Some naturally-occurring soil bacteria can produce compounds that repel mosquitoes as effectively as commercial repellents like DEET and picaridin, according to a new report. The findings of this study, published in the January 16 issue of Science Advances, suggest that bacteria can be harnessed and exploited as a potential source of deterrents for mosquitoes.

A more appealing repellent — a natural one rather than a synthetic chemical repellent — to prevent mosquito bites could aid in reducing the risk from dangerous mosquito-borne pathogens like dengue, malaria and Zika that affect millions of people around the world.

Chemical bug repellents that are applied to the skin, like DEET and picaridin, are widely used to ward off the bites of mosquitoes and other insects. Although DEET is generally considered safe when applied according to instructions, many consumers still question whether it is safe to use. Additionally, recent studies have discovered that chemicals like DEET can make their way to water bodies and harm aquatic animals like salamanders. Repellents from natural sources seem more appealing to the public than synthetic deterrents, said Mayur Kumar Kajla, a co-author of the study from University of Wisconsin, Madison.

A few studies to date have shown that natural bacteria or bacterial extracts can deter pests like ants, but researchers have not yet been able to make the connection to targets like mosquitoes, according to corresponding author Susan Paskewitz, who works with Kajla at the university.

Xenorhabdus budapestensis or Xbu bacteria that are naturally found in soil produce compounds called fabclavines that have proven to be deadly to some insects. However, the bacteria's ability to act as a mosquito repellent has not been explored. Kajla and colleagues questioned whether Xbu bacteria would have any impact on mosquito feeding because the bacteria are unlikely to naturally infect or associate with mosquitoes.

Kajla and colleagues used a membrane feeding system to screen compounds from Xbu bacteria that deter mosquito feeding. They then isolated mosquito feeding-deterrent compounds from Xbu cultures and compared deterrent activities of the Xbu compounds to DEET and picaridin. The authors found that two compounds produced by the bacteria deterred feeding in Aedes aegypti — commonly known as the yellow fever mosquito — and were as or more effective than DEET and picaridin. Additionally, these compounds interfered with feeding by two other types of mosquitoes — Anopheles gambiae, an efficient carrier of human malaria, and Culex pipiens, known for spreading West Nile virus.

The authors say their findings indicate that the compounds produced by Xbu could be exploited in a broader range of other disease-spreading mosquito species. Researchers must now look at the toxicity of the Xbu compounds on cells in the lab, they say, before testing the compounds on animals.