Virulence of Mycobacterium Tuberculosis collected during the first nationwide case finding, campaign by sputum examination in Korea during the period from 1968 to 1969 was tested for mice.
Fifty four isolates were made from newly discovered tuberculosis patients without a history of previous chemotherapy. Thirty nine isolates were sensitive to antimicrobials, and 15 were resistant to INH. None of the isolates was resistant to PAS or Streptomycin.
The reference strains of M. tuberculosis used for the study were H
37Rv from the Trudeau Institute, British and Japanese strains from the National Institute of Health in Japan, and Indian strains from the Madras Chemotherapy Center.
One tenth mgm. of a bacterial suspension from each isolate was injected into mice intravenously. Fifteen mice were used for each isolate. The average viable unit of bacilli injected per dose was 26.7×10
5.
The mortality rate was observed up to eight weeks after infection. The extent of pulmonary lesions was measured by Aoki's standard degree of tuberculosis involvement in lung. Weight ratio of lungs to body as also recorded.
The findings were:
1. The mortality rates of mice inoculated with 39 INH-sensitive isolates ranged from 100% for 9 isolates to 0% for 8 isolates, and the average was 52.9% for the 39 isolates. This was markedly higher than the rate of 24.7% previously reported from Japan.
2. The degree of macroscopic lesions in the lungs ranged from 2.1 to 7.0 (Aoki's standard). The mean was 4.7. The weight ratio of lungs to body ranged from 100 to 314 (Lung wt. mgms/body wt. gms. ×10). And these two indices for virulence were approximately proportional to the mortality rate.
3. The majority of 15 INH resistant isolates was lower in its virulence than the sensitive isolates. 11 showed negative catalase activity.
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