Detection of Salmonella enterica serover Typhi from Widal-positive blood specimens by blood culture and PCR targeting aroC and fliC genes

Objective: The study aimed at investigating the validity of multiplex-PCR for S. typhi detection in blood specimens of Widal-positive typhoid patients and to compare the detection rate of PCR with blood culture. Methodology: Blood specimens were collected from 105 clinically suspected and Widal- positive typhoid patients. For the bacterial culture, the specimens were inoculated into Brain Heart Infusion (BHI) broth. The growth was subcultured on Xylose Lysine Deoxycholate (XLD) and Salmonella-Shigella (SS) agar. Obtained colonies were Gram-stained and subjected to biochemical tests. Multiplex-PCR was performed to amplify a 639-bp fragment of aroC gene specific for Salmonella and a 495-bp fragment of fliC gene for S. typhi. Results: Of 105 Widal-positive typhoid patients, 73 (69.6%) were positive by PCR for the presence of S. typhi and 24 (22.8%) by blood culture. PCR could also amplify S. typhi DNA from 49 (46.7%) culture-negative patients. Widal test with false-positive result was observed in 32 (30.4%) suspected cases. Conclusion: Our study suggests that PCR-based diagnosis of typhoid fever is distinctly useful in culture-negative cases and also false-positive cases as detected by Widal test.