Staphylococcal pneumonia

Introduction to staphylococcal pneumonia Staphylococcal pneumonia is an acute suppurative pneumonia caused by staphylococci. In recent years, there has been an increasing trend. Heavier conditions often occur in patients with impaired immune function, especially in hospital infections of drug-resistant Staphylococcus aureus. basic knowledge The proportion of illness: 0.003% Susceptible people: no special people Mode of infection: non-infectious Complications: bacteremia, endocarditis, meningitis

Staphylococcal pneumonia

(1) Causes of the disease

1. Morphology and classification Staphylococcus is a group of Staphylococcus, a group of Gram-positive cocci of the genus Staphylococcus, a total of 22 species, bacteria in the breeding period arranged in a grape string, hence the name, Staphylococcus is mostly aerobic or anaerobic Oxygen growth, simple nutrient requirements, vigorous growth in broth culture medium, cultured after 24h incubation, turbid, and some bacteria sink to the bottom of the tube, after 24 hours of culture on broth agar plate, the colony reached 3 ~ 4mm, round The edges are neat, the surface is moist and lustrous, and opaque. On the blood agar plate, obvious hemolytic rings are visible around the colonies, and most of the hemolyzed are pathogenic strains.

In the early years, different pigments were produced on the solid medium according to Staphylococcus: Staphylococcus aureus, Staphylococcus aureus and Staphylococcus aureus. In 1965, the International Staphylococcus and Micrococcus Classification Committee divided them into coagulase-positive golden grapes. Cocci and coagulase-negative Staphylococcus epidermidis, the 1974 Bergey bacteriological identification manual added coagulase-negative staphylococcus aureus, and since then many new species have been isolated, including some of the staphylococcus, some (about 25%) pigs The staphylococcal porcine subspecies strain was positive for coagulase and was negative for coagulase.

Staphylococcus to human infection is mainly Staphylococcus aureus, Staphylococcus epidermidis in coagulase-negative staphylococci, although staphylococcus aureus can also cause disease, mainly urinary tract infection.

In recent years, it has been reported that S. lugdunensis can cause serious infection like Staphylococcus aureus.

2. Pathogenic staphylococci can secrete 34 kinds of efflux proteins, including various enzymes and toxins, which are related to their pathogenicity. Coagulase can attach fibrin in plasma or body fluid to the surface of staphylococcus. Become a fibrous coat to protect bacteria from phagocytosis and digestion by phagocytic cells, so that staphylococcal toxins or other enzymes can act. Staphylococcal toxins have , , , and hemolysin, among which and hemolysis The most common, they have hemolysis, can cause leukocytosis, platelet lysis, tissue necrosis, on the thalamus of humans and mammals, lethal, staphylococci can also produce enterotoxin, leukocidin, exfoliative toxins and Toxic shock syndrome toxin (TSST), which can cause food poisoning, destroy white blood cells, invade skin and cause scarlet fever syndrome and shock, staphylococci still produce lysozyme and hyaluronidase, protease, catalase , plasmin, lipase, nuclease, etc., extracellular polysaccharides as an adhesin, making bacteria easy to connect with catheters The adhesive material is an important factor in this type of bacteria intravascular devices and implants hospital infection occurs.

3. Drug resistance Before the 1960s, penicillin was the most effective antibiotic for the treatment of staphylococci. At present, about 90% of the clinical isolates in Shanghai and Beijing are resistant to penicillin by producing -lactamase (penicillinase). The methicillin-resistant Staphylococcus aureus (MRSA) discovered in the early 1960s is resistant to clinical -lactams. In the 1980s, gentamicin was also an effective drug for the treatment of MRSA infection. Currently, MRSA is effective for gentamicin. The resistance rate has exceeded 50%. Staphylococcus is highly sensitive to fluoroquinolones in the late 1980s. It has been used as a retention drug for the treatment of MRSA infection, but now more than 80% of MRSA and MRSE are resistant to fluoroquinolones, coagulase-negative staphylococci The drug resistance is similar to that of Staphylococcus aureus. Except for vancomycin, norvancomycin and other glycopeptides and rifampicin, the resistance rate of clinical isolates to common antibiotics in large hospitals is >50%, 1996. Since the separation of two Staphylococcus aureus strains with reduced sensitivity to vancomycin in Japan, there have been some cases in the United States and France. It has not been reported in China yet, but it is worthy of attention, and it is different from the virulence reduction of some bacterial resistant strains. MRSA and MSSA equally pathogenic.

