Food Safety and Intervention Technologies Site Logo
ARS Home About Us Helptop nav spacerContact Us En Espanoltop nav spacer
Printable VersionPrintable Version     E-mail this pageE-mail this page
Agricultural Research Service United States Department of Agriculture
Search
  Advanced Search
 
Programs and Projects
Subjects of Investigation
 

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

Submitted to: Journal of Food Safety
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 1, 2012
Publication Date: November 27, 2012
Repository URL: http://doi:10.1111/jfs.12012
Citation: Olanya, O.M., Annous, B.A., Niemira, B.A., Ukuku, D.O., Sommers, C.H. 2012. Effects of media on recovery of Escherichia coli 0157:H7 and Pseudomonas fluorescens from spinach. Journal of Food Safety. 32:492-501.

Interpretive Summary: Efficient recovery and accurate enumeration of Escherichia coli O157:H7 (a human pathogen) and Pseudomonas fluorescens (a biocontrol bacterium) from leafy greens is crucial for assessment of biocontrol efficacy. Other than the generation of antibiotic resistant strains (foodborne pathogens) or use of green fluorescent labeled mutants, there are limited options available for simultaneous recovery and enumeration of biocontrol and pathogenic bacteria. This research provides information on the recovery and assessment of E. coli O157:H7 and P. fluorescens from media and inoculated spinach using Restaino and Frampton (R & F) and E. coli O157:H7 Chromogenic Medium (RFCM). This study provides a methodology for evaluating the effectiveness of a biocontrol agent and establishes the utility of its use for other leafy green products. Accurate recovery and enumeration of biocontrol and pathogenic bacteria will promote optimal determination of biocontrol efficacy, a post-harvest food safety intervention strategy. This study validates the use of selective medium (RCPM) with specific applications for this biocontrol research.

Technical Abstract: Control the 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 from produce is crucial for assessment of biocontrol efficacy. Sensitive and effective selective media is an important tool for this study. We evaluated Restaino and Frampton (R & F) and 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.

   

 
Project Team
Niemira, Brendan
Annous, Bassam
Sites, Joseph
Olanya, Modesto
 
Publications
   Publications
 
Related National Programs
  Food Safety, (animal and plant products) (108)
 
Related Projects
   NOVEL APPROACH FOR DECONTAMINATING FRESH AND FRESH-CUT PRODUCE UTILIZING CHLORINE DIOXIDE GAS PACKAGING SYSTEM
 
 
Last Modified: 05/25/2013
ARS Home | USDA.gov | Site Map | Policies and Links 
FOIA | Accessibility Statement | Privacy Policy | Nondiscrimination Statement | Information Quality | USA.gov | White House