At home with microbes
22 Nov 2018
As I look to enter the truly grown-up world of home-owner, I started to ponder what microbes are in my current family home and how these will differ from those in the house I want to buy.
Firstly, I wanted to find out what microbes are found in homes and how these vary from house to house. Thankfully, this seems to be a popular area of research. An extensive study of microbes found in the home was carried out by Dunn et al. (2013) where they investigated 9 areas in 40 different homes.
The areas investigated included the obvious kitchen (counter, chopping board and fridge shelf) and bathroom (toilet seat), but they also looked at the front door (inside, outside and handle), the lounge (tv screen) and the bedroom (pillowcase).
Interestingly Dunn et al. (2013) found that every location had its own distinct bacteria groups, but there were overall groups for the kitchen, locations where bacteria settled (tv and door frames), and locations with high human contact (toilet, door handles and pillowcase). Fascinatingly the kitchen samples were all similar, even though one was the fridge. I expected the fridge to contain different, cold-loving bacteria.
So what microbes are common in the home? The main phyla found by Dunn et al. (2013) were Proteobacteria, Firmicutes and Actinobacteria which are all associated with the human body but can also be found in the external natural environment.
They also found that the main families of bacteria were Streptococcaceae (phylum Firmicutes), Corynebacteriaceae (phylum Actinobacteria) and Lactobacillaceae (phylum Firmicutes). But what individual species would we find?
A study by Donofrio et al. (2012) looked at different household items e.g. kitchen sponges, pet’s bowl, computer keyboards, the reservoir in coffee machines and wallets to find the abundance of yeasts and moulds (species not tested), and bacteria (total bacterial count, coliforms including Escherichia coli, Staphylococcus aureus).
They found yeast and moulds occurred on any type of material but were in lower abundance than bacterial counts. Considering the bacteria, the coliforms (including E. coli) were common on items from the kitchen and S. aureus were common on items touched by humans and their pets.
Although these bacteria species can make us sick, they also occur naturally without being pathogenic and so it is not necessary to try and remove all microbes from the home. Overall, bacteria were most abundant on pet related items followed by the kitchen items, but the item with the highest abundance of bacteria was the kitchen sponges (Donofrio et al. 2012).
The porous, damp surface of the sponge is likely to encourage the growth of bacteria and so I’m relieved my Mom will not use sponges and instead uses a cloth which she bleaches at least weekly. This is something I will have to continue when I have my own home as a sponge is likely to contaminate surfaces more than clean them.
These studies show the abundance of microbes in our homes, but all of them provide only a brief snapshot of what was present at that one second in time. However, the microbes in the home will be dynamic.
There are different inputs. Imagine opening your front door during a gale, when some leaves blow in. This will immediately introduce ‘foreign’ microbes to you home which may or may not already be present.
If you took a microbiological sample of your floor at that point in time, it will show the microbes from the leaf. But these may only be present for a brief time either because your house is not their preferred habitat, or because you removed the leaf.
Leaf us alone
By removing the leaf, you are introducing another factor which controls the microbes in your home – cleaning. I like to imagine this as the difference between a hard kitchen floor and a soft lounge carpet. The kitchen floor is the microbe equivalent to a desert with frequent ‘steam storms’ and little oases of dropped food. Conditions are harsh and the odd reward of plentiful food is soon followed by microbial extermination.
On the other hand, a soft carpet is like a party for microbes (cue Kool & the Gang - Celebration). The conditions are warm and comfy with inputs of food including our own skin sheadings and crumbs – which allow the party to continue. In a carpet the infrequent cleaning/mass mortally events also allow the microbial community to become well established. Therefore, a carpet provides a nicer warm home for all your microscopic tenants than a hard floor.
But the microbes are not only influenced by the human inhabitants as pets, including dogs, can help to shape the microbial diversity of the home (Fujimura et al. 2010; Dunn et al. 2013). In fact, dogs not only add microbes to the house, but they also seem to protect the co-inhabitant from allergic reactions to dust (Fujimura et al. 2010).
The presence of dog increases the bacteria diversity in the dust and helps to enhance the immunity of their humans so they are less likely to suffer from allergies. The house I want to buy is home to two dogs while my family home has fish. The dogs have access to the entire house and so they can shape the microbes throughout.
The dogs are likely to add different bacteria taxa including Porphyriminadaceae, Rhodocyclaceae and Pasteurellaceae which are common on dog fur (Dunn et al. 2013). Although the fish will also have their own microbial community, this is confined to their aquatic home.
The fish microbes will only be contacted during cleaning and can only enter the kitchen on water changes when most of the microbes will go straight down the sink. Therefore, the microbial diversity of my future house is likely to be higher than the diversity in my own home and this diversity is likely to benefit the current owners (until they remove their dogs).
If I get the house, my first job will be to remove the concrete so I can have a lawn. By exposing the soil, I will probably introduce soil-dwelling microbes to my home as I walk in and out of the house. Naturally I will also clean the house before I paint the walls and add carpets to the bedrooms. As I prefer carpet, my new home will have an abundance of cosy environments for my microscopic tenants – I just hope they are friendly!
Donofrio, R.S., Bechanko, R., Hitt, N., O’Malley, K., Charnauski, T., Bestervelt, L.L., Saha, N., Saha, R. (2012). Are we aware of the microbial hotspots in our households? Journal of Environmental Health, 75(2):12-19.
Dunn, R.R., Fierer, N., Henley, J.B., Leff, J.W., Menninger, H.L. (2013). Home life: factors structuring the bacterial diversity found within and between homes. PLoS one, 8(5):e64133.
Fujimura, K.E., Johnson, C.C., Ownby, D.R., et al. (2010). Man’s best friend? The effect of pet ownership on house dust microbial communities. Journal of Allergy and Clinical Immunology, 126(2):410-412.