The researchers found that 6.8 percent of samples taken from 15 delis tested positive for listeria. In a second sample, 9.5 percent of samples taken from 30 delis tested positive for listeria.
Lead researcher Haley Oliver said, “This is a public health challenge. These data suggest that failure to thoroughly execute cleaning and sanitation protocols is allowing L. monocytogenes to persist in some stores. We can’t in good conscience tell people with weak immune systems that it is safe to eat at the deli.
If a healthy individual consumes listeria bacteria, they will experience food poisoning, but if a person with a compromised immune system or a pregnant woman does, the consequences could be fatal or cause problems in the fetus. Deli meats are commonly associated with listeria, which can also grow in the refrigerator – unlike other bacteria like salmonella and E.coli.
Oliver explained, “It’s kind of the Wild West. Manufacturing has a zero-tolerance policy for listeria, but that dissipates at the retail level. The challenge of developing systematic cleaning procedures for a wide variety of delis – which are less restricted environments than processing plants – can make listeria harder to control. The prevalence of L. monocytogenes is higher than we expected in a significant percentage of delis, and the bacteria is persisting in these delis over time.”
Most of the samples that tested positive for listeria were areas that don’t even come into contact with food – floors, drains, squeegees, and the like.
Oliver stressed that the difficulty with listeria, along with other types of bacteria that cause food poisoning, is that it doesn’t change the characteristics of the food products. For example, food won’t smell bad if it is infected with bacteria, so there aren’t sure signs indicating that it’s been infected. This is why it is so important to keep up proper sanitization and follow the protocol to ensure the risk of contamination and outbreak is low.
Bacterial infection risk higher in food exposed to light
The risk of bacterial infection in food is higher if it has been exposed to light. Researchers found that listeria activates its defense mechanisms as a reaction to light. Such a discovery can help the food industry prevent future listeria outbreaks.
Researchers also found two new molecules that can be used to combat listeria and hence prevent infection.
Lead researcher Chrisopher Andersson said, “Hopefully, this new knowledge on how light and these small molecules affect the bacterium can, in future, be used to prevent the spread of listeria and help treat listeriosis.”