Organic apples hang from trees in an orchard in Forest Range, Adelaide Hills, South Australia. donkeycart/via Flickr hide caption

itoggle caption donkeycart/via Flickr

Klebsiella pneumoniae, seen here with an electron microscope, are the most common superbugs causing highly drug-resistant infections in hospitals. Kwangshin Kim/Science Source hide caption

itoggle caption Kwangshin Kim/Science Source

Giancario Gemignani-Hernandez, 2, of Pittsburgh has his ear examined by Dr. Alejandro Hoberman. Gene J. Puskar/AP hide caption

itoggle caption Gene J. Puskar/AP

Clostridium difficile bacteria produce a toxin that damages the intestine and causes severe diarrhea. Courtesy of David Goudling/Nature Genetics. hide caption

itoggle caption Courtesy of David Goudling/Nature Genetics.

Childhood obesity is on the rise in many countries and overuse of antibiotics is now on the radar as a possible factor in the epidemic. Here 18-month-old twins are weighed in a nutritionist's office in Colombia. Raul Arboleda/AFP/Getty Images hide caption

itoggle caption Raul Arboleda/AFP/Getty Images

The FDA's latest effort to end the use of antibiotics as growth promoters in animals is getting mixed reviews from activists. Rob Carr/AP hide caption

itoggle caption Rob Carr/AP

Pigs take a mud bath at the De Jofrahoeve pig farm in Esch, Netherlands. Dutch farmers treat their animals with almost three times the antibiotics that their Danish neighbors use. Robin Utrecht/AFP/Getty Images hide caption

itoggle caption Robin Utrecht/AFP/Getty Images

Many livestock groups say there's no evidence that antibiotics in livestock feed have caused a human health problem, but researchers beg to differ. Scott Olson/Getty Images hide caption

itoggle caption Scott Olson/Getty Images