Growth of Listeria monocytogenes within a Caramel-Coated Apple Microenvironment
Growth of Listeria monocytogenes within a Caramel-Coated Apple Microenvironment
复制标题
单核细胞增多性李斯特菌在焦糖涂层苹果微环境中的生长
作者：
K. Glass;M. Golden;Brandon J. Wanless;W. Bedale;C. Czuprynski
摘要2014年多个州爆发的一次炭疽病与食用焦糖苹果有关，这是一种意想不到的和以前未报告的单核细胞增生李斯特菌载体。这种爆发是意料之外的，因为苹果的pH值（<4.0）和焦糖涂层的水活度（<0.80）都太低，无法支持李斯特菌生长。在这项研究中，用大约4 log 10 CFU的L.单核细胞增多症（与爆发有关的血清型4 b菌株的混合物）在每个苹果的皮肤，茎和花萼上。一半的苹果有棍子插入核心，而其余的苹果完好无损。将苹果浸入热焦糖中，并分别在7°C或25°C下储存长达11天或28天。数据显示，苹果与插入棒支持显着更多的L。在两种贮藏条件下，单核细胞增多症的生长都比不加枝条的苹果快。在25°C条件下，L.单核细胞增多症群体在有棒的苹果中增加> 3log 10，而即使在1周后，对于没有棒的焦糖涂覆的苹果，也仅观察到1 log 10的增加。当在7°C下储存时，带棒的苹果表现出约1.5-log 10的L增加。在第28天的单核细胞增多症水平，而在没有棒的苹果中没有观察到生长。我们推断，插入一根棍子到苹果加速了果汁从苹果内部转移到其表面，在苹果-焦糖界面创造了一个微环境，L。当在室温下储存时，单核细胞增多症可以迅速生长到足以引起疾病的水平。焦糖和苹果都不是致病性单核细胞增生李斯特菌应该生长的食物，因为焦糖不含足够的自由水，而苹果太酸。然而，焦糖苹果最近与致命的炭疽病爆发有关。我们假设，将一根棍子插入苹果中会将果汁释放到苹果和焦糖之间的界面，提供一个比单独使用任何一种成分更友好的环境。为了验证这一假设，苹果接种了L。在沾焦糖之前先吃单核细胞增多症。有些苹果在蘸水之前插上了棍子，有些则没有。L.单核细胞增多症发生在冷藏的焦糖苹果上，而在冷藏的焦糖苹果上观察到缓慢的生长。与此相反，显着的病原体生长在3天内观察到在室温下与棒插入焦糖苹果。食品生产商应考虑食品中各成分之间的界面，作为病原体生长的潜在利基。焦糖和苹果都不是致病菌李斯特菌应该生长的食物，因为焦糖不含足够的自由水，而苹果太酸。然而，焦糖苹果最近与致命的炭疽病爆发有关。我们假设，将一根棍子插入苹果中会将果汁释放到苹果和焦糖之间的界面，提供一个比单独使用任何一种成分更友好的环境。为了验证这一假设，苹果接种了L。在沾焦糖之前先吃单核细胞增多症。有些苹果在蘸水之前插上了棍子，有些则没有。L.单核细胞增多症发生在冷藏的焦糖苹果上，而在冷藏的焦糖苹果上观察到缓慢的生长。与此相反，显着的病原体生长在3天内观察到在室温下与棒插入焦糖苹果。食品生产商应考虑食品中各成分之间的界面，作为病原体生长的潜在利基。
ABSTRACT A 2014 multistate listeriosis outbreak was linked to consumption of caramel-coated apples, an unexpected and previously unreported vehicle for Listeria monocytogenes. This outbreak was unanticipated because both the pH of apples (<4.0) and the water activity of the caramel coating (<0.80) are too low to support Listeria growth. In this study, Granny Smith apples were inoculated with approximately 4 log10 CFU of L. monocytogenes (a cocktail of serotype 4b strains associated with the outbreak) on each apple's skin, stem, and calyx. Half of the apples had sticks inserted into the core, while the remaining apples were left intact. Apples were dipped into hot caramel and stored at either 7°C or 25°C for up to 11 or 28 days, respectively. Data revealed that apples with inserted sticks supported significantly more L. monocytogenes growth than apples without sticks under both storage conditions. Within 3 days at 25°C, L. monocytogenes populations increased >3 log10 in apples with sticks, whereas only a 1-log10 increase was observed even after 1 week for caramel-coated apples without sticks. When stored at 7°C, apples with sticks exhibited an approximately 1.5-log10 increase in L. monocytogenes levels at 28 days, whereas no growth was observed in apples without sticks. We infer that insertion of a stick into the apple accelerates the transfer of juice from the interior of the apple to its surface, creating a microenvironment at the apple-caramel interface where L. monocytogenes can rapidly grow to levels sufficient to cause disease when stored at room temperature. IMPORTANCE Neither caramel nor apples are a food where the pathogenic bacterium Listeria monocytogenes should grow, as caramel does not contain enough free water and apples are too acidic. Caramel-coated apples, however, were recently linked to a deadly outbreak of listeriosis. We hypothesized that inserting a stick into the apple releases juice to the interface between the apple and caramel, providing a more hospitable environment than either component alone. To test this hypothesis, apples were inoculated with L. monocytogenes prior to caramel dipping. Some apples had sticks inserted into them before dipping, while others did not. No growth of L. monocytogenes occurred on refrigerated caramel apples without sticks, whereas slow growth was observed on refrigerated caramel apples with sticks. In contrast, significant pathogen growth was observed within 3 days at room temperature on caramel apples with sticks inserted. Food producers should consider interfaces between components within foods as potential niches for pathogen growth. Neither caramel nor apples are a food where the pathogenic bacterium Listeria monocytogenes should grow, as caramel does not contain enough free water and apples are too acidic. Caramel-coated apples, however, were recently linked to a deadly outbreak of listeriosis. We hypothesized that inserting a stick into the apple releases juice to the interface between the apple and caramel, providing a more hospitable environment than either component alone. To test this hypothesis, apples were inoculated with L. monocytogenes prior to caramel dipping. Some apples had sticks inserted into them before dipping, while others did not. No growth of L. monocytogenes occurred on refrigerated caramel apples without sticks, whereas slow growth was observed on refrigerated caramel apples with sticks. In contrast, significant pathogen growth was observed within 3 days at room temperature on caramel apples with sticks inserted. Food producers should consider interfaces between components within foods as potential niches for pathogen growth.