Serological cross-reaction between Yersinia enterocolitica O9 and non-O1 Vibrio cholerae bio-serogroup Hakata and antigenic analysis of their relationship by their lipopolysaccharides.

Cross-agglutination and cross-agglutinin absorption experiments were carried out on non-O1 Vibrio cholerae bio-serogroup Hakata (Hakata) and Yersinia enterocolitica O9 (O9). It was shown that the O-antigen of Hakata was closely related to that of O9 in an a, b-a, c type of relationship. The antigenic relationship between the O-antigens of the two bacteria was analyzed by passive hemolysis (PH) and passive hemolysis inhibition (PHI) tests by using their lipopolysaccharides (LPS) as antigen for sensitizing sheep red blood cells (SRBC) and, in the case of the latter, as an inhibitor in a PH system consisting of LPS-coated SRBC, guinea-pig complement and anti-Hakata or O9 antiserum, both unabsorbed and absorbed with the heterologous Hakata or O9 antigen. In the PH experiment, unabsorbed anti-Hakata antiserum had hemolytic titers of 126,100 and 2,600 against Hakata- and O9-LPS-coated SRBC, respectively, and anti-O9 antiserum had hemolytic titers of 19,400 and 38,800, respectively, against these SRBC. The PH experiment showed that anti-O9 antiserum contains a hemolysin reacting with the heterologous Hakata antigen at a high titer (19,400), while anti-Hakata antiserum contains a hemolysin reacting with the heterologous O9 antigen at a significant titer (2,600). The former was completely removed from anti-O9 antiserum with the Hakata antigen and the latter from anti-Hakata antiserum with the O9 antigen. Thus, serological cross-reactivity was demonstrated between the Hakata and O9 strains.