Who we share our beds with: How typical microbes of pets, siblings and the location influence our airways

In August 2020, the Microbiome Journal published an article about a study on the correlation between environmental impacts, microbes in children’s bed linen, and their airway microbiome (1). The study revealed that factors like location, siblings, and pets do have an influence on the composition of the microbiome in the bedding. Also, a low correlation between that microbiome and the one in the children’s airways was reported.

The authors followed the hypothesis that children spend a great deal of time indoors, today, and that the microbiome in the bedding should be a key factor for the development of their airway microbiome. The study was carried out with samples of the Copenhagen Prospective Studies on Asthma in Childhood from 2010 (2).

584 dust samples from children’s bedding were analyzed and compared to 658 airway swabs from children. The samples were sequenced with high throughput sequencing technology. The children were aged 3 rsp. 6 months when the samples were taken.

The study in the scientific context

Previous studies on microbes in the private space had focused on floors, kitchen and bathroom sinks, along with further studies on semi-public spaces such as kindergardens, schools, or hospitals. So, that study could close a gap – and the most apparent one, too: what bacteria and fungi are colonizing our beds? And are they simply living next to us or do they have an impact on us?

A newborn’s airways are close to sterile but get colonized soon after birth. Based on similar studies, the authors of the study see the early childhood as key factor for a life free of allergies and asthma (3). And as bed linen reflects kind of the cross-section of all environmental impacts, bed dust samples are especially suitable to examine the environmental impact on the child airways.

In a similar study, scientists of TU Munich found out that bacteria that are usually associated with livestock are beneficial for an allergy-free life (4). The study was conducted at 26 Bavarian farms and identified a high prevalence of actually quite pathogenic germ Listeria monocytogenes in children’s beds to be coherent with a low allergy and asthma rate for the children (5).

The tests of the Copenhagen Prospective Studies on Asthma in Childhood are an important contribution to science on the issue as they are very in-depth and profound. It was documented, for instance, if the sample was taken from a house or apartment, if the location is urban or on the country, or if pets were present in the household, with a limitation to the influence of cats and dogs on the taxonomic variety. Earlier studies on pets and risk of allergies showed contradictory results (study with the outcome of lower risks for allergies: 6. Higher risk for allergies: 7). This new study joined in the first and concludes that pets in the household, especially dogs, lower the risk for allergies.

Bacterial and fungal prevalence in children’s bed linen: these are our fellow occupants

The 6 predominant bacterial strains are Firmicutes, Proteobacteria, Actinobacteria, Cyanobacteria, Bacteriodetes, and Fusobacteria. Firmicutes are mostly of the class Bacilli and the families of Streptococcaceae and Stapylococcaceae, such as Streptococcus, Staphylococcus, Rothia, Haemophilus, Paracoccus, and Corynebacterium. Furthermore, the analyses showed an impressive 102 fungal genera. With 82%, the highest rate was Ascomycota, followed byBasidiomycota with only 7%. Less than another 1% could be classified down to phylum level, the remaining 10% could not be aligned.

A positive correlation between fungal and bacterial prevalence was observed, meaning many fungi correlate with many bacteria. So, fungi and bacteria do not compete but at least co-exist or maybe even foster each other.

What factors influence life in our beds?

The diversity of bacteria varies between house and apartment. Also, the location being based in rural vs. urban area has an influence on the average number of bacteria in the samples. This result supports the often-discussed theory that the reduced prevalence of bacteria in urban settings increases the risk for allergies (8).

The samples showed mainly Gram-positive bacteria, such as Staphylococcus, Streptococcus, and Corynebacterium, which are usually associated with environment affected by the presence of humans and can also be found on human skin.

Also, the presence of pets in a household had an impact on the composition of the bed dust microbiome. Especially dogs seemed to have a positive impact, as their presence came along with an increase in Acinetobacter, which proved to prevent allergies and inflammatory diseases of the skin in other studies (9). Families with both cat and dog had an increased prevalence in Corynebacterium und Staphylococcus. Both are also found in the human nasal microbiome and on the skin and are associated with a stable immune system.

