Microbial seeds
People with the genetic disease
Cystic Fibrosis suffer from decreased lung and pancreatic functions, the former
of which is often attributed to the thickened lung mucous that prevents
expulsion of inhaled bacteria. Many research groups are using DNA
sequencing methods to characterize the communities of bacteria that live in CF
lungs, and a smaller number of research groups have addressed the issue of
intestinal bacterial communities that could be affected by the pancreatic
deficiencies. Typically researchers are only looking at lungs or guts,
but a recent paper looks at the bacteria in both organs soon after birth of
individuals with CF. (Madan et al.:
http://mbio.asm.org/content/3/4/e00251-12).
Although lungs and intestines typically had
different genera of bacteria present, there was overlap between them: Streptococcus and Veillonella species in particular were found in both environments. In addition, genera that were
present in the intestines were later found to be present in the lung samples,
suggesting either a common source seeding these two organs, or direct
transmission from feces to air to lung (it's okay to cringe, but surely this
happens all the time). Also of interest was their finding that breast
feeding had an (albeit slight) effect on the bacterial community composition in
the lungs, which made me think of the known link between breast feeding and
decreased risk of asthma.
The data presented in this paper were indeed
interesting, but I would have liked to see healthy controls included.
Would we have seen the same results if looking at a healthy population of
infants? Surely it is much more difficult to recruit these individuals
for the research, but given they were only sampling the oropharyngeal tract and
feces, it wouldn't have been too invasive. And although I could complain
about the use of these sampling sites to represent the lungs and intestines,
I'll hold my breath today.
The main point here is this: bacterial
communities that inhabit the human body are coming from somewhere, and that somewhere
is likely to be very similar for the lungs, the skin, the intestines, etc.
What is it about these body sites that selects for the distinct bacterial
communities that exist there? Or is there no selection but merely a
"first come, first serve" colonization process? I am skeptical
of the latter, considering the well known associations between particular
bacteria and body site. If we could only figure out how to keep the good
guys and tell the bad guys to go away. The only problem is....sometimes
they might be the same guy!
In : Microbiota
Tags: "cystic fibrosis" "gut microbiota"