Lee Chi-Ching, Chen Jinru, Frank Joseph F
Department of Food Science and Technology, University of Georgia, Athens, Georgia 30605, USA.
Department of Food Science and Technology, University of Georgia, Griffin, Georgia 30223, USA.
J Food Prot. 2016 Apr;79(4):666-71. doi: 10.4315/0362-028X.JFP-15-375.
Shiga toxin-producing Escherichia coli (STEC) strains produce extracellular cellulose and colanic acid, which may influence stress tolerance. This study investigates the role of these extracellular polymers on the tolerance of STEC to chlorine treatment after attachment to lettuce and spinach. Four STEC strains, two wild-type cellulose-producing and their cellulose-deficient derivatives, were used. One strain pair produced colanic acid in addition to cellulose. Spinach and lettuce with attached cells were treated with chlorinated water (50 and 150 ppm of free chlorine). The production of the extracellular polymers by the planktonic cells had small, but significant, effects on the survival of the attached pathogen when subjected to chlorine treatment. On the lettuce surface, the colanic acid-producing, cellulose-negative mutant (49d) was most susceptible to the treatment, declining significantly (P < 0.05) in population by 0.9 and 1.4 log units after treatment with 50 and 150 ppm of chlorine, respectively. Chlorine treatment reduced populations of cellulose-deficient cells on the intact spinach surface 1.2 log units more than the wild type when treated with 150 ppm of chlorine (P < 0.05). However, populations of cellulose-producing cells were reduced by 1.5 log units more than their mutant counterparts when the cells also produced colanic acid (P < 0.05). A greater proportion of cells attached to the spinach leaf edge were injured by chlorine treatment compared with attached to the leaf surface. These results indicate that extracellular polymers do not generally increase the ability of STEC to survive chlorine treatment and that any effects on survival are influenced by location of attachment, type of leafy green, and concentration of chlorine.
产志贺毒素大肠杆菌（STEC）菌株会产生胞外纤维素和结肠酸，这可能会影响其对压力的耐受性。本研究调查了这些胞外聚合物在STEC附着于生菜和菠菜后对其耐氯性的作用。使用了四株STEC菌株，两株野生型产纤维素菌株及其纤维素缺陷衍生物。其中一对菌株除了产生纤维素外还产生结肠酸。将附着有细胞的菠菜和生菜用含氯水（游离氯浓度为50和150 ppm）处理。浮游细胞产生的胞外聚合物对附着病原体经氯处理后的存活有微小但显著的影响。在生菜表面，产结肠酸的纤维素阴性突变体（49d）对处理最为敏感，用50 ppm和150 ppm氯处理后，其数量分别显著下降（P < 0.05）0.9和1.4个对数单位。用150 ppm氯处理时，完整菠菜表面纤维素缺陷细胞的数量比野生型减少了1.2个对数单位（P < 0.05）。然而，当细胞同时产生结肠酸时，产纤维素细胞的数量比其突变体对应物减少了1.5个对数单位（P < 0.05）。与附着在叶片表面相比，附着在菠菜叶边缘的细胞经氯处理后受损伤的比例更大。这些结果表明，胞外聚合物通常不会增加STEC在氯处理下的存活能力，并且对存活的任何影响都受附着位置、绿叶蔬菜类型和氯浓度的影响。
