Antibody responses to Escherichia coli J5 lipopolysaccharide and to Salmonella porin in patients with bacteremia

Abstract

This study was undertaken in order to evaluate whether patients with bacteremia respond with antibodies directed towards two outer membrane components of Gram-negative bacteria. The antibody responses to the core of the lipopolysaccharide molecule (LPS) of the rough E. coli J5 mutant and to a purified outer membrane protein (porin) from Salmonella were studied in bacteremic patients. Two or three serum samples were consecutively collected from 77 patients having 82 episodes of bacteremia altogether, of these 50 were caused by bacteria of the genus Enterobacteriaceae. As controls, sera from 82 age and sex matched patients and 100 healthy blood donors were analysed. The antibody titers were assessed by enzyme-linked immunosorbent assays (ELISA). None of the patients with bacteremia responded with an increase in antibody level to the E. coli J5 rough LPS. This finding indicates that the core portion of the E. coli J5 LPS contains no antigenic epitopes immunologically cross-reactive with Gram-negative bacteria causing bacteremia. By contrast, 13 patients showed significant titer increases to the porin preparation derived from Salmonella. Twelve of these patients had bacteremia caused by Gram-negative organisms belonging to Enterobacteriaceae. One patient had bacteremia with Bacteroides fragilis but also suffered from a severe peritonitis with growth of both E. coli and Klebsiella. It is suggested that the measurement of antibody response to porin may be of value for differential serological diagnosis in patients with bacteremia, to distinguish between Enterobacteriaceae and other organisms.