Identification and characterization of pathogenic Aeromonas veronii biovar sobria associated with epizootic ulcerative syndrome in fish in Bangladesh

Sparse information is available on the virulence factors of Aeromonas strains isolated from diseased fish, from the environment, and from humans. In the present study, 52 Aeromonas isolates obtained from epizootic ulcerative syndrome (EUS) lesions in fish, from the aquatic environment, and from children with diarrhea in Bangladesh were identified by biochemical phenotyping (i.e., PhenePlate [PhP] typing) and DNA fingerprinting and then characterized with respect to certain putative virulence factors. The isolates from the fish exhibiting EUS symptoms were identified to be Aeromonas veronii biovar sobria by fatty acid methyl ester analysis and amplified fragment length polymorphism fingerprinting. Biochemical phenotyping revealed that all EUS-associated isolates belonged to a unique phenotype which was not identified among more than 1,600 environmental and diarrheal isolates in a previously collected database of PhP types of Bangladeshi Aeromonas isolates. The 52 Aeromonas isolates were investigated for the production of hemolysin and cytotoxin; for hemagglutination with erythrocytes from fish, human, and rabbit sources; for the presence of a cytolytic enterotoxin gene; and for adhesion to and invasion into fish cell lines. All of the EUS isolates produced all of the virulence factors investigated, as did also some of the environmental isolates, but the isolates from EUS were unique in their ability to agglutinate fish erythrocytes. Our results suggest that a clonal group of A. veronii biovar sobria is associated with, and may be a causative agent of, EUS in fish in Bangladesh.