A presumptive histopathologic diagnosis of tuberculosis is commonly based on the finding of acid- fast bacilli upon microscopic examination of a diagnostic specimens. Although this traditional histochemical staining methodis satisfactory, it is time-consuming and not species-specific. For more specific assessment, in situ hybridization assay with oligonucleotide probes is introduced.

The human surgical specimens were obtained from tuberculosis patients(,)and experimental specimens were made by injecting fresh rat liver with cultured M. tuberculosis organisms into fresh rat liver. Oligonucleotide probes complementary to ribosomal RNA portion were synthesized and labeled with multiple biotin molecules. For a rapid detection, all procedures were carried out using manual capillary action technology on the Microprobe staining system.

The in situ hybridization assay produced a positive reaction in experimental specimens (80-90% sensitivity) after pepsin- HCl pre-treatment for a good permeabilization of probes, but reliable result was not obtained from human surgical specimens.

It is, therefore, suggested that biotin- labeled oligonucleotide probes have considerable potential for identification and in situ detection of M. tuberculosis but, there are some barriers to overcome for the diagnostic use of this method.