The relation of K-antigen to virulence of Escherichia coli.

The content of K-antigen was determined for 100 strains of Escherichia coli isolated from the blood of patients with bacteremia. 30 strains isolated from urine cultures, and 30 strains isolated from the feces of patients recently admitted to the hospital. The K-antigen content of urinary isolates of E. coli was significantly greater than that of strains isolated from feces, as noted by other workers. In contrast, the amount of K-antigen of blood culture isolates was not significantly greater than that of fecal isolates and was significantly lower than that of urinary E. coli isolates. No correlation could be detected between the K-antigen content of blood culture isolates and the severity and outcome of the bacteremia.