細菌耐藥恐成為人類致命威脅

美國疾病中心（CDC）預計，未來12個月里，細菌或真菌感染對抗生素免疫的情況，將導致至少200萬起病例和2.3萬人死亡。不幸的是，這一問題毫無好轉之勢，還在不斷惡化：如今在全球范圍內，每年有70萬人因為這樣的耐藥微生物而死亡；而英國政府委托的一項權威研究顯示，到2050年，死亡數字會飆升到1,000萬，甚至超過每年因癌癥死亡的人數。

世界衛生組織（World Health Organization）警告稱，耐藥性——即通俗小報所說“超級細菌”的興起——是“對全球健康和安全最嚴重的威脅之一”。而且不要搞錯：這個威脅很大程度上是人類造成的。

在把問題歸咎于人類之前，我們首先談談自然在其中扮演的角色。簡而言之，問題在于大部分細菌極快的分裂速度，會不可避免地導致它們極快的演化速度。舉個例子，一個大腸桿菌（E. coli）在合適的情況下，僅需7個小時就能分裂成擁有2,097,152個細菌的巨大菌落，而細菌每次分裂都有可能出現突變和適應性變化，尤其是當它們處于強大的選擇壓力之下時。

這里就要談到我們自己了。在幫助細菌迅速演化上，我們人類起到了至少兩大作用。首先，我們長期對病人過度和不恰當地開具抗生素處方。這些無效的治療往往會讓存活下來的細菌進化出耐藥性，并將這種耐藥性傳遞給后代。正如俗話所說：“殺不死你的，會讓你更強大?！保纯催@條可怕的時間軸，我們就能知道抗病菌株的誕生有多快。）

其次，另一種潛在的行為也推動了細菌的演化。我們慣于給牲畜喂食低劑量的抗生素——自20世紀40年代進入抗生素時代以來，農業領域已經這樣做了近80年。

我們如何做出了這樣的決定？這是一個曲折的故事。在9月出版的非凡新著《大雞：抗生素創造現代農業、改變全球飲食的驚人往事》（Big Chicken: The Incredible Story of How Antibiotics Created Modern Agriculture and Changed the Way the World Eats）中，作者瑪麗安·麥肯納對此娓娓道來。

麥肯納寫道：“此刻，遍布這個星球大部分地區的大部分肉用家畜，在生命的大部分時間里都服用了抗生素，其消耗量多達每年63,151噸，這是養殖的輔助手段?！鞭r民們發現，抗生素有助于“讓飼料有效地轉化為可口的肌肉”，于是他們這么用了?？股貢环旁陲暳匣蚴撬?，它們可以幫助牲畜抵御疾病，農民也能因此在畜棚里養上更多牲口，并把老式農業轉換為現代的產業化模式。

麥肯納表示，動物腸道內有了耐藥細菌后，接下來的情況大抵如下：被拉進屠宰場后，消化道內的突變細菌有時就會“濺到肉上”。隨后，這些肉上的細菌可能會被直接食用，或是被帶到家里或餐廳的廚房，從而污染柜臺、砧板或其他食物。最終，它們可能感染人類。

麥肯納說：“這只是途徑之一。另一種途徑下，那些腸胃中的物質，那些耐藥細菌，會通過糞便離開動物?！奔S便會干燥，沾滿細菌的塵土會隨風飄散、滲入地下水，或是變成肥料撒到其他土地里。她表示：“總之，這些耐藥細菌會通過多種方式進入環境，隨后遷移到人類身上。更麻煩的是，它們攜帶的基因——那些控制耐藥性的基因——可能還會分裂出來，并被其他細菌吸收。途徑太多了，簡直隨心所欲?！?

盡管在美國和歐洲，對牲畜使用抗生素來“促進生長”都不再合法，但農民仍然可以在牲畜群中用抗生素來防治疾病。麥肯納表示，這里有個很廣泛和“模糊的中間地帶”，因為許多情況下抗生素產生的效果是一樣的：“人們依舊在使用少量或小劑量的抗生素”，從而營造了耐藥菌種的溫床。她保守地表示：“如果我們對人類這樣做，我們會認為這不妥當?！?

本周二，世界衛生組織發表報告，呼吁終止抗生素在食品動物上的常規使用。醫學期刊《柳葉刀》（The Lancet Planetary Health）也新發一篇分析，闡述了這種做法的危險性。（這篇文章也值得一讀。）

對此，美國農業部（Department of Agriculture）發布了新聞稿作為回應，聲稱：“世界衛生組織的指導方針與美國政策不符，也沒有可靠的科學依據?！蹦憧梢蚤喿x完整聲明，做出自己的判斷。農業部提出批評的原因，部分在于世界衛生組織的建議所采用的一些論據，連世衛組織本身都認為“證據質量較低”。

我致電了農業部，希望能得到更加徹底的說明。不過目前為止，農業部還沒有人正式對我公布任何信息。（財富中文網）

譯者：嚴匡正?

