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Experimental Escherichia coli ascending pyelonephritis in rats: changes in bacterial properties and the immune response to surface antigens

Systemic and urinary antibody responses were examined in rats with experimental ascending pyelonephritis caused by Escherichia coli O6K13H1. During 12-month follow-up of the infections, bacterial characteristics of the urinary and renal isolates were followed: O and K antigenicity, sensitivity to the bactericidal effect of normal human serum, capacity to attach to urinary tract epithelial cells, hemolytic activity, biochemical pattern, and virulence. During the long-term infection, the urinary and renal bacterial isolates changed in O and K antigenicity, serum sensitivity, and virulence. The adhesive capacity of the bacterial isolates did not change, possibly explaining the persistence of the bacteria in the urinary tract. The serum anti-O6 antibody levels remained high during the entire 1-year observation period, especially in the rats with renal involvement. Urinary anti-O6 antibodies were also found. The serum and urinary antibodies could have played a role in bringing about the observed changes in bacterial characteristics. Antibodies to lipid A were recorded in 9 of 16 rats with pyelonephritis and renal scarring and in 1 of 9 rats not having pyelonephritis or renal bacterial growth.