99D-5 |
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H. KIM, J. -H. Ryu, J. F. Frank, and L. R. Beuchat. Center for Food Safety, Dept. of Food Science & Technology, Univ. of Georgia, 1109 Experiment St., Griffin, GA 30223-1797 The role of curli produced by Escherichia coli O157:H7 in attachment of cells and formation of biofilm on stainless steel was studied. Three non-curli producing strains (E0018-, 43894-, and 43895-) and three curli over-producing mutants (E0018+, 43894+, and 43895+) were used. To compare attachment abilities on stainless steel coupons (SSC), cells grown on tryptic soy agar (TSA) at 22°C for 72 h were suspended in phosphate-buffered saline (pH 7.2). SSC were immersed in cell suspensions (108 cfu/ml) at 4°C for 24 h. Cells attached to SSC were removed and populations were determined by plating suspensions on TSA. To compare strains for their ability to form biofilm, rinsed SCC were immersed in 10% tryptic soy broth (TSB, pH 7.0) at 22°C for 6 days. Attachment was not significantly affected by ability to form curli, although non-curli producers tended to attach in higher numbers. Strains E0018-, 43894-, and 43895- attached at populations of 6.1, 5.9, and 5.9 log10 cfu/coupon, respectively; strains E0018+, 43894+, and 43895+ attached at populations of 5.6, 5.5, and 5.1 log10 cfu/coupon, respectively, indicating that curli may inhibit the attachment of cells on SSC. This is attributed in part to the hydrophobic characteristic imparted to cells by curli and the moderately hydrophilic property of SSC. Populations of strains E0018+, 43894+, and 43895+ increased from 5.6, 5.5, and 5.1 to 7.3, 7.7, and 7.9 log10 cfu/coupon, respectively, on SSC immersed in 10% TSB for 2 days but populations of non-curli producers did not increase. This suggests that although curli-producing cells have difficulty in attaching to SSC, they are better able to form biofilms. Environmental factors which affect curli production on processing equipment and foods, and the potential synergistic effect between other curli-producing microorganisms and non-curli producing E. coli O157:H7 in forming biofilm should be investigated.
Session 99D, Food Microbiology: General
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