Isolation and partial characterisation of secondary metabolites from fish-borne bacterium, Pseudomonas aeruginosa

Abstract

Partial characterisation of secondary metabolites of a potent antagonistic bacterium Pseudomonas aeruginosa FARP72 (NCBI GenBank Accession No. KC570343) isolated from the skin mucus of catfish Clarias batrachus was attempted in this study. The antagonistic activity of P. aeruginosa was confirmed by cross and parallel streaking methods against three bacterial fish pathogens (Aeromonas caviae, Edwardsiella tarda and β-haemolytic Streptococcus sp.) and seven human bacterial pathogens viz., Klebsiella pneumoniae, Enterohaemorrhagic Escherichia coli, Escherichia coli, Staphylococcus aureus ATCC 12598, Salmonella Typhi (serovar of Salmonella enterica sub sp. enterica), Vibrio cholerae and Bacillus pumilus. The antibacterial activities of the crude ethyl acetate extract of the whole cell of P. aeruginosa and the spent medium were also tested against the pathogens by well and disc diffusion assays. The ethyl acetate extract of P. aeruginosa cells was subjected to column chromatography packed with silica gel (60-120 mm mesh size) using petroleum ether and ethyl acetate in different concentrations as the mobile phase. The compounds of the bioactive fractions were semi purified and partially characterised using thin layer chromatography and mass spectroscopy. The secondary metabolites were identified to be pyrols, quinoline and phenazine compounds. The results suggested that the bioactive fractions of whole P. aeruginosa cells have potential antibacterial activity, which can be used as an alternative to conventional antibiotics to control fish and human pathogens.