Pediococcus acidolactici and Pediococcus pentosaceus isolated from a rainbow trout ecosystem have probiotic and ABF1 adsorbing/degrading abilities in vitro.

Probiotics are being used in biological control of bacterial pathogens, as an alternative to antibiotics, to improve health and production parameters in fish farming. Fish farming production is severely affected by aflatoxins (AFs), which are a significant problem in aquaculture systems. Aflatoxins exert substantial impact on production, causing disease with high mortality and a gradual decline of reared fish stock quality. Some aspects of aflatoxicosis in fish, particularly its effects on the gastrointestinal tract, have not been well documented. The aim of the present study was to evaluate probiotic properties of lactic acid bacterial (LAB) strains isolated from rainbow trout intestine and feed. Moreover, AFB1-binding and/or degrading abilities were also evaluated to assess their use in the formulation of feed additives. Growth at pH 2, the ability to co-aggregate with bacterial pathogens, inhibition of bacterial pathogens, and determination of the inhibitory mechanism were tested. Aflatoxin B1 (AFB1) adsorption and degradation ability were also tested. All strains were able to maintain viable (107 cells ml-1) at pH 2. Pediococcus acidilactici RC001 and RC008 showed the strongest antimicrobial activity, inhibiting all the pathogens tested. The strains produced antimicrobial compounds of different nature, being affected by different treatments (catalase, NaOH and heating), which indicated that they could be H2O2, organic acids or proteins. All LAB strains tested showed the ability to coaggregate pathogenic bacteria, showing inhibition percentages above 40%. Pediococcus acidilactici RC003 was the one with the highest adsorption capacity and all LAB strains were able to degrade AFB1 with percentages higher than 15%, showing significant differences with respect to the control. The ability of some of the LAB strains isolated in the present work to compete with pathogens, together with stability against bile and gastric pH, reduction of bioavailability and degradation of AFB1, may indicate the potential of LAB for use in rainbow trout culture.

Use of propyl paraben to control growth and ochratoxin A production by Aspergillus section Nigri species on peanut meal extract agar.

This study was carried out to determine the efficacy of the phenolic antioxidant propyl paraben (PP) under different interacting water activity (a(W)) and temperature regimes on lag phase, growth rate and Ochratoxin A production by Aspergillus section Nigri strains. In this experiment six Aspergillus section Nigri strains were used. Peanut meal extract agar (PMEA) was prepared at 2%. The a(W) of the medium was adjusted to 0.995, 0.980 and 0.930, PP levels of 1, 5, 10 and 20 mmol/L were added to the basic medium. Plates were inoculated and incubated for 30 days at 18 and 25 degrees C. Lag phase (h) and radial growth rates (mm/day) were calculated. In control treatments, the lag phase increased and the growth rate decreased as a(W) reduced in all assayed strains. At all a(W) levels, when antioxidant concentrations increased the growth rate decreased. At 5, 10 and 20 mmol/L of PP the strains were not able to reach the exponential phase and completely inhibited fungal growth and OTA production regardless of a(W) used in all the evaluated strains.