The human pathogenic bacterium Vibrio cholerae is the causative agent for the enteric disease cholera. V. cholerae infects its host by expressing a protein consisting of two subunits, the pentameric cholera toxin B (CTB) and cholera toxin A (CTA). CTB is frequently used as an indicator of the presence of pathogenic V. cholerae and is typically detected using enzyme-linked immunosorbant assays (ELISAs). In lieu of an enzyme-linked detection method, we have developed GM1 ganglioside-functionalized fluorescent dye-encapsulating liposomes for the detection of CTB produced by V. cholerae in a simple microtiter plate assay, both for detection of CTB from cell free supernatants and attached to human epithelial cells. Liposomes were compared to fluorescein-labeled antibodies and enzyme-linked secondary antibodies for quantification of purified CTB. Using a criterion of the background signal plus 3xStDev, a limit of detection of CTB for the gangliosomes was 0.34 ng/mL, which was comparable to the ELISA, but significantly lower than the fluorescein-labeled anti-CTB antibody used for the same purpose. The signal enhancement provided by the gangliosomes was substantial when compared to the fluorescein labeled antibody. Using a criterion of signal to noise of 1.5:1, a limit of detection of CTB for the liposomes was 0.17 ng/mL, which was 178 times lower than the fluorescein-labeled anti-CTB antibody. In addition, the liposomes required shorter assay times, exhibited less variability, and were approximately 30% less expensive than ELISAs. All three methods were highly correlated within their respective detection ranges. Further, the gangliosomes were optimized with respect to phospholipid and ganglioside concentrations and used to probe culture supernatants from V. cholerae El Tor C6706 grown in DMEM, LB, and AKI media for the presence of CTB. Finally, the liposomes were used to quantify CTB attached to the surface of human epithelia. Optimization of the on-cell assay is also discussed.

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