WASHINGTON (Reuters) - The Food and Drug Administration on Thursday banned the use of a poultry antibiotic made by Bayer, an unprecedented action aimed at preventing the rise of drug-resistant germs that infect people.The FDA, which first proposed the ban five years ago, said the use of the drug, Baytril, in chickens has made it difficult for doctors to treat human patients with food poisoning. The drug was sometimes used by farmers to treat entire poultry flocks when a few birds showed signs of respiratory disease.