I’m sure everyone has heard of the outbreak of Escherichia coli O157:H7 infections from spinach grown in California. An outbreak is defined by the Center for Disease Control (CDC) as two or more cases of the same disease related to a common exposure. As of October 10, there have been 199 cases reported to the CDC. Of those, 31 cases involved kidney failure, 102 hospitalizations and 3 deaths. Thirteen product samples were confirmed as the same strains with “fingerprinting” (DNA patterning). As noted in an article in the Democrat and Chronicle October 15, cattle on a nearby ranch have been identified as the source of contamination. With infections in 26 states, it was likely the outbreak occurred early in the distribution chain. The recent outbreak was not the first in the central California region.
Of the more than 225 unique strains or serotypes of E. coli, why is O157:H7 so deadly? The bacterium E. coli O157:H7 binds to the human gastrointestinal tract causing bloody diarrhea in healthy individuals, with symptoms usually ending within a week. In the elderly or children, kidney failure, called Hemolytic Uremic Syndrome, may occur. Cattle are the principal reservoir for the organisms. The bacteria do not bind to their intestinal tracts as in humans. Normally, E. coli is outnumbered by anaerobic bacteria, producers of weak acids inhibitory to the growth of E. coli O157:H7. The bacterium thrives in a more acid environment as found in the ruminant gut when cattle are fed diets high in grain. The flora in the gut lower pH of the rumen, which in turn promotes further development of O157:H7. Cattle will not have any symptoms of infection, but will shed the bacteria in their feces.
James Russell, microbiologist at the US Plant, Soil and Nutrition Lab in Ithaca, NY states: “Most strains of E. coli are harmless, but pathogenic strains like O157:H7 can cause extreme illness in humans. Mature cattle are unaffected by E. coli O157:H7 and more than 30% of them are carriers for this potential deadly bacterium. E. coli O157:H7 can migrate from cattle to food and water via fecal contamination at slaughter or via manure that is used as a fertilizer. Many bacteria are killed by the low pH of the human gastric stomach, but E. coli has an extreme acid resistance that is induced by low pH and volatile fatty acids. Our research has demonstrated that it is possible to decrease the acid-resistance of E. coli via a change in cattle diets (grain to hay) immediately before slaughter.” This work was highlighted by Science Magazine and many newspapers.
This simple diet change would help reduce the potential contamination of ground beef during slaughter and processing. Beef producers have been concerned about the reduction of meat grade by changing to a forage diet in the last week.
There are several potential routes for human infection from E. coli: undercooked meat, raw milk, contamination of well water from agricultural runoff, and contamination of produce. Direct or indirect human contamination is also possible. Consumers need to be educated, but on-farm practices are critical. The FDA and the state of California anticipate the industry will develop a new comprehensive plan for spinach production in the central region. Implementation would be voluntary.
So, what do we do in New York? To start, remember Best Management Practices (BMPs) when spreading manure, especially around produce. BMPs can help prevent irrigation or ground water from becoming contaminated from manure. These include:
• Properly compost or store manure six months prior to application.
• Prevent runoff or wind drift of stored or composted manure.
• Store lagoon manure 60 days in summer, 90 days in winter prior to application.
• Apply manure in fall at the end of the growing season to warm soils that are cover-cropped. Incorporate if no cover crop.
• In the spring, spread two weeks prior to planting, preferably to a grain or forage crop. Avoid growing a root or leafy produce crop. Leafy crops are susceptible to E. coli contamination.
• Do not harvest a vegetable crop for 120 days, unless composted manure has been spread.
Return to AgFocus Page