Mice tuberculosis quantified by the lung density technique

Groups of CF1 mice were respectively infected intravenously with four decreasing doses of the virulent H37Rv strain of Mycobacterium tuberculosis var. hominis and the progress of tuberculous disease was followed by three techniques yielding essentially objective results. Survival rates showed that 84% of the mice infected with the largest dose died within 30 days of infection but this technique was unable to differentiate among the other three groups of mice infected with smaller doses. Bacterial culture counts performed after increasing intervals of infection on spleen homogenates of similarly infected groups of mice showed that different degrees of tuberculous involvement had effectively been induced in the four groups. Lung density determinations performed on the same groups of animals gave results establishing that this technique was capable of distinguishing the four groups of mice one from another. The observation that the lung density technique reflects the degree of tuberculous disease accurately was further substantiated by experiments performed on groups of mice respectively injected intravenously with comparable numbers of viable cells of seven mycobacterial strains of different virulence, all harvested at the same "physiological age." Statistically significant differences existed between the experimental groups infected with the virulent strains on the one hand and those injected with the avirulent ones on the other; no differences existed among the groups infected with virulent strains or among those injected with avirulent ones. Of particular interest is the observation that the lung density technique can also differentiate groups of mice injected either with virulent or avirulent strains from those injected with the attenuated bovine BCG strain. The results of both the bacterial culture count and lung density techniques applied to the same groups of mice in the early and late phases of tuberculous disease are discussed.

Long-term preservation and storage of mycobacteria

Under contract with the National Institute of Allergy and Infectious Diseases, the Trudeau Mycobacterial Culture Collection has been greatly expanded to provide for the scientific community a collection of representative strains of mycobacteria of biomedical importance. Problems concerned with the preparation, bottling, and distribution of such organisms have been dealt with and are detailed in this paper. Examination of collected data revealed that the temperature of storage and not the suspending menstruum was more important for prolonged survival of mycobacteria stored at subzero temperatures. For optimum results, mycobacteria may be suspended either in Dubos Tween-albumin broth or in Middlebrook 7H-9 liquid medium supplemented with ADC enrichment (commercial sources used) and stored at -70 C. Either of these suspending fluids supplied a growth-supporting medium for cultures which must be shipped long distances, often without refrigeration. To avoid sublimation of suspending medium during prolonged storage at -70 C (a problem inherent in many screw-capped containers), we have chosen to use vaccine-stoppered serum bottles sealed with aluminum crimp caps. The methods described have provided suspensions with (i) excellent viability over prolonged periods of storage, (ii) stable metabolic activities, and (iii) highly reproducible inocula for animal experiments.

Comparison between the attigenic components extracted from virulent and avirulent strains of mycobacteria

The antigenic relationship between virulent and attenuated or avirulent human, bovine, and avian strains of mycobacteria has been studied with rabbit immunesera against fractions obtained from mechanically disintegrated bacilli. The antigenic comparison was carried out by Immunoelectrophoresis after cross-absorption of antisera. It was shown that the human virulent strain H37Rv, the bovine virulent strain Ravenel, and the avian virulent strain Sheard had at least two antigens which were not detected in the related attenuated or avirulent strains. Furthermore, these additional antigens were found to be different from strain to strain.The antigenic comparison between human, bovine, and avian strains of mycobacteria revealed that fewer antigenic differences existed between human and bovine than between human or bovine and avian strains.

Tuberculous morbidity in Swiss albino mice immunized with BCG

Study was made of the effect of BCG vaccination on the establishment of experimental tuberculous infection in mice. To this end, mice were infected with small quantities of virulent human bacilli administered by the respiratory route. The quantity of bacilli present for inhalation was so controlled as to permit only a finite percentage of unvaccinated animals to become infected. The relative proportion of mice infected by inhaling these small numbers of virulent bacilli was not found to be lowered by prior BCG vaccination. Thus, pulmonary tissue of immunized mice was not able to prevent the initial lodgement of virulent tubercle bacilli. The growth of virulent organisms in infected lungs, however, was significantly retarded by prior vaccination.