Evaluation of antibacterial and antifungal activity of indigenous Lactobacillus plantarum strains isolated from various foods

The purpose of this study was to evaluate the antimicrobial activity of four different strains of lactobacillus-plantarum isolated from several sources of food (fermented olives, sour dough, cottage cheese and camel milk) against four bacterial pathogens including Escherichia coli, Listeria monocytogenes, Staphylococcus aureus and Salmonella Enteritidis and two food spoilage fungi (Aspergillus flavus and Aspergillus niger ). Antibacterial and antifungal activity of each strain and its cell free supernatant (CFS) was tested in well diffusion, overlay and agar spore spot, respectively . To determine the nature of the antimicrobial compounds, CFS of Lactobacillus plantarum strains were also used for different thermal and enzymatic treatments and neutralization. The results showed that all strains had good antimicrobial activity against all bacteria and fungi and the activity level was different depending on the strain. Also, there was no significant difference between antimicrobial activity of active culture suspension and cell-free supernatant in well diffusion method, and the highest inhibition zone was observed against E.coli (13.67 ± 0.57). The high antifungal activity was observed in strains isolated from sour dough. Also, A.flavus was more sensitive to antimicrobial compounds of CFSs than A.niger. Thermal treatment of CFS did not have any effect on the reduction or increase of antimicrobial properties, while neutralization omit antimicrobial activity. Also, except two strains antimicrobial activity of all supernatants was affected by Proteinase K treatment. The results of this study showed that indigenous strains of Lactobacillus plantarum and their antimicrobial compounds have a good potential for use as a natural preservative in food.