Antimicrobial activity and biosurfactant production of bacteria isolated from fish intestinal tract

NELDA LILA OLIVERA; CECILIA HORISZNY; CARLA RIVA ROSSI

Mar del Plata

Congreso; VIII Congreso SAMIGE 2012; 2012

SAMIGE

Biosurfactants (BS) are tenso-active molecules which traditionally have been studied by their role in enhancing biodegradation of low water solubility compounds, such as hydrocarbons. However, BS may take part in many other processes as cellular motility, settlement and disruption of biofilms, and antimicrobial activity. The aim of this study was to analyze antimicrobial activity against fish pathogens and biosurfactant production of bacteria isolated from fish intestinal tract. Strains were isolated in De Man-Rogosa-Sharpe (MRS) and tryptic soy (TS) media. Antimicrobial activity was assessed by the double layer method. For evaluation of biosurfactant production, strains were cultured in the solid media where they had been isolated and the biomass was resuspended in phosphate-buffered saline (PBS). Biomass suspensions were incubated 2 h at 120 rev min-1and harvested by centrifugation (5000 ×g for 10 min) at 10 °C.The supernatant surface tension was measured using a ring tensiometer. Thirty three bacterial strains were isolated from the intestinal tract of rainbow trout (Oncorhynchus mykiss) and hake (Merluccius hubbsi); 16 showed antimicrobial activity against Carnobacterium piscicola, 5 against Lactococcus garvieae, 2 against Aeromonas salmonicida subsp. salmonicida, and no one inhibited Yersinia ruckeri. Eight strains reduced PBS surface tension indicating the release of tenso-active molecules associated to the cell. Among them, strain H8 produced the highest surface tension reduction (26.4 ± 0.6 %). Even though H8 was able to grow under anaerobic conditions, the highest biosurfactant production was reached in aerobic conditions. According to biochemical and molecular tests (16S RNAr sequencing), H8 belongs to Brochothrix thermosphacta. Although this strain did not show antimicrobial activity against the fish pathogens studied, biosurfactant production has not been reported for this genus. Thus, the characterization of H8 biosurfactant could lead to a novel tenso-active compound.