Identification of virulence genes in uropathogenic Escherichia coli by multiplex polymerase chain reaction and their association with infectivity in mice.

Objectives: To use multiplex polymerase chain reaction (PCR) to screen a large number of Escherichia coli clinical isolates for virulence factor genes and to evaluate the importance of several known factors in the etiology of urinary tract infection.

Methods: Eighty-six E. coli isolates from urine or vaginal or rectal swabs of patients with recurrent urinary tract infection were screened for P fimbria (pap), hemolysin (hly), aerobactin (aer), cytotoxic necrotizing factor 1 (cnf1), S fimbria (sfa), and afimbrial adhesion I (afaI) genes by multiplex PCR. The phenotype of the strains was determined for type 1 fimbriae and O antigen serotype. The infectivity of 11 strains with different combinations of virulence factors was tested using a mouse model of unobstructed urinary tract infection.

Results: Type 1 fimbriae were present in 81 of the 86 strains and was the only virulence factor in approximately one third of the isolates. Genes for hly, aer, cnf1, sfa, or pap were present in approximately one fourth of the strains; afaI was present less frequently. A positive type 1 fimbriae phenotype was common to all strains that induced a bladder infection in mice.

Conclusions: Multiplex PCR methods can be effectively applied to studies that require genetic screening of numerous E. coli uropathogens. Where phenotypic information was available, it was consistent with genotypes identified by PCR. Infectivity studies showed that the presence of the type 1 fimbriae gene in an E. coli isolate was required to establish a bladder infection. Other genes that were not identified in this study may also be required in mice and humans.