The microbiome: Battle of the bugs

Date:
October 5, 2021
Source:
Ludwig-Maximilians-Universita"t Mu"nchen
Summary:
Scientists have shown that, depending on the composition of the
microbiome, E. coli bacteria can prevent infections by Salmonella
strains.



FULL STORY ==========================================================================
In a new study, Ba"rbel Stecher and her team from LMU have shown that, depending on the composition of the microbiome, E. coli bacteria can
prevent infections by Salmonella strains.


========================================================================== Every individual harbors a specific microbiome, which is unlike that of
any other. Each is made up of diverse bacterial, fungal and viral species, which are found on all body surfaces -- the skin, mucous membranes and particularly in the gastrointestinal tract. Moreover, the microbiome
have an enormous influence on the immune system, the endocrine system
and the metabolism of their hosts.

Ba"rbel Stecher is Professor of Medical Microbiology and Hygiene in the
Max von Pettenkofer-Institute at LMU Munich and a member of the German
Center for Infection Research (DZIF). Her research focuses on the role
of the gut microbiome in the control of infections. In her latest study
-- whose first author is doctoral student Claudia Eberl -- her team set
out to define what a healthy microbiome needs to effectively defeat an
invasive pathogen. In this case, they asked whether the bacterial species Escherichia coli(E. coli) can provide protection against infection with
human pathogenic Salmonella species.

Many people are acquainted with the negative side of E. coli, as specific strains of the bacterium can cause diseases such as diarrhea, sepsis and
even cancer. But there are lots of benign strains of E. coli. Most of
these colonize individuals during or soon after birth, and contribute
to the establishment of a balanced host-microbial interaction. Stecher
and her research group have now investigated how these strains protect
their hosts against infection by Salmonella.

The importance of cooperation It turns out that the critical factor
is interspecies competition for resources. "We discovered that, in
particular, competition for a variety of sugars in the gastrointestinal
tract can account for the failure of Salmonella to colonize the gut,"
Stecher explains. In order to cause an infection, pathogenic bacteria
must find an appropriate niche within the gut, which provides them
with the carbon sources -- such as certain sugars -- that they need
to replicate. However, competition for carbon sources in the gut
is fierce. "If commensal E. coli consume all the sugar substrates,
leaving nothing behind for Salmonella, the risk of infection is strongly decreased," says Stecher.

However, in order to effectively exclude Salmonella, E. coli usually
needs help. The new study also shows that E. coli is not always in a
position to prevent infections caused by Salmonella. "If the complexity
of the microbiome is too low, its members cannot consume all of the
sugar substrates thatSalmonellastrains depend on, and this opens up opportunities for the pathogen to become established." Stecher and her colleagues therefore concluded that E. coli needs allies. -- And they
went on to identify these as species of the Lachnospiraceae. This group
of anaerobic bacteria is also often found in the human gut, and its
members can also metabolize various sugars.

The research strategy "Using synthetic bacterial consortia, we were able
to construct a model microbiome," Stecher explains. This microbiome was
made up of 12 bacterial species, all of which are found in the healthy
murine gut. This combination of species was then introduced into germ-free mice, which were subsequently infected with Salmonella. They discovered
that, in the absence of Lachnospiraceae, E. coli was unable to prevent Salmonella infection. "This strengthens our conclusion that a combination
of competition for carbon sources and complex interactions between
bacterial species can protect the host against bacterial infections,"
says Stecher.

To translate these findings to humans, Ba"rbel Stecher plans to work
with bacterial consortia found in the human gut microbiome. "At some
point, our work could then help to develop treatments, such as probiotic bacterial cocktails that support the maintenance of a healthy microbiome." ========================================================================== Story Source: Materials provided by
Ludwig-Maximilians-Universita"t_Mu"nchen. Note: Content may be edited
for style and length.


========================================================================== Journal Reference:
1. Claudia Eberl, Anna S. Weiss, Lara M. Jochum, Abilash Chakravarthy
Durai
Raj, Diana Ring, Saib Hussain, Simone Herp, Chen Meng, Karin
Kleigrewe, Michael Gigl, Marijana Basic, Ba"rbel Stecher. E. coli
enhance colonization resistance against Salmonella Typhimurium
by competing for galactitol, a context-dependent limiting carbon
source. Cell Host & Microbe, 2021; DOI: 10.1016/j.chom.2021.09.004 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/10/211005101834.htm

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