Antibody specific for Escherichia coli J5 cross-reacts to various degrees with an Escherichia coli clinical isolate grown for different lengths of time.

Rabbit antiserum raised against the rough mutant of Escherichia coli O111:B4, designated J5, was examined for cross-reactivity to an E. coli clinical isolate (A2385). In whole-cell enzyme-linked immunosorbent assays, J5 antiserum reacted to a greater extent with A2385 grown for 5 h than with the same bacteria grown for 19 h, while the homologous antiserum reacted similarly with bacteria grown for different lengths of time. J5 antiserum reacted to the greatest extent with lipopolysaccharide (LPS) from A2385 grown for up to 10 h, and reactivity greatly diminished thereafter; homologous antiserum showed no difference in reaction over time. LPS from smooth bacteria grown for 19 h showed no reaction with J5 antiserum in immunoblots, while LPS from A2385 grown for 5 or 10 h showed a positive reaction. Little or no difference among the three LPS samples could be seen when homologous antiserum was used. Mice vaccinated with J5 LPS before lethal challenge with live A2385 were protected from this challenge, whereas most nonimmunized mice died. Toxicity tests in mice showed LPS from A2385 grown for 19 h to be twice as lethal as LPS from A2385 grown for 3 h. Mice vaccinated with J5 LPS were protected to a greater extent when challenged with a lethal dose of LPS from A2385 grown for 3 h than when challenged with LPS from A2385 grown for 19 h. The results reported here may explain the means by which J5 vaccination (active or passive) sometimes protects against heterologous challenge.