The role of iturin A from B. amyloliquefaciens BUZ-14 in the inhibition of the most common postharvest fruit rots.

The aim of this work was to elucidate the role of the secondary metabolites produced by B. amyloliquefaciens BUZ-14 against B. cinerea, M. fructicola, M. laxa, P. digitatum, P. italicum and P. expansum both in vitro and in planta. The entire cell free supernatant (CFS) and the lipopeptide fraction (LPF) showed similar antifungal activities, completely inhibiting all the fungi at dilutions of 1:24 or even lower, whereas the non-butanolic fraction (NBF) barely inhibited the fungi. However, when the LPF and CFS were applied on fruit, only brown rot in peaches and blue rot in apples was totally inhibited. The main families of metabolites in the LPF were iturin A, fengycin and surfactin with maximum concentrations of 407, 853 and 658 µg mL-1, respectively. Subsequently, a TLC-bioautography revealed iturin A as the key metabolite in the inhibitions and allowed us to establish in vivo MICs of 16.9 and 33.9 µg mL-1 for Monilinia species and P. expansum, respectively. The application of 24 h-old BUZ-14 cultures suppressed brown rot in peaches and also blue rot in apples but failed to inhibit the other diseases. However, BUZ-14 was only able to grow and produce iturin A in peaches so we can deduce that the amount of iturin A brought with the cultures (36 ±â€¯14 µg mL-1) could be enough to control both diseases. The strong antifungal activity of the iturin A present in the BUZ-14 CFS suggests that it could be successfully used for postharvest disease control. However, future research is necessary to maximize the iturin A production by B. amyloliquefaciens BUZ-14 in order to optimize a commercial application.

Potential of a new strain of Bacillus amyloliquefaciens BUZ-14 as a biocontrol agent of postharvest fruit diseases.

The biocontrol potential of the Bacillus amyloliquefaciens strain BUZ-14 was tested against the main postharvest diseases of orange, apple, grape and stone fruit. After characterizing the temperature and pH growth curves of strain BUZ-14, its in vitro antifungal activity was determined against Botrytis cinerea, Monilinia fructicola, M. laxa, Penicillium digitatum, P. expansum and P. italicum. Subsequently, in vivo activity was tested against these pathogens by treating fruit with cells, endospores and cell-free supernatants. The in vitro results showed that BUZ-14 inhibited the growth of all the pathogens tested corresponding to the least susceptible species, P. italicum, and the most susceptible, M. laxa. In vivo tests corroborated these results as most of the treatments decreased the incidence of brown rot in stone fruit from 100% to 0%, establishing 107 CFU mL-1 as the minimum inhibitory concentration. For the Penicillium species a preventive treatment inhibited P. digitatum and P. italicum growth in oranges and reduced P. expansum incidence in apples from 100% to 20%. Finally, it has been demonstrated that BUZ-14 was able to survive and to control brown rot in peaches stored at cool temperatures, making it a very suitable biocontrol agent for application during the post-harvest storage and marketing of horticultural products.

Antimicrobial activity of extracts of edible wild and cultivated mushrooms against foodborne bacterial strains.

The antimicrobial activity of aqueous, methanol, hexane, and ethyl acetate extracts from edible wild and cultivated mushrooms against nine foodborne pathogenic bacterial strains (Escherichia coli O157:H7, Salmonella Enteritidis, Shigella sonnei, Vibrio parahaemolyticus, Yersinia enterocolitica, Bacillus cereus, Clostridium perfringens, Listeria monocytogenes, and Staphylococcus aureus) was screened with a disk diffusion assay. Twenty-nine of the 48 species tested had antimicrobial activity. Methanol, ethyl acetate, and aqueous extracts accounted for 92.8% of the positive assays, whereas the hexane extracts accounted for only 7.2%. Gram-positive bacteria were more sensitive than gram-negative bacteria to fungal extracts, and C. perfringens was the most sensitive microorganism. Aqueous extracts from Clitocybe geotropa and Lentinula edodes had the highest antimicrobial activity against all the bacterial strains tested.

In vitro antifungal activity of several antimicrobial compounds against Penicillium expansum.

Fungicides used in the prevention and control of mold rots in stored apples are subjected to legal, social, and biological limitations. The aim of this study was to find an alternative to postharvest fungicides currently used in the prevention and control of blue mold rot caused by Penicillium expansum in apples. For this purpose, the antimicrobial activity and MIC of several substances against P. expansum were evaluated in vitro using different end point methods: agar diffusion assay, volatility method, and agar dilution and broth dilution MIC assays. Most of the substances tested are common food ingredients and have a recognized antimicrobial activity. Essential oils, such as thymol, eugenol, citral and cineole, vanillin, sodium hypochlorite, acetic acid, potassium sorbate, and hydrogen peroxide, were the substances evaluated. Thymol and citral were the essential oil components that showed the greatest inhibitory effects. The effectiveness of 5 and 10% hydrogen peroxide in growth inhibition of P. expansum in the agar diffusion assay was total, and its MIC as determined by the agar and broth dilution assays was less than 0.025%. These results indicate that the application of small quantities of hydrogen peroxide to the apple skin might be an alternative to fungicides in the elimination of P. expansum.