P-038. Comparison of the Binding of E. coli K12 and O157:H7 to Alfalfa Sprouts and Cut Lettuce Leaves

R. B. Smith, A. G. Matthysse;
Univ. of North Carolina, Chapel Hill, NC.

Transmission of pathogenic E. coli by vegetable produce has become an increasing problem in recent years. These bacteria are able to bind tightly to plant surfaces and are not easily removed by washing with water. The binding of both pathogenic (DEC) and laboratory K12 strains to cut edges of lettuce leaves is rapid. More than 103 pathogenic and 102 K12 bacteria bind within the first five minutes of incubation of cut leaves in water containing the bacteria. After the initial rapid binding, additional bacteria bind at a much slower rate. The interaction of the bacteria with cut leaves is in marked contrast to their interaction with sprouts. Pathogenic strains require more than 1 day to show significant binding to sprouts. K12 strains fail to bind. Mutants of the bacteria unable to make the polysaccharides poly-ß-1, 6-N-acetyl-D-glucosamine (PGA), cellulose, or colanic acid are all reduced in binding to sprouts. Only PGA mutants are reduced in binding to cut leaves. This difference in binding of E. coli to sprouts and cut leaves was observed with several species of plants including alfalfa, lettuce, bean, tomato, and Arabidopsis thaliana. The results suggest that the mechanisms of bacterial binding to sprouts and cut leaves are different although there are some genes and gene products such as PGA which are involved in both processes.