Characterization of Two Metal Binding Lipoproteins as Vaccine Candidates for Enterococcal Infections

Abstract

Background Enterococcus faecium and faecalis are Gram-positive opportunistic pathogens that have become leading causes of nosocomial infections over the last decades. Especially multidrug resistant enterococci have become a challenging clinical problem worldwide. Therefore, new treatment options are needed and the identification of alternative targets for vaccine development has emerged as a feasible alternative to fight the infections caused by these pathogens.ResultsWe extrapolate the transcriptomic data from a mice peritonitis infection model in E. faecalis to identify putative up-regulated surface proteins under infection conditions in E. faecium. After the bionformatic analyses two metal binding lipoproteins were identified to have a high homology (>72%) between the two species, the manganese ABC transporter substrate-binding lipoprotein (PsaAfm,) and the zinc ABC transporter substrate-binding lipoprotein (AdcAfm). These candidate lipoproteins were overexpressed in Escherichia coli and purified. The recombinant proteins were used to produce rabbit polyclonal antibodies that were able to induce specific opsonic antibodies that mediated killing of the homologous strain E. faecium E155 as well as clinical strains E. faecium E1162, Enterococcus faecalis 12030, type 2 and type 5. Mice were passively immunized with the antibodies raised against recombinant lipoproteins, showing significant reduction of colony counts in mice livers after the bacterial challenge and demonstrating the efficacy of these metal binding lipoproteins as promising vaccine candidates to treat infections caused by these enterococcal pathogens.ConclusionOverall, our results demonstrate that these two metal binding lipoproteins elicited specific, opsonic and protective antibodies, with an extensive cross-reactivity and serotype-independent coverage among these two important nocosomial pathogens. Pointing these two protein antigens as promising immunogens, that can be used as single components or as carrier proteins together with polysaccharide antigens in vaccine development against enterococcal infections.

Manganese acquisition is essential for virulence of Enterococcus faecalis

“…These results expand the knowledge that bacterial Mn transport systems are promising targets for the development of novel antimicrobial therapies, which should be particularly effective to combat E . faecalis infections [ 66 ]. Work will soon be underway to uncover the significance of dietary Mn in the pathophysiology of E .…”

Mucosal Vaccination with Lactococcus lactis-Secreting Surface Immunological Protein Induces Humoral and Cellular Immune Protection against Group B Streptococcus in a Murine Model

“…Aliquots were removed after incubation and plated on blood agar plates, which were incubated overnight at 37 • C in 5% CO 2 . The percentage killed was assessed as described by Romero-Saavedra et al [33] by comparing the colony counts at 60 min (t60) that did not contain differentiated HL-60 cells to the colony counts of a tube that included all four components of the assay.…”

Manganese acquisition is essential for virulence ofEnterococcus faecalis

“…Specifically, simultaneous inactivation of efaCBA and mntH2 renders E. faecalis avirulent in two mammalian infection models while only a triple Δ efa Δ mntH1 Δ mntH2 mutant strain was attenuated in the G. mellonella invertebrate model. These results expand the knowledge that bacterial Mn transport systems are promising targets for the development of novel antimicrobial therapies, which should be particularly effective to combat E. faecalis infections [63]. Work will soon be underway to uncover the significance of dietary Mn in the pathophysiology of E. faecalis , to elucidate the organ-dependent differential transcriptional regulation of each Mn transporter, and to understand the contribution of Mn-dependent responses to oxidative stress survival in the context of infection.…”