Ceftiofur-Resistant Salmonella Strains Isolated from Dairy Farms Represent Multiple Widely Distributed Subtypes That Evolved by Independent Horizontal Gene Transfer

CSREES, USDA, under NYC-478862 and National research Initiative Award 98-35201-6211 (to L. W.). ILSI Future Leader Award (to M.W.). National Institute of Allergy and Infectious Diseases, National Institutes of Health, Department of Health and Human Services, under Contract No. N01-AI-30028.