Serotyping of Campylobacter fetus subsp. fetus and C. fetus subsp. venerealis by passive hemagglutination technique based on soluble autoclaved antigens.

Antigens for sensitization of sheep erythrocytes were released from C. fetus subsp. fetus and C. fetus subsp. venerealis suspensions by autoclaving in alkaline and neutral saline and by boiling in alkaline but not in neutral saline. Serotyping with rabbit antisera showed the same two serotypes of O-antigens, A and B, as shown by tube agglutination of heated bacteria. All C. fetus subsp. venerealis strains had the A antigen. The C. fetus subsp. fetus strains tested had either the A or B antigen. All ten human isolates tested were of the A type.