Picture*Image of A. gambiae from Dr. Larry Zwiebel lab, Vanderbilt University
Skin bacteria contribute to the mosquitoes' attraction towards humans

In a sense, we all smell different. Every human being has a particular scent that is perceivable among others. Some persons have strong odors while others have more delicate odors, and so forth. However, what is interesting about human scent is that our skin alone, is not capable of emitting any odor, so in theory, we should be odorless (for more information about this topic, follow this link). But the question is, why do we smell? It turns out that there are groups of bacteria that live throughout our bodies, specifically in our skin that produce volatile compounds that give a scent. This mixture of volatile compounds is what we perceive as our body odor, which is particular to specific areas of our body. But do not get alarmed, after all, we are holobionts, which means we live in close interaction with millions of microorganisms from the moment we are born (for more information about the microbes that first colonize our bodies follow this link) until the moment we perish, and more importantly, they are necessary for our survival.

What does any of this have to do with mosquitoes? Well, as a matter of fact, mosquitoes are experts in detecting smell, and it turns out, we produce their favorite smell. Actually, our skin bacteria produce their favorite smell. That is one of the reasons they can easily detect us, no matter where we are. Interestingly enough, there are persons that are more attractive to mosquitoes than others. The reason to this selective attraction lies in the types of microbes that are abundant within your skin microflora. In a recent study, scientists from Wageningen University and Research Centre in the Netherlands discovered that Malaria mosquitoes (Anopheles gambiae) have a differential attraction to volatile blends produced by specific groups of bacteria associated to the skin of humans (Verhulst et al. 2010). In other words, there are specific groups of bacteria in our skin (which, essentially, are part of our normal skin microflora) that produce compounds that are irresistible to mosquitoes. They identified 4 major groups of bacteria that had a huge impact in the mosquitoes attractiveness. Persons that had a great deal of Corynebacterium minutissimum, Brevibacterium epidermidis, Bacillus subtilis, or Staphylococcus epidermidis in their skin were more attractive to mosquitoes while persons that had more Pseudomonas aureginosa, Leptotrichia, and/or Delftia species were less attractive (for more information about these findings, follow this link). So, if you think you are sweet for mosquito bites then it is probable that you have an abundance of one of the 4 groups of bacteria mentioned above.

These findings are of important value for further studies that are involved in eradicating malaria and other diseases transmitted by mosquitoes. Once we understand the interactions between mosquitoes that are vectors of different types of pathogens (i.e. Dengue, Yellow Fever, Malaria), and the way they're are attracted to humans, we can start developing chemicals that attract mosquitoes to traps or ways to repulse the insects from us. At least we are still in the race that aims to eradicate malaria, and it appears we are winning.

*References:
(1) Verhulst, N.O., et al. (2010) Chemical ecology of interactions between human skin microbiota and mosquitoes. FEMS Microbiol Ecol 74: 1–9.
(2) Verhulst, N.O., et al. (2010) Differential attraction of malaria mosquitoes to volatile blends produced by human skin bacteria. PLoS One 5(12): e15829.
(3) Verhulst, N.O., et al. (2011) Composition of human skin microbiota affects attractiveness to malaria mosquitoes. PLoS One 6(12): e28991.

Picture
*Image obtained from the History of Medicine Collection (NIH)
 
Picture*Image taken from Cho and Blaser (2012) Nature Reviews Genetics
Delivery mode impacts newborn's microbiota

With the advancement of Next Generation Sequencing (NGS) techniques, many microbiologists are now able to study in depth the microbial communities within environments of great interest to human health. This is the case for microbiologist Dr. María G. Domínguez–Bello of the University of Puerto Rico-Río Piedras. In 2010, she and her colleagues published an article in which they characterized the bacterial communities of different parts of the body of human babies immediately after they were born (< 5 min), thus contributing in the understanding of the initiation stage of human microbiome development (see figure above for more information about this topic). The interesting part of her work was that she compared the bacterial communities of babies that were born through vaginal delivery vs. those born through cesarean section. Her discovery was remarkable. Not only she demonstrated that newborn babies have undifferentiated bacterial communities across different body habitats but that the composition of such communities is directly correlated to the delivery mode of birth of the infant. Babies that were born through vaginal delivery had a bacterial signature similar to that of their mother's vagina, in which Lactobacillus and Prevotella species dominate. In contrast, babies born through cesarean section showed a bacterial signature similar to their mother's skin (specifically the ventral side of the mother's forearms), in which Staphylococcus species dominate (see figure below for more details).

Picture*Figure taken from Domínguez-Bello et al. (2010) PNAS.
The trajectory of neonatal gut microbiota of human babies from the moment they are born until they reach 27 months of age.

In addition to the mode of delivery, the microbial communities that colonize the human body throughout the first stages of development (after birth) are greatly influenced by a variety of factors [see the work of Cho and Blaser (2012) for more information]. Interestingly enough, the succession patterns of microbial communities within the gut of human babies show a compositional shift in the abundance of major bacterial taxa over time (Koenig, et al. 2011). This compositional shift can be appreciated in the video below. This video was developed by members of Dr. Rob Knight's lab at the University of Colorado-Boulder. The trajectory that is well illustrated in the video was created from data published by Koenig et al. (2011) and framed against data  generated by the Human Microbiome Project (HMP). From the video, you can see that the pattern of succession of the neonatal microbiota shifts from a vaginal-like composition at birth to an adult gut-like composition after 27 months of age.




*References
(1) Cho, I., and Blaser, M.J. (2012) The human microbiome: at the interface of health and disease. Nature Reviews Genetics 13: 260–270.
(2) Domínguez–Bello, M.G. (2010) Delivery mode shapes the acquisition and structure of the initial microbiota across multiple body habitats in newborns. Proc Natl Acad Sci U S A. 107(26): 11971–11975.
(3) Koenig, J.E. et al. (2011) Succession of microbial consortia in the developing infant gut microbiome. Proc Natl Acad Sci U S A. 108(suppl. 1): 4578–4585.