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White DG, Zhao S, Sudler R, et al
Despite emphasizing prevention through appropriate food handling and food preparation, public health authorities have continued to see rising rates of Salmonella and other food-borne infection.[1] Even more alarming has been the arrival of Salmonella enterica serotype typhimurium DT104, a highly resistant strain defying some traditional antibiotic regimens.[2,3] Although processed foods would clearly appear to be the source, the extent and potential cause of the problem is ill defined. The current investigators from the Food and Drug Administration and the University of Maryland provide data indicating that resistant Salmonella are indeed in the food chain, and also provide indirect evidence attributing it to use of antibiotics in animals.
The authors cultured a total of 200 samples of ground chicken, turkey, pork, and beef from 3 supermarkets in the Washington, DC, metropolitan area. Using conventional microbiological methods, they identified 41 (20%) samples with Salmonella, including 4 samples with 2 different strains. As expected, chicken (35%) and turkey (24%) were more commonly contaminated than pork (16%) or beef (6%). A total of 13 serotypes were represented, with S enterica Istanbul (28%), S enterica agona (22%), and S enterica typhimurium (18%) most notable. Resistance was found to at least 1 antibiotic in 84% of isolates, but most disturbing was the identification of 5 agona isolates resistant to ceftriaxone, 6 Istanbul isolates resistant to sulfamethoxazole, and 7 of 8 typhimurium isolates resistant to at least 5 antibiotics. These included 5 highly resistant DT104 and 2 DT208 isolates. Four DT104 isolates showed identical pulsed-field gel electrophoretic patterns, and the 2 DT208 isolates were closely related.
The resistant agona and DT208 isolates were recovered from different meats at the same store over a 2-week period that came from different grinding facilities. This suggested to the investigators that the source was the meat itself.
The link to animals given antibiotics was the discovery that the 5 agona and the 2 DT208 isolates possessed an integron containing a specific beta-lactamase gene blaCMY-2. This gene, which confers resistance to both ceftiofur and ceftriaxone, has been found in animals fed ceftiofur.[2-4]
Though not the "smoking gun" that the accompanying editorial[5] so graphically portrays, this paper provides one more piece of evidence that there is a significant problem in our food. Can we ever expect everyone to handle and prepare food with complete safety? Probably not. The question is which is costlier, antibiotic-free food or widespread plasmid-mediated resistance? It would appear to be due time to find another way to have a chicken in every pot without antibiotics as flavoring.
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