Identification of Aeromonas veronii isolated from largemouth bass Micropterus salmoides and histopathological analysis

Aeromonas veronii is abundant in aquatic environment and could cause diseases in various kinds of aquatic animals. However, few cases of A. veronii infection were reported in largemouth bass (Micropterus salmoides), which has been widely farmed and become an important economic fish species in China in recent years. In this study, a strain of Gram-negative bacteria was isolated from the diseased largemouth bass, and was tentatively named strain HN1903. According to the results of biochemical characteristics, 16S rRNA sequencing analyses, and artificial infection experiment, the isolate was identified as A. veronii. The virulence of strain HN1903 was tested by challenge experiments, and the value of LD50 with intraperitoneal injection was 3.72 x 104 CFU/g fish weight. Eight virulent genes, including aerA, gcaT, act, fla, lip, ser, hlyA, and ahyB were screened by PCR assay. Antibiotic resistance results showed that the isolate was susceptible to gentamicin and cefotaxime, and moderately sensitive to florfenicol and streptomycin based on the 12 antimicrobial agents tested. Histopathology examination indicated the necrosis in liver, kidney, and gill, inflammatory cellular infiltration in kidney, and hemosiderin granules increase in spleen. In this study, A. veronii was isolated, identified, and its pathogenicity was clarified. The findings in this study could provide the strategy of fish disease control, preventing the outbreak of A. veronii infection.

Automated summary

This study successfully isolated and identified a strain of A. veronii from diseased largemouth bass, and investigated its virulence and antibiotic resistance. The findings provide insights for strategies in controlling fish diseases.