Report I. Growth of Mycobacteria in Rats and Gross Organ Changes (Studies on the Susceptibility of Rats to Various Strains of Mycobacteria)

Abstract

0.1mg. of Mycobacteria of various strains were injected intravenously in the albino rat, and gross organ changes at various intervals and multiplication of bacilli in various organs were determined by Ogawa's quantitative cultivation method. In infections with virulent tubercle bacilli (H37Rv strain and bovine RM strain), multiplication of bacilli inoculated into organs was marked after a while. But the bacilli ceased to multiply after two to four weeks, and then decreased in number. Considerable tubercle formation, which later decreased in size and number, were noted only in the lung of the rat. In other organs almost no gross changes were seen. None of the animals died of infection. In infection with more attenuated strains (BCG, H37Ra and variant resistant of H37Rv to isoniazid) slight multiplication of bacilli was observed in the lung, but this was very transitory and soon decreased. Almost no gross changes other than the formation of a few nodules were noted. From these results it is concluded that the albino rat has much more native resistance to tuberculosis than the rabbit and the guinea pig, and is also more resistant than the hamster. Tuberculin tests performed in the abdominal skin or the footpad skin were negative in all animals.