Monday, June 10, 2013


What does your Microbiome say to Mosquitoes?

Kristin Gloystein

 

            It sometimes seems that after a weekend of camping with a friend one of you is covered by mosquito bites while the other has not been touched. It doesn’t seem to matter the amount of bug spray you both bathe in, someone just seems to attract mosquitoes more than the other. Recent scientific finding indicate that this may be the case. The study done by Verhulst, et.al in 2011 shows that the variation in the microbial community on individual’s skin produces a body odor specific that that person. This effects how attracted mosquitoes are to that individual. Absent of bacteria human sweat does not smell like anything at all (4). They extrapolated that the more diverse your skin microbiota is the less attractive you are to mosquitoes. They believe that diversity is an important factor in the ability of the skin to host a special group of bacteria that produces compounds that repel mosquitoes (4). This and other studies on this topic have important implications for the creation of new methods for malaria prevention.

            The experiments performed by researchers in Wageningen University in the Netherlands studied specifically on the Anopheles gambiae sensu stricto mosquito (1). This particular mosquito plays a key role in malaria transmission. When females decide where to land they pay attention to a number of physical and chemical clues. (3). In order test how the microbial community of the skin effects how mosquitoes are attracted to individuals they looked at 48 men of various ethnicities. They tried to neutralize variables to make the experiment focus only on skin microbiome.  The asked that, “Volunteers were requested to refrain from drinking alcohol, eating garlic, onions or spicy food, taking a shower, using perfumed cosmetics and were asked to wear nylon socks provided by the research team for the twenty-four hours before the sampling event. Volunteers were free from chronic illnesses and not using any medication on a regular basis. The socks provided by the research team (100% polyamide, 40 denier, Hans Textiel, The Netherlands) were washed twice with 70% ethanol and dried in a ventilated oven at 80°C before use. Volunteers were instructed not to use soap the last time they showered before the experiment”(3). They then took microbial samples from the underside of the left foot using glass beads. The researchers tested those beads to see how attracted mosquitoes were to them. The beads were sterilized between each trail (3).

            They analyzed their collected data using 16S rRNA sequencing on 116 samples from the glass beads. The graph below should the results of the different individuals. PA means “Poorly Attractive” and HA stands for “Highly Attractive”.



The graph above shows that there was a large variation in the attractiveness of the participants microbes to mosquitoes.



What the above graph shows is that there is a positive correlation between the average number of bacteria in the sample from the foot and the attractiveness of the sample to mosquitoes (3). This is significant, as it shows that the number of microbes you have on our skin really does affect the degree of attractiveness has to mosquitoes.

Another very interesting result they found was in relation to phylogenetic diversity. They found that PA individuals had significantly higher phylogenetic diversity than what the HA individuals had (3). This implies that the more diversity an individual has, the less likely they are going to be attractive to mosquitoes. They also found that the abundance of a certain microbe, Staphylococcus spp., was present 2.62 times higher in HA groups than PA groups. They also saw that Pseudomonas spp. was 3.11 times more abundant in the PA groups than the HA groups (3).

There is another study that evaluated the effect of several volatile compounds commonly found on the human skin on the attractiveness to mosquitoes. The four microbes they chose were Bacillus subtilis, Brevibacterium epidermidis, Corynebacterium minutissimum, Pseudomonas aeruginosa and Staphylococcus epidermidis because of their role in producing human body odor (5).

They used a dual-choice olfactometer to look at how the mosquito Anopheles gambiae would react to the four microbial species listed above (5). Below is a representation of the apparatus they used to run the tests. They judged attractiveness by comparing the mosquitoes reaction to that of ammonia, which is a know attractant for that species of mosquitoes.



They found definite discrepancies in the mean relative attractiveness between the four different species. This is meant to give us a better idea of what parts exactly of our body odor and microbial community cause mosquitoes to be attracted to us.



It is obvious that Corynebacterium minutissimum has the highest mean relative attractiveness. This is very interesting in respect to the last study discussed in the beginning of this paper, which seemed to imply that Staphylococcus spp. was most closely associated with a high level of attractiveness to mosquitoes. In this study, it is shown that this microbe has the lowest level of attractiveness compared to the others they choose to study.

What all this suggests is that there are definitely some microbes that affect the attractiveness of an individual to a mosquito more than others. This is a great discovery with huge implications for the prevention of malaria in the future. However it seems as though maybe before we begin to develop treatments or medications from this data, further research is needed. We need to isolate exactly what microbe or combination of factors cause mosquitoes to be attracted to an individual and why a greater diversity of microbes yields less attraction. After we make these discoveries it will also be important to look at what reducing or eliminating those microbes from our skin might do to our biological processes. The human microbiome is inexplicitly linked to how malaria is transmitted. However if we find a safe and responsible way to do so, the implication would be enormous for the prevention of malaria. If we could stop mosquitoes from transmitting malaria through biting people a huge world issue would be solved.

 

 

Bibliography

-          (1) "Microbial Communities On Skin Affect Humans' Attractiveness to Mosquitoes." ScienceDaily. ScienceDaily, 10 Jan. 2012. Web. 29 May 2013. <http://www.sciencedaily.com/releases/2011/12/111229091845.htm>.

-          (2) "Microbial Communities on Skin Affect Humans' Attractiveness to Mosquitoes." Microbial Communities on Skin Affect Humans' Attractiveness to Mosquitoes. N.p., n.d. Web. 29 May 2013. <http://www.eurekalert.org/pub_releases/2011-12/plos-mco122711.php>.

-          (3) "Composition of Human Skin Microbiota Affects Attractiveness to Malaria Mosquitoes." PLOS ONE:. N.p., n.d. Web. 29 May 2013. <http://www.plosone.org/article/info:doi/10.1371/journal.pone.0028991>.



 

 

 

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