David G. White, Ph.D., Shaohua Zhao, D.V.M., Ph.D., Robert Sudler, M.S., Sherry Ayers, Sharon Friedman, B.A., Sheng Chen, D.V.M., Patrick F. McDermott, Ph.D., Shawn McDermott, B.S., David D. Wagner, Ph.D., and Jianghong Meng, D.V.M., Ph.D.
ABSTRACT
Background
Salmonella is a leading cause of food-borne illness. The emergence of
antimicrobial-resistant salmonella is associated with the use of antibiotics in
animals raised for food; resistant bacteria can be transmitted to humans through
foods, particularly those of animal origin. We identified and characterized
strains of salmonella isolated from ground meats purchased in the Washington,
D.C., area.
Methods
Salmonella was isolated from samples of ground chicken, beef, turkey, and
pork purchased at three supermarkets. The isolates were characterized by
serotyping, antimicrobial-susceptibility testing, phage typing, and pulsed-field
gel electrophoresis. The polymerase chain reaction and DNA sequencing were used
to identify resistance integrons and extended spectrum -lactamase genes.
Results
Of 200 meat samples, 41 (20 percent) contained salmonella, with a total of
13 serotypes. Eighty-four percent of the isolates were resistant to at least one
antibiotic, and 53 percent were resistant to at least three antibiotics. Sixteen
percent of the isolates were resistant to ceftriaxone, the drug of choice for
treating salmonellosis in children. Bacteriophage typing identified four
isolates of Salmonella enterica serotype typhimurium definitive type 104
(DT104), one of DT104b, and two of DT208. Five isolates of S. enterica serotype
agona had resistance to 9 antibiotics, and the two isolates of serotype
typhimurium DT208 were resistant to 12 antibiotics. Electrophoretic patterns of
DNA that were indistinguishable from one another were repeatedly found in
isolates from different meat samples and different stores. Eighteen isolates,
representing four serotypes, had integrons with genes conferring resistance to
aminoglycosides, sulfonamides, trimethoprim, and -lactams.
Conclusions
Resistant strains of salmonella are common in retail ground meats. These
findings provide support for the adoption of guidelines for the prudent use of
antibiotics in food animals and for a reduction in the number of pathogens
present on farms and in slaughterhouses. National surveillance for
antimicrobial-resistant salmonella should be extended to include retail meats.
Source Information
From the Division of Animal and Food Microbiology Office of Research, Center for Veterinary Medicine, Food and Drug Administration, Laurel, Md. (D.G.W., S.Z., S.A., S.F., P.F.M., S.M., D.D.W.); and the Department of Nutrition and Food Science, University of Maryland, College Park (R.S., S.C., J.M.).
Address reprint requests to Dr. Meng at the Department of Nutrition and Food Science, University of Maryland, College Park, MD 20742, or at jm332@umail.umd.edu
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