Somewhere on a farm in Iowa in 2010, a hen lays an egg. In just a few short weeks, this egg will be part of a massive infection event: thousands of people will fall ill, millions of eggs will be recalled, and several egg industry titans will ultimately land in jail, all thanks to a microscopic but mighty bacterium.2010年，在爱荷华州的一座农场里，一只母鸡产下了一枚鸡蛋。仅仅几个星期后，这枚鸡蛋将成为一场大规模感染事件的一部分：成千上万的人会生病，数百万枚鸡蛋将被召回，而几位蛋业巨头最终会锒铛入狱，而这一切都源于一种微小却强大的细菌。 Salmonella infects millions worldwide each year, causing fever, stomach cramps, and diarrhea. And these effects can be extreme: Salmonella is the leading cause of hospitalizations and deaths from food poisoning.↳每年，全世界有数百万人感染沙门氏菌，导致发烧、胃痉挛和腹泻。这些影响可能非常严重：沙门氏菌是食物中毒导致住院和死亡的主要原因。 So, let’s follow this microbe to find out how it makes so many people sick.那么，让我们跟随这种微生物，看看它是如何让如此多人患病的。 We begin in the chicken's digestive tract, a major source of all Salmonella infections. In chickens, Salmonella bacteria often go undetected, allowing them to spread to eggs either through the developing yolk or by passing through feces, which can then contaminate shells. Under unhygienic farming conditions, this Salmonella-laden feces may also infect or contaminate other animals and crops, causing various food-linked outbreaks. Meanwhile, chicken meat can be exposed to intestinal Salmonella during processing.我们从鸡的消化道开始，它是所有沙门氏菌感染的主要来源。在鸡体内，沙门氏菌常常不易被察觉，它们可能通过正在发育的蛋黄传播到鸡蛋中，或通过粪便排出并污染蛋壳。在不卫生的养殖条件下，这些含有沙门氏菌的粪便还可能感染或污染其他动物和农作物，导致各种与食物相关的疫情。同时，在加工过程中，鸡肉也可能接触到肠道中的沙门氏菌。 On its journey from farm to plate, the microbe can survive extreme cold, wet, and dry conditions. However, once it moves into a human body, Salmonella reveals its true talents for survival. The first hurdle is the stomach. Here, most bacterial invaders are killed off by stomach acid. But Salmonella cells can detect acidic conditions, which triggers the production of acid shock proteins. These molecules shield the bacteria from damage just long enough for it to pass into the intestines.↳在从农场到餐桌的旅途中，这种微生物能在极端的寒冷、潮湿和干燥环境中生存。然而，一旦进入人体，沙门氏菌便展现出它真正的生存本领。第一道关卡是胃。在这里，大多数细菌入侵者都会被胃酸消灭。但沙门氏菌能感知酸性环境，从而触发酸冲击蛋白的产生。这些分子保护细菌免受伤害，正好能支撑它们进入肠道。 Salmonella then faces the next gauntlet, as intestinal cells swiftly unleash microbe-destroying immune cells. But once again, the bacteria detect these changes with inbuilt sensors. And embedded within Salmonella’s genome are pathogenicity islands, clusters of adaptive genes that launch the next phase of attack. They signal the construction of a specialized system that resembles a needle and syringe. Within seconds, it injects molecules called effector proteins into the intestinal cells, causing them to change their structure and swallow up the Salmonella. Once inside, Salmonella can then exploit the cell machinery to replicate and spread.接着，沙门氏菌面对下一道挑战：肠道细胞会迅速释放出能消灭微生物的免疫细胞。但细菌再次利用内置的感应器来探测这些变化。在沙门氏菌的基因组中，存在着致病岛——一组自适应基因簇，它们会启动下一阶段的攻击。它们指令细菌构建一个类似针管的特殊系统。在几秒钟内，沙门氏菌就能将效应蛋白注入肠道细胞，使其结构发生变化并吞噬沙门氏菌。一旦进入细胞，沙门氏菌就能利用细胞的机制进行复制和扩散。 