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article imageListeria monocytogenes contamination of salad now less common

By Tim Sandle     Mar 3, 2015 in Food
Refrigerated foods, like salads, are at risk from Listeria monocytogenes contamination. While the bacterium remains a risk, a new survey suggests that antibiotic resistant strains are less common.
Listeria monocytogenes causes the infection listeriosis. The biggest risk is with meningitis in newborns. For this reason, pregnant mothers are often advised not to eat soft cheeses. The bacteirum can also be present in raw (unpasteurized) milk. The microbe can also live in food processing plants, where it poses a risk due to its ability to grow at low temperatures.
As with many types of pathogenic bacteria, antibiotic resistance is a growing problem. This limits the options of medics to treat an infection. To investigate antibiotic-resistant strains L. monocytogenes in unprocessed salad products, a team of scientists undertook sampling of processed salad products purchased from Malaysia. These products are imported into many countries.
For the study, various samples were taken from salad products and the isolated bacteria subjected to molecular identification methods. This enabled a genetic profile of any microorganisms to be made. Once the different strains of Listeria had been found, the scientists tested 14 different antibiotics against the isolates.
The results of the survey were that antibiotic resistant L. monocytogenes contamination is as widespread as earlier studies had suggested (that is, the bacterium is a common food poisoning organism.) Here, the results showed that most food products contained a low level of L. monocytogenes. However, of these isolates, four fifths were not of a type resistant to common antibiotics. This means that should someone become infected with the bacterium, in 80 percent of cases the infection should be treatable with commonly available antibiotics.
Nonetheless, the number of strains resistant to antibiotics is of concern and scientists are keen to continue to track these strains to see if they increase in number. In terms of origins, it is likely that the antibiotic resistant strains originated from farms, where some outdated farming practices administer antibiotics to farm animals in order to boost the quality of the meat.
The results of the survey have been published in the International Journal of Food Safety, Nutrition and Public Health. The article is titled “Characterisation of L. monocytogenes strains isolated from salad vegetables.”
More about Salad, Listeria, Listeria monocytogenes, Listerosis, Vegetables
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