Fungal and mycotoxin contamination of baled corn silage and isolation of AFB1 binding S. cervisiae strains.

GONZÁLEZ PEREYRA M.L.,; MAGNOLI C.E,; CAVAGLIERI L.R.,; DALCERO A.M.

Córdoba, Argentina

Congreso; VI Congreso Argentino de Microbiología General; 2009

Baled silage is a preservation method for corn and other feedstuffs based on lactic fermentation under anaerobic conditions (Miller, 20019. In argentina, corn silage constitutes a significant energy source in cattle diets. Fungal and mycotoxin contamination reduce nutritional value of ensiled feedstuffs and represent a hazard to human and animal health. The use of natural products to reduce mycotoxin contamination in animal production systems is a matter of increasing interest. The presence of yeast in ensiled feedstuffs is a constant and they are often isolated in high counts. The aims of this work were a) to the determine the natural incidence of toxigenic fungi and the mycotoxins aflatoxin B1 (AFB1) and patulin (PAT) present in baled corn silage samples and b) to isolate yeast strains able to bind AFB1 with biocontrol potential. Thirty-five samples were collected from the province of San Luis. Total fungal counts (CFU/g) were evaluated onto DRBC and DG18 culture media. Isolation frequency and relative density of Aspergillus spp., Penicillium spp. and Fusarium spp. were calculated. Potentially toxigenic isolates were evaluated for their ability to AFB1 and PAT. Natural AFB1 and PAT contamination were quantified by HPLC. Yeast isolates were identified and a S. cerevisiae strain was selected to evaluate its ability to bind AFB1 to its cell wall in vitro. Ninety percent of the samples showed counts higher than the limit recommended as a quality standard for feeds (1 x 104 CFU/g) (GMP, 2008). The prevalent fungal genera were Aspergillus spp. (63%), Penicillium spp. (31%) and Fusarium spp. (11%). Yeast isolation frequency was 97%. Main toxigenic species were A. flavus, A. fumigatus, P. griseofulvum, P. paneum, P. roqueforty y F. verticillioides. Seventy percent of A. flavus strains were able to produce 3 to 112.5 µg AFB1 per g of micellium. One P. griseofulvum and P. paneum isolate produced 366.8 µg/g and 14.2 µg/g PAT, respectively. Seventy- five percent of the samples showed AFB1 contamination containing 5 to 50 µg/g. PAT was not detected in any of the samples. Seventy- seven percent of yeast isolates corresponded to Candida genera, being C. krusei (57%) and C. parapsilopsis (43%) the most frequent species. Twenty-three percent of the total yeast isolates were identified as S. cerevisiae. Saccharomyces cerevisiae strain RC008 showed ability to bind 38.2% to 67.6% AFB1 in vitro. Screening for fungi and mycotoxins in corn silage and other animal feedstuffs in essential for preventing mycotoxicosis and chronic intoxications. Yeasts to able AFB1 such as S. cerevisiae could be playing an ecological role in silage as potential detoxifying agents.