Effect of Persistent and Transient Generic Escherichia coli, and Salmonella sp. Recovered from a Beef Packing Plant on Biofilm Formation of E. coli O157:H7

Introduction: Persistence of Escherichia coli and related pathogens like E. coli O157 at beef packing plant equipment may result from biofilm formation of these organisms. Biofilms are generally resistant to regular cleaning and sanitizing and may act as a continuous source of contamination for otherwise unadulterated beef cuts and trimmings.
Objective: To examine the influence of persistent and transient generic E. coli genotypes and Salmonella sp. recovered from a beef packing plant on biofilm formation of E. coli O157:H7.
Methods: Biofilm formation of five genotypes of persistent and transient generic E. coli and a strain of Salmonella sp. was tested alone or in dual-cultures with E. coli O157:H7 at 15 °C for up to 6 days. Biofilms were quantified using Crystal Violet (CV) staining on day 2, 4 and 6. The numbers of E. coli O157:H7 in mono- or dual-culture biofilms with persistent and transient E. coli genotypes 390 and 533, respectively, and with Salmonella sp. were determined by plating on selective agar.
Results: Strain by day interaction was found (P<0.0001) when biofilm formation of E. coli genotypes and Salmonella sp. were cultured alone or with E. coli O157:H7. In monoculture biofilm, the numbers of E. coli O157:H7 ranged between 5.87 and 6.69 log cfu at ≤6 days. E. coli genotype 390 significantly (P<0.05) reduced the numbers of E. coli O157 in dual-culture biofilms by ≥1.5 log cfu at ≥2 days, while genotype 533 caused ≥1 log cfu reduction at ≥4 days. Salmonella sp. did not affect (P>0.05) the numbers of E. coli O157:H7 in dual-culture biofilm.
Significance: The finding that generic E. coli genotypes can significantly reduce biofilm formation of E. coli O157:H7 suggests that generic E. coli may potentially be used as an agent to control E. coli O157:H7 in beef processing environment.