Antimicrobial metabolites from Probiotics, Pleurotus ostreatus and their co-cultures against foodborne pathogens isolated from ready-to-eat foods

The incidence of foodborne pathogens in ready- to-eat (RTE) can be attributed to various foodborne diseases. Most of the isolated microorganisms from RTE foods are resistant to common antibiotics and thus, resulted to treatment failure when commercially available antibiotics are administered. However, the secondary metabolites secreted by microorganisms can serve as alternative therapy that are reliable and safe. Secondary metabolites obtained from mono- and co-culture microorganisms can inhibit the growth of antibiotic-resistant microorganisms. Bioactive compounds in the secreted metabolites can be identified and utilized as sources of new antibiotics. In this study, antimicrobial activity of secondary metabolites from Lactobacillus fermentum, Saccharomyces cerevisiae, Pleurotus ostreatus, and their co-cultures were tested against foodborne pathogens isolated from RTE foods using agar well diffusion. The bioactive compounds in the metabolites were identified using gas chromatography-mass spectrometry. From a total of 100 RTE foods examined, Salmonella enterica, Shigella dysenteriae, Escherichia coli, Klebsiella pneumoniae (subsp ozaenae), Pseudomonas fluorescens, Clostridium perfringes, Bacillus cereus, Listeria monocytogens, and Staphylococcus aureus, Penicillium chrysogenum, Aspergillus flavus, and Aspergillus niger were isolated and displayed multiple antibiotic resistance. The secondary metabolites secreted by co-culture of L. fermentum + P. ostreatus + S. cerevisiae, and co-culture of P. ostreatus + S. cerevisiae have the highest (P ≤ 0.05) zones of inhibition (23.70 mm) and (21.10 mm) against E. coli, respectively. Metabolites from mono-cultured L. fermentum, P. ostreatus, and S. cerevisiae showed zones of inhibition against indicator microorganisms with values ranging from 8.80 to 11.70 mm, 9.00 to 14.30 mm, and 9.30 to 13.00 mm, respectively. Some of the bioactive compounds found in the metabolites of co-cultured microorganisms were alpha-linolenic acid (25.71%), acetic acid 3-methylbutyl ester (13.83%), trans-squalene (12.39%), pentadecylic acid (11.68%), 3- phenyllactic acid (30.13%), linolelaidic acid methyl ester (15.63%), and 4-O-methylmannose (53.74%). RTE foods contain multiple antibiotics resistance pathogens. The pronounced antimicrobial activity of the secondary metabolites against microorganisms from RTE foods could be attributed to the presence of bioactive compounds in the metabolites. These metabolites can be exploited as alternative food preservatives, biopharmaceuticals and can be used towards better health delivering systems.