A New Pneumococcal Serotype, 11E, Has a Variably Inactivated wcjE Gene

Recently, 2 serologically and biochemically distinct subtypes-11A alpha and 11A beta-were discovered among serotype 11A isolates of Streptococcus pneumoniae. Sequence comparison of the capsular polysaccharide synthesis (cps) loci of the 2 subtypes identified disruption of the wcjE gene, a putative O-acetyltransferase, as the genetic hallmark of the 11A beta phenotype. Directed disruption of wcjE in vitro in an 11A alpha strain switched the strain to the 11A beta phenotype, confirming the role played by the gene in the divergence between the subtypes. Furthermore, sequences from 7 11A beta clinical strains each contained unrelated disruptive mutations in the wcjE gene, displaying an unprecedented degree of genetic heterogeneity in a pneumococcal serotype. We propose to name the 11A alpha subtype as serotype 11A and the 11A beta subtype as 11E, a new serotype. Our findings also suggest that the diversity of pneumococcal capsules is much greater than was previously recognized.