Experimental infection of the white snook Centropomus viridis Lockington (1877) with Vibrio ponticus: Histopathological manifestations and screening for putative virulence genes

Abstract

Juvenile C. viridis (5.26 ± 0.72 g) were intraperitoneally injected with three doses of Vibrio ponticus (Vp) CAIM 1751 from 104 to 106 CFU/g, and histological analysis, haemolytic activity assessment and putative virulence genes identification were performed. The time of experimental challenge was 168 h. The virulence of Vp was dose-dependent. The mortality after 25 h post infection (p.i.) was 100% at 3.1 × 106 CFU/g and, 83% at 60 h p.i. at 2.9 × 105 CFU/g. The LC50 was 2.9 × 105 CFU/g at 32 h p.i. Congestion and petechial haemorrhages in the ventral area were observed in the infected fish. Similar histological lesions were observed at the three doses as necrosis, congestion and bacterial masses in different organs and tissues. This is the first report where Vp caused in C. viridis pathological changes associated with an acute peritonitis that caused irreversible damage to the internal organs, except in the kidney. Greater severity was identified in the liver and pancreas of the organisms exposed to the higher dose and in the stomach, intestine and nervous system of the fish infected with the lower dose. The main virulence genes of Vp CAIM 1751 were auto inducers, toxins and iron acquisition, including three types of haemolysins and metalloproteases. Furthermore, this strain had a strong β-haemolytic reaction on erythrocytes of the Pacific white snook. The combined action of the proteases and haemolysins may be responsible for the vascular fragility allowing for the rupture of small vessels and haemorrhages in the tissues. This study contributes to our understanding of Vibrio ponticus as an emerging finfish aquaculture pathogen.