Brandl Maria T, Huynh Steven
Produce Safety and Microbiology Research Unit, Agricultural Research Service, U.S. Department of Agriculture, Albany, California, USA
Produce Safety and Microbiology Research Unit, Agricultural Research Service, U.S. Department of Agriculture, Albany, California, USA.
Appl Environ Microbiol. 2014 Aug;80(16):5037-42. doi: 10.1128/AEM.00795-14. Epub 2014 Jun 6.
Salmonella enterica has the ability to form biofilms and large aggregates on produce surfaces, including on cilantro leaves. Aggregates of S. enterica serovar Thompson that remained attached to cilantro leaves after rigorous washing and that were present free or bound to dislodged leaf tissue in the wash suspension were observed by confocal microscopy. Measurement of S. Thompson population sizes in the leaf washes by plate counts failed to show an effect of 0.05% Tween 80 on the removal of the pathogen from cilantro leaves 2 and 6 days after inoculation. On the contrary, digital image analysis of micrographs of single cells and aggregates of green fluorescent protein (GFP)-S. Thompson present in cilantro leaf washes revealed that single cells represented 13.7% of the cell assemblages in leaf washes containing Tween 80, versus 9.3% in those without the surfactant. Moreover, Tween 80 decreased the percentage of the total S. Thompson cell population located in aggregates equal to or larger than 64 cells from 9.8% to 4.4% (P < 0.05). Regression analysis of the frequency distribution of aggregate size in leaf washes with and without Tween 80 showed that the surfactant promoted the dispersal of cells from large aggregates into smaller ones and into single cells (P < 0.05). Our study underlines the importance of investigating bacterial behavior at the scale of single cells in order to uncover trends undetectable at the population level by bacterial plate counts. Such an approach may provide valuable information to devise strategies aimed at enhancing the efficacy of produce sanitization treatments.
肠炎沙门氏菌有能力在农产品表面形成生物膜和大的聚集体，包括在香菜叶上。通过共聚焦显微镜观察到，肠炎沙门氏菌血清型汤普森的聚集体在经过严格清洗后仍附着在香菜叶上，并且在洗涤悬浮液中以游离状态或与脱落的叶片组织结合的状态存在。通过平板计数法测量叶片洗涤液中汤普森菌的数量，未显示出0.05%吐温80对接种后2天和6天从香菜叶上去除病原体有影响。相反，对香菜叶洗涤液中绿色荧光蛋白（GFP）-汤普森单细胞和聚集体的显微照片进行数字图像分析发现，在含有吐温80的叶片洗涤液中，单细胞占细胞组合的13.7%，而在没有表面活性剂的洗涤液中为9.3%。此外，吐温80使位于等于或大于64个细胞的聚集体中的汤普森菌细胞总数的百分比从9.8%降至4.4%（P<0.05）。对有无吐温80的叶片洗涤液中聚集体大小频率分布的回归分析表明，表面活性剂促进了细胞从大聚集体分散到较小聚集体和单细胞中（P<0.05）。我们的研究强调了在单细胞水平上研究细菌行为的重要性，以便发现细菌平板计数在群体水平上无法检测到的趋势。这种方法可能为设计旨在提高农产品消毒处理效果的策略提供有价值的信息。
