Isolation, Identification, Molecular, and Histopathological Investigations of Two Pathogenic Enterococcus Species From Tilapia in Egyptian Farms

Abstract

The rapid increase in global aquaculture have exposed many diseases in aquaculture field, enterococci are one of them. Tilapia is one of the most important and economic fish species in the world. Hundred and thirty diseased farmed Nile tilapia (Oreochromis niloticus) had been investigated for Enterococci collected from different farms in Abbassa, Sahl Elhusseineya, Altal alkabir, Bahr Albaqar, Al Manzalah, Ismailia, Port said during both spring and summer seasons. Two species were identified by automated identification and antibiotic sensitivity testing system (ID&AST) as E. faecalis and E. faecium. In vitro antibiotic susceptibility testing for these two species showed high susceptibility to ampicillin, penicillin, streptomycin, and gentamycin while, E. faecalis was sensitive to vancomycin but E. faecium was resistant to it. These species were confirmed by 16s rRNA as Enterococcus. The two species showed sensitivity and resistance to many antibiotics. Ninety fish with an average weight 50-250 g were exposed to pathogenicity test. Fish were randomly divided into three groups, each contain thirty fish then divided into triplicate (10 fish per replicate). Fish of the first and second groups were intraperitoneally injected with 0.2 ml of bacterial suspension of the 2 species, with comparison of a control group they showed high pathogenicity level (77% for E. faecium and 73% for E. faecalis), also the histopathology revealed vascular congestion and infiltration with inflammatory cells in examined organs tissues (brain, liver, kidney, spleen and heart). In conclusion, E. faecalis and E. faecium were the most common subspecies of Enterococci showing high pathogenicity for Nile tilapia fish in Egypt.Keywords: Identification, Tilapia, Enterococci, Pathogenicity, Histopathology,