Molecular identification, histopathological analysis and immunohistochemical characterization of non- pigmented Aeromonas salmonicida subsp. salmonicida in Mugil carinatus (Valenciennes, 1836)

Abstract

Aeromonas salmonicida was isolated for the first time from Mugil carinatus fish sampled from Suez Gulf, Suez governorate, Egypt. Fish samples were identified bacteriologically, molecularly and histopathologically. Biochemical identification of A. salmonicida was performed using API 20 NE kits. The universal 16 S rRNA gene of Aeromonas species was used for the molecular identification of retrieved isolates by producing amplicons at 461 bp. Serine protease (ser) and aerolysin-like protein (act) virulent genes were detected in retrieved isolates at 211 bp and 232 bp, respectively. DNA sequence analysis showed high identity with A. salmonicida subsp. salmonicida strains listed in the GenBank database. Histopathological analysis revealed localization of basophilic bacterial colonies in liver and kidney. Congestion, hepatocellular necrosis and renal tubular necrosis were the marked pathological lesions in liver and kidney tissues of infected fish. An immunohistochemistry technique was used for confirming the presence of A. salmonicida antigen. Immune positive antigen antibody reaction was observed as brown coloration in liver parenchyma and kidney sections of M. carinatus.