Abstract

The aim of this study was to evaluate the role of the regulatory small RNA (sRNA) Ern0160 in gastrointestinal tract (GIT) colonization by Enterococcus faecium. For this purpose, four strains of E. faecium were used, Aus0004 (WT), an ern0160-deleted Aus0004 mutant (Δ0160), a trans-complemented Δ0160 strain overexpressing ern0160 (Δ0160_0160), and a strain Δ0160 with an empty pAT29 vector (Δ0160_pAT29). Strains were studied both in vitro and in vivo, alone and in competitive assays. In in vitro experiments, no difference was observed between WT and Δ0160 strains cultured single while Δ0160_0160 strain grew more slowly than Δ0160_pAT29. In competitive assays, the WT strain was predominant compared to the deleted strain Δ0160 at the end of the experiment. Then, in vivo experiments were performed using a GIT colonization mouse model. Several existing models of GIT colonization were compared while a novel one, combining ceftriaxone and amoxicillin, was developed. A GIT colonization was performed with each strain alone, and no significant difference was noticed. By contrast, significant results were obtained with co-colonization experiments. With WT + Δ0160 suspension, a significant advantage for the WT strain was observed from day 5 to the end of the protocol, suggesting the involvement of ern0160 in GIT colonization. With Δ0160_0160 + Δ0160_pAT29 suspension, the strain with the empty vector took the advantage from day 3 to the end of the protocol, suggesting a deleterious effect of ern0160 overexpression. Altogether, these findings demonstrate the potential implication of Ern0160 in GIT colonization of E. faecium. Further investigations are needed for the identification of sRNA target(s) in order to decipher underlying molecular mechanisms.

Highlights

  • Enterococci are ubiquitous Gram-positive cocci that are normal inhabitants of the human gut microbiota

  • Some E. faecalis were detected at the end of colonization, but they remained a minority compared to VREF

  • Sinel et al showed that the expression level of one small RNA (sRNA), Ern0160, was significantly downregulated under sub-inhibitory concentrations (SICs) daptomycin exposure

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Summary

Introduction

Enterococci are ubiquitous Gram-positive cocci that are normal inhabitants of the human gut microbiota. According to the European Antimicrobial Resistance Surveillance Network (EARS-Net), the mean proportion of VREF among invasive isolates increased from 10.4 to 17.3% in European countries between 2014 and 2018 (European Centre for Disease Prevention and Control, 2019). These high rates of VREF prevalence could be attributable to the worldwide dissemination of a subpopulation of E. faecium hospital-adapted clones that belongs to the clonal complex 17 (CC17) and represents a public health concern (Cattoir and Giard, 2014). Two other clades exist, clade A2 that includes animal strains and sporadic human infection isolates and clade B that comprises human commensal fecal strains (Lebreton et al, 2013)

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