Distinct but Spatially Overlapping Intestinal Niches for Vancomycin-Resistant Enterococcus faecium and Carbapenem-Resistant Klebsiella pneumoniae

Abstract

Antibiotic resistance among enterococci and γ-proteobacteria is an increasing problem in healthcare settings. Dense colonization of the gut by antibiotic-resistant bacteria facilitates their spread between patients and also leads to bloodstream and other systemic infections. Antibiotic-mediated destruction of the intestinal microbiota and consequent loss of colonization resistance are critical factors leading to persistence and spread of antibiotic-resistant bacteria. The mechanisms underlying microbiota-mediated colonization resistance remain incompletely defined and are likely distinct for different antibiotic-resistant bacterial species. It is unclear whether enterococci or γ-proteobacteria, upon expanding to high density in the gut, confer colonization resistance against competing bacterial species. Herein, we demonstrate that dense intestinal colonization with vancomycin-resistant Enterococcus faecium (VRE) does not reduce in vivo growth of carbapenem-resistant Klebsiella pneumoniae. Reciprocally, K. pneumoniae does not impair intestinal colonization by VRE. In contrast, transplantation of a diverse fecal microbiota eliminates both VRE and K. pneumoniae from the gut. Fluorescence in situ hybridization demonstrates that VRE and K. pneumoniae localize to the same regions in the colon but differ with respect to stimulation and invasion of the colonic mucus layer. While VRE and K. pneumoniae occupy the same three-dimensional space within the gut lumen, their independent growth and persistence in the gut suggests that they reside in distinct niches that satisfy their specific in vivo metabolic needs.

Author Summary

Intestinal colonization precedes the development of disseminated infections and bacteremia by the nosocomial pathogens vancomycin-resistant Enterococcus (VRE) and carbapenem-resistant Klebsiella pneumoniae.

Although antibiotic treatment renders mice susceptible to dense colonization by VRE or K. pneumoniae, it is unclear whether these microbes compete for space and resources in the gut. Our quantitative studies demonstrate that the density of intestinal colonization by either VRE or K. pneumoniae is unaffected by the presence of the other species, suggesting that they occupy separate niches. Using fluorescence in situ hybridization, we show that both bacterial species indeed occupy distinct niches but inhabit the same regions within the intestine. We find that K. pneumoniae, but not VRE, induces mucus production and invades the mucus layer adjacent to colonic epithelial cells, potentially leading to increased K. pneumoniae translocation to mesenteric lymph nodes. Despite their high colonization levels, both VRE and K. pneumoniae can be displaced from the intestinal lumen following transplantation of a healthy microbiota. Our study provides insight into the interactions between VRE and K. pneumoniae with each other and with their host.