Screening Antagonistic Bacteria Against Aeronionas Hydrophilaand Its Biological Speciality Research

In our study, 11 soil samples were gathered from fields in Fuzhou, Changle and Putian, from which 184 bacterial strains were isolated by tube dilution assay. With Aeronionas hydrophila as the tested strain, 11 antibiotic bacterial strains were screened out by point to point extension inhibition assay and 19 antibiotic bacterial stains by round scrips extension inhlbition assay from 184 bacterial stains, which indicated that the round scrips method was suitable to screen the antibiotic bacteria. In order to determine the taxonomicplacement, the identification of R-15 was performed with bacterial systemic identification method. The result showed that the physiological and bio-ehemical character of R-15 was similar to that of Serratia, and identify R-15 was Serratia marcescens.Mix the R-15 strain and Aeronionas hydrophila strain and its antibiotic products of R-15 relate to time, the results indicate that from 24h to 40h the antibiotic products of R-15 was in duration, from 24h R-15 strain start produce lots of antibiotlc substance, then the Aeronionas hydrophila was quickly restrained. And its number also reduce quickly, but can not be killed all, keeped in a low level.Through orthogonal test, the optimal fermentation conditions of Producing antibiotlc products of R-15 were given out. The fermentation cultures contained(g/liter): dextrose 2%, corn syrup1%, soy meal2% , peptone 0.3% (NH4)2SO4 0.5%.seed age 22h, media(V/V)with 4% bacteria were inoculated in 250mL conical flask containing 50ml medium at 32~Cwith shaking at 200r/min for 36h.Through a modified agar well diffusion assay, antagonism of antibiotic components of R-15 against Aeronionas hydrophila was tested. The antibiotic components infermentation fluid were not precipitated after the treatment of 20-80%(NH4)2SO4, various concentration ethanol and extracted by nhexane, ether and ethyl acetate, which showed that it was infeasible that the crude concentration materials containing antibiotic components were gained by (NH4)2SO4; precipitation and extraction, The antibacterial components of bacterium R-15 against Aeronionas hydrophila could endure the treatment of a wide range of PH, but had not have strong heat resistance, and maintained the antibiotic activity after treatment of Proteinase and Trypsin. Whether all the compounds or part of them Play a role in antagonism needed further study. In addition, which a supervising measure with the Purification of antibiotic compounds.