Amplified In Situ Hybridization With Peptide Nucleic Acid Probes for Differentiation ofMycobacterium tuberculosisComplex and NontuberculousMycobacteriumSpecies on Formalin-Fixed, Paraffin-Embedded Archival Biopsy and Autopsy Samples

Abstract

The aim of this study was to evaluate sensitivity and specificity of in situ hybridization (ISH) using peptide nucleic acid (PNA) probes and tyramide-based amplification for the differentiation between Mycobacterium tuberculosis (MTB) and mycobacteria other than tuberculosis (MOTT) on formalin-fixed, paraffin-embedded tissue samples. We performed ISH simultaneously with both probes on 86 specimens from different organs: 70 obtained at autopsy and 16 by biopsy, all with a histologic evidence of mycobacterial infection confirmed by Ziehl-Neelsen–positive staining. Taking culture as the “gold standard,” 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 formalin-fixed, paraffin-embedded specimens (it is more specific than usual histologic stains) and as an alternative to polymerase chain reaction, allowing the morphologic evaluation of positive bacilli.