In this project, we developed the first skin microbial preventive treatment of animals against biting insects, thereby reducing their impact and improving animal health. We focussed on biting midges (Ceratgopogonidae, genus Culicoides, ‘no-see-ums’), which are of huge veterinary importance, mainly as vectors of disease agents, such as e.g. bluetongue virus of which there has been a large outbreak throughout Europe including Switzerland. Like mosquitoes, biting midges are attracted to their host by carbon dioxide released in their breath and by the body odours these hosts emit. These body odours are mainly produced by skin bacteria, and differences in attractiveness between individuals to mosquitoes is mediated by these volatiles released from the skin.
We first determined the skin bacterial composition of 69 sheep and cultured a large subset of them. We identified a bacterial species (Bacillus safensis) that could inhibit the feeding of wild midges by 84% in the laboratory. Next we tested our skin probiotic in an experiment with sheep. The skin bacterial treatment reduced feeding of wild midges on the sheep by 24 % for at least 3 days. We have shown that skin probiotics can reduce biting by insects, which opens a whole new research area.

Management of the human skin microbiome has gained a lot of interest with several success stories. In contrast, microbiome management of animal skin has gained very little attention. The effect of the application of skin bacteria on animals is probably more successful than in humans because they do not wash and thereby remove the treatment. To reach our goal, we combined a set of multidisciplinary techniques from the fields of vector entomology, microbiology and veterinary medicine.
Europe, including Switzerland, is currently experiencing an outbreak of bluetongue virus, which is transmitted by biting midges. Costs incurred by this disease include direct (production losses, animal deaths, and veterinary treatment) and indirect (surveillance, restrictions on animal movement, preventive vaccination and treatment with insecticides, vector monitoring) ones. The skin probiotic can become an ecologically friendly way to reduce biting by midges and thereby the impact of midges-borne diseases. It will also trigger corresponding research in other livestock or companion animal species and humans.

We isolated and cultivated sheep skin bacteria and identified at least one bacterial species that inhibited the biting by midges in the laboratory. When applied on sheep the skin probiotic was less effective but could still reduce the biting for several days. The results initiated a startup (BiSafe) that aims to optimise and commercialize the skin probiotic. Two new granted proposals were partly based on the results and knowledge obtained in this project and focus on the interaction between the skin microbiome and mosquitoes and ticks.

Bourne, M. E., D. Lucas-Barbosa, and N. O. Verhulst, Host-location by arthropod vectors: Are microorganisms in control?, Curr. Opin. Ins. Sc. (2024) 101239;
Brok, P. S., S. M. Jost, and N. O. Verhulst, Selection of sheep skin bacteria to reduce blood-feeding by biting midges (Diptera: Ceratopogonidae, Culicoides) under laboratory conditions, 172 (2024) 1062-1071;
Jost, S. M., L. Cardona, E. Rohrbach, A. Mathis, C. Holliger, and N. O. Verhulst, Environment rather than breed or body site shapes the skin bacterial community of healthy sheep as revealed by metabarcoding, Vet. Dermatol. 35 (2024) 273-283;
Lucas-Barbosa, D., C. Balvers, A. J. Bellantuono, J. S. Castillo, A. L. da Costa da Silva, C. M. De Moraes, M. DeGennaro, and N. Verhulst, Competition matters: using in vitro community models to study the impact of human skin bacteria on mosquito attraction, Front. Ecol. Evol. 11 (2023) 475.