Pneumococcus with the "6E" cps Locus Produces Serotype 6B Capsular Polysaccharide

Area of Science:

• Microbiology
• Genetics
• Immunology

Background:

• Serotyping of Streptococcus pneumoniae is crucial for epidemiological surveillance and vaccine development.
• Putative serotype 6E has been increasingly reported, suggesting a potential new serotype within serogroup 6.
• The genetic basis and capsular polysaccharide structure of putative serotype 6E remain largely unelucidated.

Purpose of the Study:

• To investigate the genetic and structural characteristics of the putative serotype 6E.
• To determine if the SPEC6B strain, a common target for serotype 6B opsonophagocytosis assays, represents a distinct serotype.
• To clarify the relationship between putative serotype 6E and serotype 6B.

Main Methods:

• Comparative genomic analysis of Streptococcus pneumoniae isolates.
• Structural elucidation of capsular polysaccharides using one-dimensional (1D) and 2D nuclear magnetic resonance (NMR) spectroscopy.
• Evaluation of the SPEC6B strain in serotype 6B opsonophagocytosis assays.

Main Results:

• The SPEC6B strain possesses genetic features consistent with the putative serotype 6E.
• Structural analysis confirmed that SPEC6B produces capsular polysaccharide identical to serotype 6B.
• Putative serotype 6E is identified as a genetic variant of serotype 6B, not a distinct serotype.

Conclusions:

• Assigning new bacterial serotypes based solely on genetic data can be misleading.
• The SPEC6B strain remains a suitable target for serotype 6B opsonophagocytosis assays.
• Distinguishing between genetic variants and true novel serotypes requires integrated genetic and structural analyses.