Failure to validate the growth of Mycobacterium leprae on M-Y 14b agar medium.

Confirmation experiments on colony formation of M. leprae on the M-Y 14b agar medium developed by Murohashi and Yoshida were carried out for two years independently by individual members of an organized research group, according to the method described by Murohashi and Yoshida. The results obtained can be summarized as follows: a) No colony production by M. leprae on M-Y 14b agar medium was seen. b) No increase in the number of cells of M. leprae on M-Y 14b agar medium during cultivation was seen. c) Light and electron microscopic observation indicated that there was an increase in the number of non-solid bacterial cells and ghost cells with time of cultivation. d) It was found by mouse foot pad inoculation that four of six samples of M. leprae used as inocula were definitely viable. e) By means of mouse foot pad inoculation, it was shown that viability of M. leprae inoculated onto M-Y 14b agar medium was lost within approximately seven weeks of cultivation. From these results, can be definitely concluded that there is no evidence indicating that multiplication of M. leprae took place on M-Y 14b agar medium.