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

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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.

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