A Salmonella outbreak linked to cantaloupes from a farm in southwestern Indiana raises concerns about—as well as academic interest in—the vulnerability of the fruit to bacterial contamination.
The FDA announced recently that the strain of Salmonella that has sickened 178 people in 21 states likely came from cantaloupes grown at Chamberlain Farms in Owensville, Ind. The agency, which took samples at the farm in mid-August, said that they contained Salmonella typhimurium with the same “DNA fingerprint” as the strain involved in the outbreak. The agency said that test results had not yet confirmed the connection, however.
Michael Doyle, PhD, director of the Center for Food Safety at the University of Georgia in Griffin, said the Salmonella outbreak wasn’t as surprising as the less-common Listeria outbreak. But, according to Dr. Doyle, this incident reinforces our understanding of how easy it is for bacteria to take up residence inside or on the fruit, pointing to the need for improved processes that better minimize the risk.
“Frankly, it’s not surprising,” Dr. Doyle said. “Cantaloupe is an excellent growth medium for harmful microbes. That’s been shown in several lab studies.” The fruit typically has a pH level in the range of six to seven, so if a harmful microbe gets into it and the temperature is suitable—cantaloupe is typically held at room temperature—bacteria find themselves in terrific conditions for growth, he said.
Dr. Doyle said his lab is making headway in better understanding the means by which cantaloupe become contaminated.
“The question is, from an academic perspective: Are those bacteria getting into the cantaloupe, or are they residing on the surface?” he said. “My guess is that the bacteria are getting into the cantaloupe through the stem scar, and then they’re growing.”
Methods of cleaning, processing, and getting cantaloupes ready for distribution vary, but the most worrisome method—and one that is commonly used—is the “dunk tank” of water into which cantaloupes are placed for cleaning. Studies have found that there is a potentially hazardous vacuum effect when cantaloupes picked in warm conditions are dropped into a cold tank of water. This vacuum effect can cause the water from the dunk tank to be sucked in through the stem scar.
“You have to disinfect the water and keep it clean, because if there are bacteria on the surface or in the mud or whatever, it’s going to be in the dunk tank,” he said. But chlorine, he warned, might not be effective, because the presence of mud and other organic material—and even the cantaloupe surface itself—can neutralize chlorine’s effect on bacteria.