160
Indian Species of Brucella
On first examination of these strains, it was thought that a technical error had crept in, but,
when the work was repeated keeping careful controls, it was found that if the above dye concentra-
tion was low enough to permit the growth of melitensis controls on both media, and if ordinary,
European abortus and undoubted Indian abortus strains were inhibited on thionin but grew on fuchsin
the results with these aberrant strains were always the same. Moreover, field strains were always
typed in lots of 10 or 12 at the same time, and it is significant that out of the 49 strains no less than
20 inescapably gave this ambiguous result. It is concluded therefore that this abortus/melitensis
type is a common indian Brucella variant, its constant characteristic being ability to grow on both
thionin and fuchsin. Variably, it will grow in air on first isolation (two cases out of 20); its antigenic
constitution is unstable, two strains out of 20 being melitensis antigenically and the rest conforming
more or less to the structure of abortus.
Agglutination absorption tests have been made on these abortus/melitensis strains to observe
whether they contain any additional, hitherto undescribed antigen, but this does not appear to be
the case.
As to the origin of these aberrant types, it is significant that all the six strains isolated from
villages of the Indian peninsula were of this nature. It is suggested, therefore, that this is a South
Indian indigenous variant and that the true Br. abortus type, as yet exclusively found on organized
farms, is an imported European strain.
Further, a consideration of the part played by climate in the dissemination of Brucella (Polding,
in press) suggests that, if there was a spread of infection from the villages of this peninsula it would
be likely to occur along the relatively humid Himalayan foot-hills and perhaps descend into the
Gangetic plain. It is of interest, therefore, that the abortus/melitensis strains, so far isolated from
organized farms, have been found at Jubbulpore—not very distant from the endemic are of Nagpur
and Raipur—, and at Bihar, Lucknow, Mukteswar and Hissar, whither infection may well have
spread viâ. the Himalaya.
Dissociation
Rough forms of Brucella can sometimes be recovered from the animal host, while they may also
arise during prolonged artificial culture, especially if grown in fluid media. The species melitensis
dissociates very much more readily than the other members of the genus, and among the present
Indian strains two out of three melitensis types were rough when examined after many subcultures.
Of 26 abortus strains, one only was partially rough in the primary culture. However, when 18 of
these strains were re-tested after some 15 or 20 transfers on liver agar, six had become partially rough
and two wholly rough. None of the abortus/melitensis strains was rough at isolation, but of 13 re-
tested after some 15 or 20 transfers four had become partially rough and one wholly rough.
Antigenic sensitivity
Most of the present collection of Indian strains have been tested for differences in antigenic
sensitivity but within the limits of ordinary error no differentiation has been observed, — even the
abortus/melitensis forms being unexceptional in this respect. Some of the results of this work are
shown in Table IV.
Virulence
As white mice are required in large numbers in assays of virulence, and as these animals are
not easy to obtain in such numbers in India, only a few Indian Brucella strains could be examined
for this property. The test is described by Priestley and McEwen [1938] and the results of some
of the present estimations are shown in Table V. For comparison, tests on three foreign vaccine
strains are included in this Table. Again, for control purposes it was necessary to compare the
virulence of Indian strains with that of type-specific strains from abroad, and in so doing few mice
were left for testing the local strains ; even then, the interest centring round the abortus/melitensis
type led to four of these and only one abortus and one melitensis being examined.