Growth parameters and AFB1 production of Aspergillus spp. In the presence of Enterococcus spp. isolates from canine faeces.

FERNANDEZ JURI M. G.,; DALCERO A.M; MAGNOLI C.E,

Mendoza

Congreso; Mycored- Argentina. Strategies to rteduce the impact of mycotoxins in Latin America in a global contex; 2011

Universidad Nacional de Río Cuarto

Biocontrol has received much attention in recent years due to the need of controlling the food and feed spoiling caused by micotoxicogenic moulds. Lactic acid bacteria (LAB) such as Lactobacillus spp., Lactococcus spp., and Enterococcus spp., are known to produce different antimicrobial compounds that are important in the biopreservation of food and feed. There are only a few reports on antifungal effects of LAB. On the other hand, one of the effects identified on LAB is the protection against mycotoxins such as aflatoxins (AFs). Dogs are particularly sensitive to the acute hepatotoxic and carcinogenic effects of AFs. In previous works, aflatoxin producer strains and AFB1 were detected from dog foods. The aim of the present study was to evaluate the effect of LAB strains on lag phase before growth, growth rate, and AFB1 production by strains of Aspergillus section Flavi on in vitro conditions. Aspergillus flavus (AF1 and AF2), A. parasiticus (AP1) and A. parasiticus reference strain (NRRL 2999) were used. Five LAB strains (GJ9, GJ40, MF5, MF8 and MF9) isolated from faeces of healthy dogs were identified as Enterococcus spp. and then used in the inhibition test. Agar well diffusion assay was performed to determinate inhibitory activity of Enterococcus spp. strains against moulds. LAB and mould were inoculated simultaneously on LAPTg medium (yeast extract, triptone, glucose 1%, peptone 1.5%, and agar 1.2%); and incubated at 37ºC for 7 days. Fungal growth was assessed every day during the incubation period and the plates were examined in order to determine lag phase and growth rate. Aflatoxin production capacity was tested in all A. flavus and A. parasiticus strains in the control and in the interaction with each LAB strain by HPLC. All LAB strains were able to extend the lag phase of Aspergillus section Flavi strains assayed, especially on A. parasiticus strains. In other hand, respecting to growth rate, a significant difference was found between A. flavus and A. parasiticus growth rate in presence of LAB strains, compared to the control. All Enterococcus spp. assayed considerably reduced mould growth rate of A. flavus (40-45%) and A. parasiticus (20%). Respect to AFB1 production, results varied from the reduction to the increase of the production among the interaction, stressing the performance of E. faecium GJ9 which reduced the production of this mycotoxin to non detectable values for both A. flavus and A. parasiticus strains, and E. faecium GJ40 which increased the production in a 20 to 100%. The results obtained show that the antifungal ability of LAB depended on lactic acid strain and the Aspergillus species assayed. Even though AFB1 was not significantly reduced in all the interactions, the possibility of extending the lag phase and reducing the growth rate of these fungal species in foods and feeds is important because it could decelerate the visible fungal growth and consequent mycotoxin accumulation on the substrates as cereal grains