Also, siblings were linked to a higher prevalence in fungi and bacteria in the beddings. Especially male siblings appeared to be a real microbial booster And, just as we would expect, the more siblings the higher the bacterial and fungal richness in the beds. Again, every additional male sibling seems to foster the richness of the microbiome. Everyone who has sons or brother or probably both should not be surprised by this outcome (all the rest might want to check that study for backup: 10).

The main impact on the dust microbiome are the inhabitants of the household (or hotel room). A study by the US-American National Institute of Health underlines that fact (12).Another interesting study on that matter was conducted by the South China Agricultural University and examined dust samples in hotel rooms across Asia and Europe. Dust samples from the doorframes of the hotel rooms were collected and sequenced. According to the above discussed evaluation of the Copenhagen Prospective Studies on Asthma, the samples showed characteristic depending on location of the hotel, material of the floor and way of ventilation of the room (11).

How the bedding impacts our microbiome

In a second step, the study focused on the impact of the microbiome in children’s beds on the airway microbiome of the children. First, smaller overlaps between the two ecosystems were observed, but there does not seem to be a transfer in a greater scale.

Conclusively, we can say that there is an obvious correlation between the outer circumstances and the composition of the bed dust microbiome. At the same time, a small and not severe correlation between bed dust microbiome and respiratory microbiome can be reported.

What can we do?

A specific call for action cannot be derived from the results. At the same time, that means that inhabitants of pet-free households do not need to panic and fear their children will all suffer from allergies and asthma. Pet owners can continue to share their beds with their little sweethearts. The presence of siblings and pets and the associated transmission of microbes seems to have a positive outcome in case of doubt.

Links to sources:

(1) https://microbiomejournal.biomedcentral.com
(2) www.sciencedirect.com/
(3) Thorsen J, Rasmussen MA, Waage J, Mortensen M, Brejnrod A, Bønnelykke K, et al. Infant airway microbiota and topical immune perturbations in the origins of childhood asthma. Nat Commun. 2019; 10: 5001
(4) www.lungenaerzte-im-netz.de
(5) europepmc.org/article/med/18377890
(6) Pelucchi C, Galeone C, Bach J-F, La Vecchia C, Chatenoud L. Pet exposure and risk of atopic dermatitis at the pediatric age: a meta-analysis of birth cohort studies. J Allergy Clin Immunol. 2013; 132: 616-622.e7.
(7) Pyrhönen K, Näyhä S, Läärä E. Dog and cat exposure and respective pet allergy in early childhood. Pediatr Allergy Immunol. 2015; 26: 247–255.
(8) Hanski I, von Hertzen L, Fyhrquist N, Koskinen K, Torppa K, Laatikainen T, et al. Environmental biodiversity, human microbiota, and allergy are interrelated. Proc Natl Acad Sci U S A. 2012; 109: 8334-8339.
(9) Fyhrquist N, Ruokolainen L, Suomalainen A, Lehtimäki S, Veckman V, Vendelin J, et al. Acinetobacter species in the skin microbiota protect against allergic sensitization and inflammation. J Allergy Clin Immunol. 2014; 134: 1301–1309.e11.
(10) Ege MJ, Mayer M, Normand A-C, Genuneit J, Cookson WOCM, Braun-Fahrländer C, et al. Exposure to environmental microorganisms and childhood asthma. N Engl J Med. 2011; 364: 701–719.
(11) Lax S, Smith D, Hampton-Marcell J, Owens S, Handley K, et.al. Longitudinal analysis of microbial interaction between humans and the indoor environment. Science. 2014;345: 1048-1052.
(12) Fu X, Li Y, Yuan Q, Cai G-H, Deng Y, Zhang X, Norbäck D, Sun Y. Continental-scale microbiome study reveals different environmental characteristics determining microbial richness, composition, and quantity in hotel rooms. mSystems. 2020; 5:e 00119-20.