In recent years, the demand for organic fruits and vegetables has surged as concerns have been rising about the excessive use of toxic fertilizers and pesticides in farmlands. In 2020, the sales of organic fruits and vegetables rose by 12.5% in the US, and for the first time, it crossed the mark of $60 billion globally. But organic vegetables may have some problems of their own.

A new study from researchers at Valencia Polytechnic University (UPV) in Spain highlights that organic leafy vegetables can carry harmful bacteria that pose a risk to human health. 

The study was recently presented at the 32nd European Congress of Clinical Microbiology & Infectious Diseases (ECCMID) and reports that organic vegetables are home to unicellular organisms like free-living amoeba (FLA) that mostly eat bacteria and don’t generally cause disease. However, some of these bacteria species which are pathogenic may enter the human body via the amoeba (after evading their digestion by the FLA) and cause various health problems. 

“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,” said Dr. Yolanda Moreno, lead researcher, senior lab technician, and contractor professor at UPV.

Organic vegetables are susceptible to contamination from ground

We’ve previously covered the numerous benefits of an organic diet and also how sometimes market players misrepresent these benefits to attract more buyers and increase their sales. For instance, a common belief promoted by organic food sellers is that organic edibles are always healthier than their conventional alternatives, which is not entirely true — at least not always. In 2012,  a systematic review of 240 studies concerning the nutritional content of organic food was published in the journal Annals of Internal Medicine, finding a complex picture that is not always straightforward.

The review highlighted that although compared to conventionally grown vegetables, organic food items are less likely to have pesticide residues, there is no strong evidence that suggests that the latter have higher nutritional value than the former. The recent UPV study has gone one step further by revealing that similar to conventional vegetables, organic produce can also lead to health risks. However, the degree and type of health risks may vary.

Dr. Moreno and her team wanted to detect the types of bacteria the FLAs were carrying on leafy green vegetables. So they visited a local supermarket in Valencia and collected organic vegetables such as spinach and lettuce as samples for their study. A total of 17 samples were collected between November 2021 and May 2021 and then, using a metagenomic analysis (study of nucleotide sequences isolated from microbes), the researchers detected the different bacterial strains present inside the FLAs.

Harmless bacteria like Pseudomonas and Flavobacterium were found in most of the samples. However, some of the findings were more striking. In total, the researchers also detected 52 types of disease-causing bacteria (such as Salmonella, Arcobacter, and Legionella) in one-third of the samples. The identified bacteria are capable of causing typhoid fever, diarrhea, endocarditis, pneumonia, and various other serious ailments in humans. 

The researchers also revealed the presence of Acanthamoeba castellanii in 63% of the samples. Acanthamoeba is an FLA that houses bacterium which can promote blindness and encephalitis in humans. 

When asked about how the organic vegetables get contaminated, Dr. Moreno explained:

“Contamination can arise as a consequence of treating the soil with organic fertilizers such as manure and sewage sludge and from irrigation water.” He further added that as compared to conventionally produced edibles, “leafy greens are particularly susceptible to fecal contamination due to their proximity to the ground and the likelihood of humans consuming them without cooking.”

Dr. Moreno and her colleagues highlight that more research is required to understand the “microbiological quality and safety” of organically grown vegetables. Moreover, since people in general, don’t know much about the health implication of organic food, such studies hold great importance as they can also spread awareness on how organic vegetables should be handled before consumption. 

“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 researcher concludes.