Buzz
With Halloween just around the corner, it's time to prepare for parties, parades, and of course, the usual worry about people poisoning treats. While rumors of razor blades in apples and tainted candy are baseless, one treat you should approach with extra care is the caramel apple.
Between November 2014 and February 2015, at least 35 people from 12 different states were affected by listeriosis. Nearly 90 percent of them had eaten prepackaged caramel apples before falling ill. A recent study sheds light on how this happened.
Listeriosis is caused by the bacterium Listeria monocytogenes. It primarily impacts the elderly, pregnant women, and individuals with weakened immune systems, but in rare cases, even healthy people can be affected. Early signs of listeriosis include fever, muscle aches, and diarrhea, with the infection often spreading beyond the gut to other parts of the body.
Once listeriosis spreads, it can be fatal. Of the 35 individuals affected by the outbreak last winter, all but one required hospitalization, and seven died, at least three directly from the infection. In response to the alarming news, three prepackaged caramel apple brands and one apple producer recalled their products.
The source of the bacteria's introduction into the apples was initially a mystery. Normally, caramel is too thick, and apples too acidic for bacteria to thrive. However, a study published this week in mBio by researchers from the University of Wisconsin-Madison's Food Research Institute identified two key conditions that led to the outbreak.
Bacteria that lands on the apple's skin usually faces an obstacle. However, when a stick is inserted, it breaks the skin and forms a small pool of juice on the surface. Coating that sugary pool with caramel creates an ideal breeding ground for bacteria.
The researchers discovered that temperature significantly affects bacterial growth. They tested caramel apples with and without sticks, swabbing them with Listeria bacteria. Half of the apples were refrigerated, and the other half were left at room temperature. After three days, bacterial growth on apples with sticks at room temperature had increased by 1,000 times. Apples with sticks kept in the fridge resisted bacteria for a week before succumbing. No bacteria grew on the chilled apples without sticks.
