The identification of M. tuberculosis depends
primarily on the niacin production test. Runyon
and others (1959) described a method based on
the observations of Konno (1956) using aniline
as the reagent. However, the aniline reagent
gives a yellow colour which can cause difficulty
in the interpretation of the results, particularly
in the case of the chromogenic mycobacteria.
Hence several workers prefer the test employing
benzidine (Medveczky, 1960) or o-tolidine
(Guttierrez-Vazquez, 1960), since the pink colour
produced in these tests is easier to read.
The standard method for niacin production
test at this Centre has been the one using
benzidine. However, satisfactory supplies of
benzidine are no longer available, as the manufacture
of this compound’ has recently been
stopped. Hence it was decided to investigate the
test using o-tolidine. Though other workers
(Tarshis, 1960, 1961; Gangadharam and Droubi,
1971) have compared the benzidine and o-tolidine
methods on small numbers of cultures, no large
scale investigation of these two methods has been
reported. Therefore a direct controlled comparison
of these two methods was undertaken, the
results of which are reported here