Staphylococcus resistance mechanisms are:

(1) Production of inactivated enzymes and modified enzymes: Penicillinase produced by staphylococci can destroy a variety of penicillin antibiotics, and some strains with high enzyme production can be expressed as resistant to oxacillin, and aminoglycoside-modifying enzymes can be produced. Inactivation of aminoglycosides makes the strain appear to be resistant to aminoglycosides, and staphylococci can also produce acetyltransferase to inactivate chloramphenicol and render it resistant.

(2) Target position change: Penicillin-binding protein (PBP) is a transpeptidase for staphylococcal cell wall synthesis, Staphylococcus has four PBP, and methicillin-resistant Staphylococcus has a mecA gene on its chromosome. A new penicillin-binding protein PBP2a is produced. PBP2a has low affinity with -lactam antibiotics, can maintain bacterial cell wall synthesis in a high concentration of -lactam environment, and makes bacteria appear resistant and resistant to methoxy The distribution of Staphylococcus aureus and Staphylococcus epidermidis in Xilin is abbreviated as MRSA and MRSE, and the resistance mechanism is the same. These resistant bacteria are resistant to methicillin and all penicillins, cephalosporins and other - Amide antibiotics are resistant, and the resistance rate to quinolones, tetracyclines, certain aminoglycoside antibiotics, chloramphenicol, erythromycin, and lincomycin is also high (>50%); DNA gyrase target Positional changes and topoisomerase IV mutations are the main mechanisms of staphylococcal resistance to staurones. In addition, staphylococci can also alter folate inhibitors such as sulfa drugs, rifampicin, mupirocin, macrolides and Linke These antibacterial agents are resistant to the target sites such as hormones.

(3) efflux effect: Staphylococcus can excrete intracellular tetracyclines, macrolides and clindamycin and are resistant to these drugs.

(two) pathogenesis

Under normal circumstances, the human body has many opportunities to contact with staphylococcus, but it does not cause disease and has certain immunity. However, this immunity is weak. When local or systemic resistance declines, the patient inhales contains a large amount of colonization in the nose. Staphylococcus or airway staphylococcus, which causes bacteria to multiply in the lungs and produce purulent lesions. Coagulase produced by S. aureus reduces phagocytosis of neutrophils and produces various enzymes that cause bronchial wall and alveolar necrosis. Inhaled staphylococcal pneumonia often has a large leafy distribution or extensive, confluent bronchiolitis, bronchial and alveolar rupture, allowing gas to enter the pulmonary interstitium and communicate with the bronchus, when necrotic tissue and secretions The formed pus obstructs the bronchioles and constitutes a one-way valve. It produces tensional pulmonary air sacs, especially in children and adolescents. If the superficial lung air swell is too high, it can break into the pleural cavity to form pneumothorax, pus. Pneumothorax, the lesion can be widely developed into a honeycomb lung, pus often around the bronchus to form multiple small abscess and fusion, abscess can break through the interlobular invasion and adjacent lung lobe, Pleural empyema perforation may be formed, pus pneumothorax, and bronchial fistula formation, adults 20% to 30% were single or multiple abscesses, containing a large number of staphylococci, red blood cells, white blood cells and necrotic tissue.

Blood staphylococcal pneumonia is secondary to staphylococcal bacteremia or sepsis, caused by bacterial emboli to the lungs through the circulation of blood. The primary infection is often skin blemishes, folliculitis, impetigo, osteomyelitis, cellulitis , wounds, etc., the lesion is characterized by multiple, peripheral pulmonary infiltration, bacterial embolism caused by multiple pulmonary arterial embolism, resulting in multiple suppurative inflammation of the lungs, and then tissue necrosis to form multiple lung abscess, and may involve the pleura to produce pus Chest or pus pneumothorax, a few cases are directly caused by blood line spread empyema.

Inhalation pneumonia is mainly Staphylococcus aureus, blood-borne disseminated pneumonia is more than Staphylococcus aureus, coagulase-negative staphylococci can also be seen.

Staphylococcal pneumonia prevention

Although a variety of subsequent immune responses can occur after staphylococcal infection, and attempts have been made to produce immunological preparations such as staphylococcal bacterins, staphylococcal toxoids, and so on, no immunological preventive measures have been proven to be effective.

