A recent study conducted by researchers from the University of Valencia and Darwin Bioprospecting Excellence SL revealed that microwave ovens harbor a surprising diversity of bacterial communities capable of withstanding extreme conditions, including high temperatures and electromagnetic radiation. The findings challenge longstanding beliefs about the sterilizing effects of microwaves and raise important questions about household hygiene.
The study identified a total of 747 different types of bacteria in microwave ovens, including Klebsiella and Brevundimonas, which are associated with foodborne illnesses, and 101 bacterial strains belonging to genera such as Brachybacterium, Micrococcus, and Priestia.
Researchers collected samples from 30 microwave ovens distributed among individual home kitchens, shared spaces such as break rooms and university cafes, and molecular biology laboratories. The sample collection process involved taking swabs from the internal surfaces of the microwaves, including the walls and rotating plates, and transferring them to Petri dishes where the bacteria could grow.
Laboratory microwaves demonstrated the greatest biodiversity due to the extreme conditions of their use, accumulating bacteria that can resist radiation and extreme temperatures. The microbiome found in microwaves was dominated by Proteobacteria, Firmicutes, Actinobacteria, and Bacteroidetes. "Some of the genera that were significantly more abundant in this group of samples included species known for their resistance to high doses of radiation, such as Deinococcus, Hymenobacter, Kineococcus, Sphingomonas, and Cellulomonas," the team reported, as noted by Science Alert.
Microwaves work by causing water molecules in food to vibrate, generating frictional heat that cooks food and kills potential bacteria. However, the study raises questions about how bacteria survive in this environment. Dr. Ahmed Yousef, a food microbiology professor at Ohio State University, pointed out that household microwaves heat food unevenly, which can allow bacteria to survive in areas that do not receive adequate microwave energy, according to UDN Health.
"The drier the food, the less likely it is to be heated effectively by microwave energy," explained Dr. Yousef, as reported by UDN Health.
Among the microbes found in home microwaves are health risk species such as Klebsiella, Enterococcus, Aeromonas, and Staphylococcus aureus, known to cause a variety of infections in humans. Although the likelihood of bacteria in microwaves contaminating food is low, the presence of these bacteria indicates the need for proper hygiene in microwave ovens.
Few people clean the inside of their microwaves regularly, typically only addressing spills. This underscores the importance of hygiene in preventing bacterial accumulation and provides a suitable environment for the growth of these microbes. "The microwave is as dirty as your kitchen table, so don't forget to clean it," stated Manuel Porcar, one of the researchers, according to UDN Health.
The origin of bacterial contamination in microwaves is primarily related to human contact, either by introducing food or touching the appliance. This suggests that these appliances can be colonized by microorganisms from different sources, indicating the need for regular cleaning, as reported by Infobae.
The researchers recommend regularly cleaning the interior of the microwave with detergent, paying special attention to spills, to minimize bacterial proliferation and prevent health risks. "Given that even skin bacteria seem to survive the microwave's waves, it's best to give your microwave a regular thorough clean with detergent and stay on top of spills," advised Science Alert.
This article was written in collaboration with generative AI company Alchemiq