Bacterial attachment to fish surfaces and the capacity to compete with pathogens for adhesion sites are essential characteristics in order to select a candidate probiotic for aquaculture. Twelve lactic acid bacteria (LAB) isolated from fish and sediments from Bahía Blanca Estuary, Argentina, were examined for in vitro adhesion to rainbow trout mucus, cell surface properties and competitive exclusion against two salmonid pathogens, Yersinia ruckeri and Aeromonas salmonicida. In order to assess their survival through the digestive tract, pH and rainbow trout bile tolerance were evaluated. All LAB strains survived for 1.5 h incubation in 10% rainbow trout bile. Most of the strains survived 1.5 h at pH 3.0 and three of them showed a reduction of viable counts lower than 2 logarithms, with respect to control (pH 6.5). Only a few strains showed tolerate pH 2.0. All the strains were able to attach to rainbow trout skin mucus (10(4)-10(6) cells/cm(2)), to glass (10(4)-10(5) cells/cm(2)) and to stainless steel (10(3)-10(4) cells/cm(2)). Sixty percent of LAB strains were capable of competing with and successfully excluding Y. ruckeri and all strains were able to displace it. Against A. salmonicida, 75% of LAB strains competed successfully, 50% were capable of displacing and 60% excluded this pathogen. Our data suggest the potential of these strains as anti-infective agents for use in rainbow trout culture. This study is the first report on the probiotic potential of LAB strains isolated from an estuarine environment from Argentina.
Isolation, identification and antimicrobial activity of lactic acid bacteria from the Bahía Blanca Estuary Aislamiento, identificación y actividad antimicrobiana de bacterias del ácido láctico del estuario de Bahía Blanca
The region of Sierra de la Ventana is located in the southwest of Buenos Aires Province, Argentina. Traditionally, this area has been devoted to livestock and agriculture, but tourism has had a significant development in recent years. In the region, there are many rivers and streams that are used for swimming and bathing. A survey of the occurrence of Shiga toxin-producing Escherichia coli (STEC) in these waters was conducted, and the microbiological quality of rivers and streams was investigated. No E. coli O157 was recovered by immunomagnetic separation. Nevertheless, the Shiga toxin gene, exclusively stx2 genotype, was detected in four non-O157 E. coli strains. Two STEC strains carried eae factor, but none of them harbored the EHEC-hlyA gene. Three of the STEC isolates belonged to samples obtained in the warm months, and one to the winter sampling. In the sample sites where STEC strains were isolated the counts of E. coli/100 ml exceeded or were close to the limit recommended by the United States Environmental Protection Agency for bathing water. The relationship observed between the rainy season and E. coli counts suggests that among the main causes for the hygienic indicator increase is the runoff of manure deposited on soils that may also induce the entrance of pathogens into the aquatic environment. This research, the first reporting STEC isolation from recreational waters in this area, revealed that streams and rivers from a beef-producing area of Argentina are a reservoir of STEC strains.
Summary
A lactic acid bacterial strain, Lactobacillus paracasei subsp. tolerans F2, isolated from the intestine of Ramnogaster arcuata, was evaluated as a growth promoter in juvenile rainbow trout Oncorhynchus mykiss (Walbaum, 1972) farming. In addition, the safety of the strain was assessed according to the FAO recommendations. Strain F2 was susceptible to most antibiotics tested and no evidence of hemolytic activity was found. When the strain of Lactobacillus paracasei subsp. tolerans F2 was administered with food, no adverse effects on health were observed and fish biomass increased 12% more in the treatment group than in the control group. Significant differences were detected in the specific growth rate and feed conversion ratio. In the group receiving Lactobacillus paracasei subsp. tolerans F2‐supplemented feed, quantitative differences in the microbial composition of fish feces with respect to the control group were observed. An important decrease in fungi and enterobacteria was observed in feces from the treatment group, coincident with an increase in lactic acid bacteria. This result would indicate a change in the composition of the intestinal microbiota of fish treated with the putative probiotic. These results suggest that the strain of Lactobacillus paracasei subsp. tolerans F2 has the application potential to improve the performance in rainbow trout farming.
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