Amplified in situ hybridization with peptide nucleic acid probes for differentiation of Mycobacterium tuberculosis complex and nontuberculous Mycobacterium species on formalin-fixed, paraffin-embedded archival biopsy and autopsy samples

The aim of this study was to evaluate sensitivity and specificity of in sit u hybridization (ISH) using peptide nucleic acid (PNA) probes and tyramide- based amplification for the differentiation between Mycobacterium tuberculo sis (MTB) and mycobacteria other than tuberculosis (MOTT) on formalin-fixed , paraffin-embedded tissue samples. We performed ISH simultaneously, with b oth probes on 86 specimens from different organs: 70 obtained at autopsy an d 16 by biopsy, all with a histologic evidence of mycobacterial infection c onfirmed by Ziehl-Neelsen-positive staining. Taking culture as the "gold st andard," the sensitivity and the specificity of the MTB probe were 100% (41 /41) and 95% (38/40), respectively. In only 2 cases ISH failed to identify mycobacteria. Culture results were not available in 3 cases. We propose ISH as a relatively simple and rapid method to differentiate mycobacteria on f ormalin-fixed, paraffin-embedded specimens (it is more specific than usual histologic stains) and as an alternative to polymerase chain reaction, allo wing the morphologic evaluation of positive bacilli.