title: Influence of Vacuum Cooling on Escherichia coli O157:H7 Infiltration in Fresh Leafy Greens via a Multiphoton-Imaging Approach.
abstract: 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.
authors.affiliation: Department of Biological and Agricultural Engineering, University of California, Davis, Davis, California, USA.
authors.forename: Erica
authors.initials: E
authors.lastname: Vonasek
authors.affiliation: 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 nnitin@ucdavis.edu.
authors.forename: Nitin
authors.initials: N
authors.lastname: Nitin
mesh_terms: D058948:Cell Tracking / Q000379:methods; D019453:Escherichia coli O157 / Q000737:chemistry / Q000235:genetics / Q000502:physiology*; D005506:Food Contamination / Q000032:analysis*; D005511:Food Handling / Q000295:instrumentation / Q000379:methods*; D017930:Genes, Reporter; D018545:Lactuca / Q000382:microbiology*; D008156:Luciferases / Q000235:genetics / Q000378:metabolism; D018613:Microscopy, Confocal; D018515:Plant Leaves / Q000382:microbiology*; D014618:Vacuum
chemical_list: D008156:Luciferases