EVALUATION OF THREE BACTERIAL STRAINS ISOLATED FROM RAINBOW TROUT WITH INHIBITORY ACTIVITY AGAINST CARNOBACTERIUM PISCICOLA

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

Mar del Plata

Congreso; VIII Congreso SAMIGE 2012; 2012

SAMIGE

In Argentina the main pisciculture crop is the rainbow trout, this species is sensitive to cool-water streptococcosis. Carnobacterium piscicola is one of the etiological agents responsible for such disease. The aim of this study was to compare the characteristics of three bacterial strains (T4, T15, and M5) which were isolated from the intestinal microbiota of rainbow trout and showed antimicrobial activity against the fish pathogen Carnobacterium piscicola. Two inhibition tests were used: the double layer method and the agar-well diffusion test. The three strains showed antimicrobial activity against C. piscicola by both methods, while T15 also presented inhibitory activity against Lactococcus garvieae by the double layer method. The bacterial growth and the antimicrobial agent production were studied for the three strains. T4 started to produce the inhibitory agent after 4 h of incubation at 25ºC while T15 and M5 started the antimicrobial production after 12 and 24 h of incubation, respectively. After incubation for 24 h, the antimicrobial activity titers were 40960, 5110, and 40 UA/ml for T4, T15, and M5, respectively. Antimicrobial activity of the three strains after treatment at 100°C for 10 min (at pH 7) suggesting that the antimicrobial agent could be a bacteriocin. T4 and T15 were susceptible to 9 of 12 antibiotics tested; they were resistant to oxacillin, clindamycin, and gentamicin. M5 was susceptible to 10 antibiotics; it showed intermediate susceptibility to oxacillin, and resistance to gentamicin. Although different results were obtained for antimicrobial activity and antibiotic sensitivity, sequencing of 16S rDNA showed that the three strains belong to C. piscicola. T4, T15 and M5 were isolated from the intestinal microbiota of healthy Patagonian rainbow trout, while the indicator C. piscicola was isolated from diseased European fish. Considering that T4 produced the highest antimicrobial activity titer after 48 h of incubation, we conclude that this strain is the most suitable for studying its action as a biological control agent in aquaculture.