Fulano Alex M, Elbakush Ahmed M, Chen Li-Hong, Gomelsky Mark
Department of Molecular Biology, University of Wyoming, Laramie, WY, United States.
Faculty of Veterinary Medicine, Tripoli University, Tripoli, Libya.
Front Microbiol. 2023 Apr 27;14:1126940. doi: 10.3389/fmicb.2023.1126940. eCollection 2023.
Fresh produce contaminated with has caused major listeriosis outbreaks in the last decades. Our knowledge about components of the listerial biofilms formed on fresh produce and their roles in causing foodborne illness remains incomplete. Here, we investigated, for the first time, the role of the listerial Pss exopolysaccharide (EPS) in plant surface colonization and stress tolerance. Pss is the main component of biofilms synthesized at elevated levels of the second messenger c-di-GMP. We developed a new biofilm model, whereby EGD-e and its derivatives are grown in the liquid minimal medium in the presence of pieces of wood or fresh produce. After 48-h incubation, the numbers of colony forming units of the Pss-synthesizing strain on pieces of wood, cantaloupe, celery and mixed salads were 2-12-fold higher, compared to the wild-type strain. Colonization of manmade materials, metals and plastics, was largely unaffected by the presence of Pss. The biofilms formed by the EPS-synthesizing strain on cantaloupe rind were 6-16-fold more tolerant of desiccation, which resembles conditions of whole cantaloupe storage and transportation. Further, listeria in the EPS-biofilms survived exposure to low pH, a condition encountered by bacteria on the contaminated produce during passage through the stomach, by 11-116-fold better than the wild-type strain. We surmise that strains synthesizing Pss EPS have an enormous, 10-10-fold, advantage over the non-synthesizing strains in colonizing fresh produce, surviving during storage and reaching small intestines of consumers where they may cause disease. The magnitude of the EPS effect calls for better understanding of factors inducing Pss synthesis and suggests that prevention of listerial EPS-biofilms may significantly enhance fresh produce safety.
在过去几十年中，被 污染的新鲜农产品引发了多次严重的李斯特菌病疫情。我们对新鲜农产品上形成的李斯特菌生物膜的成分及其在食源性疾病中的作用的了解仍然不完整。在此，我们首次研究了李斯特菌Pss胞外多糖（EPS）在植物表面定殖和胁迫耐受性中的作用。Pss是在第二信使c-二鸟苷单磷酸水平升高时合成的生物膜的主要成分。我们开发了一种新的生物膜模型，即让EGD-e及其衍生物在含有木块或新鲜农产品的液体基本培养基中生长。培养48小时后，与野生型菌株相比，合成Pss的菌株在木块、哈密瓜、芹菜和混合沙拉上的菌落形成单位数量高出2至12倍。Pss的存在对人造材料、金属和塑料的定殖影响不大。EPS合成菌株在哈密瓜表皮上形成的生物膜对干燥的耐受性提高了6至16倍，这类似于整个哈密瓜储存和运输的条件。此外，EPS生物膜中的李斯特菌在暴露于低pH环境（细菌在受污染农产品通过胃部时遇到的情况）下的存活能力比野生型菌株强11至116倍。我们推测，合成Pss EPS的菌株在定殖新鲜农产品、储存期间存活以及到达消费者小肠（在那里它们可能致病）方面比非合成菌株具有巨大的（10至100倍）优势。EPS效应的程度要求更好地了解诱导Pss合成的因素，并表明预防李斯特菌EPS生物膜可能会显著提高新鲜农产品的安全性。
