deformed children and cystic fibrosis and other elderly patients are also prone to serious P. aeruginosa infection.
The pathogenic role of Pseudomonas aeruginosa is related to a variety of virulence factors, mainly in the following categories:
(1) Adhesion and colonization to form adhesion conditions include: 1 capsular polysaccharide on the surface of Pseudomonas aeruginosa prevents phagocytosis of leukocytes and phagocytic cells; 2 adhesin on the surface of bacteria (mainly pili) and epithelial cells Corresponding receptor binding; 3 host defense mechanisms are abnormal. The latter allows the bacteria to stop and maintain prolonged contact with the epithelial cells.
The intact skin mucosa is a natural barrier, so Pseudomonas aeruginosa rarely becomes the primary pathogen of healthy people, but changes or damages the host's normal defense mechanisms, such as skin mucosal destruction, indwelling catheter, tracheotomy intubation Or immunological mechanisms such as neutropenia, hypoproteinemia, various tumor patients, patients with hormones and broad-spectrum antibiotics often cause infection. Burns of eschar, the skin of the baby or child, the umbilical cord and the intestine, and the urethra of the elderly are the more common primary lesions or invasion portals. If the body's resistance is reduced or the bacteria are toxic, and the number is large, it can grow and multiply in the blood, and sepsis occurs.
(2) Exotoxin A is the main virulence factor and is the most potent toxin produced by Pseudomonas aeruginosa. It inhibits protein synthesis and has necrosis effect on skin mucosa. About 90% of strains produce exotoxin A. In burn patients, Its lethal effect is particularly prominent.
(3) Other proteases, extracellular enzymes S, hemolysin, enterotoxin, pigment, leukocidin, endotoxin, etc.
3. Microbiological test
(1) Specimen collection Different clinical specimens, such as wound secretion, urine, pus and puncture fluid, blood, cerebrospinal fluid, chest and ascites, joint fluid, etc., are taken according to the disease and examination purpose. Hospital environmental testing can be sampled from air, water, surface of objects, etc.
(2) Inspection method
1) Microscopic examination Cerebrospinal fluid, pleural and ascites were centrifuged and a sediment smear was taken. The green pus and secretions were directly smeared with Gram staining microscopy. For Gram-negative bacilli, there are flagella.
2) Separation and culture Blood and body fluid specimens can be directly inoculated into the above medium by transferring the blood agar plate and the MacConkey plate, pus, secretions, and mid-stage urine.
3) Identification and identification A preliminary identification can be made based on the colony characteristics of the culture, the production of a water-soluble green pigment, a special ginger odor, an oxidase test, an OF test, and the like. However, Pseudomonas aeruginosa, which is atypical to the pigment, also needs other biochemical reactions (such as gelatin liquefaction, arginine double hydrolysis test, 42 ° C growth test, etc., acetamidase test has certain value), and other fakes. Identification of monocytogenes.
Isolation of Pseudomonas aeruginosa from clinical specimens requires exclusion of contamination. The bacteria are isolated from the patient's blood and sterile body fluids, urine, especially repeated detection, combined with clinical manifestations can be determined to be infectious pathogens, patina Pseudomonas lower respiratory tract infection requires three consecutive sputum culture positives to establish, such as the clinical manifestations of patients without infection, although Pseudomonas aeruginosa should be isolated as a normal flora.
4) Drug resistance Pseudomonas aeruginosa is not sensitive to most antibiotics and exhibits obvious intrinsic resistance. The intrinsic resistance of Pseudomonas has long been thought to be due to the low permeability of the outer membrane (mainly the outer membrane microporous protein mutation, which prevents the antibiotic from entering the cytoplasm from the outer membrane). Recent studies have shown that The mechanism of production of cytotoxicity is related to the energy-dependent active efflux system of bacteria, and other resistance mechanisms may exist at the same time. Since Pseudomonas aeruginosa may be resistant during long-term antibiotic treatment, it is necessary to test the antibiotic susceptibility of the replicate isolates after 3 to 4 weeks of treatment. At present, combined treatment is used for Pseudomonas infection, such as the use of a β-lactam antibiotic combined with an aminoglycoside or a quinolone antibiotic to treat severe P. aeruginosa infection.
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