Comparative Genetics of Capsular Polysaccharide Biosynthesis in Streptococcus pneumoniae Types Belonging to Serogroup 19

The genetic basis for the structural diversity of capsule polysaccharide (CPS) in Streptococcus pneumoniae serogroup 19 (consisting of types 19F, 19A, 19B, and 19C) has been determined for the first time. In this study, the genetic basis for the 19A and 19C serotypes is described, and the structures of all four serogroup 19 cps loci and their flanking sequences are compared. Transformation studies show that the structural difference between the 19A and 19F CPSs is likely to be a consequence of differences between their respective polysaccharide polymerase genes (cps19aI and cps19fI). The CPS of type 19C differs from that of type 19B by the addition of glucose. We have identified a single gene difference between the two cps loci (cps19cS), which is likely to encode a glucosyl transferase. The arrangement of the genes within the cps19 loci is highly conserved, with 13 genes (cps19A to -H and cps19K to -O) common to all four serogroup 19 members. These cps genes encode functions required for the synthesis of the shared trisaccharide component of the group 19 CPS repeat unit structures. Furthermore, the genetic differences between the group 19 cps loci identified are consistent with the CPS structures of the individual serotypes. Functions have been assigned to nearly all of the cps19 gene products, based on either gene complementation or similarity to other proteins with known functions, and putative biosynthetic pathways for production of all four group 19 CPSs have been proposed.     

Predicted functions and linkage specificities of the products of the Streptococcus pneumoniae capsular biosynthetic loci

The sequences of the capsular biosynthetic (cps) loci of 90 serotypes of Streptococcus pneumoniae have recently been determined. Bioinformatic procedures were used to predict the general functions of 1,973 of the 1,999 gene products and to identify proteins within the same homology group, Pfam family, and CAZy glycosyltransferase family. Correlating cps gene content with the 54 known capsular polysaccharide (CPS) structures provided tentative assignments of the specific functions of the different homology groups of each functional class (regulatory proteins, enzymes for synthesis of CPS constituents, polymerases, flippases, initial sugar transferases, glycosyltransferases [GTs], phosphotransferases, acetyltransferases, and pyruvyltransferases). Assignment of the glycosidic linkages catalyzed by the 342 GTs (92 homology groups) is problematic, but tentative assignments could be made by using this large set of cps loci and CPS structures to correlate the presence of particular GTs with specific glycosidic linkages, by correlating inverting or retaining linkages in CPS repeat units with the inverting or retaining mechanisms of the GTs predicted from their CAZy family membership, and by comparing the CPS structures of serotypes that have very similar cps gene contents. These large-scale comparisons between structure and gene content assigned the linkages catalyzed by 72% of the GTs, and all linkages were assigned in 32 of the serotypes with known repeat unit structures. Clear examples where very similar initial sugar transferases or glycosyltransferases catalyze different linkages in different serotypes were also identified. These assignments should provide a stimulus for biochemical studies to evaluate the reactions that are proposed.     

Evolutionary genetics of the capsular locus of serogroup 6 pneumococci

The evolution of the capsular biosynthetic (cps) locus of serogroup 6 Streptococcus pneumoniae was investigated by analyzing sequence variation within three serotype-specific cps genes from 102 serotype 6A and 6B isolates. Sequence variation within these cps genes was related to the genetic relatedness of the isolates, determined by multilocus sequence typing, and to the inferred patterns of recent evolutionary descent, explored using the eBURST algorithm. The serotype-specific cps genes had a low percent G+C, and there was a low level of sequence diversity in this region among serotype 6A and 6B isolates. There was also little sequence divergence between these serotypes, suggesting a single introduction of an ancestral cps sequence, followed by slight divergence to create serotypes 6A and 6B. A minority of serotype 6B isolates had cps sequences (class 2 sequences) that were approximately 5% divergent from those of other serotype 6B isolates (class 1 sequences) and which may have arisen by a second, more recent introduction from a related but distinct source. Expression of a serotype 6A or 6B capsule correlated perfectly with a single nonsynonymous polymorphism within wciP, the rhamnosyl transferase gene. In addition to ample evidence of the horizontal transfer of the serotype 6A and 6B cps locus into unrelated lineages, there was evidence for relatively frequent changes from serotype 6A to 6B, and vice versa, among very closely related isolates and examples of recent recombinational events between class 1 and 2 cps serogroup 6 sequences.     

