Pneumococci
Last reviewed: 23.04.2024
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A special position in the genus Streptococcus takes the form of S. Pneumoniae, which plays a very important role in human pathology. He was discovered by L. Pasteur in 1881. His role in the etiology of croupous pneumonia was established in 1886 by A. Frenkel and A. Weixelbaum, as a result of which S. Pneumoniae is called pneumococcus. Its morphology is unique: cocci have a shape resembling a candle flame: one end of the cell is sharpened, the other is flattened; are usually arranged in pairs (the flat ends face each other), sometimes in the form of short chains. They do not have flagellum, they do not form a spore. In the human body and animals, as well as on media containing blood or serum, form a capsule. Gram-positive, but in young and old cultures are often gram-negative. Optional anaerobes. The temperature optimum for growth of 37 ° С, at temperature below 28 ° С and above 42 ° С do not grow. The optimum pH for growth is 7.2-7.6. Pneumococci form hydrogen peroxide, but they do not have catalase, so for growth they require the addition of substrates containing this enzyme (blood, serum). On blood agar, small round colonies are surrounded by a green zone formed by the action of exotoxin hemolysin (pneumolysin). Growth on sugar broth is accompanied by turbidity and precipitation of a small precipitate. In addition to the O-somatic antigen, pneumococci have a capsular polysaccharide antigen, which is distinguished by a wide variety: pneumococcus polysaccharide antigen is divided into 83 serovariants, 56 of them are divided into 19 groups, 27 are presented independently. From all other streptococci pneumococci differ morphology, antigen specificity, and also by fermenting inulin and showing high sensitivity to optohin and bile. Under the influence of bile acids in pneumococci, intracellular amidase is activated. It breaks the bond between alanine and muramino acid peptidoglycan, the cell wall collapses, and lysis of pneumococci occurs.
The main factor of pathogenicity of pneumococci is a capsule of polysaccharide nature. The encapsulated pneumococcus loses its virulence.
Pneumococci are the main pathogens of acute and chronic inflammatory diseases of the lungs, which occupy one of the leading places in the incidence, disability and mortality of the world's population.
Pneumococci along with meningococci are the main culprits of meningitis. In addition, they cause creeping ulcer of the cornea, otitis, endocarditis, peritonitis, septicemia and a number of other diseases.
[Laboratory diagnostics
Diagnosis of pneumococcal disease is based on the isolation and identification of S. Pneumoniae. The material for the study is sputum and pus. Pneumococci are very sensitive to white mice, so often to isolate pneumococcus use a biological test. In dead mice, pneumococci are found in the smear from the spleen, liver, lymph nodes, and when sowing from these organs and from the blood, a pure culture is isolated. To determine the serotype of pneumococci, an agglutination reaction is used on the glass with typical sera or the phenomenon of "swelling of capsules" (in the presence of homologous serum, the capsule of pneumococci swells sharply).
Specific prevention
Prevention of pneumococcal disease is carried out with the help of vaccines prepared from highly purified capsular polysaccharides of those 12-14 serovariants that most often cause diseases (1, 2, 3, 4, 6A, 7, 8, 9, 12, 14, 18C, 19, 25 ). Vaccination against pneumococcal infection is highly immunogenic.