Organic vegetables are often contaminated with harmful disease-causing bacteria, warns a new study. People who buy produce that has been treated with organic fertilisers such as manure could live to regret their choice, say scientists.
More than 50 species of potentially harmful bacteria were discovered on samples of organic spinach and lettuce. Organic fruit and vegetables are becoming increasingly popular as more people eat healthy diets and avoid pesticides, fertilisers and herbicides.
But now scientists in Spain have found they could be contaminated with harmful bacteria from human or animal sources. These are likely transferred to the vegetables during their growth, harvest, transport, processing and handling.
Vegetables in particular can contain single-celled organism's like free-living amoebae (FLA), which feed on bacteria, some of which can be extremely harmful to humans. These nasty bacteria, dubbed Trojan horses, resist the organism's digestion and present a serious threat to whoever eats them.
Dr Yolanda Moreno at the Universitat Politècnica de València said: "Food and food-related environments create an ideal meeting place for free-living amoebae and pathogenic bacteria. However, comparatively little is known about the occurrence and diversity of free-living amoebae on organic vegetables and their role in transmitting human pathogens.”
Samples of lettuce and spinach were collected from local supermarkets in Valencia between November 2020 and May 2021. A special scientific technique was then used to identify the DNA of any bacteria found inside the amoebae.
The main types of bacteria identified were Flavobacterium and Pseudomonas, which generally do not cause disease in humans. But 52 types of harmful bacteria, including Legionella, Salmonella and Arcobacter were discovered in a third of the samples.
These can cause serious diseases like pneumonia and gastrointestinal illnesses. Another species called Vermamoeba vermiformis which often causes severe infections was found in a fifth of the vegetable samples. Acanthamoeba castellanii, a bacteria capable of causing blindness and encephalitis was also recorded in almost two thirds of samples - 63 per cent.
Dr Moreno said: "The presence of bacteria of public health concern contained inside the free-living amoebae suggests that they are vehicles that can easily transmit pathogens capable of reaching humans and causing health problems through contaminated organic vegetables. Contamination can arise as a consequence of treating soil with organic fertilisers such as manure and sewage sludge and from irrigation water."
Larger studies are needed from different countries to understand more about the quality and safety of organic vegetables. Dr Moreno said: "Leafy greens are particularly susceptible to faecal contamination due to their proximity to the ground and the likelihood of humans consuming them without cooking. Our results also stress the need to educate the public on safe and proper handling of fresh organic vegetables before eating them fresh or slightly cooked.”
The findings were due to be presented at the European Congress of Clinical Microbiology & Infectious Diseases (ECCMID)in Lisbon, Portugal.
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