Antifungal activity of lactic acid bacteria isolated from raw camel milk againts Alternaria alternata and identification of antifungal substance
Keywords:: Lactic acid bacteria ; Alternaria alternata ; transcribed internal spacer ; antifungal activity ; well method ; nature of the antifungal substance.
The phytopathogenic filamentous fungi are responsible for the deterioration of various food products, such as fruits or vegetables, causing significant economic losses. They are also capable of producing several mycotoxins in infected plants and fruits.Lactic acid bacteria (LAB) are considered to be natural antagonists of these dangerous microorganisms. In the present study, 16 strains of LAB isolated from raw camel milk from various regions of Algeria, were the subject of phenotypic and genotypic identification, and they were tested for their antifungal activity. The well method was performed on five strains of lactic acid bacteria against four strains of the toxigenic and spoilage phytopathogenic fungus, Alternaria alternata, isolated from the stems, leaves, roots and fruits of tomatoes and carrots. A study of nature metabolites showed that these metabolites are stable at temperature, and keep the nature of the metabolites with the treatment with proteolytic enzymes such as Pepsin, Lysozyme and Trypsin, so their activity increases with increasing the pH of the culture medium. No loss of antifungal activity of the five selected strains was observed after treatment of the metabolites by heating at 4°C, 30°C, 45°C and 90°C. Internal transcribed spacer polymerase chain reaction (ITS-PCR) analysis and 16S rDNA sequencing were used to characterize and identify LAB isolates that showed varying levels of inhibition of fungal growth. Two strains of LAB, identified as Enterococcus lactis and E. faecium, had the strongest antifungal activity, suggesting potential application in food technology as bio-preservatives against phytopathogenic and food-altering fungi.