Detection of anti-lipopolysaccharide antibodies to Vibrio cholerae O1 and O139 using a novel microtiter limulus amebocyte lysate (LAL) assay

This paper describes a new assay for measuring antibodies to lipopolysaccharide (LPS) of Vibrio cholerae using blocking of the limulus amebocyte lysate (LAL) reaction in a microtiter plate. When V. cholerae LPS was coated onto a microtiter plate, and then LAL reagent was added, a typical gel reaction occurred. However, when the LPS-coated plates were first incubated with serum containing anti-cholera antibodies, the gel reaction did not occur. Blocking of the gel reaction was serotype specific, in that anti-O1 serum blocked the O1 LAL reaction but not the O139 LAL reaction, and anti-O139 serum neutralized the O139 reaction but not the O1 reaction. Preliminary data suggested that the LAL titers were comparable to the vibriocidal titers but that titers using the LAL assay may have been slightly higher. This study showed that antibodies to V. cholerae blocked the LAL reaction and suggested that the LAL blocking assay could be applicable for determining antibodies to other endotoxin-containing bacteria and microorganisms.