Antigens that determine agglutination reactions, and are distinct from the O-, H- and Vi-antigens, were demonstrated in the type-1 fimbriae of bacteria in fimbriate-phase cultures of salmonellae. Most strains of salmonellae produced fimbriate cultures when grown for a sufficient period, e.g., 24–48 hr, at 37°C in aerobic static broth. The same strains produced non-fimbriate-phase cultures lacking fimbrial antigens when grown for only 6 hr in broth, for 12 hr in glucose broth or for 24 hr on an agar plate. The independence of the fimbrial antigens from the O-, H- and Vi-antigens was shown by the finding that an antiserum raised against a fimbriate-phase culture and freed from O-, H- and other non-fimbrial agglutinins by absorption with non-fimbriate-phase bacteria (“pure fimbrial antiserum”) strongly agglutinated fimbriate-phase bacteria, but did not agglutinate either non-fimbriate-phase bacteria or fimbriate bacteria that had been defimbriated by heating at 100°C.

Crude (unabsorbed) and pure (absorbed) fimbrial antisera to strains of several salmonella serotypes agglutinated fimbriate-phase bacteria of a wide variety of heterologous serotypes. The reactions indicated the presence of a common fimbrial antigen in all of 95 fimbriate strains in 79 serotypes of and two strains each of and . Absorption findings suggested that other fimbrial antigens were present in addition to the common one in strains of certain serotypes, but that the same antigens were present in different strains of the same serotype. A common fimbrial antigen was demonstrated in strains of and , but there was no sharing of antigens between this group of bacteria and the salmonella-arizona-citrobacter group.

Misleading cross-reactions may be obtained in diagnostic agglutination tests unless only non-fimbriate bacteria are used for the preparation of agglutinable suspensions and the production of diagnostic antisera. The development of cross-reacting fimbrial agglutinins in persons who have been infected with a salmonella or immunised with a TAB vaccine containing fimbrial antigens may lead to false-positive reactions being obtained in Widal tests.


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