Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
11032646 | Food Microbiology | 2019 | 12 Pages |
Abstract
This study determined the variability in population uniformity of an applied mixture of attenuated E. coli O157:H7 (attEcO157) on spinach leaves as impacted by sampling mass and detection technique over spatial and temporal conditions. Opportunistically, the survival and distribution of naturally contaminating pathogenic E. coli O157:H7 (EcO157), in a single packaged lot following commercial postharvest handling and washing, was also evaluated. From the main study outcomes, differences in the applied inoculum dose of 100-fold, resulted in indistinguishable population densities of approximately Log 1.1â¯CFUâ¯gâ1 by 14 days post-inoculation (DPI). Composite leaf samples of 150â¯g and the inclusion of the spinach petiole resulted in the greatest numerical sensitivity of detection of attEcO157 when compared to 25 and 150â¯g samples without petioles (Pâ¯<â¯0.05). Differences in population density and protected-site survival and potential leaf internalization were observed between growing seasons and locations in California (Pâ¯<â¯0.05). A Double Weibull model best described and identified two distinct populations with different inactivation rates of the inoculated attEcO157. Linear die-off rates varied between 0.14 and 0.29 Log/Day irrespective of location. Detection of EcO157- stx1-negative and stx2-positive, resulting from a natural contamination event, was observed in 11 of 26 quarantined commercial units of washed spinach by applying the 150â¯g sample mass protocol. The capacity to detect EcO157 varied between commercial test kits and non-commercial qPCR. Our findings suggest the need for modifications to routine pathogen sampling protocols employed for lot acceptance of spinach and other leafy greens.
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Authors
Eduardo Gutiérrez-RodrÃguez, Amy Gundersen, Adrian Sbodio, Steven Koike, Trevor V. Suslow,