Comparative structural and molecular characterization of Streptococcus pneumoniae capsular polysaccharide serogroup 10

Streptococcus pneumoniae serogroup 10 includes four cross-reactive capsular polysaccharide (CPS) serotypes (10F, 10A, 10B, and 10C). In the present study, the structures of CPS10B and CPS10C were determined by chemical and high resolution NMR methods to define the features of each serotype. Both CPS10C and CPS10F had β1-6-linked Galf branches formed from the termini of linear repeating units by wzy-dependent polymerization through the 4-OH of subterminal GalNAc. The only difference between these polysaccharides was the wcrC-dependent α1-2 or wcrF-dependent α1-4 linkages between Gal and ribitol-5-phosphate. The presence of one linkage or the other also distinguished the repeating units of CPS10B and CPS10A. However, whereas these polysaccharides both had β1-3-linked Galf branches linked to GalNAc, only CPS10A had additional β1-6-linked Galp branches. These Galp branches and the reaction of a CPS10A-specific monoclonal antibody were eliminated by deletion of wcrG from the cps10A locus. In contrast, deletion of this gene from the cps10B locus had no effect on the structure of CPS10B, thereby identifying wcrG as a pseudogene in this serotype. The β1-3-linked Galf branches of CPS10A and CPS10B were eliminated by deletion of wcrD from each corresponding cps locus. Deletion of this gene also eliminated wcrG-dependent β1-6-linked Galp branches from CPS10A, thereby identifying WcrG as a branching enzyme that acts on the product of WcrD. These findings provide a complete view of the molecular, structural, and antigenic features of CPS serogroup 10, as well as insight into the possible emergence of new serotypes.     

Analysis of the 5' portion of the type 19A capsule locus identifies two classes of cpsC, cpsD, and cpsE genes in Streptococcus pneumoniae.

Analysis of the sequence data obtained from the 5' portion of the Streptococcus pneumoniae type 19A capsular polysaccharide biosynthesis locus (cps19a) revealed that the first seven genes are homologous to the first seven genes in the type 19F (cps19f) locus. The former genes were designated cps19aA to -G and were 70 to 90% identical to their cps19f counterparts. Southern hybridization analysis of the cps loci from various S. pneumoniae serotypes with probes specific for the cps19aC, cps19aD, and cps19aE genes indicated a hybridization pattern complementary to that previously reported for cps19fC, cps19fD, and cps19fE. That is, all serotypes tested contained high-stringency homologues of either the cps19aC to -E genes or the cps19fC to -E genes, but not both. On this basis S. pneumoniae cps loci can be divided into two distinct classes. Long-range PCR was used to amplify the cps regions between cpsB and aliA from a variety of pneumococcal serotypes. Direct sequencing of the 5' end of these PCR products, and phylogenetic analysis of the sequence data, confirmed the presence of the two distinct classes of cpsC. Whereas members within one class are greater than 95% identical to each other, the DNA sequence identity between the two classes is only approximately 70%.     

