Background: Streptococcus pneumoniae serotype 11D capsular polysaccharide (CPS) structure is unknown. Results: Serotype 11D PS contains two different repeating units; one has αGlcNAc, and the other contains αGlc. Conclusion: The 11D CPS is due to the bispecific glycosyltransferase WcrL. Based on codon 112, WcrL can transfer αGlc, αGlcNAc, or both. Significance: Minimal genetic changes can make bacteria produce different polysaccharides.