A rough skinned melon does not seem to be a likely suspect in causing illness, but cantaloupe is the current host for one of the most deadly food borne illnesses, caused by bacteria called Listeria monocytogenes.
“It’s the first time ever, in the U.S. that there has been an outbreak of listeriosis from cantaloupe,” said Aubrey Mendonca, an associate professor of food science at Iowa State U.
While the media has been covering the cantaloupe-listeria outbreak, it is important to remember that listeria can be found in everything, not just cantaloupe.
“Cantaloupe is not hiding in the dark, waiting for you,” said James Dickson, ISU professor of animal science. Foods such as deli meat, coleslaw, unpasteurized milk and many other foods can contain it, but it is only dangerous when there is a large amount of the bacteria present.
“Listeria is an environmental organism, and it is found literally everywhere. We could probably vacuum this carpet and find it,” Dickson said.
Mendonca said furthered, “It’s widespread in nature. It lives in the soil, and decaying vegetation. And it could be carried in the intestines of animals.”
Although listeria can be found everywhere in nature, people should not obsess or worry over it.
There must be a large amount of listeria bacteria within the food to cause infection.
“Normally it’s not a problem, unless it gets into a certain environment,” Dickson said.
“The people who get sick from listeria are, first off, those who have some type of compromised immune system, which, in our society, tends to be the elderly, the people on chemotherapy for cancer, [and] people that have some long-term chronic illness. Normal, healthy people don’t get listeria,” Dickson said.
“Even pregnant women are at risk,” Mendonca said. “What nature does [is] it suppresses the women’s immune system a little bit to prevent rejection of the fetus. So listeria mostly affects pregnant women, the very young, the elderly and other immune-suppressed persons.
“[But] healthy people have probably been ingesting this all their lives and not realized it,” Mendonca said.
But for those who are infected, it can be deadly.
“It’s hard to diagnose,” Mendonca said, who said listeriosis mimics the symptoms of the flu. “You really feel like you’re getting a flu.”
Another reason it’s so deadly is because of the bacteria itself.
“In the patients that are susceptible, listeria has the ability to avoid the immune system,” Dickson said.
“Somehow listeria learned how to live in white cells,” Mendonca said.
By hiding in the white blood cells, the anti-bodies can’t latch on to it to draw the attention of the white blood cells, which would eat it. “It’s always a fight or a race between the organism and our immune system,” Mendonca said.
The listeria bacterium, according to Mendonca, can be considered unique. “Listeria monocytogenes is one of few human-enteric pathogens that can grow at refrigeration temperatures.” Not only can it survive in a refrigeration setting, listeria grows well at human temperatures — about 37 degrees Celsius.
“It’s really unusual to have an organism that can grow across such an extreme spread in temperature, from the refrigerator to the human body,” Dickson said.
A listeria bacterium can multiply fairly quickly within food products, such as fruits.
“Listeria can come up before the mold grows,” Mendonca said.
The bacterium that gets on the cantaloupes’s skin can be much harder to wash off because of the rough surface.
“The inside of a cantaloupe should be free [of listeria], unless the skin is damaged,” Mendonca said.
If an infected melon is cut, the bacteria can spread to the inside. If left alone for a while, the bacteria will multiply to a level where it could cause infection.