Quantitative detection of Escherichia coli from urine of patients with bacteriuria by real-time PCR.

Abstract

Introduction: Compared with the classical urine culture method, PCR is more rapid, and can detect smaller numbers of bacteria, however it is inferior for quantification. Because of the lack of quantification in routine PCR, the meaning of a positive PCR test result has not been validated for all infections. We report on the development of a novel quantitative detection system for the urinary tract infection (UTI) Escherichia coli using real-time PCR.

Patients: We enrolled 200 patients with suspected bacteriuria.

Methods: The gene encoding the universal stress protein (uspA) was found to be highly specific for E. coli. We quantified the copy numbers of E. coli in the urine of patients with UTI by using a real-time PCR assay (the TaqMan system) targeting uspA genes in genomic DNAs isolated from urine samples (n=200). To evaluate the feasibility of this method, the results were compared with those of a standard urine culture.

Results: The incidence of positive urine cultures was 75% (150 of 200), and various doses of E. coli were detected in 84 of 150 specimens. The real-time PCR method also detected 84 cases of urinary infections of E. coli in the same specimens. Furthermore, the result of the quantification of E. coli using real-time PCR strongly correlated (r2=0.925) with the result of urine culture.

Conclusion: Our results suggest that using quantitative-PCR means a faster and simpler diagnosis of E. coli urinary infection can be made compared with the traditional urine culture method.