Tuberc Respir Dis.  1973 Jun;20(2):5-18. 10.4046/trd.1973.20.2.5.

The Study on Virulence of Mycobacterium Tuberculosis Isolated from the Second National Tuberculosis Survey in 1970

• KMID: 2529045
• DOI: http://doi.org/10.4046/trd.1973.20.2.5

Abstract

Writers observed the virulence (to mice) of the strains of M. tuberculosis isolated during the 1970 prevelance survey. There were 114 strains of M. tuberculosis, of which 72 strains were sensitive to SM, INH and PAS, 38 strains were resistant to INH alone, INH and PAS or INH and SM, and 4 were resistant to PAS or SM alone. An emulsified fine suspension of each strain was made and inoculated to Dubos liquid media, which was incubated for 12 days (at 37 ℃). Then using the Bauch and Lomb Spectronic 20, a suspension containing 9.0 X10⁵ viable units per ml (0. D. 0.16 at 660 mμ) was made. 0. 2ml of the suspension was injected into the tail vein of a mouse (10 mice were inoculated for each of the 114 strains). The results were as follows: 1. After 8 weeks of observation, the death rate of the mice inoculated with the strains sensitive to SM, INH and PAS was 72.1 %. The range of death rates was very large ranging from 0% to 100%. 77.8% of the strains showed death rate more than 50%, 36.1 % of the strains showed 100% death, and 8.3% of the strains showed no deaths. The death rate among the mice inoculated with the resistant strains was 53.0%. This shows that the virulence of the resistant strains is lower than that of sensitive strains. The range of death rates caused by the resistant strains was from 0% to 100% as it was for the sensitive strains. There were several strains that were highly resistant to INH, with low catalase activity which showed high death rates among the mice. 2. During the 56 days of observation, the average survival time for the mice inoculated with the sensitive strains was 37 days while the average survival time for those inoculated with resistant strains was 40 days. 3. At the time of autopsy, the degree (Aoki’s standard) of macroscopic lesion in the lungs of the animals inoculated with sensitive strains was 5.9 and 4. 9 for the animal inoculated with resistant straíns. 4. The lung to body weight ratio [lung weight (mgms)/ body weight (gms) X 10] for the animals inoculated with sensitive strains was 480 while it was 399 for the animals inoculated with resistant strains. 5. The virulence of the bacilli to mice had no relationship to the extent of the patient' s disease, from whom the bacilli were isolated. 6. As death rate increases survival time is shorter, lung to body weight ratio and degree of macroscopic lesions of the lung is larger and catalase activity of the bacilli tends to be higher. It appears that these factors are related to the virulence of the bacilli. 7. Among the strains resistant to INH, 14 were classified as primary resistance and 58 were classified as acquired resistance. The death rate of the mice inoculated with the strains having primary resistance was 72.9% while for the mice inoculated with the strains having acquired resistance was 41. 5%. The writers feel that the difference in virulence between primary resistant strains and aquired resistant strains should be studied futher.