Microwave ovens host thriving communities of microbes: What a new study says

“What is clear is that one cannot trust a microwave to be a cleaner environment in terms of microorganisms compared to another kitchen surface. They must be cleaned like the rest of the kitchen,” Manuel Porcar, a microbiologist at the University of Valencia in Spain and co-author of the study, told New Scientist magazine in an interview.

The new study, ‘The microwave bacteriome: biodiversity of domestic and laboratory microwave ovens’, was published in the journal Frontiers in Microbiology last week.

How was the study carried out?

The team of researchers took samples from 30 microwave ovens in homes, scientific laboratories, and shared kitchens, such as in office spaces and cafeterias.

The researchers then cultured its samples — a method of multiplying microorganisms to determine the type of organism in the sample being tested — in Petri dishes, and identified the genera or groups of the microbes that flourished. They also sequenced the DNA in the samples to get further information about bacteria found in the microwaves.

What were the findings of the study?

The researchers found 747 different genera of bacteria in the cultured samples. “The dominant ones belonged to the Bacillus, Micrococcus and Staphylococcus genera, which commonly live on human skin and surfaces that people frequently touch. Human-skin bacteria were present in all three types of microwave ovens, but were more abundant in the household and shared-use appliances,” according to a report on the study by the journal Nature.

Some bacteria found in domestic microwaves, such as Klebsiella, Enterococcus, and Aeromonas, may pose a risk to human health.

Samples from lab microwave ovens contained the most diverse bacteria, including “extremophiles” or microbes that can withstand high radiation, high temperatures, and extreme dryness.

Belinda Ferrari, a researcher at the University of New South Wales (Australia) told New Scientist that she was not surprised that the researchers found bacteria living in microwaves. “They can survive in almost any extreme-exposure environment and they can adapt to everything,” she said.

Ferrari also underlined the importance of cleaning microwave ovens regularly with disinfectant products. “Some workplace microwaves are disgusting and no one cleans them,” she said.