Antibiotic-resistant mutants of lactic acid bacteria: potential food control agents

Background: One of the most pressing challenges facing global agriculture today is the restoration of degraded farmland. Organic fertilisers are increasingly being used as a safer alternative to synthetic forms. The most promising form of environmentally friendly fertiliser is a bioconsortium based on different groups of microorganisms. Lactic acid bacteria (LAB) with high antifungal activity, isolated from Armenian dairy products, can form part of such a bioconsortium and protect plants from phytopathogens. In addition, LAB can be used as a preservative in the food industry due to its GRAS (generally recognised as safe) status. Objective: To obtain antibiotic-resistant pleiotropic lactic acid bacterial mutants with higher antifungal activity and broad-spectrum activity compared to natural strains. Methods: The objects of the study were LAB, whose antifungal activity was studied against phytopathogenic fungi of the genera Penicillium, Aspergillus, Alternaria and Fusarium, which cause crop/food spoilage. To increase antifungal activity, spontaneous pleiotropic mutants resistant to the streptomycin, kanamycin or rifampicin were obtained on the basis of original strains. Results: Among all the LAB tested, Lactobacillus bovis MDC 1061, L. paracasei MDC 10898 and L. buchneri BKM 1599 were selected for their antifungal activity. Based on the latter, 78 antibiotic-resistant mutants with different levels of antifungal activity were obtained. L. bovis MDC 1061 STR-25 and L. buchneri BKM 1599 RIF-7 mutants with up to 98% and 95% inhibition of fungal growth, respectively, were selected as potential food control agents. Conclusion: Antibiotic-resistant mutants L. bovis MDC 1061 STR-25 and L. buchneri BKM 1599 RIF-7 with high antifungal ability and a wide range of its effects were obtained. For the first time, the phenomenon of pleiotropic effect has been used in LAB to improve antifungal activity. After extensive study, these mutants can be used as promising components for creating an effective bioconsortium, as well as a preservative in food production, especially in the case of plant-based functional foods to protect against contamination by fungi. Keywords: lactic acid bacteria, pleiotropic mutants, antifungal activity