Apples are among the most consumed fruits worldwide. They represent a source of direct human exposure to bacterial communities. A new study, published in the journal Frontiers in Microbiology, shows that consuming the whole apple — organic or conventional — includes an approximate uptake of 100 million bacterial cells; however, freshly harvested organic apples harbor a significantly more diverse, more even and distinct microbiota, compared to conventional ones.

“Bacteria, fungi and viruses in our food transiently colonize our gut. Cooking kills most of these, so raw fruits and vegetables are particularly important sources of gut microbes,” said Professor Gabriele Berg, a researcher at the Graz University of Technology.

To help us choose our colonic colonists wisely, Professor Berg and colleagues analyzed the apple microbiome.

The scientists compared the bacteria in conventional store-bought apples with those in visually matched fresh organic ones.

Different tissues (stem, peel, fruit pulp, seeds, and calyx) were analyzed separately.

Overall, the organic and conventional apples were occupied by similar numbers of bacteria.

“Putting together the averages for each apple component, we estimate a typical 240 g apple contains roughly 100 million bacteria,” Professor Berg said.

Interestingly, fruit pulp and seeds were bacterial hot spots, while the peel was less colonized.

“Freshly harvested, organically managed apples harbor a significantly more diverse, more even and distinct bacterial community, compared to conventional ones,” the researcher said.

“This variety and balance would be expected to limit overgrowth of any one species, and previous studies have reported a negative correlation between human pathogen abundance and microbiome diversity of fresh produce.”

Specific groups of bacteria known for health-affecting potential also weighed in favor of organic apples.

“Escherichia-Shigella, a group of bacteria that includes known pathogens, was found in most of the conventional apple samples, but none from organic apples. For beneficial Lactobacilli, the reverse was true,” he said.

“And there may even be vindication for those who can taste the difference in organic produce.”

“Methylobacterium, known to enhance the biosynthesis of strawberry flavor compounds, was significantly more abundant in organic apples; here especially on peel and flesh samples, which in general had a more diverse microbiota than seeds, stem or calyx.”

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Birgit Wassermann et al. An Apple a Day: Which Bacteria Do We Eat With Organic and Conventional Apples? Front. Microbiol, published online July 24, 2019; doi: 10.3389/fmicb.2019.01629