Nano-Biosensors Lab, Biosystems and Agricultural Engineering, Michigan State University, East Lansing, Michigan 48824, USA (ORCID: http://orcid.org/0000-0003-1020-0543 [L.L.M.]).
J Food Prot. 2018 Dec;81(12):1941-1949. doi: 10.4315/0362-028X.JFP-18-040.
Rapid detection of bacterial contamination in the food supply chain is critically important for food safety monitoring. Reliable extraction and concentration of bacteria from complex matrices is required to achieve high detection sensitivity, especially in situations of low contamination and infective dose. Carbohydrate ligands that attach to microbial cell-surface epitopes are promising economical and biocompatible substitutes for cell-targeting ligands and antibodies. Two different carbohydrate ligands immobilized onto magnetic nanoparticles (MNPs) were easily suspended in liquid food (milk) and allowed expedient extraction of microbes within minutes, without the need for centrifugation or loss in capture capacity. In this pilot study, 25-mL samples of undiluted milk were spiked with 5 mg of MNPs and artificially contaminated with bacteria at 3 to 5 log CFU/mL. MNPs and bacteria formed MNP-cell complexes, which were rapidly separated from the milk matrix with a simple magnet to allow supernatant removal. MNP-cell complexes were then concentrated by resuspension in 1 mL of fresh milk and plated per Bacteriological Analytical Manual procedures. Capture was carried out in vitamin D, 2% reduced fat, and fat-free milk spiked with Salmonella Enteritidis, Escherichia coli O157:H7, and Bacillus cereus for a combined total of 18 experiments (three replicates each). An additional eight experiments were conducted to investigate the effect of competitive bacteria on capture. All experiments were carried out over several months to account for environmental variations. Capture efficiency, on a log basis, for all combinations of milk and bacteria was 73 to 90%. Long-term exposure of the MNPs to milk did not markedly affect capture efficiency. These carbohydrate-functionalized MNPs have potential as nonspecific receptors for rapid extraction of bacteria from complex liquids, opening the door to discovery of biocompatible ligands that can reliably target pathogens in our food.
快速检测食品供应链中的细菌污染对于食品安全监测至关重要。为了实现高检测灵敏度，特别是在低污染和感染剂量的情况下，需要从复杂基质中可靠地提取和浓缩细菌。附着在微生物细胞表面表位上的碳水化合物配体是替代细胞靶向配体和抗体的有前途的经济和生物相容替代品。两种不同的碳水化合物配体固定在磁性纳米颗粒（MNP）上，可以很容易地悬浮在液体食品（牛奶）中，并在几分钟内方便地提取微生物，而无需离心或丧失捕获能力。在这项初步研究中，25 毫升未稀释的牛奶样品中加入 5 毫克 MNP，并以 3 至 5 对数 CFU/mL 的浓度人工污染细菌。MNP 和细菌形成 MNP-细胞复合物，用简单的磁铁快速从牛奶基质中分离出来，以允许去除上清液。然后通过重新悬浮在 1 毫升新鲜牛奶中来浓缩 MNP-细胞复合物，并按照《细菌分析手册》程序进行平板接种。在添加了维生素 D、2%低脂和无脂牛奶的沙门氏菌肠炎、大肠杆菌 O157:H7 和蜡样芽孢杆菌的情况下进行了 18 次实验（每个实验重复 3 次），共进行了 18 次实验。进行了另外 8 次实验以研究竞争细菌对捕获的影响。所有实验在几个月内进行，以考虑环境变化。所有牛奶和细菌组合的对数捕获效率为 73%至 90%。MNP 长期暴露于牛奶中不会显著影响捕获效率。这些碳水化合物功能化的 MNP 有可能作为从复杂液体中快速提取细菌的非特异性受体，为发现能够可靠靶向我们食物中病原体的生物相容配体开辟了道路。
