A new type of pathogenic Salmonella for the fowl has been described. Its somatic “O” antigen corresponds with factors VI, VII of potsdam. It occurs only in the specific phase, but its flagellar “H” antigen contains at least two distinct and separate antigenic complexes, which commonly occur in organisms that are not even remotely related. The one complex (the first, en-, antigen, α phase of Kauffmann and Mitsui) contains factors enx, which represent also the factors of the specific phase of abortus-equi. The other complex (the second, d-, antigen, β phase of Kauffmann and Mitsui) contains factor d, which comprises the type phase of stanley, muenchen and typhi.
Single cells containing factors enx on multiplying constantly yield variants containing factor d as well as offspring that retain antigenic complex enx. In the same way single cells containing apparently only specific factor d will bring forth new cells, most of which retain the parental antigenic structure, but a small proportion of the progeny will acquire specific factors enx instead of d.
When a broth culture of amersfoort in either the enx or d phase in an apparently pure form, as judged by the agglutination test, using heterologous sera which contain agglutinins either against factors enx (or en) or d, is used for the preparation of sera, agglutinins of approximately the same titre for both variants are produced in the sera.
As a result of the information given above the following antigenic structure is proposed for Salmonella amersfoort:
Somatic “O” antigen—VI, VII.
Flagellar “H” antigen—
(1) α phase of Kauffmann and Mitsui—enx.
(2) β phase of Kauffmann and Mitsui—d.