A comparative study of detection methods for Lactococcus garvieae in experimentally infected rainbow trout (Oncorhynchus mykiss, W.)

Abstract

This study was carried out to detect Lactococcus garvieae from experimentally infected rainbow trout (Oncorhynchus mykiss, W.) using bacteriological, serological, and histopathological techniques. Rainbow trout were experimentally infected with two Lactococcus garvieae strains (L1 and L2) by intraperitonal injection. These strains caused bilateral exophthalmia with periocular hemorrhage, corneal opacification, darkening of the skin, strong internal congestion in the visceral organs, and enlargement of the spleen in the infected rainbow trout. The two L. garvieae strains were re-isolated from experimentally infected fish groups and identified with standard biochemical methods and API 20 STREP system. The presence of L. garvieae in the tissue of experimentally infected fish was confirmed by Indirect Fluorescent Antibody Technique (IFAT). The humoral antibody response of the infected fish was confirmed by slide agglutination, IFAT, and Enzyme Linked Immunosorbent Assay (ELISA). Histopathologically, liquefactive necrosis in the liver, spleen, and kidney, epithelial cells hyperplasia, hemorrhages and telangiectasia of the gill filaments, and sub-retinal hemorrhages in the eyes were observed.