科学美国人60秒:Rain and Irrigation Can Make Crops Temporary Bacteria Farms

In 2011 a 28-state outbreak of Listeria from cantaloupes infected 147 people—and 33 of them died. After that, many Americans evidently thought twice about bringing one of the melons home—cantaloupe consumption dropped by half after the infections. But paying closer attention to the ecology of our fields—like tracking when they've been rained on—could be a step toward beating bacteria, and preventing that sort of food poisoning. So says a study in the journal Applied and Environmental Microbiology. [Daniel Weller et al, Spatial and temporal factors associated with an increased prevalence of Listeria monocytogenes in New York State spinach fields]

Researchers monitored spinach fields in New York State, both before and after irrigation and rain. And they found that levels of Listeria bacteria in the soil spiked in the 24 hours after water hit the field—up to 25 times the levels that were present a week after the rain. 

The scientists cite two factors. Listeria is exceedingly common in the environment—from the soils of national parks to, yes, irrigation water. So Listeria could be getting dumped directly on fields during irrigation. But rain also creates more favorable conditions for a bacterial bloom—and that holds for any type of bacteria present in the soil, the researchers say—whether Salmonella, E. coli or the Listeria studied here.

The lesson for farmers, they say? Hold off on harvesting after rains or watering. And if you can't wait—consider rinsing the fruits or veggies after they come off the field. The researchers are developing a web app that'll help farmers forecast bacterial loads in their fields—to make sure that the only thing that makes it farm to table is your food, and not infections.

—Christopher Intagliata