Antibacterial Activities of Striped Snakehead Murrel Fish Channa striata Autochthonous Gut Bacterium Achromobacter xylosixidans against Bacterial Fish Pathogens

In the present study, a total of 25 healthy and infected striped snakehead murrel fishes (Channa striata) were collected from Veeranam Lake of Cuddalore district. Eight morphologically distinct autochthonous bacteria (VLFAu 1-8) were isolated from the healthy fish gut and ten different bacterial fish pathogens were isolated from the infected fish samples. Screening of autochthonous isolates for antibacterial activity against bacterial fish pathogens revealed VLFAu 6 as the potential strain and it was identified as Achromobacter xylosixidans using 16S rRNA sequencing. The observed antibacterial activities were Vibrio cholerae (2.2cm), Vibrio parahaemolyticus (2.5cm), Vibrio flavius (2.2cm), Salmonella typhi (1.9cm), Salmonella paratyphi (2.3cm), Vibrio fischeri (2.3cm), E. coli (2.4cm), Aeromonas hydrophila (3.1cm), Pseudomonas aeruginosa (2.7 cm) and Pseudomonas fluorescens (2.9 cm). The ideal conditions for the maximum growth of A. xylosixidans were 36 h incubation, 160 rpm agitation, pH 7, 37oC, 2.5 % salinity, 2 % glucose as carbon source and 1.5 % yeast extract as nitrogen source and the antimicrobial activity was found to be growth dependent. Hence this study proved that the autochthonous bacterial isolates of fish gut are the capable of producing of antimicrobial compound against fish pathogens tested.