Abstract
Although the infectivity of recently isolated strains of pneumococci has been tested both in routine injection of mice for type-identification, and in special studies, 1 the difference in ability of recovered strains to produce experimental pneumonia in animals has not been determined.
We have compared experimental pneumonic infections in rats with the clinical course in the patient from whom the pneumococci were isolated, and have correlated certain characteristics of the disease in man and rat with the type of pneumococcus involved. Cultures were obtained from 23 patients with pneumonia, and from one with otitis media during the winters of 1937-38 by Mr. Gerhardt Burde, of the Michigan State Department of Health. The pneumococci were retyped, and used in these experiments within 2 weeks of their initial isolation.
Rats were inoculated intrabronchially in the left lobe of the lung with 10-5 cc of cultures of these organisms suspended in sterile mucin, according to a method previously described. 2 Surviving animals were etherized on the seventh day after inoculation. All animals were necropsied, and gross changes were observed.
In Table I the severity of the disease in the patient, as well as in the experimentally inoculated rats, is indicated. The number of animals showing varying degrees of consolidation of the infected lobe, the number having marked pleurisy, and the number that died are recorded. Also, an estimation is given of the minimal lethal dose of “toxins” produced from the same strains of pneumococci by Burde, Barret and Glassen, 3 according to the procedure described by Dick and Boor. 4
It will be noted that in the group of 17 rats infected with Type 1 pneumococci, the mortality was 18%, whereas in a group of 14 animals infected with Type 2 strains, the mortality was 100%.
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