Virulence Properties of a Newly Identified Species Aeromonas sp. T8 Group Isolated from EUS-affected Fish

Abstract

The present study was conducted to determine the virulence and virulence properties of 4 bacterial strains belonging to a newly identified species Aeromonas sp. T8 group, isolated from epizootic ulcerative syndrome (EUS) -affected fish of Southeast Asian countries. Virulence of a representative strain T8 to fish was investigated through intramuscular injection to silver barb Barbodes gonionotus, striped snakehead Channa striatus and tilapia Oreochromis sp., where the LD50 value was determined to be 1.5×105, 3.2×105 and 2.9×105 CFU/fish, respectively.However, all strains were found non-virulent for mice upon intraperitoneal or intravenous injections at a concentration of 3×107 CFU/mouse. Live bacterial cells of these strains showed lipase, protease and hemolytic activities in agar plate assays. The hemolytic activity of the extracellular products (ECPs) was found to be higher for fish blood cells than for mammalian blood cells. Heat stability, EDTA and PMSF sensitivities of β-hemolytic activity of the ECPs differed from that of A. hydrophila and A. caviae reference strains. ECP of only one strain (P2) showed cytotoxicity against both fish (RTG-2, FHM, EPC, BF-2 and SNN-1) and human (HeLa) cell lines, while none of the strains exhibited enterotoxicity to suckling mice. All of the strains also failed to amplify aerolysin and cytolytic enterotoxin (AHCYTOEN) genes by PCR.