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Updated: Jun 19, 2026
Capsular Serotyping of Streptococcus pneumoniae Using the Quellung Reaction
Published on: February 24, 2014
Identification of a capsular polysaccharide from Enterococcus faecium U0317 using a targeted approach to discover
Diana Laverde1, Samantha Armiento2, Antonio Molinaro2
1Division of Paediatric Infectious Diseases, Dr. von Hauner Children's Hospital, Ludwig-Maximilians-University, Munich, Germany.
Abstract:
Enterococcus faecium, a gram-positive opportunistic pathogen, has become a major concern for nosocomial infections due to its resistance to several antibiotics, including vancomycin. Finding novel alternatives for treatment prevention, such as vaccines, is therefore crucial. In this study, we used various techniques to discover a novel capsular polysaccharide. Firstly, we identified an encapsulated E. faecium strain by evaluating the opsonophagocytic activity of fifteen strains with antibodies targeting the well-known lipoteichoic acid antigen. This activity was attributed to an unknown polysaccharide. We then prepared a crude cell wall glycopolymer and fractionated it, guided by immunodot-blot analysis. The most immunoreactive fractions were used for opsonophagocytic inhibition assays. The fraction containing the inhibitory polysaccharide underwent structural characterization using NMR and chemical analyses. The elucidated structure presents a branched repeating unit, with the linear part being: →)-β-d-Gal-(1 → 4)-β-d-Glc-(1 → 4)-β-d-Gal-(1 → 4)-β-d-GlcNAc-(1→, further decorated with a terminal α-d-Glc and a d-phosphoglycerol moiety, attached to O-2 and O-3 of the 4-linked Gal unit, respectively. This polysaccharide was conjugated to BSA and the synthetic glycoprotein used to immunize mice. The resulting sera exhibited good opsonic activity, suggesting its potential as a vaccine antigen. In conclusion, our effector-function-based approach successfully identified an immunogenic capsular polysaccharide with promising applications in immunotherapy.
Insights
Researchers discovered a novel, immunogenic capsular polysaccharide from vancomycin-resistant Enterococcus faecium. This finding offers a promising new vaccine antigen for preventing dangerous nosocomial infections.
Area of Science:
- Microbiology
- Immunology
- Carbohydrate Chemistry
Background:
- Enterococcus faecium is a significant cause of hospital-acquired infections.
- Antibiotic resistance, particularly to vancomycin, limits treatment options.
- Development of novel vaccines is crucial for preventing E. faecium infections.
Purpose of the Study:
- To identify and characterize a novel capsular polysaccharide from E. faecium.
- To evaluate the capsular polysaccharide's potential as a vaccine antigen.
Main Methods:
- Screening of E. faecium strains for opsonophagocytic activity.
- Isolation and purification of capsular polysaccharide using immunodot-blot and fractionation.
- Structural elucidation via NMR and chemical analyses.
- Conjugation of polysaccharide to BSA and immunization of mice.
Main Results:
- Identification of an encapsulated E. faecium strain with an unknown polysaccharide antigen.
- Elucidation of a branched polysaccharide structure with specific linkages and decorations.
- Immunization with the polysaccharide-glycoprotein conjugate induced sera with significant opsonic activity.
Conclusions:
- A novel, immunogenic capsular polysaccharide from E. faecium was successfully identified and characterized.
- The identified polysaccharide shows potential as a vaccine candidate for immunotherapy against E. faecium infections.
