Quantitative detection of Salmonella enterica serovar Typhi from blood of suspected typhoid fever patients by real-time PCR

We quantified the gene copies from Salmonella enterica serovar Typhi (S. Typhi) in the blood of patients suspected of having typhoid fever by using TaqMan-based real-time PCR (TaqMan assay) to target the S. Typhi flagellin gene in genomic DNAs isolated from blood samples. Of 55 blood samples taken from suspected typhoid fever patients, eight blood samples with a positive blood culture had S. Typhi loads ranging from 1.01×103 to 4.35×104 copies/ml blood, and from 47 blood samples with negative blood culture, there were 40 (85.1%) TaqMan assay-positive samples with loads ranging from 3.9 to 9.9×102 copies/ml blood. In the present study, the TaqMan assay detected more than 103 copies/ml blood of S. Typhi in all of the blood culture-positive samples, whereas less than 103 copies/ml blood of S. Typhi were detected in the blood culture-negative samples. Our findings suggest that a TaqMan assay may be useful for assessing S. Typhi loads, especially in cases of suspected typhoid fever with negative results from the standard blood culture test.