Attenuation of Virulence of M. lepraemurium after Serial Mouse Passages During Long Years

This paper deals with the pathogenicity of cultivated M. lepraemurium from rough colonies of Hawaiian-M (HM) and Hawaiian-B (HB) strains in mice.The tested bacilli, HMOR and HBOR, were isolated on Ogawa's 1% egg yolk medium from HM bacilli-induced and/or HB bacilli-induced leproma. Subcutaneous and visceral lesions induced by the bacilli from rough colonies of Hawaiian-M-Ogawa (HMOR bacilli) and of Hawaiian-B-Ogawa strain (HBOR bacilli) were found to be similar to those induced by HM and HB bacilli, respectively, when the subcutaneous infection was carried out in several inbred strains, C3H, C3H/He, BALB/c, KK and DDD. In these mouse strains, as shown in Part 1 of this series, there were notable differences in the pathogenicity between HM and HB bacilli.It was stated in our previous paper that the bacilli from rough colonies grown on 1% Ogawa's egg yolk medium were much more virulent for mice than the bacilli of the original Hawaiian strain maintained only by C3H mouse passage. However, at present time, this phenomenon is considered to be very particular one and to occur in unstable status of tested Hawaiian bacilli which were in a changeable process from virulent to attenuated.It is generally accepted from the results of the present experiments that HMOR and HBOR bacilli, cultivated M. lepraemurium, possess the same virulence with the original bacilli, HM and HB. And it is necessary to say that attenuated HM bacilli did not revert to the highly virulent bacilli, such as HB, after cultivation by Ogawa's method.