The relationship between the presence of bacterial
virulence factors and the severity of
urinary tract infection (UTI) was analized in this study. The production of alpha-
hemolysin (Hly), the expression of P-fimbriae and the
mannose-resistant hemagglutination (MRHA) type IVa (associated with the presence of P-fimbriae), were all detected more frequently in Escherichia coli strains from acute
pyelonephritis than in strains isolated from
cystitis and asymptomatic
bacteriuria. In contrast, the production of
cytotoxic necrotizing factor type 1 (CNF1) and the expression of MRHA types III and IVb were distributed uniformly between strains causing different clinical categories of UTI. Thus 88% of the E. coli strains from acute
pyelonephritis showed some of the
virulence factors investigated in this study, whereas only 60% (p < 0.01) and 56% (p < 0.01) repectively of the strains isolated from
cystitis and asymptomatic
bacteriuria possessed
virulence factors. There were no significant differences in the prevalence of virulence properties between strains isolated from patients with or without complicating factors. Only 16% (p < 0.001) of the fecal isolates from healthy individuals showed
virulence factors. The
virulence factors were concentrated in strains belonging to 10 (O1, O2, O4, O6, O7, O14, O18, O22, O75 and O83) of the 12 serogroups most frequently detected in uropathogenic E. coli strains. The majority of uropathogenic O4, O6, O14, O22, O75 and O83 E.coli strains were Hly+CNF1+ and expressed P-fimbriae or MRHA type III, whereas the strains of serogroup O18 were Hly+CNF1- and P-fimbriated. Among O1 and O7 strains we found Hly-CNF1-strains that expressed P-fimbriae. Among O2 strains we found Hly+CNF1+ strains that expressed P-fimbriae or MRHA type III and other Hly-CNF1-strains that possessed P-fimbriae. We conclude that E.coli strains isolated from
pyelonephritis show
virulence factors more frequently than those from
cystitis and asymptomatic
bacteriuria, and that strains that cause
urinary tract infections in Spain belong to the same serogroups as uropathogenic E.coli isolated in other areas of the world. Our results support the special pathogenicity theory and suggest that many cases of serious
urogenital disease may be caused by a limited number of P-fimbriated E.coli strains that usually produce alpha-
hemolysin.