Evaluation of a specific nested PCR targeting domain III of the 23S rRNA gene of "Tropheryma whippelii" and proposal of a classification system for its molecular variants

"Tropheryma whippelii"-associated infections are usually confirmed histopat hologically by using light microscopy. PCR assays targeting the 16S rRNA ge ne (16S rDNA) of "T. whippelii" are increasingly being applied for this pur pose. Compared to microscopic analysis, PCR seems to be more sensitive, as indicated by the fact that several cases of Whipple's disease with negative histopathological findings but positive PCR results have been reported. Co nsidering the lack of pathognomonic clinical features for this disease and the fact that "T. whippelii" DNA has repeatedly been found in patients with out clinical Whipple's disease, such PCR results should be confirmed by add itional tests. We have, therefore, evaluated a "T. whippelii"-specific nest ed PCR targeting domain III of the 23S rDNA with 41 clinical specimens know n to contain "T. whippelii" 16S rDNA, All of these specimens were also posi tive for "T. whippplii" 23S rDNA, The specificity of the test was shown by sequencing of the amplicons and by the absence of amplicons in 38 negative controls. We consider this PCR test to be a suitable tool for confirming th e presence of "T. whippelii" DNA in specimens with inconclusive histopathol ogical findings. The information derived from sequencing of the partial "T. whippelii" 23S rDNA was then combined with our recent data of the 16S-23S rDNA spacer region of this organism. Overall, four different rDNA types are recognized in our proposed classification system for molecular variants of "T. whippelii." This preliminary scheme may provide a basis for further ep idemiological and clinical studies with "T, whippelii" and associated disea ses.