SEPTEMBER, 1948]
JOHN
B.
POLDING
145
The 20 strains termed unclassified all differed from true Br. abortus types in one main character-
istic i.e. they grew on both thionin and fuschin. Also the majority although undeniably abortus
antigenically showed a slight tendency not to differentiate so sharply as pure abortus types on sero-
logical tests against monospecific sera and two were distinctly melitensis in this respect. One strain
isolated from Patna and one from Mukteswar, whilst conforming to the above grouping, also grew
in air at isolation.
Table XXVII illustrates the typing results of some of these ambiguous strains ; those not shown
in the Table were unexceptional in their behaviour as A/M strains, and are typified by the Madras
or Orissa village strains of the Table.
On first examining 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 dye concentration was low
enough to permit the growth of melitensis on both media, and if ordinary European, and undoubted
Indian, abortus strains were inhibited on thionin, but grew on fuschin, the results with these aberrent
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 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 its ability to grow on both thionin and fuschin. Variably,
it will grow in air on first isolation [2 cases out of 20 (10 per cent)] again its antigenic constitution
shows in stability two strains out of 20 (10 per cent) being melitensis in antigenic form, the remainder
conforming more or less to the abortus structure.
Regarding the origin of these aberrent types, it is significant that all the six strains isolated from
the village endemic area of the Indian peninsula were of this nature. It is suggested, therefore, that
this is a south Indian indigenous variant and the true Br. abortus type, hitherto found exclusively
in organized farms, is an imported European strain. This finding strengthens the postulate that
there is an area of indigenous infection almost exclusively confined to the Indian peninsula.
Further, a consideration of the part played by climate in Brucella dissemination suggests that,
if there was a spread of infection from south India it would be likely to occur along the relative 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 area of Nagpur and Raipur, and at Bihar, Lucknow, Mukteswar
and Hissar, whither infection may well have spread in the manner suggested.
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.
Dissociation
Rough forms of Brucella can sometimes be recovered from the animate host, while they may
also arise after prolonged artificial culture, especially if grown in fluids. The species melitensis
dissociates very much more readily than the other members of the genus, and amongst the present
collection of Indian strains, two out of three melitensis types were rough when examined several
sub-cultures after isolation, whereas, of 26 Br. abortus strains, one only was semi-rough at the culture
of isolation. However, of 18 Br. abortus strains retested 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 retested after some 15 or 20 transfers four had become partially rough
and one wholly rough. Rough strains are of course antigenically unstable and are not used for
ordinary purposes.
Strains were examined for dissociation as follows. Two-day old agar cultures were suspended
in 12 per cent saline and adjusted to a density of 1 to 2 on the Brown's scale. The suspensions were
placed in a boiling water-bath, readings for agglutination being made after 5, 15, 30 and 60 minutes.
The suspensions were then removed and left on the bench until the following morning when they
were again examined for agglutination. A strain showing any agglutination in these circum-
stances was regarded as antigenically unstable.