By Jonathan Lambert What does dry soil, like this stretch in South Africa, have to do with antimicrobial resistance? A new study offers an unexpected hypothesis: drought can drive higher antibiotic resistance in soil bacteria. Rodger Bosch/AFP/via Getty Images hide caption It's one of the highest-stakes battles on earth: bacteria versus antibiotics. And in the human realm, bacteria appear to be gaining ground. Worldwide, many antibiotics are starting to lose their bite. About 1 in 6 human infections tested in labs are resistant to antibiotics, contributing to over 4 million deaths a year. Researchers know that human use, and especially overuse, have given bacteria opportunities to develop resistance. But antibiotics, and resistance to them, are much older than the pills we pop for infections. Both are the product of one of the longest-running battles on Earth, playing out in soil. "In nature, organisms are duking it out, it's a competitive environment," says Dianne Newman, a microbiologist at Cal Tech.…