Entomologists Discover New Way For Humans to Avoid Being Bitten By Mosquitoes

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Michael Sanders stands with the mosquito cage used in the experiments. Photo by Rob Williams.

Summer is usually a time for get-togethers, barbecues, and spending time outdoors. It also means a time where mosquitoes are the most active.

A group of scientists, led by Dr. Jeff Tomberlin, is looking at a possible way of making humans unattractive to these biting insects by outsmarting mosquitoes simply by using the chemical communications systems bacteria on the skin.

Tomberlin, along with Drs. Craig Coates, Tawni Crippen from USDA and Tom Wood from Pennsylvania State University, and former TAMU graduate student researcher Ms. Xinyang Zhang have discovered that they can disrupt mosquito attraction to a potential blood-meal by manipulating microbial communication (aka, quorum sensing).

Quorum sensing is a communications system between bacterial cells that allows cells to communicate amongst each other for various functions. The cell-to-cell communication is used in controlling or preventing such processes such as swarming or reproducing. To communicate, bacteria produce compounds that contain specific biochemical messages. The more these compounds are made, the more concentrated the chemical message becomes until it creates a group response, thus creating a behavior. The behaviors are likely to occur when the chemical messages are very concentrated, which makes it easy for other organisms to listen to the “conversation”.

Tomberlin said that this had derived from his previous research in forensics that determine why blow flies were attracted to dead animals. Like with blow flies, Tomberlin said that mosquitoes are influenced by several factors. For mosquitoes, these include, but are not limited to, the volume of carbon dioxide exhaled, our body temperature, and body odor including those odors associated with the microbes on our skin. He also said that the insects use chemoreceptors on their antennae to “listen in” to various communications systems of microbes on our skin.

He said that this “quorum sensing” of microbes ability has always occurred in nature, and the mosquitoes have evolved the ability to perceive these pathways via natural selection over time. The mosquitoes benefit from this ability by selecting a blood host based on the information received by the bacteria.

Tomberlin noted that if they can find the right code that the bacteria are producing to signal unattractiveness, this could be used to keep mosquitoes from biting us.

During the experiments, the group used a mutant form of bacteria that could be found on our skin (Staphylococcus epidermidis) and removed the genetic mechanism that encodes quorum sensing. They then carried out several experiments using blood feeder containers covered either with the silenced or unmodified wild-type bacteria to test how attractive the feeders were to the female Aedes Aegypti, which is known to be the main vector for yellow fever, he said.

Tomberlin said that each of the feeders was fitted with a paraffin film containing a millimeter of rabbit blood that was injected between the flask and the film. The feeders were then kept at average body temperature via warm water pumped through the flask and placed in mosquito cages containing 50 mosquitoes each for 15 minutes.

Some of the different scenarios tested included placing each of the feeders in separate cages, then putting both types in the same cage at the same time. Based on the results, Tomberlin said that they believe that inhibiting bacterial communications could lead to newer, safer methods for deterring mosquitoes than conventional methods that include DEET.

Tomberlin also said that this discovery of manipulating bacterial conversations has other applications, including blocking communications between bacteria in the lungs of patients with cystic fibrosis that lead to new treatments and helping to reduce pipeline corrosion that could be caused by microorganisms.

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