Lactobacillus paracasei subsp tolerans isolated from intestinal microbiota of fish of Bahía Blanca estuary for use as biological control agent in aquaculture

SICA, MARÍA GABRIELA; BRUGNONI, LORENA INÉS; MARUCCI, PATRICIA LILIANA; LÓPEZ CAZORLA, ANDREA; CUBITTO, MARÍA AMELIA

San Miguel de Tucumán

Congreso; VII Congreso Argentino de Microbiología General; 2011

Sociedad Argentina de Microbiología General

The aim of the current study was to evaluate the probiotic properties of a lactic acid bacteria strain for rainbow trout (Oncorhyncus mykiss) culture. The strain F2 was isolated from the fish saraquita (Ramnogaster arcuata). According to 16S rDNA phylogenetic analysis, the isolate was affiliated as Lactobacillus paracasei subsp tolerans (GenBank accession FJ892732), and was selected for this study by presenting growth inhibitory effects against the salmonid pathogens: Aeromonas salmonicida subsp. salmonicida, Yersinia ruckeri and two strains of Lactococcus garvieae.The characteristic evaluated were: a) tolerance to rainbow trout gastric pH, b) tolerance to rainbow trout bile, c) in vitro adhesion to rainbow trout mucus, e) competitive exclusion of salmonid pathogens: Y. ruckeri and A. salmonicida, and f) assessment in vivo of possible pathogenicity in rainbow trout.When the strain F2 was exposed at pH 3.0 for 1.5 h, no changes in viable count were observed. Although the strain can survive at pH 2.0, a reduction of 4 logarithmic units with respect to control (pH 6.5) was detected. F2 tolerated a fish bile concentration of 10% for 1.5 h of incubation and no significant changes in viable counts were observed. The strain was able to attach to rainbow trout skin mucus, between 104-105 cells/cm2. F2 inhibited the attachment of salmonid pathogens, Y. ruckeri and A. salmonicida, to mucus at different assay conditions (competition, exclusion and displacement). Under conditions of competition, F2 showed a high percentage of inhibition of Y. ruckeri (92.3% ± 2.9) and A. salmonicida (97.0 % ± 3.0). Futhermore, F2 was able to exclude Y. ruckeri and to displace A. salmonicida adhered to mucus (75.5 ± 2.9 % and 91.1 ± 5.2 % of inhibition, respectively).To evaluate the pathogenicity of the potential probiotic against rainbow trout, the strain F2 was added daily to the water of a close recirculating-water system for intensive culture of rainbow trout in a final density of 103 UFC/mL. Under probiotic supplement, among the experimental fish normal behaviour and no pathology were observed and no differences in the survival were detected, compared to the control tanks (without probiotic supplement) during 45 days of treatment. F2 showed the capacity of colonizing the rainbow trout mucus, ability to compete with pathogens or remove them, stability against fish bile and the usual gastric pH (2.5-3.5). On other hand, the strain has not been harmful to rainbow trout under culture conditions. These results suggest a probiotic potential of Lactobacillus paracasei subsp tolerans, isolated from Bahía Blanca Estuary, for application in rainbow trout culture and encourage further studies.