  If bacteria can exchange information between different species, then a Salmonella Typhimurium carrying resistance to five common antibiotics is a formidable addition to the microbial mix in any gut. Such a Salmonella subtype exists, both in England and in several locations across the United States, including the Pacific Northwest. Salmonella Typhimurium DT104 is the particularly virulent strain in question. On both continents, it went from rare to common in six years. Salmonella Typhimurium is able to infect many animal species, though humans and cattle are the two of most concern. The increase in the resistant subtype occurred in both of these species at the same time. When this is considered along with the concurrent development on two continents, it raises an interesting question. "How did the same subtype emerge in different species and in different places at essentially the same time?" asks Tom Besser of the Washington Animal Disease Diagnostic Lab at WSU. Part of the question was relatively easy to answer, for in both geographic locations, people who worked with cattle were more likely to have the DT104 subtype than those who didn't. In the Northwest, for example, exposure to livestock meant a six to eight times increased likelihood. Besser's work with DT104 began after co-worker Clive Gay spent a sabbatical year in England during the rise of DT104 there. When Gay returned, he asked Besser to determine whether DT104 had arisen here. Together, Gay and Besser analyzed a bank of frozen samples and found the answer was "Yes." Infection with Salmonella Typhimurium causes diarrhea, fever, cramping, and nausea, but is usually not life-threatening in humans. Most cases of Salmonella, like other food-borne illnesses, go unreported, for people typically attribute their symptoms to a "flu bug." This makes it more difficult to track subtypes such as DT104. Tracking the disease in cattle is harder yet, for even fewer cases of cattle disease are reported. However, Besser can get an idea of what's going on via the samples tested in the lab and the number of calls he gets from vets in the field. At this time it's hard to say what the DT104 subtype will do over time, says Besser. There's certainly precedent for subtypes emerging, becoming common, and then fading. If that's the fate of DT104, we can simply hope it does so before it passes any of its resistance information along to other bacterial species. —Mary Aegerter |