Prevalence and characteristics of Streptococcus pneumoniae "putative serotype 6E" isolates from Asian countries

Draft Genome Sequences of Clinical Isolates of Serotype 6E Streptococcus pneumoniae from Five Asian Countries

Although serotype 6E Streptococcus pneumoniae consistently expresses capsules of either vaccine-serotype 6A or 6B, certain genetic variants of serotype 6E may evade vaccine induced immunity. Thus, draft genome sequences from five clinical isolates of serotype 6E from each of five different Asian countries have been generated to provide insight into the genomic diversity in serotype 6E strains.

Long-Term Epidemiology of Streptococcus pneumoniae Serogroup 6 in a Region of Southern Europe with Special Reference to Serotype 6E

Streptococcus pneumoniae serotype 6E has recently been described, but its long-term epidemiology is not well known. From 1981–2013, 704 serogroup 6 clinical isolates were obtained in Gipuzkoa, Basque Country, Spain. All invasive and one in four non-invasive isolates were included. Overall, 75, 97, 51 and 45 serotypes 6A, 6B, 6C and 6E isolates, respectively, were detected. No serotype 6D isolates were identified. The prevalence of serotypes 6E and 6B, but not that of serotypes 6A and 6C, declined after the introduction of pneumococcal conjugate vaccines. Serotype 6E isolates showed the highest resistance rate. Most serotype 6E isolates were ST90.

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

Genetic studies of serogroup 6 isolates ofStreptococcus pneumoniaeidentified putative serotype 6E. Although its capsular polysaccharide structure has not been elucidated, putative serotype 6E is described in an increasing number of studies as a potentially new serotype. We show here that SPEC6B, which is widely used as a target strain for serotype 6B opsonophagocytosis assays, has the genetic features of the putative serotype 6E but produces capsular polysaccharide identical to 6B capsular polysaccharide as determined by one-dimensional (1D) and 2D nuclear magnetic resonance (NMR). Thus, putative serotype 6E is a mere genetic variant of serotype 6B. Also, SPEC6B is appropriate as a target strain for serotype 6B opsonophagocytosis assays. This example illustrates the difficulties of assigning new bacterial serotypes based on genetic findings alone.

Genomics Reveals the Worldwide Distribution of Multidrug-Resistant Serotype 6E Pneumococci

The pneumococcus is a leading pathogen infecting children and adults. Safe, effective vaccines exist, and they work by inducing antibodies to the polysaccharide capsule (unique for each serotype) that surrounds the cell; however, current vaccines are limited by the fact that only a few of the nearly 100 antigenically distinct serotypes are included in the formulations. Within the serotypes, serogroup 6 pneumococci are a frequent cause of serious disease and common colonizers of the nasopharynx in children. Serotype 6E was first reported in 2004 but was thought to be rare; however, we and others have detected serotype 6E among recent pneumococcal collections. Therefore, we analyzed a diverse data set of ∼1,000 serogroup 6 genomes, assessed the prevalence and distribution of serotype 6E, analyzed the genetic diversity among serogroup 6 pneumococci, and investigated whether pneumococcal conjugate vaccine-induced serotype 6A and 6B antibodies mediate the killing of serotype 6E pneumococci. We found that 43% of all genomes were of serotype 6E, and they were recovered worldwide from healthy children and patients of all ages with pneumococcal disease. Four genetic lineages, three of which were multidrug resistant, described ∼90% of the serotype 6E pneumococci. Serological assays demonstrated that vaccine-induced serotype 6B antibodies were able to elicit killing of serotype 6E pneumococci. We also revealed three major genetic clusters of serotype 6A capsular sequences, discovered a new hybrid 6C/6E serotype, and identified 44 examples of serotype switching. Therefore, while vaccines appear to offer protection against serotype 6E, genetic variants may reduce vaccine efficacy in the longer term because of the emergence of serotypes that can evade vaccine-induced immunity.