Experimental Escherichia coli urinary infection in the rat.

Twenty-six urinary strains of Escherichia coli belonging to O-sero-groups commonly associated with urinary infection but differeing in serum sensitivity and K antigen content were examined for their ability to survive in the kidneys following inoculation into the bladder of male Wistar rats. Reproducibility studies showed that some strains consistently caused kidney infection whereas others were consistently unable to do so. However, the ability to infect the kidneys was not correlated with serum resistance or K antigen content. Some evidence for the nature of the factors responsible for kidney infection came from a study of various mutants derived from E.coli LP729 (serotype 09), which produces negligible amounts of K antigen and is rapidly killed by serum after a delay of one hour. Both LP729 and a serum-resistant mutant derived from it caused kidney infections, but two rough variants derived from the serum-resistant mutant were unable to infect the rat kidneys. One variant was devoid of lipopolysaccharide O-side chains; the other showed the delayed serum-killing effect characteristic of LP729 and retained 09 specificity with a full complement of O-side chains, suggesting that loss of surface components unrelated to O or K specificity may be responsible for failure to invade the kidneys.