More than 100 bacteria species can flourish in microwave ovens

Even the microwave oven in your kitchen is not immune to bacteria.

The irradiating environment within a microwave oven might seem inhospitable to microbes. But swabs from microwave ovens in several different locales identified over 100 bacterial strains, researchers report August 7 in Frontiers in Microbiology. This is the first time that scientists have documented microbial communities living in microwave ovens, according to the researchers.

Microbiologist Manuel Porcar and colleagues swabbed the insides — including the walls and rotating platter — of 30 microwave ovens that were being actively used in three different settings: 10 from kitchens, 10 from labs and 10 from other shared spaces such as cafeterias. The swabbed samples were then transferred to lab dishes, all of which led to significant bacterial growth.

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DNA analysis of the bacterial colonies showed they were dominated by Proteobacteria, Firmicutes, Actinobacteria and Bacteroidetes, all of which are commonly found on human skin and surfaces that people frequently touch. The cultures from kitchen microwave ovens included bacteria that can cause food-borne disease, including Klebsiella and Brevundimonas. It’s unclear how these bacterial strains could survive in microwave ovens, the team says, and further work is needed to understand how they’ve adapted to high temperatures and electromagnetic radiation.

Porcar, of the University of Valencia in Spain, notes that the microorganisms they found in domestic microwave ovens were the same as those that can be found on a kitchen surface (SN: 3/1/22). “Some of them are pathogenic, and one must clean the microwave as much as any other kitchen surface,” he says. However, he stresses that kitchen microwave ovens aren’t a particular cause for concern. “Nothing to be more worried about than the cleaning of any other part of a kitchen in contact with food.”