Loss of Ethanolamine Utilization in Enterococcus faecalis Increases Gastrointestinal Tract Colonization

Abstract

Enterococcus faecalis is paradoxically a dangerous nosocomial pathogen and a normal constituent of the human gut microbiome, an environment rich in ethanolamine. E. faecalis carries the eut (ethanolamine utilization) genes, which enable the catabolism of ethanolamine (EA) as a valuable source of carbon and/or nitrogen. EA catabolism was previously shown to contribute to the colonization and growth of enteric pathogens, such as Salmonella enterica serovar Typhimurium and enterohemorrhagic Escherichia coli (EHEC), in the gut environment. We tested the ability of eut mutants of E. faecalis to colonize the gut using a murine model of gastrointestinal (GI) tract competition and report the surprising observation that these mutants outcompete the wild-type strain.IMPORTANCE Some bacteria that are normal, harmless colonizers of the human body can cause disease in immunocompromised patients, particularly those that have been heavily treated with antibiotics. Therefore, it is important to understand the factors that promote or negate these organisms' ability to colonize. Previously, ethanolamine, found in high concentrations in the GI tract, was shown to promote the colonization and growth of bacteria associated with food poisoning. Here, we report the surprising, opposite effect of ethanolamine utilization on the commensal colonizer E. faecalis, namely, that loss of this metabolic capacity made it a better colonizer.

Keywords: Enterococcus; ethanolamine; intestinal colonization.

FIG 1

Competitive colonization of the gastrointestinal tract by the E. faecalis wild type and mutant strains following combined inoculation. Percentages of CFU of E. faecalis strains from the initial inoculum mix and from stool samples collected 4 h and 1, 2, and 3 days after mixed inoculation of E. faecalis OG1RF and the ΔeutVW mutant (AR2) (A), OG1RF::gfp and the ΔeutVW mutant (AR2) (B), OG1RF::gfp and the ΔeutV mutant (SD54) (C), and OG1RF::gfp and the ΔeutV::P_eutS eutV mutant (SD209) (D). In panel A, 10 CFU per mouse per time point were randomly picked and PCR screened to confirm the strains’ identities. For panels B, C, and D, >100 CFU were scored for GFP fluorescence per mouse per time point. An unpaired t test with Welch’s correction for the percentages of bacteria recovered from the stool samples versus the amounts in the initial inoculum mixture was used to calculate the P values.

FIG 2

Murine gastrointestinal tract colonization by different E. faecalis strains following mixed inoculation. Percentages of CFU of E. faecalis strains from the initial inoculum mix and from stool samples collected 4 h and 1, 2, and 3 days after mixed inoculation of E. faecalis OG1RF::gfp (SD234) with the ΔeutBC strain (EFKK4) (A), OG1RF::gfp with the eutB mutant (eutBL3*) (EFKK12) (B), the ΔeutVW::gfp mutant (EFKK1) with the ΔeutBC mutant (C), and the ΔeutVW::gfp mutant with the eutB mutant (eutBL3*) (D). More than 100 CFU were scored for GFP fluorescence per mouse per time point. P values were calculated using an unpaired t test with Welch’s correction for the percentages of bacteria recovered from the fecal samples versus the amounts in the initial mixed inoculum.