Our Bacterial Flora

Looking in the mirror you may or may not be pleased by your appearance. But regardless of the aspects of your appearance you consider, most likely you haven't considered your personal 'bacteria database' - the enormous number of bacteria that swarm every inch of your body, in and out. Or that the mouth has specialized microbial populations differing from those on your ears or nose (not to mention your fingers). The bacteria we inherit when we are born and those that accumulate over the years have a tremendous effect on our lives, health and disease.

The unseen "others"

MRSA ingestion by a Neutrophil.

MRSA ingestion by a Neutrophil.

Last year The Human Microbiome Project (HMP) consortium published their data and analysis of 5 specific areas of the human bacterial ecology: Airways, skin, oral cavity, gastrointestinal tract and vagina. The ambitious project, funded and led by the NIH since 2007, serves as a tool to determine the bacterial flora diversity of the healthy human. The researchers pointed out, among other findings, that the microbiota is diverse among tested individuals and that this diversity is important for maintaining the microbial genetic pool (these findings had also been suggested by previous publications).

The work of the HMP and other mega-genomic efforts were reviewed in Nature Reviews Genetics and some additional interesting points were highlighted:

  • High taxonomy microbial groups are highly conserved between individuals (in the same organs) while low taxonomy groups vary much more. Variance is so dominant that even monozygous twins have substantial differences in the identity of their gut's microbes - highlighting the effect of the postnatal environment on an individual's physiological development.

  • Resilience in the face of disturbance comes into play when considering antibiotic use and introduction of new microbial species. Although common belief postulates that microbial communities recover from such treatments, monitoring a marker bacteria such as Heliobacter Pylori has demonstrated that extinction can occur within an individual's gut, even long after cessation of treatment.

  • Research has also indicated that although a fetus is essentially sterile of any microbial colonies, and the rupturing of the amniotic sac and exposure to the vaginal canal are generally the first encounter of the human body with bacteria. These bacteria as well as those within the mother's milk (mostly lactobacilli) are the pioneering bacteria that populate the baby's gastrointestinal (GI) tract and prepare it for future succession by other bacteria. One can now realize how such natural microbiotal development can be compromised due to modern lifestyle and medicine practices such as caesarean deliveries, bottle feeding or early antibiotic administration.

  • It has been shown in flies that microbiome population influences mating preferences – does it apply to humans too? It is possible as it is known that odour impacts mating preferences and both oral and other body odour sources are affected by microbial products.
  • As we age, our microbiome changes as well. It has been shown that  gut microbiome dynamics change dramatically - for example while many are generally negative in youth for H.pylori , the species dominates when we're older. Since H. Pylori is associated in part with stomach cancer, such a dynamic population change process has a potential risk to develop into a life threatening disease. The authors suggest that a bacteria that is beneficial early in life might be a hazardous risk at an elderly stage, H.pylori being an example for promoting atrophy and oncogenesis.

  • Regarding health and disease, the authors discuss the initial findings of several investigations demonstrating the apparent connection between certain bacteria species and organ-specific disease (table 1., page 265). For example, the authors note the connection between obesity and gut microbiota. Genetically-obese mice show a decreased level of the Bacteroidetes:Firmicutes ratio. In one publication researchers transferred obese mice's gut microbiota onto heterozygous or wild type mice (both healthy and with no obese phenotype). The recipient mice developed obesity and thus demonstrated the existing connection between gut microbiota population and development of obesity. Even so, it remains unclear which came first, the initial symptoms of the disease or the appearance of the microbiota which lead to it.

Concluding the article the authors suggest that once our knowledge deepens with regards to the effect of the microbiota on our body we can develop specific medical applications that can be initiated to restore or shift the microbiome population toward the desired composition.  

It seems that our medical future is partly in the hands of our microscopic others – what do you think? Will we shape and control our microbiome such that we can improve our health? Share your comment below!