A semi-automated vibriocidal assay for improved measurement of cholera vaccine-induced immune responses.
Vibriocidal antibody assay has been a surrogate standard assay in the evaluation of cholera vaccine efficacy because it has a good correlation with protection. Although the optical density-based vibriocidal assay in a 96-well microtiter-plate format is widely used in clinical trials, it has limitations as vibriocidal titers are altered by incubation time and samples with the same end-point titers could have potentially different vibriocidal kinetics. In the present study, we developed an improved agar-plate assay coupled with an automated colony counting system. Through testing 30 pairs of human sera from vaccinees administered with a cholera vaccine or placebo, these two assays showed good correlations for the vibriocidal titers and fold increases in titers between pre- and post-vaccinated sera as determined by the Pearson correlation coefficient and the Regression coefficient. Notably, the newly-developed semi-automated assay demonstrated that serum samples with the same end-point titers turned out to have distinct vibriocidal kinetics that were not distinguishable by the microtiter-plate assay. The semi-automated assay responded specifically to Vibrio cholerae but not to irrelevant bacteria such as Salmonella typhi and Escherichia coli. These results demonstrate that the semi-automated assay provides better sensitivity, accuracy, and stability of the assay results with minimized efforts than conventional microtiter-plate assay and could provide a useful tool as an in vitro surrogate assay for the evaluation of cholera vaccine efficacy.
Yang
Jae Seung
JS
Laboratory Sciences Division, International Vaccine Institute, Seoul 151-600, Republic of Korea.
Kim
Hye Jin
HJ
Yun
Cheol-Heui
CH
Kang
Seok-Seong
SS
Im
Jintaek
J
Kim
Hak-Sung
HS
Han
Seung Hyun
SH
D000907:Antibodies, Bacterial / Q000097:blood / Q000276:immunology; D002771:Cholera / Q000517:prevention & control; D022121:Cholera Vaccines / Q000276:immunology*; D015169:Colony Count, Microbial; D004926:Escherichia coli / Q000276:immunology; D006801:Humans; D007118:Immunoassay / Q000379:methods*; D050296:Microbial Viability / Q000276:immunology*; D012485:Salmonella typhi / Q000276:immunology; D012680:Sensitivity and Specificity; D044967:Serum / Q000276:immunology; D014734:Vibrio cholerae / Q000276:immunology*
D000907:Antibodies, Bacterial; D022121:Cholera Vaccines