Case Studies: Food Poisoning and Antibiotic Resistance

Food poisoning from pathogens resistant to antibiotics is becoming an increasing concern, according to two reports summarized by the Union of Concerned Scientists http://www.ucsusa.org. In April 1998, a 12-year-old boy in western Nebraska became ill with diarrhea, fever, and abdominal pain. The culprit was quickly identified as Salmonella and fortunately the boy fully recovered, according to an April 4, 2000 article from the New England Journal of Medicine, summarized by UCS. Laboratory analysis revealed that the bacterium was resistant to thirteen different antibiotics, including ceftriaxone (an important antibiotic for treating Salmonella infections in children) and ceftiofur (an antibiotic used for animals). One month before the boy became sick, his father, a veterinarian, had treated calves on the family farm and on three nearby farms for diarrhea. After drug-resistant Salmonella was identified in the boy, researchers turned to these animals as potential sources of his infection. Nebraska public health scientists used molecular methods to establish a connection between the Salmonella infection in the boy and the four herds of cattle. Using DNA fingerprinting tests they found that the boy and all four herds were infected with the same strain of Salmonella. The samples of Salmonella also showed similar patterns of drug resistance, with the bacterial strain on the boy's family farm having the same, rare antibiotic-resistance pattern found in the boy -- including ceftriaxone resistance. While ceftriaxone is not approved for use in cattle, the closely related and widely used drug, ceftiofur is. The development in bacteria of cross-resistance to closely related antibiotics is common. The authors (Fey, et al.) of the New England Journal of Medicine article concluded that the boy acquired the ceftriaxone-resistant Salmonella infection through contact with the infected cattle on his family farm. While they were not able to pinpoint the means of transmission, the sequence of events -- the treatment of sick cattle with antibiotics prior to the boy becoming ill -- and the molecular evidence identifying the same rare resistance pattern in the cattle and the boy strongly support their conclusion. In a separate article (also originally published in the New England Journal of Medicine http://www.nejm.org ) the UCS Antibiotic Resistance Program researchers report on a Danish study that tracked the transmission of a resistant, and deadly, strain of salmonella from two farms, a slaughter house, pork eating consumers, and, finally, to a hospital. An elderly patient who did not eat pork from the farm but who came in contact with a hospitalized patient who did was infected by the salmonella and died. A slaughter house worker who didn't eat the pork also became infected. In the past it was thought that only people who ate the contaminated food could become ill.

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