Antagonistic Activity Of Lactic Acid Bacteria Research Articles

Effect of lactic acid bacteria on the control ofFusarium oxysporumandRalstonia solanacearumon singly infected and co-infected tomato plants

To evaluate the effect of lactic acid bacteria (LAB) on the control of Fol59 and Rs on singly infected and co-infected tomato plants and to address molecular pathways that may be involved in this interaction. To assess the development of the disease, individual infection and coinfection were stimulated in plants under controlled conditions, at two concentrations of Rs and Fol59 applied at two different moments. Additionally, the antagonistic activity of LAB against Rs and Fol59 in vitro and its biocontrol efficacy in planta were evaluated. Preliminary results indicate that inoculation with 1×106 microconidia ml-1 of Fol59 and 1×108 cfu ml-1 of Rs may be a reliable synchronous coinfection method. Of the 68 LAB strains evaluated in vitro, AC13, AC40, and AC49 had an antagonistic effect on both pathogens, with AC40 showing the highest efficacy rate after submerging the seeds in suspension and sowing them in substrate. Finally, gene expression experiments confirmed the AC40 effect on the expression of PR-1a, ERF1, and LoxA genes. The delayed appearance of symptoms and the reduced severity of the disease may be associated with the expression of PR-1a, ERF1, and LoxA genes related to salicylic acid, ethylene, and jasmonic acid pathways respectively.

In Vitro Evaluation of Bacteriocin-Like Inhibitory Substances Produced by Lactic Acid Bacteria Isolated During Traditional Sicilian Cheese Making.

Bacteriocins are antimicrobial proteins produced by bacteria that inhibit the growth of other bacteria with a bactericidal or bacteriostatic mode of action. Many lactic acid bacteria (LAB) produce a high diversity of different bacteriocins. Bacteriocinogenic LAB are generally recognised as safe (GRAS) and useful to control the frequent development of pathogens and spoilage microorganisms. For this reason they are commonly used as starter cultures in food fermentations. In this study, the authors describe the results of a screening on 699 LAB isolated from wooden vat surfaces, raw milk and traditional Sicilian cheeses, for the production of bacteriocin-like inhibitory substances, by comparing two alternative methods. The antagonistic activity of LAB and its proteinaceous nature were evaluated using the spot-on-the-lawn and the well-diffusion assay (WDA) and the sensitivity to proteolytic (proteinase K, protease B and trypsin), amylolytic (a-amylase) and lipolytic (lipase) enzymes. The indicator strains used were: Listeria monocytogenes, Staphylococcus aureus, Escherichia coli, Salmonella enteritidis. A total of 223 strains (belonging to the species Enterococcus spp., Lactobacillus spp., Pediococcus spp., Streptococcus spp., Leuconostoc spp. and Lactococcus lactis) were found to inhibit the growth of Listeria monocytogenes by using the spot-on-the-lawn method; only 37 of these were confirmed by using the WDA. The direct addition of bacteriocin-producing cultures into dairy products can be a more practical and economic option for the improvement of the safety and quality of the final product.