Virulence of Mycobacterium tuberculosis for guinea pigs: a quantitative modification of the assay developed by Mitchison.
One of the more accepted methods of assay of virulence of tubercle bacilli is one developed by Mitchison in which guinea pigs were infected by the intramuscular route with 1.0 mg of tubercle bacilli freshly harvested from Lowenstein Jensen medium and in which virulence was based on a subjective score of the extent of gross disease in the animal 6 weeks after infection. Due to the practical difficulties involved in such an assay when routinely performed, the following modifications were made: frozen stocks of the culture were prepared prior to the date of infection, the inoculum was quantitated by means of colony forming units, and virulence was based on the number of tubercle bacilli recovered from the spleen of infected animals 6 weeks after infection. A significant correlation was obtained between the findings from the Mitchison assay of virulence and the modification. The latter assay is recommended for its quantitative and objective features.
Balasubramanian
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V
Department of Medical Microbiology and Immunology, University of Wisconsin, Madison.
Guo-Zhi
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W
Wiegeshaus
E
E
Smith
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D
D000818:Animals; D001431:Bacteriological Techniques; D015169:Colony Count, Microbial; D005260:Female; D005615:Freezing; D006168:Guinea Pigs; D006801:Humans; D009169:Mycobacterium tuberculosis / Q000254:growth & development / Q000472:pathogenicity*; D013154:Spleen / Q000382:microbiology; D013183:Sputum / Q000382:microbiology; D014774:Virulence