Enterococcus faecalisreadily colonizes the entire gastrointestinal tract and forms biofilms in a germ-free mouse model

Abstract

The mammalian gastrointestinal (GI) tract is a complex organ system with a twist-a significant portion of its composition is a community of microbial symbionts. The microbiota plays an increasingly appreciated role in many clinically-relevant conditions. It is important to understand the details of biofilm development in the GI tract since bacteria in this state not only use biofilms to improve colonization, biofilm bacteria often exhibit high levels of resistance to common, clinically relevant antibacterial drugs. Here we examine the initial colonization of the germ-free murine GI tract by Enterococcus faecalis-one of the first bacterial colonizers of the na€ ıve mammalian gut. We demonstrate strong morphological similarities to our previous in vitro E. faecalis biofilm microcolony architecture using 3 complementary imaging techniques: conventional tissue Gram stain, immunofluorescent imaging (IFM) of constitutive fluorescent protein reporter expression, and lowvoltage scanning electron microscopy (LV-SEM). E. faecalis biofilm microcolonies were readily identifiable throughout the entire lower GI tract, from the duodenum to the colon. Notably, biofilm development appeared to occur as discrete microcolonies directly attached to the epithelial surface rather than confluent sheets of cells throughout the GI tract even in the presence of high (>10 9 ) fecal bacterial loads. An in vivo competition experiment using a pool of 11 select E. faecalis mutant strains containing sequence-defined transposon insertions showed the potential of this model to identify genetic factors involved in E. faecalis colonization of the murine GI tract.

Sortase-Dependent Proteins Promote Gastrointestinal Colonization by Enterococci

“…Although controversial (48), these speculations were substantiated by observations of biofilm-like structures on luminal surfaces of normal intestinal tissue from mice (49) and humans (50). More recently, biofilms were observed in the GIT of germfree mice colonized with E. faecalis (51). Whether these structures are present in the GIT of conventional animals is unknown.…”

Effects of artificially introduced Enterococcus faecalis strains in experimental necrotizing enterocolitis

“…Biofilm formation, which may be associated with efficient colonization [21], is yet another potentially pathogenic phenotype. We measured biofilm formation in our E. faecalis strains by overnight culturing in polystyrene plates, washing off suspended bacteria, and biofilm staining with crystal violet ( Fig 3A ).…”

“…E. faecalis is a bacterial species of potential relevance to NEC. These bacteria constitute up to 1% of adult intestinal microbiome [17] and are readily transmitted from mothers to neonates in both humans [18, 19] and rodents [20, 21]. NEC patients tended to harbor lower percentages of E. faecalis in their microbiomes compared to healthy controls, but this tendency was not significant [22, 23].…”

Using Precisely Defined in vivo Microbiotas to Understand Microbial Regulation of IgE

“…We identified induction of IgA and mucosa association as key characteristics of the bacteria that were involved in inhibition of IgE. Indeed, both A. muciniphila and E. faecalis are present near the epithelial surface of the small and large intestines (51,52). Although A. muciniphila is known to have barrier-protective functions (53,54), it is also a potent inducer of bacteria-specific systemic IgA and IgG1 responses (48).…”