Preliminary in vitro study on antifungal activity of some local lactobacilli and lactic streptococci isolates

Abstract EN

The agar–well diffusion method was used to assay in vitro the antifungal activity (AA) of the metabolites of five lactobacilli (Lb) and five Lactic streptococci (LSt) isolates obtained from samples of Egyptian dairy products towards four indicator phytopathogenic fungi: Rhizoctonia solani, Sclerotuim cepivorum, Fusarium oxysporum and Penicillium sp.The AA was expressed as percent of fungal growth inhibition (FGI %).

The results revealed that the crude cell-free culture supernatants (crude CFCS) of both Lb and LSt isolates showed variations in their AA, and the ranges were 48–63 % FGI and 38–52 % FGI for Lb and LSt isolates, respectively .Also ,the four indicator fungi showed differences in their sensitivity to the CFCS of the tested bacteria.

The Penicillium sp.

was the most sensitive indicator fungi with 60% FGI and 54 % FGI for Lb and LSt isolates, respectively.

In general, the AA of Lb isolates was relatively higher (54 % FGI is average) than that of LSt isolates (44 % FGI in average).

Neutralization (pH 6.5) of crude CFCS, elimination of H2O2 or both caused a decrease in AA in most cases indicating a role of organic acids and H2O2 in AA.

Treatment of the neutralized, H2O2–free CFCS with the proteolytic enzymes , Pronase completely inactivated the AA in most cases and slightly reduced it in some cases, indicating the presence of a proteinaceous antifungal substances in the crude CFCS of both Lb and LSt isolates.

This study has proven the in vitro potential of some local Lb and LSt isolates to inhibit growth of some plant pathogenic fungi.