Selective and Genetic Constraints on Pneumococcal Serotype Switching

Streptococcus pneumoniae isolates typically express one of over 90 immunologically distinguishable polysaccharide capsules (serotypes), which can be classified into “serogroups” based on cross-reactivity with certain antibodies. Pneumococci can alter their serotype through recombinations affecting the capsule polysaccharide synthesis (cps) locus. Twenty such “serotype switching” events were fully characterised using a collection of 616 whole genome sequences from systematic surveys of pneumococcal carriage. Eleven of these were within-serogroup switches, representing a highly significant (p < 0.0001) enrichment based on the observed serotype distribution. Whereas the recombinations resulting in between-serogroup switches all spanned the entire cps locus, some of those that caused within-serogroup switches did not. However, higher rates of within-serogroup switching could not be fully explained by either more frequent, shorter recombinations, nor by genetic linkage to genes involved in β–lactam resistance. This suggested the observed pattern was a consequence of selection for preserving serogroup. Phenotyping of strains constructed to express different serotypes in common genetic backgrounds was used to test whether genotypes were physiologically adapted to particular serogroups. These data were consistent with epistatic interactions between the cps locus and the rest of the genome that were specific to serotype, but not serogroup, meaning they were unlikely to account for the observed distribution of capsule types. Exclusion of these genetic and physiological hypotheses suggested future work should focus on alternative mechanisms, such as host immunity spanning multiple serotypes within the same serogroup, which might explain the observed pattern.     

Genetic analysis of the capsular polysaccharide synthesis locus in 15 Streptococcus suis serotypes

The capsular polysaccharide (CPS) synthesis locus of 13 Streptococcus suis serotypes (serotype 1, 3, 4, 5, 7, 8, 9, 10, 14, 19, 23, 25 and 1/2) was sequenced and compared with that of serotype 2 and 16. The CPS synthesis locus of these 15 serotypes falls into two genetic groups. The locus is located on the chromosome between orfZ and aroA. All the translated proteins in the CPS synthesis locus were clustered into 127 homology groups using the tribemcl algorithm. The general organization of the locus suggested that the CPS of S.?suis could be synthesized by the Wzy-dependent pathway. The capsule of serotypes 3, 4, 5, 7, 9, 10, 19 and 23 was predicted to be amino-polysaccharide. Sialic acid was predicted to be present in the capsule of serotypes 1, 2, 14, 16 and 1/2. The characteristics of the CPS synthesis locus suggest that some genes may have been imported into S.?suis (or their ancestors) on multiple occasions from different and unknown sources.     

Construction of otherwise isogenic serotype 6B, 7F, 14, and 19F capsular variants of Streptococcus pneumoniae strain TIGR4

The polysaccharide capsule is the primary virulence factor in Streptococcus pneumoniae. There are at least 90 serotypes of S. pneumoniae, identified based on the immunogenicity of different capsular sugars. The aim of this study was to construct pneumococcal strains that are isogenic except for capsular type. Serotype 4 strain TIGR4 was rendered unencapsulated by recombinational replacement of the capsular polysaccharide synthesis (cps) locus with the bicistronic Janus cassette (C. K. Sung, J. P. Claverys, and D. A. Morrison, Appl. Environ. Microbiol. 67:5190-5196, 2001). In subsequent transformation with chromosomal DNA, the cassette was replaced by the cps locus derived from a strain of a different serotype, either 6B, 7F, 14, or 19F. To minimize the risk of uncontrolled recombinational replacements in loci other than cps, the TIGRcps::Janus strain was "backcross" transformed three times with chromosomal DNA of subsequently constructed capsular type transformants. Capsular serotypes were confirmed in all new capsule variants by the Quellung reaction. Restriction fragment length polymorphism (RFLP) analysis of the cps locus confirmed the integrity of the cps region transformed into the TIGR strain, and RFLP of the flanking regions confirmed their identities with the corresponding regions of the recipient. Transformants had in vitro growth rates greater than or equal to that of TIGR4. All four strains were able to colonize C57BL/6 mice (female, 6 weeks old) for at least 7 days when mice were intranasally inoculated with 6 x 10(6) to 8 x 10(6) CFU. The constructed capsular variants of TIGR4 are suitable for use in studies on the role of S. pneumoniae capsular polysaccharide in immunity, colonization, and pathogenesis.     

