Organic vegetables regularly contaminated with disease-causing bacteria, study warns

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Lisbon, Portugal – Organic vegetables often harbor harmful, disease-causing strains of bacteria, a new study warns. Researchers from Spain say people who buy products treated with organic fertilizers like manure may regret their choice for a long time.

They discovered more than 50 types of potentially harmful bacteria on samples of organic spinach and lettuce. Organic fruits and vegetables are growing in popularity as more and more people switch to a fully organic diet to avoid pesticides, fertilizers and herbicides.

Unfortunately, the team notes that these foods could instead be contaminated with harmful bacteria from human or animal sources. These are likely to be transferred to vegetables during growth, harvesting, transportation, processing and handling.

Vegetables, in particular, can contain unicellular organisms such as free-living amoebas (FLA) that feed on bacteria. Some can be extremely harmful to humans. These nasty bacteria, called Trojan horses, resist the body’s digestion and pose a serious threat to anyone who eats them.

Food and food-related environments create an ideal meeting place for free-living amoebas and pathogenic bacteria,” says Dr. Yolanda Moreno from the Universitat Politècnica de València in a press release.

“However, comparatively little is known about the occurrence and diversity of free-living amoebas on organic vegetables and their role in the transmission of human pathogens.”

What is hidden in your organic products?

The team collected samples of lettuce and spinach from local supermarkets in Valencia between November 2020 and May 2021. They then used a special scientific technique to identify the DNA of all the bacteria found in the amoebas. The main bacterial species identified were Flavobacterium and Pseudomonas, which do not generally cause disease in humans.

However, in a third of the samples, they found 52 types of harmful bacteria, including Legionella, Salmonella and Arcobacter. These strains can cause serious illnesses such as pneumonia and gastrointestinal disorders.

Called another species Vermamoeba vermiformis which often cause serious infections were hiding in a fifth of the vegetable samples. Researchers found Acanthamoeba castellaniia bacterium that can cause blindness and encephalitis, in nearly two-thirds of the samples (63%).

“The presence of bacteria of health importance contained in the free-living amoebas suggests that they are vehicles that can easily transmit pathogens that can reach humans and cause health problems through contaminated organic vegetables,” says dr Moreno.

“Contamination can result from treating the soil with organic fertilizers such as manure and sewage sludge, as well as from irrigation water.”

Studies conducted in different countries are still needed to learn more about the quality and safety of organic vegetables worldwide.

“Leafy greens are particularly susceptible to fecal contamination due to their proximity to the ground and the likelihood of people consuming them uncooked,” concludes Dr. Moreno. “Our findings also emphasize the need to educate the public about the safe and proper handling of fresh organic vegetables before they are consumed fresh or lightly cooked.”

Researchers presented their results at the 32nd European Congress of Clinical Microbiology and Infectious Diseases (ECCMID) in Lisbon, Portugal.

Tom Campbell, author for the South West News Service, contributed to this report.

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