Aeromonas veronii isolated from climbing perch (Anabas testudineus) suffering from epizootic ulcerative syndrome (EUS)

Motile Aeromonads are responsible for various diseases in fishes that cause significant economic losses in aquaculture. Aeromonas spp. are also frequently isolated from fish suffering from Epizootic Ulcerative Syndrome (EUS). The present study was conducted to isolate and identify A. veronii from Vietnam climbing perch (Anabas testudineus) suffering from EUS, evaluate the pathogenicity of the isolates, and find out antibiogram profile and susceptibility of the isolates to medicinal plant extracts. Vietnam climbing perch (A. testudineus) suffering from EUS was collected from fish farms located at Savar, Dhaka and bacteria were isolated from the external ulcerative lesion, and kidney and liver of the infected fish on nutrient agar plates. Preliminary phenotypic identification of the bacterial isolates was performed following morphological, physiological and biochemical characterization tests. The 16S rRNA gene sequencing was accomplished for further molecular identification of five selected isolates. To evaluate the pathogenicity of the isolates in vivo artificial infection challenge test was conducted through immersion method. Another in vivo pathogenicity test was done at three different temperatures (18 °C, 28 °C, and 37 °C) to examine the effects of temperature on the pathogenicity of the isolates. Ten commercial antibiotics were used to find out the antibiogram profile of the isolates. Finally, susceptibility of the isolates was screened against 19 medicinal plants extracts. A total of 38 out of 46 isolates isolated from Vietnam climbing perch (A. testudineus) suffering from EUS were phenotypically identified as Aeromonas sp. Five randomly selected isolates were further confirmed as A. veronii by analyzing the 16S rRNA gene sequence homology. The pathogenicity of the isolates was found moderate to high (41%–80% mortality) in the artificially challenged fish. The highest and lowest mortality was obtained in the fish challenged with the isolates BFKA33 and BFKA12, respectively. The isolates were found resistant to several antibiotics, including amoxicillin, ampicillin, penicillin-G, and vancomycin. Nevertheless, extracts of three medicinal plant (Allium sativum, Syzygium aromaticum, and Tamarindus indica) demonstrated antibacterial activity to the isolates (BFKA12, BFKA15, BFKA18, BFKA29, and BFKA33).