Effect of curli expression and hydrophobicity of Escherichia coli O157:H7 on attachment to fresh produce surfaces.

AIM: To investigate the effect of curli expression on cell hydrophobicity, biofilm formation and attachment to cut and intact fresh produce surfaces. METHODS AND
RESULTS: Five Escherichia coli O157:H7 strains were evaluated for curli expression, hydrophobicity, biofilm formation and attachment to intact and cut fresh produce (cabbage, iceberg lettuce and Romaine lettuce) leaves. Biofilm formation was stronger when E. coli O157:H7 were grown in diluted tryptic soy broth (1:10). In general, strong curli-expressing E. coli O157:H7 strains 4406 and 4407 were more hydrophobic and attached to cabbage and iceberg lettuce surfaces at significantly higher numbers than other weak curli-expressing strains. Overall, E. coli O157:H7 populations attached to cabbage and lettuce (iceberg and Romaine) surfaces were similar (P>0·05), indicating produce surfaces did not affect (P<0·05) bacterial attachment. All E. coli O157:H7 strains attached rapidly on intact and cut produce surfaces. Escherichia coli O157:H7 attached preferentially to cut surfaces of all produce types; however, the difference between E. coli O157:H7 populations attached to intact and cut surfaces was not significant (P>0·05) in most cases. Escherichia coli O157:H7 attachment and attachment strength (S(R) ) to intact and cut produce surfaces increased with time.
CONCLUSIONS: Curli-producing E. coli O157:H7 strains attach at higher numbers to produce surfaces. Increased attachment of E. coli O157:H7 on cut surfaces emphasizes the need for an effective produce wash to kill E. coli O157:H7 on produce. SIGNIFICANCE AND IMPACT OF THE STUDY: Understanding the attachment mechanisms of E. coli O157:H7 to produce surfaces will aid in developing new intervention strategies to prevent produce outbreaks.