The gold-standard synthetic repellent, N,N-diethyl-m-toluamide (DEET), offers protection against mosquitoes for a mere four to eight hours. Extended protection would not only save us from numerous mosquito bites but also curb the spread of mosquito-borne diseases such as dengue fever, Zika, and malaria.
Encouragingly, scientists at the University of California, San Diego, are developing a potential DEET alternative that promises more lasting protection. In mouse tests, this new solution reduced mosquito attraction and feeding for up to 11 uninterrupted days.
The alternative involves genetically engineered versions of common human skin commensals, specifically Staphylococcus epidermidis and Corynebacterium amycolatum. These “living repellents” produce significantly less L-(+)-lactic acid, a compound known to attract mosquitoes.
Details of this innovative approach were published in the journal PNAS Nexus in an article titled, “Engineered skin microbiome reduces mosquito attraction to mice.”
“We engineered bacteria by deleting the L-lactate dehydrogenase (ΔL-LDH) gene,” the authors reported. “We also demonstrated that mosquitoes are less attracted to the scent of the ΔL-LDH strains compared to wild-type in vitro. These findings prove that skin bacterium deprived of the ability to produce L-(+)-lactic acid is key to reducing mosquito attraction, despite these bacteria producing other human skin-derived odorants.”
Led by Omar S. Akbari, PhD, professor of cell and developmental biology, the research team found that in culture-based experiments, the engineered version of S. epidermidis attracted about half as many Aedes aegypti and Anopheles gambiae mosquitoes and about 22% fewer Culex quinquefasciatus compared to the wild-type microbes.
When tested on mice, those painted with wild-type S. epidermidis attracted more mosquitoes. However, mice treated with engineered S. epidermidis experienced a 64.4% reduction in mosquito attraction compared to wild-type, starting three days post-application. The effect persisted for 11 days. Similar results were observed with engineered C. amycolatum. Additionally, fewer mosquitoes that landed on mice treated with engineered microbes bit the mice.
The researchers suggest these results indicate the feasibility of developing a living, long-lasting microbiome-based mosquito repellent.
“This study demonstrates the potent effect of human skin commensal-derived L-(+)-lactic acid on mosquito attraction and feeding efficiency,” the authors concluded. “Living mosquito repellents benefit from (i) durable, self-replicating protection (no lapse in protection concerns), (ii) low logistical burden, and (iii) significantly cheaper lifetime protection.”
Although DEET and picaridin provide higher protection rates (90–100%), the engineered microbes offer significantly reduced attraction (55.3–68%) and deterrence (60.7–80.6%) that lasts 7–11 days post-application. In contrast, DEET and picaridin are only effective for a few hours, requiring frequent reapplication. In summary: less spray, more stay.
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