Quality and Safety Assessment Research Unit, Richard B. Russell Research Center, Agricultural Research Service, Athens, Georgia 30605, USA.
J Food Prot. 2013 Jul;76(7):1129-36. doi: 10.4315/0362-028X.JFP-12-497.
The U.S. Department of Agriculture, Food Safety Inspection Service has determined that six non-O157 Shiga toxin-producing Escherichia coli (STEC) serogroups (O26, O45, O103, O111, O121, and O145) are adulterants in raw beef. Isolate and phenotypic discrimination of non-O157 STEC is problematic due to the lack of suitable agar media. The lack of distinct phenotypic color variation among non-O157serogroups cultured on chromogenic agar poses a challenge in selecting colonies for confirmation. In this study, visible and near-infrared hyperspectral imaging and chemometrics were used to detect and classify non-O157 STEC serogroups grown on Rainbow agar O157. The method was first developed by building spectral libraries for each serogroup obtained from ground-truth regions of interest representing the true identity of each pixel and thus each pure culture colony in the hyperspectral agar-plate image. The spectral library for the pure-culture non-O157 STEC consisted of 2,171 colonies, with spectra derived from 124,347 of pixels. The classification models for each serogroup were developed with a k nearest-neighbor classifier. The overall classification training accuracy at the colony level was 99%. The classifier was validated with ground beef enrichments artificially inoculated with 10, 50, and 100 CFU/ml STEC. The validation ground-truth regions of interest of the STEC target colonies consisted of 606 colonies, with 3,030 pixels of spectra. The overall classification accuracy was 98%. The average specificity of the method was 98% due to the low false-positive rate of 1.2%. The sensitivity ranged from 78 to 100% due to the false-negative rates of 22, 7, and 8% for O145, O45, and O26, respectively. This study showed the potential of visible and near-infrared hyperspectral imaging for detecting and classifying colonies of the six non-O157 STEC serogroups. The technique needs to be validated with bacterial cultures directly extracted from meat products and positive identification of colonies by using confirmatory tests such as latex agglutination tests or PCR.
美国农业部食品安全检验局已确定，六种非 O157 型产志贺毒素大肠杆菌（STEC）血清群（O26、O45、O103、O111、O121 和 O145）是生牛肉中的掺杂物。由于缺乏合适的琼脂培养基，对非 O157 型 STEC 的分离和表型鉴别存在问题。由于在显色琼脂上培养的非 O157 血清群之间缺乏明显的表型颜色变化，因此在选择用于确认的菌落时存在挑战。在这项研究中，使用可见和近红外高光谱成像和化学计量学来检测和分类在 Rainbow 琼脂 O157 上生长的非 O157 STEC 血清群。该方法首先通过为每个血清群建立光谱库来开发，该光谱库来自代表每个像素真实身份的地面实况感兴趣区域，从而来自高光谱琼脂平板图像中每个纯培养菌落的光谱库。纯培养非 O157 STEC 的光谱库由 2171 个菌落组成，来自 124347 个像素。使用 K 最近邻分类器为每个血清群开发分类模型。在菌落水平的总体分类训练准确率为 99%。使用人工接种 10、50 和 100 CFU/ml STEC 的牛肉增菌物对分类器进行验证。STEC 目标菌落的地面实况感兴趣区域由 606 个菌落组成，包含 3030 个像素的光谱。总体分类准确率为 98%。由于假阳性率为 1.2%，该方法的平均特异性为 98%。由于 O145、O45 和 O26 的假阴性率分别为 22%、7%和 8%，灵敏度范围为 78%至 100%。这项研究表明，可见和近红外高光谱成像技术具有检测和分类六种非 O157 STEC 血清群的潜力。该技术需要通过直接从肉类产品中提取细菌培养物并使用乳胶凝集试验或 PCR 等确认试验对菌落进行阳性鉴定来进行验证。
