SELECTION OF LACTIC ACID BACTERIA FOR THE FORMULATION OF MIXED INOULANTS INTENDED FOR SILAGE

AGOSTO, M E; GARCÍA, G; DOGI C.A; CAVAGLIERI L.R.

Congreso; XIII Congreso Argentino de Microbiología General; 2018

Preservation of forage crops for animal feed by ensiling is a well-known method.The process is based on fermentation of water-soluble carbohydrates by the epiphytic lactic acid bacteria (LAB) present on the crop and the exclusion of air. The fermentation lowers the pH due to lactic acid production which inhibits the growth of many spoilage organisms. Silage quality could be improved by addition of LAB inoculants, alone or in combination with chemical additives. The aims were to select lactic acid bacteria with potential silage inoculants properties in order to the future development of a mixed inoculant that allows to fulfill different purposes. Ten LAB strains previously isolated from maiz silage without inoculants, were evaluated on their efficacy in reducing the pH of maize extract medium, their bio-control ability against mycotoxicogenic fungi, commonly found in silages, (Aspergillus fumigatus, A. parasiticus, Penicillium griseofulvum) and against pathogenic bacteria (Escherichia coli, Salmonella spp, Staphylococcus aureus and Streptococcus haemolyticus). With regard to the antifungal properties, studies on lag phase, growth rate and macroscopic characteristics of the fungi were carried out. Lactobacillus acidophilus RC015 was the most efficient in reducing the pH of a maize extract medium, followed by L. rhamnosus RC007; L. plantarum RC009 and Pediococcus acidolactici RC004, achieving pH 4 or less after 12 h of fermentation. All the LAB strains were able to inhibit the growth of pathogenic bacteria and this fact was more strongly with L. rhamnosus RC007. Aspergillus parasiticus growth rate and lag phase were inhibited by L. plantarum RC009; L. acidophilus RC015 and P. acidolacticci RC004. Aspergillus fumigatus proved to be the most resistant fungi against the LAB tested, only L. plantarum RC009 was able to significantly inhibit their growth rate. With regard to P. griseofulvum, macroscopic changes were observed with several LAB interactions, such as development of white mycelium and absence of conidiogenesis. L. rhamnosus RC007 increased the lag phase of this fungus.Taking into account all the results obtained, L. rhamnosus RC007, L. plantarum RC015, L. plantarum RC009 and P. acidolactici RC004 were selected to formulate a mixed inoculant able to fulfill different purposes. The ?generally recognized as safe? (GRAS) status of LAB offers the potential to use these bacteria in commercial applications as biological control agents in foods or feeds. The selected strains could be able to prevent mould growth, to improve quality of fermented silage and to reduce the health hazards associated with mycotoxins in inoculated silages. Future assays will be conducted in laboratory-scale silos in order to provide more knowledge for the future development of a new mixed inoculant intended for silage.