By Lisa Baertlein LOS ANGELES (Reuters) – Hamburger chain In-N-Out Burger is the newest target in a push by public health, environmental and consumer groups to convince high-profile food sellers to stop serving meat from animals fed a routine diet of antibiotics. The new campaign from CALPIRG Education Fund, Friends of the Earth, the Center for Food Safety and other public interest groups was launched amid growing concern that the overuse of such drugs is contributing to increasing numbers of life-threatening human infections from antibiotic-resistant bacteria, known as “superbugs.” Privately held In-N-Out, which has more than 300 restaurants in California, Nevada, Arizona, Utah, Texas and Oregon, is known for using fresh ingredients such as never-frozen ground beef and hand-cut french fries.