Some people advocate the treatment of carriers, people with positive results after nasopharyngeal swab sampling can be given rifampicin 0.45 ~ 0.6g per day, even for 5 days, or combined with other sensitive antibacterial drugs can significantly reduce staphylococcus Infection, after 6 to 12 weeks, depending on the individual's specific conditions, repeat a course of treatment if necessary. There are also antibiotics such as bacitracin or neomycin nasal drops, mupirocin or bacitracin ointment for nasal vestibular topical treatment. Reported that medical staff should be strict aseptic technique, disinfection and isolation in the ward, wash hands after touching each patient.

For those with staphylococcal infections, especially those infected with drug-resistant strains in hospitals, isolation should be carried out to block the source of infection and the route of transmission. Relevant medical personnel should also carry out nasopharyngeal swab culture. If the same type of bacteria is cultivated, medical personnel It is also a carrier related to staphylococcal infection in hospitals, and should be replaced when necessary.

Staphylococcal pneumonia complications Complications bacteremia endocarditis meningitis

If the treatment is not timely, it can be complicated by bacteremia, endocarditis, meningitis and so on.

Staphylococcus pneumonia symptoms common symptoms purulent hypothermia empyema high fever chills snoring dyspnea coma shock

1. Rapid onset, severe symptoms of systemic poisoning, chills, high fever, cough, purulent sputum, pus and blood stasis, difficulty breathing, cyanosis, etc.

2. The disease develops rapidly, changes in consciousness, convulsions, coma and even shock. These conditions are common in people who are infected by extrapulmonary infection.

3. In-hospital infections appear in the post-operative intensive care unit and long-term inpatients. The onset is latent and the symptoms are covered by the original underlying diseases. Therefore, it is not typical, often overlooked, respiratory symptoms are mild, low fever, coughing a small amount of purulent, but the condition changes. fast.

4. Blood-borne staphylococcal pneumonia is secondary to the spread of extrapulmonary infection. The symptoms of systemic poisoning are severe. Symptoms and signs of infection in the primary lesion or other parts can be found. In addition, empyema occurs in the pleura.

5. In the early stage, the local breath sounds are reduced, there is dry and wet sputum sound, and the pus and chest is diagnosed with dullness, the breath sound is reduced or disappeared; if there is pneumothorax, the drum sound is diagnosed, and the breath sound is reduced or disappeared.

Examination of staphylococcal pneumonia

The white blood cell count is obviously increased, often (15 ~ 25) × 109 / L, neutral more than 80%, sputum bacterial smear examination found a large number of staphylococci and pus cells, sputum white blood cells can also find Gram-positive bacteria, The liquid bacteria are cultured as staphylococci, blood culture: high positive rate, pleural fluid culture: easy to culture to staphylococcus.

X-ray chest radiograph is characteristic, polymorphic and variability, X-ray can be flaky, patchy inflammatory infiltration; one inflammatory infiltration disappears and another new lesion appears, or the lesion develops into a large shadow, small Abscess, emphysema and bullae (pulmonary emphysema and bronchial communication with one-way flap) empyema and pneumothorax.

Diagnosis and identification of staphylococcal pneumonia

According to typical clinical manifestations, X-ray signs, respiratory secretion smear and culture can make a diagnosis, but the early clinical manifestations of this disease are not consistent with X-ray changes, early diagnosis is often difficult, X-ray examination follow-up to track the dynamic changes of lung lesions It is helpful for diagnosis.

Bacteriology examination is the basis for the diagnosis of staphylococcal pneumonia. A large number of pus cells can be seen in the sputum smear test, and a pile of Gram-positive cocci can be seen. Gram-positive cocci, sputum, nasopharyngeal swab, serous cavity fluid can be seen in the leukocytes. Lower respiratory secretions, lung puncture and blood culture should be carried out as early as possible. Specimens should be taken before the use of antibacterial drugs. Since normal people can carry bacteria in the nasopharynx, the cough must be cleaned before culture and cultured several times. The positive rate of adult sputum culture is as high as 87%-95%, and the positive rate of blood culture is low. It should be taken several times during high fever (2~3 times, once every 1/2~1 hour) or from two different parts. Adult blood specimens should be 10ml, and Staphylococcus epidermidis blood culture requires 2 positives to confirm the significance. In addition to pleural fluid, lung puncture and blood culture, staphylococcus is positively diagnosed. Other specimens include lower respiratory tract pollution prevention technology. The collected specimens are cultured to Staphylococcus, and their diagnostic value needs to be judged in combination with clinical (such as rapidly developing necrotizing pneumonia).

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