Salad and raw vegetables often contaminated with germs: You should pay attention to this!

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Resistant pathogens detected in finished products with lettuce
Raw food and salads are healthy and important for a balanced and low-calorie diet. Many manufacturers now offer “salad to go”. The healthy fast food variant offers a healthier alternative to many other ready meals in the form of ready-to-serve slices, packaged and portioned dressings. Unfortunately, a recent study found that these products often contain germs – some with antibiotic resistance. What are the health hazards of these products and who should avoid them? A team of experts will explain!

A research team led by Professor Dr. Kornelia Smalla of the Julius Kühn Institute (JKI) investigated the germ load in finished products with lettuce that are consumed unheated. It has often been found that such products can be contaminated with hygiene-relevant germs. The researchers got to the bottom of this finding and looked at the risks posed by salad germs. The team describes the results as worrying. Not only pathogenic germs were found – among the detected pathogens were also antibiotic-resistant bacterial strains. The study was recently published in the journal “mBio” of the American Society for Microbiology.

Are finished fresh products a health risk?
It has long been known that antibiotic-resistant bacteria are found in liquid manure, sewage sludge, soil and water. The JKI team has now shown that such germs can also be found in unheated finished products. Finished raw food products and salads are particularly affected. Based on these findings, the Federal Institute for Risk Assessment (BfR) recently issued a warning message aimed at clarifying the correct handling of such products.

Which salads were examined?
Professor Smalla’s working group investigated several mixed ready-made salads, packaged rocket salads and coriander from various supermarkets. The intestinal germ Escherichia coli was found in many products. This coli bacterium has numerous pathogenic strains and is more often the cause of severe infectious diseases with diarrhoea as a leading symptom – such as EHEC. According to the research team, the bacteria found included a considerable variety of bacterial strains with resistance genes.

How do resistant intestinal germs get into vegetables?
The JKI researchers explain that antibiotics containing tetracycline are often used in livestock breeding. The constant use of antibiotics promotes the development of resistance in the intestinal bacteria of animals. The increasingly resistant germs are excreted by the animals and thus get into the liquid manure. This in turn is used to fertilize the plants that are used for ready-to-eat salads.

Salad germs can pass on their resistance to human intestinal germs.
According to Smalla, the resistant plasmids found in the pathogens are of particular concern. These are genes that bacteria can pass on to other strains. This process is called horizontal gene transfer. There is a danger that plasmids of resistant germs will transfer their resistance to other pathogens in the human intestine.

Federal Institute explains how to handle plasmids correctly
“In general, consumers should wash raw vegetables, leaf salads and fresh herbs thoroughly with drinking water before eating them in order to minimise the risk of the absorption of pathogens or antibiotic-resistant bacteria,” explains the Federal Institute for Risk Assessment in a press release.

These persons should better do without finished fresh products
“Pregnant women and persons whose immune system is weakened by old age, pre-existing conditions or taking medication should avoid eating pre-cut and packaged salads as a precaution to protect themselves from food-borne infections,” recommends the Federal Institute for Risk Assessment. Naturally one should not do therefore generally without salad. It is better to prepare salads yourself from fresh and thoroughly washed ingredients.

People with a weak immune system should be particularly careful.
However, not all germs could be removed by washing alone. “Particularly immunocompromised persons should heat vegetables and fresh herbs sufficiently before consumption, according to the instructions of their attending physicians,” according to the Federal Institute. At least a temperature of 70 degrees Celsius must be reached inside the food over a period of two minutes, so that all germs are killed. (vb)

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