Molecular Cloning and Immunogenicity Evaluation of PpiC, GelE, and VS87_01105 Proteins of Enterococcus faecalis as Vaccine Candidates

Abstract

Background: Among the enterococci strains, Enterococcus faecalis is considered as one of the important nosocomial pathogens affecting immunocompromised patients. In this study, the immunogenicity of PpiC, GelE, and VS87_01105 proteins against enterococcal infection was investigated in a mice model. Methods: The genes encoding these proteins were cloned into pET21a expression vector, and the recombinant proteins were produced. Mice and rabbits were immunized with the purified recombinant proteins, and subsequently, mice were challenged with E. faecalis for the evaluation of their survival and bacterial clearances. The antibody responses to recombinant proteins were determined by ELISA assay, and opsonophagocytic activities of the antibodies were also measured. Passive immunization was performed using purified antibodies. Mice were challenged, and their survival and bacterial clearance were determined. Results: Immunized mice with PpiC, GelE, and VS87_01105 recombinant proteins showed 80%, 70%, and 40% survival rate, respectively. The survival rates among passively immunized mice that received 500 µg of IgG fraction in 100 µl PBS buffer of each of anti-PpiC, anti-GelE, and anti-VS87_01105 were 60%, 50%, and 20%, respectively. The rates of opsonization with anti-PpiC, anti-GelE, and anti-VS87_01105 antibodies at 1/10 dilution were 77%, 64%, and 23%, respectively. Conclusion: Based on our findings, PpiC, and GelE proteins can protect the mice against E. faecalis ATCC 29212 and effectively induce a protective antibody response. Thus, these proteins could be used as an additional therapeutic tool against enterococcal infections. Further studies to determine the role of PpiC in ligand binding and demonstration of epitope mapping may establish a credible target for vaccination.

Targeting Protein Folding: A Novel Approach for the Treatment of Pathogenic Bacteria

“…Infection of Caco-2/T7 epithelial cells resulted in low levels of cell cytotoxicity indicating that the parvulin Ef0685 in E. faecalis is involved in cellular cytotoxicity . Ef0685 was also found to be a protective antigen against E. faecalis infections in mice, indicating it is either secreted or present on the outer membrane and is potentially a vaccine candidate …”

“…101 Ef0685 was also found to be a protective antigen against E. faecalis infections in mice, indicating it is either secreted or present on the outer membrane and is potentially a vaccine candidate. 174 Listeria monocytogenes encodes for two PrsA homologues, PrsA1 and PrsA2. Deletion of the prsA2 gene in L. monocytogenes results in decreased invasion of murine macrophages, an 80% reduction in plaque size in L2 fibroblast cells, and decreased levels in secreted factors listeriolysin O (LLO) and a broad-specificity phospholipase (PC-PLC) both of which are important for virulence in L. monocytogenes.…”

Advances and Prospects in Vaccine Development against Enterococci

“…These results suggest that active immunotherapy using only SagA or SagA conjugated with polysaccharides could serve as a promising vaccine candidate against enterococcal infections [93,94]. Lately, GelE was also introduced as a putative vaccine candidate [95].…”

“…These results suggest that active immunotherapy using only SagA or SagA conjugated with polysaccharides could serve as a promising vaccine candidate against enterococcal infections [93,94]. Lately, GelE was also introduced as a putative vaccine candidate [95]. Another class of virulence factors is the microbial surface components recognizing adhesive matrix molecules (MSCRAMMs), such as Ace [19] and Acm [96], and the pilus proteins that promote biofilm formation [97,98].…”