Simple sequence repeat-based assessment of genetic relationships among Prunus rootstocks

Ten SSR loci, previously developed for Prunus, were analyzed to examine genetic relationships among 23 rootstock candidates for sweet and sour cherries, of the species P. avium, P. cerasus, P. mahaleb, and P. angustifolia. Five genotypes of P. laurocerasus, not used as rootstock, were included in the molecular analysis. The number of alleles per locus ranged from 8 to 12, with a mean of 9, while the number of microsatellite genotypes varied from 8 to 17, indicating that the SSRs were highly informative. The degree of heterozygosity (0.61) was high. Clustering analysis resulted in two main clusters. The first cluster was divided into two subclusters; the first subcluster consisted of P. avium and P. cerasus, and the second subcluster consisted of P. laurocerasus. The second cluster was divided into two subclusters. The first subcluster consisted of P. mahaleb genotypes and the second consisted of P. angustifolia genotypes. The reference rootstocks also clustered with their associated botanical species. Unweighted pair-group method with arithmetic mean analysis demonstrated that P. laurocerasus genotypes had less genetic variation and that P. avium genotypes were more closely related to P. cerasus. The SSR-based phylogeny was generally consistent with Prunus taxonomy information, suggesting the applicability of SSR analysis for genotyping and phylogenetic studies in the genus Prunus.     

Sequence diversity within the capsular genes of Streptococcus pneumoniae serogroup 6 and 19

The main virulence factor of Streptococcus pneumoniae is the capsule. The polysaccharides comprising this capsule are encoded by approximately 15 genes and differences in these genes result in different serotypes. The aim of this study was to investigate the sequence diversity of the capsular genes of serotypes 6A, 6B, 6C, 19A and 19F and to explore a possible effect of vaccination on variation and distribution of these serotypes in the Netherlands. The complete capsular gene locus was sequenced for 25 serogroup 6 and for 20 serogroup 19 isolates. If one or more genes varied in 10 or more base pairs from the reference sequence, it was designated as a capsular subtype. Allele-specific PCRs and specific gene sequencing of highly variable capsular genes were performed on 184 serogroup 6 and 195 serogroup 19 isolates to identify capsular subtypes. This revealed the presence of 6, 3 and a single capsular subtype within serotypes 6A, 6B and 6C, respectively. The serotype 19A and 19F isolates comprised 3 and 4 capsular subtypes, respectively. For serogroup 6, the genetic background, as determined by multi locus sequence typing (MLST) and multiple-locus variable number of tandem repeat analysis (MLVA), seemed to be closely related to the capsular subtypes, but this was less pronounced for serogroup 19 isolates. The data also suggest shifts in the occurrence of capsular subtypes within serotype 6A and 19A after introduction of the 7-valent pneumococcal vaccine. The shifts within these non-vaccine serotypes might indicate that these capsular subtypes are filling the niche of the vaccine serotypes. In conclusion, there is considerable DNA sequence variation of the capsular genes within pneumococcal serogroup 6 and 19. Such changes may result in altered polysaccharides or in strains that produce more capsular polysaccharides. Consequently, these altered capsules may be less sensitive for vaccine induced immunity.     

The serotype of type Ia and III group B streptococci is determined by the polymerase gene within the polycistronic capsule operon

Streptococcus agalactiae is a primary cause of neonatal morbidity and mortality. Essential to the virulence of this pathogen is the production of a type-specific capsular polysaccharide (CPS) that enables the bacteria to evade host immune defenses. The identification, cloning, sequencing, and functional characterization of seven genes involved in type III capsule production have been previously reported. Here, we describe the cloning and sequencing of nine additional adjacent genes, cps(III)FGHIJKL, neu(III)B, and neu(III)C. Sequence comparisons suggested that these genes are involved in sialic acid synthesis, pentasaccharide repeating unit formation, and oligosaccharide transport and polymerization. The type III CPS (cpsIII) locus was comprised of 16 genes within 15.5 kb of contiguous chromosomal DNA. Primer extension analysis and investigation of mRNA from mutants with polar insertions in their cpsIII loci supported the hypothesis that the operon is transcribed as a single polycistronic message. The translated cpsIII sequences were compared to those of the S. agalactiae cpsIa locus, and the primary difference between the operons was found to reside in cps(III)H, the putative CPS polymerase gene. Expression of cps(III)H in a type Ia strain resulted in suppression of CPS Ia synthesis and in production of a CPS which reacted with type III-specific polyclonal antibody. Likewise, expression of the putative type Ia polymerase gene in a type III strain reduced synthesis of type III CPS with production of a type Ia immunoreactive capsule. Based on the similar structures of the oligosaccharide repeating units of the type Ia and III capsules, our observations demonstrated that cps(Ia)H and cps(III)H encoded the type Ia and III CPS polymerases, respectively. Additionally, these findings suggested that a single gene can confer serotype specificity in organisms that produce complex polysaccharides.     

