胎盘也有微生物吗？| Nature Podcast

来源：Nature自然科研

又到了每周一次的 Nature Podcast 时间了！欢迎收听本周由Benjamin Thompson和 Shamini Bundell 带来的一周科学故事，本期播客片段讨论胎盘中是否存在微生物群。欢迎前往iTunes或你喜欢的其他播客平台下载完整版，随时随地收听一周科研新鲜事。

音频文本：

Interviewer: Nick Howe

You may think of the microbiome as the collection of microorganisms that live in our gut, and that would be right… to a point. But our gut isn’t the only place to host that party of microbes and for the record, the word ‘microbiome’ specifically refers to the genetic information of those microbes. But anyway, they don’t just live in our gut. They also live on our skin, our mouths, even in our eyes, but there is a part of the body where scientists can’t seem to agree on whether or not microbes dwell, and that is the placenta – the organ which grows during pregnancy to deal with the fetus’ vital functions. Here’s Gordon Smith, a researcher in maternal fetal medicine.

Interviewee: Gordon Smith

So, the sort of original view of the placenta has been that it was thought to be sterile and there was a paper a few years back in Science Translational Medicinewhich really sort of turned around the thinking on that, suggesting that there could be a placental microbiome – that is a population of bacteria that would normally be living in the placenta.

Interviewer: Nick Howe

If true, this could have important implications for the developing baby. Bacteria in the placenta could cause disease or be associated with complications in pregnancy. Alternatively, the placenta could be part of how the baby acquires its own microbiome. Since the Science Translational Medicine study, there have been various papers going back and forth questioning whether or not a placental microbiome exists. This week in Nature, Gordon throws his own hat into the ring with the biggest study so far, using samples from 537 British women. Gordon sequenced all of the material in the samples, discounted any human genetic material and then looked to see if any bacterial DNA was left. But it isn’t quite that simple.

Interviewee: Gordon Smith

One of the questions that we were aware of was how do you differentiate real signal that’s in the sample from contamination that might be caused by any number of different sources. So, the key thing that we did was to use two methods and also then to look at the level of agreement between the two methods.

Interviewer: Nick Howe

Gordon looked at fragmented DNA from his samples and also searched for specific bacterial genes. If he didn’t get the same result from both methods, he discounted the signals as contamination.

Interviewee: Gordon Smith

And we saw lots and lots of signals with each method but they didn’t agree, and what we’ve concluded is that the most likely reason they didn’t agree is that they were introduced through some form of contamination in the sort of laboratory analysis.

Interviewer: Nick Howe

Contamination was a real issue. For example, Gordon found cholera in his samples, but given that there hasn’t been a cholera outbreak in the UK for quite a while, it seemed unlikely it was in women’s placentas. And indeed, using the two-method approach, Gordon concluded that the cholera was more likely to have come from the sequencing facility itself. He also found evidence that some of the supposedly sterile reagents they were using were occasionally contaminated. After discounting suspected contamination, Gordon found that there was no bacteria present on the placenta in healthy pregnancies, but that’s not to say there wasn’t anything at all.

Interviewee: Gordon Smith

We found one real signal and that is a species of Streptococcus which is called group B strep.

Interviewer: Nick Howe

This bacterium was found in 5% of samples and Gordon and his team believe that they were due to infections during pregnancy rather than a microbiome. Altogether, they conclude there is no microbiome associated with the placenta. So that’s it, debate settled.

Interviewee: Kjersti Aagaard

Not at all.

Interviewer: Nick Howe

This is Kjersti Aagaard, a researcher in maternal fetal medicine who is the lead author on the Science Translational Medicine paper Gordon mentioned earlier.

Interviewee: Kjersti Aagaard

I actually think they are describing a placental microbiome.

Interviewer: Nick Howe

Kjersti believes that a lot of what Gordon is dismissing as contamination are actually examples of the placental microbiome. Gordon only considered a signal real if he detected the same exact species using both methods. Kjersti pointed out that it could be tricky to identify bacteria at a species level using these techniques. Also, some bacteria were dismissed as they were thought to have been acquired during vaginal birth, but Kjersti disagreed.

Interviewee: Kjersti Aagaard

We cannot shut down crucial lines of investigation that may make a real difference for women and their families, including their babies. I think there is a real signal here. I am thrilled and I applaud these investigators for the incredible work they’ve done, but I think we look at it through a different lens and we don’t necessarily need to disregard things as contaminate when we consider the biology and some fundamentally important technical considerations that led to some different conclusions.

Interviewer: Nick Howe

In fact, looking at Gordon’s data, Kjersti would conclude there is a placental microbiome. The difference, she says, is in the interpretation. So, the debate on whether or not the placental microbiome exists may not be settled, but studies like Gordon’s are still useful to understand how infections like the group B Streptococcus he found can occur during pregnancy. Here’s Gordon.

Interviewee: Gordon Smith

Infection of the baby with group B strep is the most common cause of death of the baby in the first weeks of life due to sepsis, and so that’s really our current area of study. What we’re now trying to do is to go through a large number of samples and see if the presence of this group B strep in the placenta carries any predictive association with complications for the baby.

Host: Nick Howe

That was Gordon Smith of Cambridge University here in the UK. You also heard from Kjersti Aagaard of the Baylor College of Medicine in the US. You can find Gordon’s paper over at nature.com, along with a News and Views article.ⓝ

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