During the next 12 months, the CDC estimates that at least 2 million illnesses and 23,000 deaths will be caused by bacterial or fungal infections that no longer respond to antibiotics. And this problem, unfortunately, is getting worse, not better: Across the globe, 700,000 now die each year from such drug-resistant microbes; by 2050, according to a formidable blue-ribbon study commissioned by the UK government, that figure could well soar to 10 million, surpassing even worldwide deaths from cancer.

Antimicrobial resistance—or the rise of “Superbugs,” as the tabloids call it—is “one of the most serious threats to global health and security,” the World Health Organization warns. And make no mistake: the threat is also, largely, human-made.

Before I get to our culpability on this front, let’s start with nature’s. The problem, in a nutshell, is the superfast division speed of most bacteria, which leads inevitably to a revved up process of evolution. Under the right circumstances, a single E. colibacterium, for instance, can divide into a 2,097,152–strong colony in a mere seven hours—and with each division comes the potential for mutation and adaptation, particularly if these organisms are exposed to strong selective pressures.

That’s where we come in. We mortals help push that fast evolutionary process into warp speed in at least two ways. First, we do it through our long practice of overprescribing and inappropriately prescribing antibiotics to patients. These ineffective treatments often leave in their wake surviving microbes that develop resistance to the drugs used and then pass along those adaptations to subsequent generations. As the saying goes: “Whatever doesn’t kill you, makes you stronger.” (To see how feverishly fast resistant strains can emerge, see this scary timeline.)

Secondly, we egg on evolution through another insidious process: routinely giving sub-therapeutic antibiotics to livestock—something that the agriculture industry has been doing for nearly eight decades, or since the age of antibiotics began in the 1940s.

How we came to do this is a twisting tale that science writer Maryn McKenna elegantly unspools in her extraordinary new book, Big Chicken: The Incredible Story of How Antibiotics Created Modern Agriculture and Changed the Way the World Eats, which was published in September.

“At this moment, most meat animals, across most of the planet, are raised with the assistance of doses of antibiotics on most days of their lives: 63,151 tons of antibiotics per year,” McKenna writes. Farmers began to use the drugs when they discovered that it helped “convert feed to tasty muscle more efficiently.” The drugs, which could be administered in both feed and water, helped shield the livestock from disease, which also allowed farmers to pack more animals into barns and transformed old-fashioned agriculture into its modern industrialized form.

Once resistant bacteria are in the gut of an animal, then one of several things happens, McKenna says: When the animal is taken to the slaughterhouse, the mutated microbes in their digestive tracts can sometimes “get splashed on the meat.” And then, those resistant bacteria on the meat might either be consumed directly or be carried into a home or restaurant kitchen, where they might also contaminate a counter, cutting board, or other food. Eventually, they can infect people.

“That’s one pathway,” she says. “Another is when those gut contents, those resistant bacteria, exit the animal through manure.” That waste can dry up, leaving its bacteria-strewn dust to be blown away by the wind, or it can seep into groundwater, or be sprayed as fertilizer onto other fields. “So in a variety of ways,” she says, “these resistant bacteria make their way into the environment and they can then migrate to people in that manner. Or more troubling, the genes that they contain—the genes that control those processes of becoming resistant—can break free of the bacteria and be taken up by other bacteria. It’s a choose-your-own-adventure set of pathways.”

While it’s no longer legal in either the United States or in Europe to use antibiotics for “growth promotion” of livestock, farmers can still rely on them to prevent or control disease in a flock or herd. And herein lies a very broad and “mushy middle,” says McKenna, with the effect, in many cases, being the same: “It’s still using smaller-than-treatment doses, or sub-therapeutic doses of antibiotics,” which creates a literal breeding ground for resistant microbial strains. “If we did that in humans, we would call it inappropriate,” she says with understatement.

On Tuesday, the WHO issued a report calling for the end to the routine use of antibiotics in food-producing animals, which was accompanied by a fresh analysis of the dangers of this practice in The Lancet Planetary Health. (Also worth reading.)

The U.S. Department of Agriculture responded with a press release of its own, stating: “The WHO guidelines are not in alignment with U.S. policy and are not supported by sound science.” You can read the agency’s full statement here and decide for yourself. Part of their criticism is that some of the World Health Organization’s recommendations are supported by what the WHO itself terms “low-quality evidence.”

I called the USDA looking for a more thorough explanation than what’s provided here. But no one at the department was able to speak to me on the record.