Antibiotic-Driven Dysbiosis Mediates Intraluminal Agglutination and Alternative Segregation of Enterococcus faecium from the Intestinal Epithelium
Authors: Hendrickx Antoni P. A. , Top Janetta , Bayjanov Jumamurat R. , Kemperman Hans , Rogers Malbert R. C. , Paganelli Fernanda L. , Bonten Marc J. M. , Willems Rob J. L. 
Published: November 2015

The microbiota of the mammalian gastrointestinal tract is a complex ecosystem of bacterial communities that continuously interact with the mucosal immune system. In a healthy host, the mucosal immune system maintains homeostasis in the intestine and prevents invasion of pathogenic bacteria, a phenomenon termed colonization resistance. Antibiotics create dysbiosis of microbiota, thereby decreasing colonization resistance and facilitating infections caused by antibiotic-resistant bacteria. Here we describe how cephalosporin antibiotics create dysbiosis in the mouse large intestine, allowing intestinal outgrowth of antimicrobial-resistant
Enterococcus faecium
. This is accompanied by a reduction of the mucus-associated gut microbiota layer, colon wall, and Muc-2 mucus layer.
E. faecium
agglutinates intraluminally in an extracellular matrix consisting of secretory IgA (sIgA), polymeric immunoglobulin receptor (pIgR), and epithelial cadherin (E-cadherin) proteins, thereby maintaining spatial segregation of
E. faecium
from the intestinal wall. Addition of recombinant E-cadherin and pIgR proteins or purified IgA to enterococci
in vitro
mimics agglutination of
E. faecium
in vivo
. Also, the Ca
2+
levels temporarily increased by 75% in feces of antibiotic-treated mice, which led to deformation of E-cadherin adherens junctions between colonic intestinal epithelial cells and release of E-cadherin as an extracellular matrix entrapping
E. faecium
. These findings indicate that during antibiotic-induced dysbiosis, the intestinal epithelium stays separated from an invading pathogen through an extracellular matrix in which sIgA, pIgR, and E-cadherin are colocalized. Future mucosal vaccination strategies to control
E. faecium
or other opportunistic pathogens may prevent multidrug-resistant infections, hospital transmission, and outbreaks.

IMPORTANCE
Infections with antibiotic-resistant enterococci are an emerging worldwide problem because enterococci are resistant to most of the antibiotics used in hospitals. During antibiotic treatment, the normal bacteria are replaced by resistant enterococci within the gut, from which they can spread and cause infections. We studied antibiotic-mediated intestinal proliferation of multidrug-resistant
Enterococcus faecium
and the effects on intestinal architecture. We demonstrated that antibiotics allow proliferation of
E. faecium
in the gut, alter the mucus-associated gut bacterial layer, and reduce the colon wall, mucus thickness, and amount of Muc-2 protein.
E. faecium
is agglutinated in the intestine in a matrix consisting of host molecules. We hypothesize that this matrix maintains a segregation of
E. faecium
from the epithelium. Understanding the processes that occur in the gut during antibiotic treatment may provide clues for future mucosal vaccination strategies to control
E. faecium
or other multidrug-resistant opportunistic pathogens, thereby preventing infections, hospital transmission, and outbreaks.