DETECTION OF SALMONELLA-TYPHI IN THE BLOOD OF PATIENTS WITH TYPHOID-FEVER BY POLYMERASE CHAIN-REACTION

A polymerase chain reaction (PCR)-based test was developed for the det ection of Salmonella typhi in the blood specimens from patients with t yphoid fever. Two pairs of oligonucleotide primers were designed to am plify a 343-bp fragment of the flagellin gene of S. typhi. Amplified p roducts were analyzed by agarose gel electrophoresis and Southern blot hybridization by using a P-32-labeled 40-base probe internal to the a mplified DNA. The nested PCR with two pairs of primers could detect 10 organisms of S. typhi as determined by serial dilutions of DNA from S . typhi. The peripheral mononuclear cells from 11 of 12 patients with typhoid fever confirmed by blood culture were positive for DNA fragmen t of the flagellin gene of S. typhi, whereas 10 blood specimens of pat ients with other febrile diseases were negative. With the nested PCR, S. typhi DNAs were detected from blood specimens of four patients with suspected typhoid fever on the basis of clinical features but with ne gative cultures. We suggest that the PCR technique could be used as a novel diagnostic method of typhoid fever, particularly in culture-nega tive cases.