Determination of Sources of Escherichia coli on Beef by Multiple-locus Variable-number Tandem Repeat Analysis

Introduction: The microbiological condition of beef carcasses has been greatly improved in recent years, likely as a result of well controlled dressing process. Some plants at least in North America can produce most dressed carcasses essentially free of Escherichia coli. However, outbreaks of verotoxigenic E. coli (VTEC), particularly of the serotype O157 still occur. It is generally assumed that E. coli on final products are deposited on the meat during dressing process.

Purpose: The objective was to determine the origin of E. coli on cuts and trimmings.

Methods: E. coli were enumerated in samples obtained from 160 carcasses entering the breaking facility before work and during each of three breaks throughout the day, from the conveyor belt before work and after each break, and from cuts and trimmings when work commenced and after each break. Selected E. coli isolates were genotyped by MLVA.

Results: E. coli was recovered from 7 (< 5%) chilled carcasses, with total numbers being mostly ≤ 1.0 log CFU/160,000 cm². The log total numbers of E. coli recovered from the conveyor belt, cuts and trimmings were mostly between 1 and 2 log CFU/80,000 cm². MLVA of 327 isolates revealed 80 genotypes, with 37 (46%) each containing one isolate. However, 27% of the isolates were of genotypes that were recovered from more than one day. Of isolates recovered from cuts, 49%, 3% and 19% were of the genotypes that were found among isolates from the belt, carcasses, and both the belt and carcasses, respectively. A similar composition was also found for E. coli isolates from trimmings.

Significance: This study unequivocally identified conveying equipment to be the main source of contamination of cuts and trimmings from carcasses that carried very few E. coli and persisting strains of E. coli in beef breaking facility.