Influence of cell envelope components on the attachment of Escherichia coli O157:H7 to lettuce and spinach under different ionic environments
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Produce-related outbreaks of Escherichia coli O157:H7 are the second most common foodborne outbreaks since it was first recognized an enteric pathogen in 1982. The mechanism of attachment of E. coli O157: H7 on leafy greens is complex and dependent on a variety of factors including properties of the cell surface, substratum and bulk fluid. The objective of this study was to determinate the role of cell envelope components on attachment of E. coli O157:H7 to lettuce and spinach leaf surface and cut edge under different environments. Cell surface charge, hydrophobicity, and capsule characteristics were investigated. In addition, cellulose-deficient derivatives of Shiga toxin–producing Escherichia coli (STEC) have been used. The lower surface hydrophobicity, less negative charge, as well as capsule containing more D-Mannose and α-Fucose of cells grown in tryptic soy broth combined to increase attachment to spinach leaves. Cellulose-producing STEC cells attached significantly 0.5 log greater on lettuce leaf surface than cellulose-deficient cells. However, cellulose-deficient cells attached significantly 0.7 log greater to cut edge of lettuce than parental cells. In high water hardness environment, attachment of wild type cells to leafy greens surface also could be enhanced. In addition, chlorine treatment reduced the population of cellulose-deficient cells at 1.2 log units more than the wild type in 150ppm of chlorine on spinach leaves surface. However, the population of cellulose-producing cells was reduced significantly by 1.5 log units more than its mutant when cells also produced colanic acid. Extra-cellular cellulose production protects STEC cells attached to leafy greens from the effects of chlorine on spinach leave surface.