Comparative Study of Ziehl Neelsen's Technique and the Fite-Faraco Technique in the Histopathological Diagnosis of Mycobacteriosis in Fish

Mycobacteria are widespread in the natural environment, both in terrestrial and aquatic environments, and some species can be zoonotic. In aquatic organisms, especially in fish and crustaceans, they are diagnosed with certain frequency. Taking into account that mycobacteria affecting fish, as well as the species causing leprosy, have less mycolic acid, the authors used the Fite-Faraco (FF) technique in this work and compared it with the classic Ziehl Neelsen (ZN) staining. In the Laboratory of Immunology and Pathology of Aquatic Organisms (LIPOA), the authors chose from their tissue archive tissue material belonging to 10 specimens of fish of different species, belonging to LIPOA, which were reported cases over a period of 15 years (from 2002 to 2017). The specimens had in common the presence of lesions classified as granulomatous inflammation, but with the ZN technique it was not possible to obtain a definitive diagnosis of mycobacteriosis. The authors observed that in tissues from fish infected with Mycobacteria, the FF technique was more useful, since the presence of bacilli can be observed, where previously the ZN technique was used and no bacilli were observed.