Submitted to: International Journal of Food, Agriculture, and the Environment
Publication Type: Peer reviewed journal
Publication Acceptance Date: 4/20/2013
Publication Date: 8/15/2013
Citation: Olanya, O.M., Ukuku, D.O., Annous, B.A., Niemira, B.A., Sommers, C.H. 2013. Efficacy of Pseudomonas fluorescens for biocontrol of Escherichia coli 0157:H7 on spinach. International Journal of Food, Agriculture, and the Environment. 11:86-91. Interpretive Summary: Control of human pathogens on leafy green vegetables is important for food safety. To complement existing post-harvest intervention measures, this study examined the possibility of controlling Escherichia coli O157:H7 (a foodborne pathogen) on spinach using Pseudomonas fluorescens a bacterium used for biocontrol that is commonly found on surfaces of leafy greens and on roots of crop plants. The P. flourescens strains applied are non-spoilage bacteria. Laboratory studies compared three strains of the biocontrol agent in its ability to control the foodborne pathogen when applied on spinach and stored at different temperatures. It was found that a low to moderate reduction (50-99%) of the levels of foodborne pathogen were achieved with various combinations of the biocontrol agent. This is important because the control measure can be used singularly to protect leafy greens from foodborne pathogen contamination and complement existing post-harvest intervention control measures. Future studies will explore how to fine-tune application of the bicontrol agent and the types of the biocontrol agent that can give us the best results on leafy greens, and how it can be integrated with other control measures.
Technical Abstract: Control of foodborne pathogens on leafy green vegetables is crucial for consumer food safety. Biocontrol microbes may inhibit or suppress foodborne pathogen growth and enhance existing post-harvest intervention controls. The efficacy of Pseudomonas fluorescens for biocontrol of Escherichia coli O157:H7 was determined on baby spinach. P. fluorescens strains 2-79, Q2-87, and Q8R-1 (non-pectolytic and non plant pathogenic) were applied on spinach using the dip inoculation method, prior to inoculation with E. coli strains 43894, 43895, and 35150 individually or as a cocktail mixture. The inoculated spinach was stored at 20 deg C for 24 and 48 hours, prior to stomaching and plating (100 ul) on Restaino and Frampton (R & F) and E. coli O157:H7 chromogenic medium (RFCM). In subsequent experiments, the effects of storage time (24 and 48 hrs) and temperatures (5, 10, 15, 20, 25, and 30 deg C) on the efficacy of biocontrol were determined. The reduction of E. coli O157:H7 by P. fluorescens was computed relative to the control. The mean reduction of E.coli O157:H7 by P. fluorescens ranged from 0.5-2.1 log CFU/g of spinach. The greatest reduction of E. coli O157:H7 (1.4 log CFU/g) was achieved by P. fluorescens strain Q2-87. The efficacy of biocontrol was significantly (P<0.05) affected by storage temperature as suppressive effects were greater at 15 deg C (1.5-2.4 log CFU/g of spinach) than at other temperatures (<0.93 log CFU/g). As expected, the reduction of E. coli O157:H7 populations varied between storage times of 24 and 48 hrs. These results imply that P. fluorescens may provide low to moderate reductions of E. coli O157:H7 populations in spinach. However, biocontrol efficacy may be improved when combined with existing post-harvest intervention strategies.