Unnecessarily large antibiotic doses allow resistant strains to overgrow susceptible ones. If resistant strains spread to other patients, a superinfection occurs. Drug companies promote antibiotics, patients pressure doctors for quick cures, doctors prescribe instead of running costly tests, patients don't finish antibiotics. Antibiotics are available over the counter in developing countries, allowing for overuse and incorrect use. Antibiotic use is widespread in livestock feeds; they can be transmitted to humans through meat consumption. Bacterial cells can pass resistance genes to other bacterial cells.