Vonasek Erica, Nitin Nitin
Department of Biological and Agricultural Engineering, University of California, Davis, Davis, California, USA.
Department of Biological and Agricultural Engineering, University of California, Davis, Davis, California, USA Department of Food Science & Technology, University of California, Davis, Davis, California, USA
Appl Environ Microbiol. 2015 Oct 16;82(1):106-15. doi: 10.1128/AEM.02327-15. Print 2016 Jan 1.
Microbial pathogen infiltration in fresh leafy greens is a significant food safety risk factor. In various postharvest operations, vacuum cooling is a critical process for maintaining the quality of fresh produce. The overall goal of this study was to evaluate the risk of vacuum cooling-induced infiltration of Escherichia coli O157:H7 into lettuce using multiphoton microscopy. Multiphoton imaging was chosen as the method to locate E. coli O157:H7 within an intact lettuce leaf due to its high spatial resolution, low background fluorescence, and near-infrared (NIR) excitation source compared to those of conventional confocal microscopy. The variables vacuum cooling, surface moisture, and leaf side were evaluated in a three-way factorial study with E. coli O157:H7 on lettuce. A total of 188 image stacks were collected. The images were analyzed for E. coli O157:H7 association with stomata and E. coli O157:H7 infiltration. The quantitative imaging data were statistically analyzed using analysis of variance (ANOVA). The results indicate that the low-moisture condition led to an increased risk of microbial association with stomata (P < 0.05). Additionally, the interaction between vacuum cooling levels and moisture levels led to an increased risk of infiltration (P < 0.05). This study also demonstrates the potential of multiphoton imaging for improving sensitivity and resolution of imaging-based measurements of microbial interactions with intact leaf structures, including infiltration.
新鲜绿叶蔬菜中的微生物病原体侵入是一个重大的食品安全风险因素。在各种采后操作中，真空冷却对于保持新鲜农产品的质量至关重要。本研究的总体目标是使用多光子显微镜评估真空冷却导致大肠杆菌O157:H7侵入生菜的风险。与传统共聚焦显微镜相比，由于多光子成像具有高空间分辨率、低背景荧光和近红外（NIR）激发源，因此被选作在完整生菜叶片中定位大肠杆菌O157:H7的方法。在一项针对生菜上大肠杆菌O157:H7的三因素研究中，对真空冷却、表面湿度和叶片面等变量进行了评估。总共收集了188个图像堆栈。对图像分析了大肠杆菌O157:H7与气孔的关联以及大肠杆菌O157:H7的侵入情况。使用方差分析（ANOVA）对定量成像数据进行统计分析。结果表明，低湿度条件会增加微生物与气孔关联的风险（P < 0.05）。此外，真空冷却水平和湿度水平之间的相互作用会增加侵入风险（P < 0.05）。本研究还证明了多光子成像在提高基于成像测量微生物与完整叶片结构相互作用（包括侵入）的灵敏度和分辨率方面的潜力。
