Tracking Contamination through Ground Beef Production and Identifying Points of Recontamination Using a Novel Green Fluorescent Protein (GFP) Expressing, Escherichia coli O103, Non-pathogenic Surrogate

Introduction: Commonly, ground beef processors conduct studies to model contaminant flow through their production systems using surrogate organisms. Typical surrogate organisms may not behave as Escherichia coli O157:H7 during grinding and are not easy to detect at very low levels.

Purpose: Develop and validate a trackable E. coli O157:H7 surrogate, then model contamination passing through commercial grinding equipment using the surrogate.

Methods: The adherence, injury resistance, and recovery from low temperatures were determined for a non-virulent E. coli serogroup O103 constitutively expressing GFP (GFP-O103).  Three 1,000lb (454Kg) combo-bins of beef trim were inoculated with 10⁶ CFUs GFP-O103.  Each inoculated combo-bin and four non-inoculated bins were sequentially used to produce 4lb (1.8Kg) ground beef loaves for monitoring GFP-O103 presence (n=90 tested per repetition).
Additionally, a single repetition of loaves prepared using 2,000lb (907Kg) combo-bins and initial inoculum of 10⁴ CFUs was tested (n=178).
After each repetition, surface and residual meat samples were collected from processing equipment. 

Results: The GFP-O103 was determined to be an ideal surrogate for E. coli O157:H7 and had a 1-5CFU/375g of ground beef limit of detection.
The grinding studies found contamination initially reached 0% prevalence in 10 sequential samples after a mean additional 2,480lb (1,125Kg) of non-inoculated material, however further sporadic positives indicated contamination persisted.
Regression analysis estimated that a total of 9,300lb (4,200Kg) non-inoculated material was required to attain a non-detectable level in our situation.
Potential recontamination points were identified on belts and augers where residual meat containing the GFP-O103 persisted through the end of production.

Significance: Disposition and recall decisions are based on data citing one 2,000lb (907Kg) combo-bin before and after an affected combo will clear contamination. Our results emphasize that each facility should perform their own studies due to unique line configurations and process complexities. The GFP-O103 is available for this use.