Immunochemistry of the capsular polysaccharide of an acinetobacter.

The capsular polysaccharide of a strain, BD4, of Acinetobacter calco-aceticus (A.c-a), composed of L-rhamnose and D-glucose, 4:1, precipitates all streptococcal group B antisera tested, as well as streptococcal group G antisera and antipneumococcal (Pn) type XXIII serum. Nonreducing end groups of L-rhamnose, known to be major determinants of the antigens giving rise to these antisera, are thus identified in A.c-a, which also precipitates anti-Pn VI sera. Both the rhamnose and glucose in the capsular polysaccharide (S) of Pn VI are linked 1,3-, as is the rhamnose in Pn S II, which also precipitates anti-Pn VI because of this linkage. A.c-a and S II precipitate the same fraction of anti-Pn VI, identifying a second portion of the rhamnose of A.c-a as 1,3-linked. This is confirmed by the stability of a portion of the rhamnose on oxidation of A.c-a with periodate, and 1,3-linked glucose or a periodate-stable branch point is also indicated in the same way. Two features of the fine structure of A.c-a have thus been established and a third indicated.