Bacteria in Microwaves? Scientists Find Hundreds, Some Dangerous

As experts from the University of Valencia remind us, microorganisms are inhabiting new, unusual niches – oil slicks at sea, plastic floating in the ocean or polluted post-industrial areas. Now, Spanish researchers have found another place that bacteria like: microwave ovens.

“Our results show that the microbiome of domestic microwave ovens is more typical of human activity, similar to that found on kitchen surfaces, whereas laboratory microwaves harbor bacteria that are more resistant to radiation,” said Daniel Torrent, one of the authors of the study, published in the journal Frontiers in Microbiology on Thursday.

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Scientists examined samples taken from the inside of 30 microwaves used in homes, shared spaces (e.g. workplaces), fast food restaurants, and research institutes, including microbiology laboratories. They found almost 750 types of bacteria belonging to 25 phyla. The most common types were Firmicutes, Actinobacteria, and Proteobacteria.

They found that the composition of typical microbial flora overlapped in household microwaves used by multiple people and those used by single-person households. However, laboratory microwaves were most often inhabited by different bacteria. Microbial diversity was lowest in microwaves from single households and highest in laboratory microwaves.

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Some bacteria may be dangerous, the researchers warn. “Some species from the genera found in household microwaves, such as Klebsiella, Enterococcus and Aeromonas, may pose a risk to human health. However, it is important to note that the microbial population found in microwaves does not pose a unique or increased risk compared to other common kitchen surfaces,” explains Dr. Torrent.

Some of the bacteria found in the microwaves were the same ones previously found on photovoltaic cells. The researchers explain that thermal shock, electromagnetic radiation, and drying in highly irradiated environments repeatedly selected for highly resistant microbes.

“We recommend that both the general public and laboratory personnel regularly disinfect microwaves with a bleach solution or a commercial disinfectant spray. Additionally, it is important to wipe the interior surfaces with a damp cloth after each use to remove any residue and to wipe up any spills immediately to prevent the growth of bacteria,” Dr. Torrent emphasizes.

At the same time, researchers emphasize that some bacteria living in microwave ovens may prove useful – for example, in industrial processes that require resistant strains.

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