A Pennsylvania woman developed a urinary tract infection cased by Escherichia coli bacteria that were found to be resistant to colistin, an antibiotic that is seen as the last line of defense. Nature's Geometry/Science Source hide caption

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An employee of the drug company Apotex, examines some Ciprofloxacin at the plant in Canada. Cipro is commonly given to travelers for diarrhea. More than 20 million Cipro doses are prescribed each year in the U.S. Getty Images hide caption

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Yonta, 6, rests with her sister Montra, 3, and brother Leakhena, 4 months, under a mosquito net in the Pailin province of Cambodia — an epicenter of drug-resistant malaria. Paula Bronstein/Getty Images hide caption

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