Farming practices examined | Study finds a diverse group of bacteria on fruit and vegetables, but most are beneficial
LINDELL BEACH, B.C. — Recent research has found that fruit and vegetables carry a diverse range of bacteria on their surfaces.
It is well known that produce can harbor bacterial populations, such as harmful E. coli and salmonella, but this is the first study to look at the diversity of non-pathogenic bacterial communities. These communities of microbes vary depending on the type of produce, farming methods, storage and transportation.
“We were not looking at pathogens but bacteria in general,” said research associate Jonathan Leff with the Fierer Lab Group at the University of Colorado, Boulder.
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“The vast majority of bacteria on fruits and vegetables are probably beneficial to you. The study was very preliminary as we didn’t know a lot about the majority of bacteria on fruits and vegetables across a wide array of items.”
Leff, whose study was published by the open access journal PLoS ONE, said most of the work on bacteria associated with produce has focused on a relatively small number of path-ogenic bacteria.
As a result, there was a lack of understanding about the harmless bacteria and how those communities differ according to different produce and farming and handling practices.
Leff’s team based the study on common produce types: bean sprouts, alfalfa sprouts, lettuce, spinach, tomatoes, strawberries, apples, peaches, grapes, peppers, and mushrooms.
“We saw that enterobacteriaceae dominated many of the types of produce we looked at,” said Leff. “This is a diverse group of bacteria that includes some harmful bacteria, but the vast majority are harmless and are typically common to plant leaves.”
He found significant differences in bacterial community composition when comparing conventional and organic farming methods.
“These differences were often attributable to distinctions in the relative abundances of Enterobacteriaceae taxa, which were generally less abundant in organically grown produce,” he wrote in his paper.
However, several factors contribute to the differences he observed.
“We can’t say that the differences we saw between organic and conventionally labelled produce were due necessarily to the way they were grown, but we did notice there were very distinct differences in the bacteria growing on fresh items labelled conventional or organic,” he said.
“It might not be how they were grown, but differences in storage, transportation, etc. Types of bacteria that survive on the surface of fruits and veggies could change if affected by cooler temperatures while being stored or transported, or whether it’s warmer or how long they are stored.
However, I would say that we did notice some differences between organic and conventional labelled variety and we saw a greater abundance of bacteria on the conventional types.”
The results suggest that humans are exposed to substantially different bacteria depending on the types of fresh produce they consume. Differences between conventionally and organically farmed varieties contribute to this variation.
Consumers in developed nations have choices between conventionally farmed and organically farmed produce. As a result, they are exposed to the changes in the makeup of microbial communities de-pending on the produce’s exposure to fertilizer and pesticides.
“However, we do not know if these potential effects of farming practices on produce-associated microbial communities are evident across a wide range of produce types and whether such effects persist up until the point that produce is purchased and consumed,” he wrote.
The research has raised further questions:
- Do the differences in the microbial communities and the farming practices influence how the bacteria might degrade the produce?
- Do these differences have a factor in the abundance of human pathogens or human health generally?
- Do they influence taste, quality, texture or appeal of the fruit or the vegetable?
A future question could rest on the influence of climate change and how warming temperatures and changing local weather patterns in key growing areas could change those complex bacterial communities and to what degree of risk.
Leff said it will be important to find out which factors drive the differences between bacterial communities, different produce types and conventional and organic-labelled varieties.
“There is a substantial body of literature focused on the potential effects of farming practices on food chemistry and quality with many studies finding inconsistent results,” Leff wrote.
“This work demonstrates that the effects of different farming practices on produce-associated microbial communities can be significant and are clearly worthy of further investigation.”
