Department of Food Science, College of Agriculture and Veterinary Medicine, UAE University, Al Ain, 15551, United Arab Emirates.
Department of Biology, College of Science, United Arab Emirates University, Al Ain, 15551, United Arab Emirates; Khalifa Centre for Genetic Engineering and Biotechnology, United Arab Emirates University, Al Ain, 15551, United Arab Emirates.
Food Microbiol. 2023 Oct;115:104326. doi: 10.1016/j.fm.2023.104326. Epub 2023 Jun 23.
Salmonella is known to survive in raw/pasteurized milk and cause foodborne outbreaks. Lactoferrin, present in milk from all animal sources, is an iron-binding glycoprotein that limits the availability of iron to pathogenic bacteria. Despite the presence of lactoferrins, Salmonella can grow in milk obtained from different animal sources. However, the mechanism by which Salmonella overcomes iron scarcity induced by lactoferrin in milk is not evaluated yet. Salmonella employs the DNA binding transcriptional regulator Fur (ferric update regulator) to mediate iron uptake during survival in iron deplete conditions. To understand the importance of Fur in Salmonella milk growth, we profiled the growth of Salmonella Typhimurium Δfur (ST4/74Δfur) in both bovine and camel milk. ST4/74Δfur was highly inhibited in milk compared to wild-type ST4/74, confirming the importance of Fur mediated regulation of iron metabolism in Salmonella milk growth. We further studied the biology of ST4/74Δfur to understand the importance of iron metabolism in Salmonella milk survival. Using increasing concentrations of FeCl, and the antibiotic streptonigrin we show that iron accumulates in the cytoplasm of ST4/74Δfur. We hypothesized that the accumulated iron could activate oxidative stress via Fenton's reaction leading to growth inhibition. However, the inhibition of ST4/74Δfur in milk was not due to Fenton's reaction, but due to the 'iron scarce' conditions of milk and microaerophilic incubation conditions which made the presence of the fur gene indispensable for Salmonella milk growth. Subsequently, survival studies of 14 other transcriptional mutants of ST4/74 in milk confirmed that RpoE-mediated response to extracytoplasmic stress is also important for the survival of Salmonella in milk. Though we have data only for fur and rpoE, many other Salmonella transcriptional factors could play important roles in the growth of Salmonella in milk, a theme for future research on Salmonella milk biology. Nevertheless, our data provide early insights into the biology of milk-associated Salmonella.
沙门氏菌存在于生/巴氏杀菌奶中，可导致食源性疾病爆发。乳铁蛋白存在于所有动物来源的奶中，是一种铁结合糖蛋白，可限制致病菌获得铁。尽管存在乳铁蛋白，沙门氏菌仍能在从不同动物来源获得的奶中生长。然而，沙门氏菌克服乳铁蛋白在奶中引起的铁缺乏的机制尚未得到评估。沙门氏菌利用 DNA 结合转录调节因子 Fur（铁更新调节因子）来介导在缺铁环境中的铁摄取。为了了解 Fur 在沙门氏菌在奶中生长中的重要性，我们在牛奶中对鼠伤寒沙门氏菌 Δfur（ST4/74Δfur）的生长进行了分析。与野生型 ST4/74 相比，ST4/74Δfur 在牛奶中受到高度抑制，这证实了 Fur 介导的铁代谢调节在沙门氏菌在奶中生长中的重要性。我们进一步研究了 ST4/74Δfur 的生物学特性，以了解铁代谢在沙门氏菌在奶中生存中的重要性。使用递增浓度的 FeCl 和抗生素链霉素，我们表明铁在 ST4/74Δfur 的细胞质中积累。我们假设，积累的铁可以通过 Fenton 反应激活氧化应激，导致生长抑制。然而，ST4/74Δfur 在奶中的抑制不是由于 Fenton 反应，而是由于奶中的“缺铁”条件和微需氧孵育条件，这使得 Fur 基因的存在对于沙门氏菌在奶中的生长是必不可少的。随后，在牛奶中对 ST4/74 的 14 个其他转录突变体的存活研究证实，RpoE 介导的对细胞外应激的反应对于沙门氏菌在牛奶中的存活也很重要。尽管我们只有 Fur 和 rpoE 的数据，但许多其他沙门氏菌转录因子可能在沙门氏菌在奶中的生长中发挥重要作用，这是沙门氏菌奶生物学的未来研究主题。尽管如此，我们的数据为与奶相关的沙门氏菌的生物学提供了早期的见解。
