A small number of niacin-negative strains were found among the human tubercle bacilli isolated from the patients who had received a prolonged combined chemotherapy. It was also noted that the proportion of strongly positive strains in niacin test was lower in the group of the drug-resistant strains. On the basis of these observations an assumption was raised that there might be some relationship between the ability of niacin production and the drug resistance, particularly multiple one.
The serial passage method was app lied to 64 niacin-positive patient strains which had been confirmed eugonic and resistant to one or more drugs. At the beginning of the transfer, 39strains were found strongly positive to the test, 19 strains moderately and 6 weakly positive. Each strain was then exposed on Ogawa egg slants to progressively and simultaneously increasing concentrations of the three-major drugs (1.25 to 640 mcg per m
l).
On transfer at monthly intervals, all the tubes were subjected to n i acin test, with the exception of those showing poor or no growth. Tables 1-6 represent changes in level of the niacin test in the course of these passages. It can be seen that none of the strains became negative throughout the period. One strain, however, whose initial test had proved moderately positive became doubtfully positive after 6 passages, the culture growing in the presence of 80mcg per ml each of the drugs. This strain was lost by mistake so that no further information was obtained. Although a decrease or even an increase in the extent of niacin test was noted in a considerable number of the strains, no definite correlation was found between these fluctuations and the number of passages or the level of multiple resistance attained.
View full abstract