Application of nested polymerase chain reaction for Salmonella enterica var. typhi in the diagnosis of typhoid fever

Enteric fever caused by Salmonella typhi is a major public health problem. There is an immediate need for the development of molecular techiques for rapid sensitive diagnosis. A nested PCR was developed to detect S. typhi DNA in the blood specimens from patients with typhoid fever by amplification of the dH flagellin gene. Primers were designed from gene sequence internal to RK1 & RK2 primers reported previously by us to amplify a 342bp fragment of flagellin gene of S. typhi. Amplified products were analyzed by gel electrophoresis. The PCR was found to be specific for dH flagellin gene of S. typhi. The nested PCR could detect 40 organisms of S. typhi as determined by serial dilution of DNA. S. typhi DNA was detected from blood specimens of 11 patients out of 28 tested with suspected enteric fever who were culture negative; 4 by first round of PCR and 7 by nested PCR. Nested PCR holds promise to be used as a diagnostic technique for suspected enteric cases which are culture negative and/liave received prior antibiotic therapy.