Detection of Francisella tularensis by the polymerase chain reaction

Francisella tularensis is the causative agent of tularaemia. Effective antibiotic treatment of tularaemia is now available, but the early diagnosis of tularaemia remains a problem. Four primers (three pairs) were designed to detect F. tularensis by the polymerase chain reaction (PCR), based on the previously published nucleotide sequence of T-cell epitopes of a F. tularensis membrane protein. Amplification of purified F. tularensis chromosomal DNA with the three pairs of primers resulted in three different products with sizes consistent with those predicted from sequence data (211 bp, 347 bp and 568 bp). The specificity of the PCR was confirmed as no amplification was detected with a range of other bacteria. The sensitivity of the PCR was determined with limiting dilution PCR and viable counts. The preliminary application of the PCR to the detection of F. tularensis in aerosols and experimentally infected mice was investigated. Comparison of the results with those from traditional culture indicated that PCR was more sensitive. The animal challenge test showed that, 24 h after inoculation with 15 cfu of F. tularensis, 38 (82.6%) of 46 blood samples were positive by PCR, whereas only 22 (47.8%) were positive by culture. The results showed that PCR is a helpful tool for the detection of F. tularensis in blood, liver and spleen which should enable the rapid confirmation of clinical diagnoses of tularaemia.