Detection of Salmonella Typhi in blood with real time fluorescent quantitative reverse transcriptive polymerase chain reaction

Objective To establish an assay of real time fluorescent quantitative reverse transcriptive polymerase chain reaction (rRT-PCR) to detect Salmonella Typhi in blood. Methods Specific primers STY1631 gene of S. Typhi were designed and modified to establish rRT-PCR assay and the specificity and sensitivity of rRT-PCR with RNA as template were evaluated and verified by checking cultured Salmonella spp. in 51 serotypes, predominant non-salmonella enteric diarrheal pathogens and eight species of bacteria inducing bacteremia with fever as major symptom. The simulative blood specimens supplemented with S. Typhi were tested by the rRT-PCR assay. Results The established rRT-PCR assay successfully detected STY1631 gene of S. Typhi. Totally 48 S. Typhi isolates were amplified to be positive. Other isolates, including non-salmonella strains in 33 serotypes, predominant non-salmonella enteric diarrheal pathogens and eight species of bacteria causing bacteremia with fever, were amplified to be negative. For purified total RNA from pure cultured isolates, the detection limit of the assay was 1 pg per reaction, equal to 194 copies per reaction. The sensitivity achieved 1?102 cfu /ml with the purified nucleotide from simulative blood. Conclusion The rRT-PCR assay for detecting S. Typhi with high sensitivity and specificity was established, which would be suitable for the rapid diagnosis of S. Typhi infection and identification of other pathogens causing fever for the early warning, prevention and treatment of typhoid fever.