MARINE BACTERIA WITH ANTAGONISTIC PROPERTIES AGAINST FISH PATHOGENS FROM the GENUS VIBRIO

MELANIA FERNÁNDEZ; NELDA LILA OLIVERA; MARISA GARCÉS; CYNTHIA SEQUEIROS,

Mar del Plata

Congreso; VIII Congreso SAMIGE 2012; 2012

SAMIGE

One of the most important problems in aquaculture is the high fish mortality due to microbial diseases. The development of environmental friendly procedures such as the use of probiotics is gaining attention as alternatives to avoid the use of antibiotics. Such procedures focus on the prevention of colonization by opportunist pathogens. The inhibitory activity of probiotic microorganisms may be due to competition for adhesion sites and nutrients or production of several antibacterial substances including bacteriocins, hydrogen peroxide, siderophores or organic acid. The aim of this study was to isolate bacteria from sediments, algae and marine organisms (Golfo Nuevo, Chubut) and assess their antagonistic properties against fish pathogens from the genus Vibrio. Strains were isolated on TS (Trypticase Soy), BHI (Brain-heart Infusion), and MRS (de Man, Rogosa and Sharpe) agar plates with NaCl (2% w/v). Plates were incubated at 25°C for 24-72h. To detect antimicrobial activity the double layer method was performed using the fish pathogens Vibrio alginolyticus and Vibrio anguillarum as indicator strains. In addition, cultures of strains that performed positive by the double layer method were harvested and the supernatant antimicrobial activity assessed by the well diffusion agar technique. Phenotypic production of slime was assessed by culturing the strains on Congo red agar plates. The Congo red-positive strains were evaluated for their ability to produce biofilms on different surfaces using the Crystal Violet assay. From 111 isolates, 35 inhibited V. alginolyticus and 63 V. anguillarum. From them, no one showed extracellular antimicrobial activity. Using Congo red, 26 strains produced pigmentation and 19 of them grew as biofilms. The results showed that strain growth was different according to the surface evaluated, 13 isolates formed bigger biofilms on hydrophobic surfaces like polypropylene. On the other hand, 3 showed more important biofilm development on glass, which is a hydrophilic surface. Therefore, adhesion properties along with production of antimicrobial substances are very important characteristic when we select strains with probiotic characteristics.