Inhibition of Anti-colonizing Effect of Positive Serum from Humans Inoculated with the Attenuated Strain 638 Vibrio cholerae O1

As a part of the study to obtain an oral vaccine against cholera, the anti-colonizing capacity of the human serum, extracted after an oral dose with the attenuated strain 638, was evaluated. Inhibition studies with somatic antigens of Vibrio cholerae O1-like, Ogawa and Inaba lipopolysaccharide (LPS), outer membrane proteins (OMP) and the 20-kD antigenic complex as well as the LPS of the O139 serogroup, were done. The neonatal mice model was utilized. The positive serum showed a high anti-colonizing activity. In the antigen inhibition studies, it was observed that the Ogawa LPS reduced the anti-colonizing capacity of the positive serum. The 20-kD antigenic complex, the Inaba LPS and the OMP showed a lower and differential inhibitory effect. These results confirm that the most protective antigen is the homologous LPS, although there are other cellular surface antigens involved in the induction of protective immunity. The results here described contribute to understand the mechanism of protective immunity against V. cholerae and stimulate to employ of conjugated vaccine.