• Escherichia coli;
  • acute pyelonephritis;
  • bacteraemia;
  • diabetes mellitus;
  • virulence factors;
  • serum resistance

The capacity of Escherichia coli to resist the bactericidal action of serum was examined in 367 clinical isolates obtained from children with acute pyelonephritis (n = 57), adults with acute pyelonephritis (n = 55), non-diabetic patients with bacteraemia (n = 101), diabetic patients with bacteraemia (n = 65) and from the faecal flora of healthy controls (n = 89). The incidence of serum-resistant E. coli strains was significantly higher in pyelonephritogenic strains from children and adults (93% and 82%) as compared to faecal control strains (57%, p < 0.001 and p< 0.005 respectively). Strains causing bacteraemia in non-diabetic and diabetic patients were more often serum resistant (72% and 80%) as compared to control strains (p < 0.05 and p < 0.001 respectively). The frequency of serum-sensitive strains was similar in diabetic patients with decreased renal fuction or proteinuria compared to those with normal renal function. There were no significant correlations between serum resistance of E. coli and expression of P fimbriae, type I fimbriae or mannose-resistant haemagglutination, cell surface hydrophobic properties, production of aerobactin, haemolysin or cytotoxic necrotizing factor in 53 pyelonephritogenic strains from adult patients.