US Department of Agriculture, Food Safety and Inspection Service, Eastern Laboratory Outbreaks Section, Athens, Georgia 30605, USA.
J Food Prot. 2012 Sep;75(9):1548-54. doi: 10.4315/0362-028X.JFP-12-110.
It is estimated that at least 70% of human illnesses due to non-O157 Shiga toxin-producing Escherichia coli (STEC) in the United States are caused by strains from the top six serogroups (O26, O45, O103, O111, O121, and O145). Procedures for isolating STEC from food products often use plating media that include antimicrobial supplements at concentrations that inhibit background microflora growth but can also inhibit target STEC growth. In this study, an agar medium with lower supplement concentrations, modified Rainbow agar (mRBA), was evaluated for recovery of STEC serogroups O26, O45, O103, O111, O121, and O145 from ground beef enrichments. A post-immunomagnetic separation (IMS) acid treatment step was additionally used to reduce background microflora and increase recovery of target STEC strains. Ground beef samples (325 g) were artificially contaminated with STEC and confounding organisms and enriched for 15 h. Recovery of the target STEC was attempted on the enrichments using IMS and plating onto mRBA and Rainbow agar (RBA). Additionally, acid treatment was performed on the post-IMS eluate followed by plating onto mRBA. Using the combination of mRBA and acid treatment, target STEC were isolated from 103 (85.8%) of 120 of the low-inoculated samples (1 to 5 CFU/325-g sample) compared with 68 (56.7%) of 120 using no acid treatment and plating onto RBA with higher levels of novobiocin and potassium tellurite. The combination of acid treatment and mRBA provides a significant improvement over the use of RBA for isolation of STEC serogroups O26, O45, O103, O111, O121, and O145 from raw ground beef.
据估计，在美国，至少有 70%的人类疾病是由非 O157 型志贺毒素产生大肠杆菌（STEC）引起的，这些细菌来自六个主要血清群（O26、O45、O103、O111、O121 和 O145）。从食品中分离 STEC 的程序通常使用含有抗菌添加剂的平板培养基，这些添加剂的浓度可以抑制背景微生物的生长，但也可以抑制目标 STEC 的生长。在这项研究中，评估了一种补充剂浓度较低的琼脂培养基，即改良 Rainbow 琼脂（mRBA），用于从牛肉基质中回收 O26、O45、O103、O111、O121 和 O145 型 STEC。另外还使用免疫磁分离（IMS）后的酸处理步骤来减少背景微生物，并提高目标 STEC 菌株的回收率。将牛肉样品（325 g）人工污染 STEC 和混杂生物体，并进行 15 h 的富集。使用 IMS 对富集物进行目标 STEC 的回收，并在 mRBA 和 Rainbow 琼脂（RBA）上进行平板培养。另外，对 IMS 洗脱液进行酸处理，然后在 mRBA 上进行平板培养。使用 mRBA 和酸处理的组合，从低接种量的 120 个样本（1 至 5 CFU/325 g 样本）中的 103 个（85.8%）分离到目标 STEC，而在没有酸处理和在含有更高浓度新生霉素和碲酸钾的 RBA 上进行平板培养的 120 个样本中，只有 68 个（56.7%）分离到目标 STEC。与使用 RBA 相比，酸处理和 mRBA 的组合可显著提高从生牛肉中分离 O26、O45、O103、O111、O121 和 O145 型 STEC 的效率。
