Virulence of Escherichia coli strains isolated from urine of patients with acute cystitis and from faeces of healthy women.

E. coli strains were isolated from the urine of patients with acute cystitis in general practice and from the faeces of a comparable reference group of healthy individuals. These strains were serotyped and tested for virulence in an experimental mouse model. Of 30 cystitis-strains 18 were virulent, and of 30 faeces-strains 15 were virulent. It is concluded that the cystitis-strains were not more often virulent than the faeces-strains. O antigens commonly found among urinary E. coli isolates were present in 60% of the cystitis-strains and in 37% of the faeces-strains. K antigens commonly found in urinary E. coli strains were present in 33% of the cystitis-strains and in 12% of the faeces-strains. Neither the presence of common urinary O-antigens, nor the presence of common urinary K antigens could be associated with virulence of the isolated strains. However, it is suggested that certain O and K antigens (O2,O6, K23) may be associated with virulence for the urinary tract.