Abstract

Ghydaa H. Aljebourya, Sameer N Mahmouda

The present research was conducted to evaluate the antagonistic potential of lactic acid bacteria (LAB) isolates in vitro using agar well diffusion method. In this research, four LAB isolates were selected to investigate their antifungal and antibacterial activity against two phytopathogenic fungi and four pathogenic bacteria. Cell-free supernatants at different fold concentrations (50, 25 and 12.5) ml/l of the four LAB isolates were employed. It was found that all cell-free supernatant folds of the four selected LAB isolates were able to inhibit the growth of all phytopathogenic fungi (Fusarium oxysporum and Alternaria sp) and pathogenic bacteria (E. coli, Klebsiella sp, Salmonella sp, Staphyllococcus aureus). However, the degree of inhibition varied depending upon LAB isolate and microorganism involved. Some LAB isolates revealed effective inhibition activity while others exhibited lower response. Among different LAB isolates, lactobacillus bulgaricus exhibited the strongest antifungal activity against Fusarium oxysporum in all three cell-free supernatant fold concentrates. On the other hand, L.paracasei, L. acidophilus and L. rhamnosus cell-free supernatants showed higher inhibition activity against pathogenic bacteria whereas L. bulgaricus was least active. E. coli was the most inhibited bacterium by L. paracasei and L. acidophilus. LAB cell-free supernatants also showed wide spectrum inhibition activity against both gram positive and gram-negative bacteria. It was also found that the third fold concentrate showed higher inhibition activity than first- and second-fold concentrates against all tested microorganisms, except the second fold concentrate of L. acidophillus which showed higher inhibition effect against both tested fungi. Antibiotics were used to investigate