The gold-standard synthetic repellent, N,N-diethyl-m-toluamide (DEET), protects against mosquitoes for just four to eight hours. More lasting protection would be invaluable. Not only would it save us from untold numbers of annoying mosquito bites, but it would also reduce the spread of mosquito-borne diseases such as dengue fever, Zika, and malaria.
Encouragingly, a potential DEET alternative, one that promises more lasting protection, is being developed by scientists at the University of California, San Diego. In tests with mice, this alternative reduced mosquito attraction and feeding for up to 11 uninterrupted days.
What’s the alternative? Genetically engineered versions of the common human skin commensals Staphylococcus epidermidis and Corynebacterium amycolatum. These “living repellents” produce much less l-(+)-lactic acid, a form of lactic acid that is known to attract mosquitoes.
Details about this new means of keeping mosquitoes at bay appeared 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 article’s authors wrote. “We also demonstrated that mosquitoes are less attracted to the scent of the Δl-ldh strains than 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.”
The scientists, led by Omar S Akbari, PhD, professor of cell and developmental biology, found that in their 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 as the wild-type versions of the microbes.
The authors also tried the engineered microbes on mice. Painting the mice with wild-type S. epidermidis attracted mosquitos. However, painting the mice with engineered S. epidermidis reduced mosquito attraction by up to 64.4%, compared with wild-type, starting three days after the microbe was applied. The effect lasted for 11 days. Trials with engineered C. amycolatum had similar results. In addition, a smaller proportion of mosquitoes that landed on mice painted with engineered microbes bit the mice.
According to the authors, the results suggest the feasibility of creating a living and long-lasting engineered 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 article’s authors concluded. “As an approach, 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.”
The authors acknowledged that the protection conferred by DEET or picaridin (90–100%) was greater than that conferred by their living repellent, the new approach nonetheless offered significantly reduced attraction (55.3–68%) and deterrence (60.7–80.6%). “Notably,” they added, “this protection lasted 7–11 days post-application, whereas DEET/picaridin is only effective for a few hours, requiring constant re-application.” In other words: less spray, more stay.
