New research has confirmed fresh fruit and vegetables carry an abundance of non-pathogenic bacteria on their surfaces; and certain organic fruits are among the worst offenders. The family of microbes also varies wildly, depending on the type of produce and the cultivation methods used.
Researchers at the University of Colorado tested the surface of eleven produce types with a focus on fruits and vegetables that are often consumed raw. The researchers found that distinct bacterial communities and substantial variation in bacterial richness were present across all produce analysed.
We found the surface bacterial communities of spinach, lettuce, and tomatoes to be numerically dominated by Gammaproteobacteria. Similarly, we found the family Sphingomonadaceae within the class Alphaproteobacteria was the most abundant family present on apples.
The report also found differences in surface bacteria between produce grown using different farming practices, with farm locations, storage temperature and transport conditions all playing their part.
“Our results suggest that differences in farming practices could be influencing the relative abundance of specific taxa on the surfaces of fresh produce available at grocery stores,” the report states.
Interestingly, the study also found bacteria levels varied greatly between conventional and organic-labeled produce. However, the scales were sometimes tipped in the conventional produce’s favour, particularly when it came to grapes and peaches. The researchers put this down to a variety of factors, including growing location, fertilizer use, pesticide use and shipping/handling procedures.
Below is a full table detailing the research team’s bacterial findings:
| Produce Type | OTU classification | Relative Abundance (%) |
| Sprouts (bean) | Pantoea sp.
Klebsiella/Raoultella sp. |
57.5
14.4 |
| Spinach | Pantoea sp.
Klebsiella/Raoultella sp. |
32.4
9.0 |
| Lettuce | Xanthomonas sp.
Pantoea sp.
Pectobacterium sp.
Leuconostoc sp.
Janthinobacterium sp. |
10.0
8.9
8.0
6.9
5.7 |
| Tomato | Klebsiella/Raoultella
Pectobacterium sp. |
26.9
9.8 |
| Sprouts (alfalfa) | Acinetobacter sp. | 9.3 |
| Strawberries | Buchnera aphidicola
Bacillus sp. 1
Pantoea sp. |
23.6
17.1
10.4
|
| Apple | Photobacterium sp. | 5.6 |
| Peach | Microbacterium sp.
Undetermined microbacteriaceae |
6.2
6.1
|
| Grapes | Bacillus sp. 1
Gluconacetobacter sp
Bacillus sp. 2 |
18.2
6.0
5.0
|
| Pepper | Pantoea sp. | 11.1 |
| Mushrooms | Pseudomonas sp.
Pedobacter sp. |
11.3
5.5 |
Although none of the above microbes cause disease directly, they can impact the rate at which food spoils and may also play a role in the spread of harmful microbes in the kitchen.
In other words, it’s probably a good idea to thoroughly wash your fruit rather than giving it a trusty shirt rub.
Bacterial Communities Associated with the Surfaces of Fresh Fruits and Vegetables [PLOS ONE]
This story has been updated since its original publication.
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