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Studies on the biocontrol mechanisms of Pseudomonas graminis strain CPA-7 against food-borne pathogens in vitro and on fresh-cut melon

Collazo, Cyrelys, Abadias, Maribel, Aguiló-Aguayo, Ingrid, Alegre, Isabel, Chenoll, Empar, Viñas, Inmaculada
Lebensmittel-Wissenschaft + [i.e. und] Technologie 2017 v.85 pp. 301-308
Escherichia coli O157, Listeria monocytogenes, Pseudomonas graminis, Salmonella enterica, alginates, antagonists, bacteria, biofilm, biological control, biological control agents, biosurfactants, carboxylic acids, culture media, food pathogens, fresh-cut produce, hydrophobicity, in vitro studies, mechanism of action, melons, metabolites, nutrient content, polystyrenes, proteolysis
The present study was aimed at gaining insight into the mode of action of the antagonistic bacteria Pseudomonas graminis CPA-7, which has been previously identified as an effective biocontrol agent against Listeria monocytogenes, Salmonella enterica and Escherichia coli O157:H7 on fresh-cut fruit. In vitro experiments did not reveal any antimicrobial or proteolytic activity on solid media or any biosurfactant activity on hydrophobic surfaces. Metabolites produced by CPA-7 in two different culture media and on 'Galia' melon were unable to inhibit L. monocytogenes populations on 'Galia' melon plugs at 25 °C or 5 °C. In contrast, at 25 °C the population of this pathogen on 'Galia' plugs was reduced by 2.1 and 3.3 log-units when co-inoculated with the antagonist in water, after 24 and 48 h, respectively. CPA-7 did not form biofilms after 72 h at 25 °C (OD = 0.03) or at 30 °C (OD = 0.01) on polystyrene plates and the production of alginate was close to the negative control. Studies of nutritional profiles showed high overlap (NOI > 0.9) between CPA-7 and E. coli O157:H7 regarding the use of carboxylic acids. This functional group could also contain putative targets for competiveness between CPA-7 and S. enterica, although overlapping was not restrictive enough (NOI = 0.83).