But these invaded intestinal cells don’t go down without a fight— as soon as this breach begins, they release cytokines, chemical messengers that prompt the immune system to launch into action. Fleets of white blood cells seek out and destroy Salmonella microbes and infected cells. This inflammatory response is also what leads to symptoms like abdominal pains and fever. And it further damages the breached intestinal cells, limiting their usual ability to absorb water. So, whatever’s in the digestive tract gets released in watery diarrhea.但这些被入侵的肠道细胞并不会坐以待毙——一旦入侵开始，它们就会释放细胞因子，这是一种化学信使，能促使免疫系统立即行动。大量白细胞会追踪并摧毁沙门氏菌以及被感染的细胞。这种炎症反应也正是导致腹痛和发烧等症状的原因。此外，它还会进一步损伤受侵的肠道细胞，限制它们正常吸收水分的能力。于是，消化道中的物质就会以水样腹泻的形式排出体外。 While this inflammatory response may feel unpleasant, it effectively purges Salmonella from the body within 2 to 7 days for most people, without the need for antibiotics.虽然这种炎症反应令人不适，但对大多数人而言，它能在 2 到 7 天内有效清除体内的沙门氏菌，而无需使用抗生素。 But there are times when a Salmonella infection may require more treatment. It can lead to severe dehydration, particularly in children and older patients. And in some unusual cases, Salmonella can continue to spread through the body, hiding inside immune cells, invading other organs and tissues, and even poisoning the blood. These cases occur if a person is infected by a rare but powerful type of Salmonella called S. typhi. Unlike other strains, S. typhi doesn’t infect chickens— It spreads from person to person, mainly via poor sanitation and untreated drinking water. Although it’s uncommon in many parts of the world, typhoid fever, the disease that S. typhi causes, still kills over 100,000 people yearly.但有时沙门氏菌感染需要更多治疗。它可能导致严重脱水，尤其是在儿童和老年患者中。而在一些少见的情况下，沙门氏菌会继续在体内传播，藏身于免疫细胞中，侵入其他器官和组织，甚至引发败血症。这些情况多发生在感染了一种罕见但强大的沙门氏菌——伤寒沙门氏菌（S. typhi）时。与其他菌株不同，S. typhi 不会感染鸡，它主要通过人际传播，尤其是因卫生条件差或饮用未处理的水而传播。尽管在世界许多地区并不常见，但由 S. typhi 引起的伤寒每年仍导致超过 10 万人死亡。 Thankfully, there are vaccines to prevent infection by S. typhi. To avoid milder variants, there are steps that everyone can take, like washing your hands, avoiding unpasteurized milk, and cooking meat and eggs thoroughly. Cookie dough should be off limits: raw eggs and flour both carry a Salmonella risk.幸运的是，目前已有疫苗可以预防 S. typhi 的感染。为了避免较轻型的变种感染，每个人都可以采取一些措施，比如勤洗手、避免饮用未经消毒的牛奶、彻底煮熟肉类和鸡蛋。饼干生面团则应避免食用：因为生鸡蛋和面粉都存在沙门氏菌风险。 And there are ways to stop Salmonella at its source. Investigations into the outbreak in 2010 revealed one company's dark history of unhygienic farming conditions, bribery of health officials, and mislabeled eggs. Since then, the United States has taken steps to put stricter regulations in place. In Europe, many countries have successfully reduced Salmonella by requiring testing on farms and before products reach shelves. But there's still work to be done if we want to stop the spread of this incredibly crafty pathogen.同时，也有办法从源头阻止沙门氏菌。对2010年疫情的调查揭示了一家公司不为人知的黑暗历史：不卫生的养殖环境、行贿卫生官员以及错误标记鸡蛋。自那以后，美国采取了更严格的监管措施。而在欧洲，许多国家通过要求在农场和产品上架前进行检测，成功减少了沙门氏菌的传播。但如果我们想要彻底阻止这种极具狡猾性的病原体传播，仍有大量工作要做。
