Medical Examiner

All Happy Families Are Microbially Alike

Your house, household, and pets share the same microbes.

Photo by shironosov/Thinkstock
Bacteria are also a part of the family.

Photo by shironosov/Thinkstock

This article originally appeared in the Conversation.

Microbial communities vary greatly between different households but are similar among members of the same household—including pets—according to research published in Science last week.

Microbes are everywhere. They live on and inside us, and cover most things we come into contact with, including our personal belongings. We also know that microbes play a role in human health, and the destruction of our personal microbial community (known as our microbiome) is thought to be contributing to the rapid rise of certain diseases.

The research shows humans affect the microbial populations of their surroundings rather than the other way around.

Studying the dynamics of microbial transmission revealed that, more often than not, humans are the microbial vectors, or transporters. When we move into a new house, rather than acquire microbes from the new location, we bring our unique microbial profile with us.

Andrew Holmes, a microbial ecologist from the University of Sydney, said the results indicate microbial communities on household surfaces are “ecologically inert.” Rather than harboring actively growing microbes, he said, surfaces “are continually reloaded with what you had already growing in and on you.

“To put it another way: We inoculate the house, rather than the house inoculating us,“ he said.

The results of the study highlight the complex exchanges between humans and the microbes residing with us and contribute to an understanding of how these microscopic communities may play a role in human health, disease treatment, and transmission.

Researchers from Argonne National Laboratory studied seven families and their homes over six weeks, including three families immediately before and after they moved to a new home. The researchers sequenced the genomes of bacteria found daily on the subjects’ skin, household surfaces, and pets. Four million different microbial DNA sequences were identified.

Within households, the most microbial similarity between individuals was found on the hands. Intriguingly, the most microbial variation was found in the nose.

Samples were taken from three dogs and one cat, the authors of the study write, revealing “ubiquitous sharing of [distinct microbial genetic sequences] between homes and the humans and pets that occupy them.”

Frequent physical contact between members of a household was also a factor, with those in close relationships sharing the most microbes.

The researchers suggest that samples of household microbial communities could potentially serve as a forensic tool to predict which family the sample came from.

Silvana Gaudieri, associate professor in the Centre for Forensic Science at the University of Western Australia, said that in the context of forensic microbiology, there is potential “predictive value” in the relationship between home surfaces’ microbiomes and those of occupants.

The research also showed that when individuals (and their microbes) leave a house, the microbial community changes markedly in the following days. This suggests that the decay of a microbial signature could be used to assess not only if, but when, a person was in the house.

While the study suggests that humans may routinely encounter potentially harmful microbes, they cause problems only for those with otherwise compromised immune systems.

“[The results] most certainly do not mean that the microbes occupying the household surfaces are biologically significant to the health of the household,” Holmes said.

“What it does emphasize is that we are continually surrounded by bacteria. In our domestic residences our bacterial environment strongly reflects our personal microbiota—which are essentially beneficial.”

“One reason for household members sharing similar microbial communities is that we have a high likelihood of exchanging microbes within a household,” he said. “This is relevant for control of the spread of antibiotic resistant bacteria within household members or in hospital wards.”

Cheryl Power, an honorary fellow in microbiology and immunology at the University of Melbourne, said other studies have shown excessive use of antibacterial compounds selects for more resilient bacteria.

“We should relax about the need to forensically clean our home spaces and not feel the need to use products that contain antibacterial chemicals claimed to make our home safe from ‘house germs,’ as we are so often encouraged to do,” she said. “This research shows that the microbiota of different home spaces are basically our normal microbiota with whom we live peacefully, even productively, most of the time.”