Laboratory of Food Quality Control and Hygiene, Department of Food Science and Human Nutrition, Agricultural University of Athens, Iera Odos 75, 118 55, Athens, Greece.
Laboratory of Food Quality Control and Hygiene, Department of Food Science and Human Nutrition, Agricultural University of Athens, Iera Odos 75, 118 55, Athens, Greece.
Food Microbiol. 2022 Sep;106:104053. doi: 10.1016/j.fm.2022.104053. Epub 2022 Apr 30.
Salmonella enterica is capable of entering the interior of leafy greens and establishing in the apoplastic area, a phenomenon known as internalization. The ability of internalized bacteria to evade common disinfection practices poses a well-established risk. Our aim was to study the effect of: i) inoculum size and ii) prior adaptation of Salmonella to sublethal stresses, on the internalization of the pathogen in four leafy vegetables. Spinach, lettuce, arugula and chicory were inoculated, by immersion for 2 min at room temperature with: i) Salmonella Enteritidis at 3.0, 4.0, 5.0, 6.0, 7.0 log CFU/mL and ii) non-adapted or adapted S. Enteritidis to acid (in TSB with 1% glucose, incubated for 24 h at 37 °C), cold (in TSB for 7 days at 4 °C), starvation (0.85% NaCl of pH 6.6, 48 h at 37 °C) or desiccation (1.5 h at 42 °C, 4 days at 21 °C) stress at appx 3.5 log CFU/mL). Inoculated leafy greens were subsequently stored at 5 °C and 20 °C for 2 h and 48 h (n = 2 × 2). Population of internalized Salmonella, after surface decontamination with 1% w/v AgNO, was assessed on selective media. Even the lowest initial bacterial inoculum was adequate for internalization of Salmonella to occur in leafy vegetables. Non-adapted Salmonella inoculum of 7.0 (maximum) and 3.0 log CFU/mL (lowest inoculation level tested) after short storage (2 h) resulted in 3.7-4.3 and 1.3-1.5 log CFU/g internalized bacterial population, respectively. Colonization (including both attachment and internalization processes), as well as internalization process, were positively correlated to initial inoculum level. These processes reached a different plateau beyond which, no further increase in internalization was observed. Adaptation of the pathogen to mild stresses enhanced internalization (P < 0.05), with desiccation- and acid-adapted Salmonella demonstrating the highest internalization capacity, regardless of the vegetable and storage temperature. These findings could contribute to further elucidation of colonization capacity of Salmonella in leafy vegetables and assist in selecting the proper conditions that contribute to the prevention of fresh produce contamination with Salmonella.
肠炎沙门氏菌能够进入绿叶蔬菜的内部并定殖在质外体区域，这种现象称为内化。内化细菌逃避常见消毒措施的能力构成了既定风险。我们的目的是研究：i）接种物大小和 ii）沙门氏菌先前适应亚致死应激对四种绿叶蔬菜中病原体内化的影响。通过在室温下将：i）肠炎沙门氏菌 3.0、4.0、5.0、6.0、7.0 log CFU/mL 浸入 2 分钟，或 ii）非适应或适应于酸（在含有 1%葡萄糖的 TSB 中，在 37°C 下孵育 24 小时）、冷（在 TSB 中 4°C 下 7 天）、饥饿（pH 6.6 的 0.85%NaCl，37°C 下 48 小时）或干燥（42°C 下 1.5 小时，21°C 下 4 天）应激，以适应肠炎沙门氏菌的接种，对菠菜、生菜、芝麻菜和菊苣进行接种。随后将接种的绿叶蔬菜在 5°C 和 20°C 下储存 2 小时和 48 小时（n=2×2）。用 1%w/v AgNO3 进行表面去污后，在选择性培养基上评估内化的沙门氏菌的数量。即使是最低的初始细菌接种量也足以使沙门氏菌内化到绿叶蔬菜中。在短期储存（2 小时）后，非适应的肠炎沙门氏菌接种量为 7.0（最大）和 3.0 log CFU/mL（测试的最低接种水平）导致 3.7-4.3 和 1.3-1.5 log CFU/g 内化细菌种群，分别。定植（包括附着和内化过程）以及内化过程与初始接种物水平呈正相关。这些过程达到一个不同的平台，在此之后，没有观察到进一步的内化增加。病原体对温和应激的适应增强了内化（P<0.05），无论蔬菜和储存温度如何，干燥和酸化适应的沙门氏菌表现出最高的内化能力。这些发现可能有助于进一步阐明肠炎沙门氏菌在绿叶蔬菜中的定植能力，并有助于选择有助于防止沙门氏菌污染新鲜农产品的适当条件。
