Studies of Human Microbiome Yield New Insights - NYT

[Guest guest]

http://www.nytimes.com/2012/06/19/science/studies-of-human-microbiome-yield-new-\

insights.html

Tending the Body’s Microbial Garden

By CARL ZIMMER

For a century, doctors have waged war against bacteria, using

antibiotics as their weapons. But that relationship is changing as

scientists become more familiar with the 100 trillion microbes that call

us home — collectively known as the microbiome.

“I would like to lose the language of warfare,” said Segre, a

senior investigator at the National Human Genome Research Institute. “It

does a disservice to all the bacteria that have co-evolved with us and

are maintaining the health of our bodies.”...

A number of recent reports shed light on how mothers promote the health

of their children by shaping their microbiomes. In a study published

last week in the journal PLoS One, Dr. Kjersti Aagaard-Tillery, an

obstetrician at Baylor College of Medicine, and her colleagues described

the vaginal microbiome in pregnant women. Before she started the study,

Dr. Aagaard-Tillery expected this microbiome to be no different from

that of women who weren’t pregnant.

“In fact, what we found is the exact opposite,” she said.

Early in the first trimester of pregnancy, she found, the diversity of

vaginal bacteria changes significantly. Abundant species become rare,

and vice versa.

One of the dominant species in the vagina of a pregnant woman, it turns

out, is Lactobacillus johnsonii. It is usually found in the gut, where

it produces enzymes that digest milk. It’s an odd species to find

proliferating in the vagina, to say the least. Dr. Aagaard-Tillery

speculates that changing conditions in the vagina encourage the bacteria

to grow. During delivery, a baby will be coated by Lactobacillus

johnsonii and ingest some of it. Dr. Aagaard-Tillery suggests that this

inoculation prepares the infant to digest breast milk.

The baby’s microbiome continues to grow during breast-feeding. In a

study of 16 lactating women published last year, M. Hunt of

the University of Idaho and her colleagues reported that the women’s

milk had up to 600 species of bacteria, as well as sugars called

oligosaccharides that babies cannot digest. The sugars serve to nourish

certain beneficial gut bacteria in the infants, the scientists said. The

more the good bacteria thrive, the harder it is for harmful species to

gain a foothold.

As the child grows and the microbiome becomes more ecologically complex,

it also tutors the immune system. Ecological disruptions can halt this

education. In March, Dr. S. Blumberg of Harvard and his

colleagues reported an experiment that demonstrates how important this

education is....

- - - -

*/A Metagenomic Approach to Characterization of the Vaginal Microbiome

Signature in Pregnancy/*

Kjersti Aagaard et al

PLoS ONE 7(6): e36466.

http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0036466

.....Primate fetal development is thought to occur within an intrauterine

microbiota-free environment, and yet within a short interval following

birth the human microbiome is colonizes and “differentiates” until the

adult complement of 90 trillion or so microbiota is achieved [1], [4],

[7], [9]. Based on a relative paucity of data, it is proposed that the

naïve neonatal microbiome is first established with rupture of the

amniotic membranes, with further microbiota being introduced as the

fetus traverses the vaginal birth canal. By the time of delivery, the

neonate has been exposed to the maternal vaginal microbial ecosystem

[9]–[12]. Passage through the vaginal canal is an integral part of this

process, as mode of delivery alters the neonatal microbiome [7]–[12]....

Since the infant is exposed to several environmental sources of bacteria

in the early neonatal interval (maternal vaginal canal and feces,

swallowing and breathing, skin to skin contact, maternal breastmilk,

etc.) it is important to discern the relative potential contribution of

the maternal vaginal community to the neonate....