Pathogens get comfy in designer goo
Custom hydrogels used to mimic insides of intestines, study infectious bacteria

Date:
July 22, 2021
Source:
Rice University
Summary:
New hydrogels mimic intestines when lined with epithelial cells. A
study demonstrated hydrogels in various stiffnesses are valuable
for learning the dynamics of pathogens that cause diarrhea and
other intestinal diseases.



FULL STORY ========================================================================== Researchers who want bacteria to feel right at home in the laboratory
have put out a new welcome mat.


==========================================================================
Rice University bioengineers and Baylor College of Medicine scientists
looking for a better way to mimic intestinal infections that cause
diarrhea and other diseases have built and tested a set of hydrogel-based platforms to see if they could make both transplanted cells and bacteria
comfy.

As a mechanical model of intestinal environments, the lab's soft, medium
and hard polyethylene glycol (PEG) hydrogels were far more welcoming to
the cells that normally line the gut than the glass and plastic usually
used by laboratories. These cells can then host bacteria like Escherichia
coli that are sometimes pathogenic. The ability to study their dynamics
under realistic conditions can help scientists find treatments for the
maladies they cause.

The researchers found strong correlation between the stiffness of
hydrogels, which mimic intestinal mucus, and how well a diarrhea-causing
strain of E. coli adhered to and aggregated atop the epithelial cells
that normally line the intestines. They reported that softer hydrogels
promoted "significantly greater bacterial adhesion," which they attribute
to mucus and other extracellular matrix components expressed by the cells.

The study led by bioengineer Jane Grande-Allen of Rice's Brown School
of Engineering and Anthony Maresso at Baylor, which appears in Acta Biomaterialia, proved the gels' value in experiments involving the soft interface between organs and microbial or bacterial pathogens.

The Estes lab at Baylor built its model cultures using enteroids,
constructs of intestinal cell cultures that scientists use to understand
how epithelial cells respond to infectious invaders. Enteroids can
incorporate a variety of cells found in the gut, but before Rice's
hydrogels, they were grown on platforms that did not easily mimic the
squishy tissues in host bodies.



========================================================================== "Tissue culture plastic is the standard for growing cells, but it's
a really artificial environment because it's so rigid," Grande-Allen
said. "It's hard plastic, like a glass slide. Certain cells grow just
fine on tissue culture plastic, but they're not consistently easy to
infect that way.

"This is the case with the cells in the jejunum, where most nutrient
absorption happens in the small intestine," she said. "Our collaborators
obtain human intestinal tissues from biopsies and bariatric surgeries to
make enteroids, but the enteroids derived from jejunal cells had been
difficult to infect with this pathogenic E. coli." In Grande-Allen's
lab, enteroid cells were grown on top of the hydrogel substrates. After
a time, the researchers in Maresso's lab added bacteria and found that
the enteric E. coli clustered easily on the intestinal cells grown on
the medium and soft gels, but not on glass slides or stiff hydrogels.

All of the hydrogel-cultured enteroids showed significant enrichment
of gene and signaling pathways related to epithelial differentiation,
cell junctions and adhesions, extracellular matrix and mucins compared
to those cultured on rigid surfaces.

The Rice lab reported its successful development of hydrogels for enteroid
use in a previous paper with the Baylor researchers. "Getting the cells
to adhere and spread on the hydrogels was tricky, which is why we wrote
the methods paper," Grande-Allen said.

"But with that coating approach established, the hydrogel underneath
could have a range of different stiffnesses," she said. "That was the
variable in the new paper, and we were floored to find the effect that
it had on bacterial adhesion.

"In general, stiffness and its effect on bacteria is rather understudied," Grande-Allen said. "Others have reported that bacteria grown directly
on hydrogels prefer stiffer gels, and that finding will help to study
biofilms.

But here, our focus was trying to mimic the infectious disease process
that actually happens in the gut, so we needed to involve the epithelial cells." Grande-Allen said the hydrogels will be used to study other types
of diarrhea- causing bacteria, including patient-specific cultivates,
but in the near term said her lab will look at the combined effect of
stiffness and shear stress on bacterial adhesion to enteroids.

========================================================================== Story Source: Materials provided by Rice_University. Note: Content may
be edited for style and length.


========================================================================== Journal Reference:
1. Ganesh Swaminathan, Nabiollah Kamyabi, Hannah E. Carter, Anubama
Rajan,
Umesh Karandikar, Zachary K. Criss, Noah F. Shroyer, Matthew J.

Robertson, Cristian Coarfa, Chenlin Huang, Tate E. Shannon,
Madeleine Tadros, Mary K. Estes, Anthony W. Maresso, K. Jane
Grande-Allen. Effect of Substrate Stiffness on Human Intestinal
Enteroids' Infectivity by Enteroaggregative Escherichia coli. Acta
Biomaterialia, 2021; DOI: 10.1016/j.actbio.2021.07.024 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/07/210722131345.htm

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