Detection by immunofluorescence of common antigenic determinants in unrelated gram-negative bacteria and their lipopolysaccharides.

Various gram-negative bacteria were subjected to mild acid hydrolysis. The acid-treated bacteria exhibited strong cross-reactivity with fluorescein isothiocyanate-conjugated antiserum to the Re mutant of Salmonella minnesota. Hydrolyzed bacteria showed considerably stronger fluorescence than heat-treated bacteria. It is assumed that acid hydrolysis uncovers shared glycolipid determinants that are responsible for cross-reactivity. Isolated homologous and heterologous lipopolysaccharides were allowed to react with antibody to S. minnesota Re insolublized by covalent binding to aminohexyl Sepharose 4B. The resulting antigen-antibody complexes were visualized by exposure to the fluorescent antiserum. This treatment allows the demonstration of glycolipid structures of intact lipopolysaccharides.