Studies on the antimicrobial activity of a locally isolated lactic acid bacterium and its application on fusarium solani-infected plants

Abstract

Background Lactic acid bacteria (LAB) have proven a great inhibitory effect toward phytopathogenic bacteria and fungi, giving them the importance as natural biological control agents without hazards to the surrounding eco-system. Objective This study aims for the local isolation of a lactic acid bacterial strain active against different microorganisms especially phytopathogens. Materials and methods Of the 40 isolated bacterial strains, 36 were preliminarily characterized as LAB using both Gram staining and catalase test methods. Their antimicrobial activities were then tested against different bacterial and fungal strains. The most potent isolate was molecularly identified and tested, in vitro, on different pathogens, and then, in vivo, against infected Phaseolus vulgaris plants. Results and conclusion Results revealed that 17 isolates showed antimicrobial activities against Pectobacterium carotovorum and four of them were solely effective against Staphylococcus aureus (inhibition zones of diameters ranging between 0.4 and 0.8 cm). However, only isolate 32 showed satisfactory antimicrobial activity (inhibition zones of ∼0.8 cm) against both of the two aforementioned test microorganisms. Moreover, isolate 32, molecularly identified as Enterococcus faecium, was also found to be active against Fusarium solani phaseoli, a common phytopathogen fungus that affects many economically important crops. The addition of 1.5% (v/v) of the 24-h old fermentation broth of this isolate, in vitro, resulted in a shrinking percent of the fungus growth of more than 51% and gave very promising results when applied in the field experiment. Therefore, the use of the selected LAB culture broth as a bioagent to control some plant pathogens, as well as a plant growth stimulator, could be a promising approach to reduce the economic losses in agricultural crops.