In vitro Antibacterial Potential of Halophilic Bacterial Secondary Metabolites from Salted Fish

Abstract

Living organisms can be found over a wide range of extreme conditions. Most of the organisms living in extreme environments (i.e, extremophiles) belong to the prokaryotes. Halophiles are interesting class of extremophilic organisms that have adapted to harsh, hypersaline conditions. They are able to compete successfully for water and resist the denaturing effects of salts. The present study was an investigation on the in vitro antibacterial effect of secondary metabolites from halophilic bacteria isolated from salted fish samples. The cured salted fish samples were collected and enumerated using halophilic Nutrient Agar supplemented with 4% NaCl. The isolated and purified bacterial cultures are numbered as SF1, SF2, SF3, SF4 and SF5 are further identified using VITEK 2 system as Bacillus vallismortis, Ralstonia mannitolytica, Bacillus subtilis, Rhizoboum radiobacter and Kocuria kristina. Growth kinetics of halobacterial isolates were determined by spectrophotometric assay. The antibiotic resistance pattern of tested pathogenic microorganisms using the commercial antibiotics was screened and almost all the tested microorganisms are resistant to Penicillin. The antimicrobial activity of secondary metabolites of halophilic bacteria against drug resistant microbes was assessed using the Agar well diffusion assay. Among the different extracts of the halophilic bacteria, the chloroform extracts of R. mannitolytica showed maximum antibacterial activity against Bacillus subtilis MTCC 441 and Xanthomonas campestris MTCC 2286. The results of antimicrobial activity are considerable because it enables the identification of potential secondary metabolites present in marine halophilic bacteria, which act as source of innumerable therapeutic agents. Further research is highly warranted to find out the active principle responsible for the antibacterial property and to elucidate the structure of particular compound.