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

Introduction: Persistence of Escherichia coli and related pathogens like E. coli O157 on beef packing plant equipment may result from biofilm formation by 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.

Purpose: This study examined the influence of persistent and transient generic E. coli genotypes and Salmonella spp., 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 spp. was tested alone or in dual-cultures with E. coli O157:H7 at 15°C for up to six 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 spp. 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 spp. 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 ≤ six days. Escherichia coli genotype 136 significantly (P<0.05) reduced the numbers of E. coli O157 in dual-culture biofilms by ≥1.5 log CFU at ≥ two days, while genotype 533 caused ≥ one log CFU reduction at ≥ four days. Salmonella spp. 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 significantly reduced biofilm formation by E. coli O157:H7 suggested that generic E. coli may potentially be used as an agent to control E. coli O157:H7 in beef processing environment.