Report II. Histological Examination of Rats Infected with Various Strains of Mycobacteria (Study on the Susceptibility of Rats to Various Strains of Mycobacteria)

Abstract

Histological examination of the organs of rats infected with various mycobacteria (H37Rv, bovine RM, BCG, H37Ra and variant of H37Rv resistant to isoniazid) were performed at various intervals until after six months. Among organs of rats the lung is most susceptible to all strains used, and the spleen is next most. The liver and kedney are almost nonsusceptible. Among the strains used the H37Rv has the strongest virulence, and the bovine RM the next strongest. The BCG strain was the weakest. This order was apparently shown in the histological examinations. Histological changes induced by infection are similar to tuberculous changes found in other susceptible animals, .....epithelioid tubercles, infiltration of large exudate cells, and formation of giant cells. A unique and very important difference is the lack of necrosis or caseation in the rat. These tissue changes developed for a while, and then ceased to develop, and at last, several months after the infection, disappeared completely or left a small amount of scar tissue. The author wishes to express her sincere thanks to Dr. Y. Kobara for the assistance in carrying out this work.