Selection of lactic acid bacteria for the formulation of mixed inoculats intended for silage.

AGOSTO E.; GARCÍA G.; DOGI C.; CAVAGLIERI L.

Congreso; XIII Congreso Argentino de Microbiología general; 2018

Asociación Civil de Microbiología

Preservation of forage crops for animal feed by ensiling is a well-known method. The process is basedon fermentation of water-soluble carbohydrates by the epiphytic lactic acid bacteria (LAB) present onthe crop and the exclusion of air. The fermentation lowers the pH due to lactic acid production whichinhibits the growth of many spoilage organisms. Silage quality could be improved by addition of LABinoculants, alone or in combination with chemical additives.The aims were to select lactic acid bacteria with potential silage inoculants properties in order to thefuture development of a mixed inoculant that allows to fulfill different purposes. Ten LABstrainspreviously isolated from maiz silage without inoculants,were evaluated on their efficacy in reducingthe pH of maize extract medium, their bio-control ability against mycotoxicogenic fungi, commonlyfound in silages, (Aspergillus fumigatus, A. parasiticus, Penicillium griseofulvum) and againstpathogenic bacteria (Escherichia coli, Salmonella spp, Staphylococcus aureus and Streptococcushaemolyticus). With regard to the antifungal properties, studies on lag phase, growth rate andmacroscopic characteristics of the fungi were carriedout. Lactobacillus acidophilus RC015 was themost 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 offermentation. All the LAB strains were able to inhibit the growth of pathogenic bacteria and this factwas more strongly with L. rhamnosus RC007. Aspergillus parasiticus growth rate and lag phase wereinhibited by L. plantarum RC009; L. acidophilus RC015 and P. acidolacticci RC004. Aspergillusfumigatus proved to be the most resistant fungi against the LAB tested, only L. plantarum RC009 wasable to significantly inhibit their growth rate. With regard to P. griseofulvum, macroscopic changeswere observed with several LAB interactions, such as development of white mycelium and absence ofconidiogenesis. L. rhamnosus RC007 increased the lag phase of this fungus.Taking into account all the results obtained, L. rhamnosus RC007, L. plantarum RC015, L. plantarumRC009 and P. acidolactici RC004 were selected to formulate a mixed inoculant able to fulfill differentpurposes. The ?generally recognized as safe? (GRAS) status of LAB offers the potential to use thesebacteria in commercial applications as biological control agents in foods or feeds. The selected strainscould be able to prevent mould growth, to improve quality of fermented silage and to reduce the healthhazards associated with mycotoxins in inoculated silages. Future assays will be conducted inlaboratory-scale silos in order to provide more knowledge for the future development of a new mixedinoculant intended for silage.