Microbe-wave: radiation-resistant microbes in microwaves

Microwave ovens harbour a thriving bacterial community adapted to surviving the extreme conditions, according to a new study in the journal Frontiers in Microbiology.

The microbiomes in some microwaves are similar to those found on solar panelsThe authors propose this is due to constant thermal shock, electromagnetic radiation, and desiccation (extreme drying) selecting for highly resistant bacteria.

The findings have important implications for hygiene. It could also inform the development of biotechnology if the strains found in microwaves can be used for processes that require hardy bacteria.

“Our results reveal that domestic microwaves have a more ‘anthropised’ microbiome, similar to kitchen surfaces, while laboratory microwaves harbor bacteria that are more resistant to radiation,” says co-author Daniel Torrent, a researcher at Darwin Bioprospecting Excellence SL in Spain.

Torrent and collaborators swabbed the inside of microwaves from single-family domestic homes, shared spaces (such as cafeterias), and molecular biology and microbiology laboratories. They identified the types of bacteria present by cultivating microbes on different media and using genomic sequencing.

This revealed some overlap in the bacterial communities of domestic homes and shared spaces. In reassuring news, home microwaves showed the lowest bacterial diversity.

“Some species of genera found in domestic microwaves, such as Klebsiella, Enterococcus and Aeromonas, may pose a risk to human health,” says Torrent.

“However, it is important to note that the microbial population found in microwaves does not present a unique or increased risk compared to other common kitchen surfaces.”

Lab microwaves, however, had a very distinct composition which the authors say underscores the influence of usage patterns on microbial communities.

“Household microwaves, enriched in food-associated genera, reflected their primary culinary use, while laboratory microwaves harboured radiation-, desiccation-, and high temperature-resistant taxa, indicating prolonged exposure to microwave radiation and suggesting a selective pressure of such harsh factors in shaping the distinctive microbial profile we found,” the study authors write.

The researchers’ recommendation remains the same for both the general public and laboratory personnel: regularly disinfecting microwaves with a diluted bleach solution or a commercially available disinfectant spray.

“In addition, it is important to wipe down the interior surfaces with a damp cloth after each use to remove any residue and to clean up spills immediately to prevent the growth of bacteria,” says Torrent.