Purpose: The purpose of this research was to determine the efficacy of Pseudomonas fluorescens strains 2-79, Q2-87, and Q8R-1 (non-pectolytic and non-plant pathogenic) for biocontrol of Escherichia coliO157:H7 on baby spinach.
Methods: P. fluorescens strains 2-79, Q2-87, and Q8R-1 were applied on spinach using the dip inoculation method, prior to inoculation with E. coli O157:H7 strains 43894, 43895, and 35150 individually or in a cocktail mixture. The inoculated spinach was stored at 20ºC for 24 and 48 h, and then evaluated for E. coli O157:H7 populations using Restaino and Frampton E. coli O157:H7 chromogenic medium. The effects of storage temperatures (5, 10, 15, 20, 25, and 30ºC) on biocontrol efficacy were determined. The reduction of E. coli O157:H7 was computed relative to the control.
Results: The efficacy of biocontrol was significantly (P < 0.05) affected by storage temperature as suppressive effects were greater at 15ºC (1.5-2.4 log CFU/g) than at other temperatures (< 0.93 log CFU/g). The mean reduction of E. coli O157:H7 by P. fluorescens varied between storage times and ranged from 0.6-2.1 log and 0.5-0.9 log CFU/g of spinach at 24 and 48 h, respectively. The low to moderate reductions of the pathogen may be attributed to the equal ratios (1:1) of P. fluorescens to E. coli O157:H7 inoculum.
Significance: These results imply that P. fluorescens may provide low to moderate reductions of E. coli O157:H7 populations on spinach. Biocontrol efficacy may be improved, by increasing the ratios of biocontrol agent to pathogen and combining it with other post-harvest intervention measures.