Pneumococcus

PNEUMOCOCCUS (Pneumococcus, sive Streptococcus lanceolate Pasteuri, sive Diplococcus pneumoniae Frankel), a paired coccus (diplococcus), which is one of the most frequent (94% of all cases) causative agents of lobar pneumonia. It was first described in 1881 by Pasteur and Sternberg. It was studied in detail and isolated in pure culture in 1884 by Frankel. In smears from pneumonic sputum or from the blood of mice infected with sputum, P. has the appearance of elongated cocci connected in pairs, pointed toward one (usually outer) edge; each pair of cocci is enclosed in a single common capsule [see separate table (st. 623-624), fig. 6]; the latter P. lose upon subculturing onto artificial media. P. is a facultative anaerobe. Optimum growth +37°, minimum +25°, maximum +42°. It grows best on weakly alkaline broth (pH = 7.6-7.8). On broth it causes a slight uniform turbidity and a small flocculent precipitate. Upon prolonged cultivation in broth it begins to form long chains and grows similarly to streptococcus at the bottom of the test tube. On simple meat-peptone agar it forms small colonies with a darker center and a lighter periphery; on serum or ascitic agar it gives somewhat larger colonies of a grayish color; on blood agar it does not cause hemolysis, but forms colonies of green color due to the conversion of Hb erythrocytes into methemoglobin. Upon the addition of bile (1:10) or bile salts to broth culture, P. dissolve (the culture clears); this sign is used to distinguish P. from streptococcus. Another differential sign for distinguishing P. from streptococcus is the ability of P. to decompose the polysaccharide inulin, which is usually not decomposed by streptococcus. The specific relationship of P. to optochin (a derivative of hydroquinone), which kills P. as opposed to streptococcus, both in vivo and in vitro in very large dilutions (Morgonroth, Levy), is also specific. White mice (death through 12-36 hours with signs of septicemia) and rabbits are most susceptible to P.; pigeons are the least susceptible. P. fairly quickly lose their virulence on ordinary nutrient media. The best way to preserve virulence is drying in a desiccator of the heart or spleen of a mouse that died of pneumococcal septicemia. Serologically, four types of P. are distinguished (Dochez, Gillespie). Each of the first three (fixed) types of P. is agglutinated only by the corresponding serum. Types I and II are the typical P., encountered in the sputum and saliva of patients with lobar pneumonia, as well as in healthy persons having contact with such patients (carriers). Type III is Pneumococcus mucosus, identical with Streptococcus mucosus Schottmuller, characterized by a sharply expressed capsule, preserved even on artificial media (with serum or blood); on agar it gives colonies that merge into a mucous deposit. Type IV, or type X, is a collective group uniting all strains of P. that are not agglutinated by the sera of the three fixed types; this group is divided into a number of smaller serological subgroups (Park, Cooper, Olmstead). Type IV is encountered very frequently in the oral cavity of healthy persons and in pneumonia in children. (On the frequency of finding different types of P. in lobar pneumonia and bronchopneumonia - see Pneumonia.) To determine the type of P., experiments on white mice are used. A small piece of sputum, the size of a pea, is washed several times in sterile physiological solution, rubbed, in a small amount of broth, and injected into the abdominal cavity of a mouse. The blood from the heart of a mouse that died of septicemia is sown in ascitic or serum broth, and with the pure culture of P. obtained the next day, agglutination reaction is set up with standard (types I, II, III) pneumococcal sera. In cases where a rapid determination of the type of P. is required (e.g., during serum treatment of lobar pneumonia), the following method is used: a mouse infected with sputum is killed through 5-8 hours after infection; the contents of the abdominal cavity are washed out with 4-5 cm³ of physiological solution and centrifuged for some time at a low number of revolutions to precipitate blood cells and fibrin. The uniformly turbid liquid is subjected to a second strong centrifugation until the P. is completely precipitated. From the precipitate a suspension of P. in physiological solution is prepared for the agglutination reaction, and the liquid above the precipitate is used for the precipitation reaction. The latter is set up as follows: three narrow test tubes are filled with 0.2 cm³ of undiluted serum of types I, II, and III, and carefully layered on top with the wash liquid; in case of a positive result, a white ring appears at the place of contact of the two liquids. The precipitation reaction can also be set up directly with sputum; the latter is mixed with a small amount of physiological solution, boiled to precipitate proteins, and centrifuged; the clear liquid is used for the precipitation reaction. In liquid cultures, as well as in the body of a patient, P. excrete specific soluble substances (Avery, Dochez), representing chemically pure carbohydrates of the polysaccharide type (Heidelberger, Zverev); these substances, which are carriers of the type-specific properties of P., belong to the group of so-called residual antigens (Restantigene), participating in immunity reactions, they themselves are not antigens, but can be such only in combination with the protein of the microbial cell. Pneumococcal serum prepared with the protein of P. possesses only species specificity (with respect to P. of all species), but not type specificity. The antigenic complex capable of giving specific type (agglutinating and precipitating) serum is the intact cell, consisting of the protein of P. plus its polysaccharide.