Food and Drug Administration, Bothell, WA, USA.
Lett Appl Microbiol. 2012 Jun;54(6):499-503. doi: 10.1111/j.1472-765X.2012.03250.x. Epub 2012 Apr 30.
Rapid detection and selective isolation of E. coli O157:H7 strains have been difficult owing to the potential interference from background microflora present in high background food matrices. To help selectively isolate E. coli O157H7 strains, a useful plating technique that involved acidifying the cultures to pH 2 was evaluated with a large number of E. coli O157:H7 strains to ensure response to treatment was consistent across strains.
Escherichia coli O157, 46 strains including ATCC 35150, were acidified to pH 2 following enrichment and plated onto Tryptic Soy Agar + 0.6% Yeast Extract (TSA-YE) and Sorbitol MacConkey Agar + cefixime and tellurite (CT-SMAC). Samples were enumerated and modest decreases in plate counts were observed on TSA-YE media, with a greater reduction observed on CT-SMAC.
The acid-resistant character of E. coli O157:H7 is a consistent trait and may be used for improved isolation of the organism from mixed cultures.
There was little difference observed between the commonly used laboratory strain E. coli O157:H7 35150 and 45 other strains of E. coli O157 when subjected to acidifying conditions prior to plating, demonstrating that an acid rinse procedure was equally effective across a wide variety of E. coli O157 strains and broadly applicable for isolating unknown strains from food samples.
由于高背景食品基质中存在背景微生物群，因此难以快速检测和选择性分离大肠杆菌 O157:H7 菌株。为了帮助选择性分离大肠杆菌 O157:H7 菌株，评估了一种有用的平板技术，该技术涉及将培养物酸化至 pH 2，并用大量大肠杆菌 O157:H7 菌株进行评估，以确保处理的反应在菌株之间一致。
在富集后，将大肠杆菌 O157 46 株，包括 ATCC 35150，酸化至 pH 2，然后接种到胰蛋白酶大豆琼脂+0.6%酵母提取物（TSA-YE）和山梨醇麦康凯琼脂+头孢克肟和碲酸盐（CT-SMAC）上。对样品进行计数，并观察到 TSA-YE 培养基上的平板计数略有减少，而 CT-SMAC 上的减少更为明显。
大肠杆菌 O157:H7 的抗酸性特征是一致的特征，可用于从混合培养物中改进分离该生物体。
在进行平板接种之前，将常用的实验室菌株大肠杆菌 O157:H7 35150 与其他 45 株大肠杆菌 O157 菌株进行酸化处理后，观察到的差异很小，这表明酸化冲洗程序在各种大肠杆菌 O157 菌株中同样有效，并且广泛适用于从食品样品中分离未知菌株。
