Isolation, identification, and virulence gene analysis of pathogenic Aeromonas dhakensis in Macrobrachium rosenbergii and histopathological observation

To identify the cause of mass mortality of adult Macrobrachium rosenbergii in a farm in Gaoyou City, Jiangsu Province, China, a dominant strain named DKQ-1 was isolated from the hepatopancreas of dying M. rosenbergii and identified as Aeromonas dhakensis by purification culture, biochemical characterization, and 16S rRNA and gyrB gene sequence analysis. The results of the challenge test revealed that the strain was highly pathogenic and the 50% lethal dose (LD 50 ) in 72 h to M. rosenbergii was 1.54×10 5 CFU/mL. The amplification results of virulence genes show that strain DKQ-1 carried 9 virulence genes, including ascV, aexT, aer, act, lip, ompAI, gcaT, acg , and exu , supporting the strong virulence of strain DKQ-1 to M. rosenbergii . Histopathological observation of the hepatopancreas, gills, and intestines indicated that DKQ-1 injection into M. rosenbergii could cause serious tissue damage, which further supported the strong virulence of this strain. In addition, a drug susceptibility test revealed that strain DKQ-1 was sensitive to 16 kinds of antibiotics, resistant to 9 kinds of antibiotics, and had intermediate resistance to spectinomycin and kanamycin. This study is the first report of A. dhakensis isolated from M. rosenbergii and provided a reference for the pathogen identification of bacterial diseases in M. rosenbergii , and for the prevention and treatment caused by A. dhakensis .