Specific detection and semiquantitation of micro-organisms in tissue by nucleic acidhybridization. I. Characterization of the method and application to model systems.

On the basis of circumstantial evidence, a number of human diseases have been postulated to result from the presence of occult infection. To investigate this problem amethod of specifically detecting and semiquantitaing trace quantities of bacterial DNA in infected tissue has been devised. It is based on RNA-DNA hybridization using radiolabeled RNAcomplementary to the DNA of the organism being sought. The characteristics of the reaction are shown to conform to those expected for RNA-DNA hybridization and the sensitivity of the method is shown to correspond to approximately one organism per 50 mammalian cells. Specificity at this level of sensitivity is sufficient to clearly distinguish between infections with Listeria monocytogenes and Erysipelothrix insidiosa. This approach may have general applicability forthe study of diseases putatively caused by chronic infection not readily demonstrable bythe usual cultural or immunologic techniques. It may also be useful for helping distinguish contaminants from pathogens when isolates are obtained from diseases tissue. Unique to this approach is the value of negative information in excluding the presenceof an organism within its limits of sensitivity.