基于酸处理的产志贺毒素大肠埃希菌选择性增菌方法研究

Study of a selective enrichment method for Shiga toxin-producing Escherichia coli based on acid treatment

中文关键词:  产志贺毒素大肠埃希菌  酸处理  选择性增菌  胁迫状态

英文关键词:Shiga toxin-producing Escherichia coli  acid treatment  selective enrichment  stressed strains

中文摘要:

      目的 开发一套基于酸处理的产志贺毒素大肠埃希菌(Shiga toxin-producing Escherichia coli, STEC)选择性增菌方法, 提高食品中STEC菌株的检出率。方法 选择12株不同血清型STEC菌株及13株常见干扰菌, 评价其对不同酸处理条件(pH=2.0、2.5、3.0)的耐受性; 考察筛选的酸处理条件对营养胁迫和冷冻胁迫状态STEC菌株生长活性的影响; 比较研究酸水解酪蛋白、酵母提取物和丙酮酸钠等成分对胁迫状态STEC菌株的促生长作用, 优化酸处理后中和/促生长培养基配方; 比较增菌前与增菌后2种酸处理方式对STEC菌株分离效果的影响; 最后通过人工污染样品, 评价本研究建立的STEC酸处理选择性增菌方法的检测效果。 结果 本研究建立了一种不依赖于抑菌成分的STEC选择性增菌方法, 样品在增菌前经酸处理培养基室温处理2 h, 降低背景杂菌干扰, 再通过中和/促生长培养基[胰蛋白胨大豆肉汤培养基(tryptone soybean broth, TSB)-1.5% Tris-0.1%丙酮酸钠]进行目标菌的增菌培养; 人工污染试验结果表明, 本方法与我国现行GB 4789.36—2016《食品安全国家标准 食品微生物学检验 大肠埃希氏菌O157:H7/NM检验》标准方法相比, 能够有效减少背景杂菌的干扰、获得更高的STEC分离效率。结论 本研究建立的基于酸处理的STEC选择性增菌方法能够有效提高食品中STEC菌株的检测效率和检测准确性。

英文摘要:

      Objective To develop a selective enrichment method for Shiga toxin-producing Escherichia coli (STEC) based on acid treatment which can improve the detection rate of STEC strains in food samples. Methods Twelve STEC strains with different serotypes and 13 potential competing species were selected to evaluate their tolerance to different acid treatment conditions (pH=2.0, 2.5, 3.0). The growth of nutrition and freezing stressed STEC strains were evaluated under acid treatment conditions. The effects of acid hydrolyzed casein, yeast extract and sodium pyruvate on the growth promotion of stressed STEC strains were evaluated. After acid treatment, the formula of neutralization / growth promoting medium was optimized. The effects of acid treatment timing (before or after enrichment) on the isolation of STEC strains were also compared. Finally, the established acid treatment selective enrichment method was evaluated through artificially contaminated samples. Results A kinds of STEC selective enrichment method was established in this study, which including procedures of acid treatment under room temperature for 2 h, and the enrichment by using the neutralization/growth-promoting medium [tryptone soybean broth (TSB)-1.5%Tris-0.1% sodium pyruvate]. Compared with the current GB 4789.36—2016 National standard for food safety-Microbiological examination of food-Examination of Escherichia coli O157:H7/NM standard method, this method could effectively reduce the interference of background miscellaneous bacteria and obtain higher STEC separation efficiency. Conclusion The established STEC selective enrichment method based on acid treatment in this study can improve the detection efficiency and accuracy of STEC strains.