Correlation of E. coli K-1 bacteremia and capsular polysaccharide antigenemia in acute and chronic infection.

The K-1 polysaccharide is an important virulence factor in human E. coli infections. Using E. coli 016K1, we investigated the kinetic association of bacteremia and K-1 antigenemia in acute lapine and canine infections and in a chronic infection model of neutropenic rats. Additionally, we assessed the presence of K-1 antigenemia in E. coli K-1 bacteremic patients. K-1 was measured by a solid phase radioimmunoassay (RIA) using cross-reactive equine anti-Group B meningococcal IgM. In acute infections, none of the dogs or rabbits developed antigenemia even with a bacteremia of 2 X 10(4) CFU/ml or 5 X 10(5) CFU/ml, respectively. Antigenemia appeared in the rabbit only with an infecting dose of greater than or equal to 5 X 10(8) CFU. In the rat model we observed an initial bacteremia of 10(3) CFU/ml, which increased to 10(6) CFU/ml at 24 hrs. However, antigenemia was most often delayed, appearing in only greater than or equal to 30 hrs postinfection. Percent mortality was directly associated with the degree of bacteremia and antigenemia. In acute human E. coli K-1 bacteremia, 11 of 22 (50%) of patients were positive for K-1 antigenemia. The data demonstrated that K-1 polysaccharide was not usually detectable in the early stages of bacteremia, but occurred only after prolonged infection or very high infecting doses. The RIA to measure K-1 antigenemia would not be a useful diagnostic tool.