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

Abstract

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 coinoculated 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 2 targets for competiveness between CPA-7 and S. enterica, although overlapping was not restrictive enough (NOI=0.83).

Evaluation of behaviour ofLachancea thermotoleransbiocontrol agents on grape fermentations

“…NS values were evaluated as the ratio between number of compounds used by each of the yeasts and number of compounds assayed in total (Collazo et al . ).…”

“…NOI values of >0Á9 represent competence between yeasts while scores of <0Á9 represent occupation of separate niches. NS values were evaluated as the ratio between number of compounds used by each of the yeasts and number of compounds assayed in total (Collazo et al 2017).…”

Effect of Pseudomonas graminis strain CPA-7 on the ability of Listeria monocytogenes and Salmonella enterica subsp. enterica to colonize Caco-2 cells after pre-incubation on fresh-cut pear

“…Although a number of in vitro and in vivo experiments related to the production of antibiotics, biosurfactants and exo-proteases were performed, its mode of action could not be elucidated (Collazo et al, 2017). Hence the impairment of pathogenesis-related characteristics of foodborne pathogens was explored as another putative mechanism for antagonism.…”

Pseudomonas graminis strain CPA-7 differentially modulates the oxidative response in fresh-cut ‘Golden delicious’ apple depending on the storage conditions

“…Salmonella enterica and Listeria monocytogenes on fresh cut apples, melons and 83 peaches (Abadias et al, 2014;Alegre et al, 2013aAlegre et al, , 2013bCollazo et al, 2017). 84…”

“…Although attempts to elucidate the mechanisms underlying its antagonistic activity have 85 been carried out, they still remain poorly understood (Collazo et al, 2017). Thus, we 86 hypothesized that a putative mode of action for CPA-7 could be the activation of 87 defense mechanisms in fresh-cut fruit leading to a better control of foodborne 88 pathogens populations.…”