Around 23 people have died from a nationwide cantaloupe listeria outbreak that began in late September. A team of University of Idaho students have designed a way to test for the deadly bacteria for an international competition.
The Waste-Management Education and Research Consortium’s contest challenged collegiate teams to create an apparatus that would wash melons with clean water and then test for microbial content.
“At first we really didn’t know how to tackle it … it’s an interesting project that’s never been done before, so there’s not that much research that we could look up and refer to, so we had to go our own way,” said Karina Intan, UI student.
“We thought about a couple of different methods. One of the two prominent ones were using a Magnasonic water bath, just like a jewelry cleaner, and another one was a golf ball washer.”
To test for bacteria in the water, the cantaloupe needed to be undamaged by the cleaning device. The team decided to make a large golf-ball washer from 8-inch-diameter PVC pipe. The device holds a cantaloupe in place, but is able to rotate it against a wraparound brush.
Intan said they exposed test cantaloupes to UV radiation for an hour to kill all the existing bacteria on the skin, then dropped a known amount of E. coli onto the melon. After washing, they grew cultures from the captured water. Intan said they recovered about 85 percent of the bacteria with seven minutes of brushing.
“It was to find a device that could detect bacterial contamination early, so that the cantaloupes don’t go out to shipment and affect a lot of people,” Intan said. “With our prototype — with our apparatus — it doesn’t use a lot of space, it’s very simple. It’s very accurate.”
The bacteria that has caused the recent deaths, listeria monocytogenes, can survive in refrigeration, is tolerant to heat, resistant to low pH and found in some fermented products, said Gulhan Unlu, UI associate professor of food microbiology and biotechnology.
Unlu said listeria has been found in almost all kinds of food, and the best precaution is to discard fruit with broken skin and to carefully wash all produce with running water, making sure to rub the fruit’s surface.
When a person is infected with listeria, it multiplies in the intestines, then migrates into the body’s cells, cloaking its presence from the immune system inside vacuoles, Unlu said.
“This organism makes people sick slowly,” Unlu said. “And depending on the person, you know, we are talking about five to eight weeks after consumption of the cantaloupe or another other suspect food. So just because you ate your cantaloupe today, and then tomorrow you feel good, that doesn’t mean you are free of listeria.”
In healthy people, the infection feels like a flu, with symptoms lasting about a week. In weakened victims, the infection can be life threatening, and in pregnant women, the bacteria can cross a placenta and cause meningitis in the child.
David Hylsky, an epidemiologist with Idaho Health District No. 1, said the long incubation time makes a listeria outbreak, once detected through a blood test, hard to track.
“People really don’t test for this unless someone gets, you know, pretty sick,” Hylsky said. “It’s gotten into the bloodstream and causing the really high fevers, inflammation.”
When a case is reported, the health department is notified.
“Then we contact the ill patient, and we go through our epidemiology investigation forms,” Hylsky said. “And we go through and ask them all sorts of questions, you know, ‘What foods?’ ‘Where have you been traveling?’ ‘Anybody else in the household ill?’ We call it getting a food history on these individuals.”
Hylsky said they go back as far as they can, sometimes only a week, sometimes 10 days.
“We try to get the most complete information we can,” Hylsky said. “It is an investigation.”
The epidemiology department compares the lists as the cases come in and watches for any connections, Hylsky said.
“As we review each case, we look down and see that it looks like they all ate these cantaloupes from this one firm, and that sends the signal out that this very well could be the source,” Hylsky said.
They trace the food back to the store, from the store to the distributer, and finally to the farm.
“Each case is very time-consuming and each one’s different,” Hylsky said. “It takes a lot of time to track down where these food sources come from.”
When the UI team was testing its device in March, another outbreak was just beginning.
“We got our cantaloupes from Costco,” Intan said. “And one of those times we unknowingly tested one of those contaminated cantaloupes. It was obviously a different strain than the bacteria we were working with, so when we plated the results of those cantaloupes on the plates, we saw that there was a different type of colony.”
Intan said they thought they had contaminated the melon in their handling.
“About a month after we had written our formal report, Del Monte (Foods) came out with a public statement saying they were recalling the cantaloupes we had just bought,” Intan said. “So we were like, ‘Cool, we found contamination on your cantaloupes, and you don’t want to talk to us, even though we have this really cool product that could save you.’ Politics – right?”