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United States Department of Agriculture

Agricultural Research Service

Research Project: Intervention Technologies for Minimally Processed Foods

Location: Food Safety and Intervention Technologies

Title: Effects of media on recovery of Escherichia coli 0157:H7 and Pseudomonas fluorescens from spinach

Authors
item Olanya, Modesto
item Annous, Bassam
item Niemira, Brendan
item Ukuku, Dike
item Sommers, Christopher

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: February 12, 2013
Publication Date: July 13, 2013
Citation: Olanya, O.M., Annous, B.A., Niemira, B.A., Ukuku, D.O., Sommers, C.H. 2013. Effects of media on recovery of Escherichia coli 0157:H7 and Pseudomonas fluorescens from spinach. Meeting Abstract. IFT13., July 13-16,2013, Chicago, Illinois., Page 104.

Technical Abstract: Control of post-harvest contamination of leafy greens by Escherichia coli O157:H7 is important for food safety. Efficient recovery and enumeration of E. coli O157:H7 and the biocontrol microbe Pseudomonas fluorescens (non-pectolytic and non-plant pathogenic) from produce is crucial for assessment of biocontrol efficacy. We evaluated Restaino and Frampton E. coli O157:H7 Chromogenic Medium (RFCM) for the recovery of E. coli O157:H7 and Pseudomonas fluorescens from co-inoculated cultures relative to other media. The effects of storage time and temperatures on bacterial recovery from spinach inoculated with monocultures or both microbes were determined. Microbial counts of E. coli O157:H7 on RFCM were based on color (blue-black precipitate) in contrast to P. fluorescens, which had distinct white /translucent colonies that fluorescence under ultraviolet light. Bacterial populations from mixed cultures plated on different media and recovered ranged from 3.6-8.7 and 4.2-7.7 log CFU/ml for E. coli O157:H7 and P. fluorescens, respectively. Microbial counts on spinach ranged from 6.0-8.2 and 6.5-8.6 log CFU/g for the above bacteria; respectively. Bacterial recovery increased with storage time of 0 to 48 h, implying a possible increase of contact time for bacterial attachment. A greater recovery of E. coli O157:H7 and P. fluorescens was attained at 10 and 20 deg C than at 5 deg C. The RFCM was best suited for simultaneous recovery of E. coli O157:H7 and P. fluorescens based on color and size on media. Efficient recovery of E. coli O157:H7 and P. fluorescens from inoculated spinach can greatly enhance assessment of biocontrol efficacy as a post-harvest intervention strategy. This study shows that RFCM can be an effective tool for biocontrol research.

Last Modified: 7/10/2014
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