The glucosyl-1-phosphate transferase WchA (Cap8E) primes the capsular polysaccharide repeat unit biosynthesis of Streptococcus pneumoniae serotype 8

The gene wchA (cap8E) belongs to the cps8 locus that is involved in biosynthesis of the capsular polysaccharide (CPS) repeat unit (RU) of the virulent Streptococcus pneumoniae serotype 8. We report here the biochemical characterization of the membrane-associated protein WchA (Cap8E), overexpressed in Escherichia coli BL21(DE3)/pLysS. Our results demonstrate that the recombinant enzyme transfers in vitro a glucosyl-1-phosphate from UDP-glucose to an endogenous phosphoryl-polyprenol, thereby priming the RU biosynthetic pathway of S. pneumoniae CPS 8. We also show that the C-terminal half of WchA is the glycosyltransferase domain as observed for the galactosyl-1-phosphate transferase WbaP from Salmonella enterica, previously described to prime the first step of O-antigen biosynthesis. These results demonstrate that WchA plays a prominent function in the capsule biosynthesis and explain the key role it occupies in the pneumococcal capsule variation.     

Elucidation of structural and antigenic properties of pneumococcal serotype 11A, 11B, 11C, and 11F polysaccharide capsules

Despite the emerging impact of serogroup 11 serotypes in Streptococcus pneumoniae epidemiology, the structures of serogroup 11 capsule types have not been fully elucidated, particularly the locations of O-acetyl substitutions. Here, we report the complete structures of the serotype 11B, 11C, and 11F polysaccharides and a revision to the serotype 11A capsular polysaccharide using nuclear magnetic resonance (NMR). All structures shared a linear, tetrasaccharide backbone with a pendant phosphopolyalcohol. Three of four saccharides are conserved in all serotypes. The individual serotype capsules differed in the identity of one saccharide, the pendant phosphopolyalcohol, and the O-acetylation pattern. Though the assigned locations of O-acetate substitutions in this study differed from those of previous reports, our findings were corroborated with strong correlations to serology and genetics. We examined the binding of serotyping sera to serogroup 11 polysaccharides by using flow cytometry and an inhibition-type enzyme-linked immunosorbent assay (ELISA) and found that de-O-acetylation of capsular polysaccharides by mild hydrolysis decreases its immunoreactivity, supporting the crucial role of O-acetylation in the antigenicity of these polysaccharides. Due to strong correlations between polysaccharide structures and capsule biosynthesis genes, we were able to assign target substrates for the O-acetyltransferases encoded by wcwC, wcwR, wcwT, and wcjE. We identified antigenic determinants for serogroup 11 serotyping sera and highlight the idea that conventional serotyping methods are not capable of recognizing all putative variants of S. pneumoniae serogroup 11.     

Analysis of Campylobacter jejuni capsular loci reveals multiple mechanisms for the generation of structural diversity and the ability to form complex heptoses

We recently demonstrated that Campylobacter jejuni produces a capsular polysaccharide (CPS) that is the major antigenic component of the classical Penner serotyping system distinguishing Campylobacter into >60 groups. Although the wide variety of C. jejuni serotypes are suggestive of structural differences in CPS, the genetic mechanisms of such differences are unknown. In this study we sequenced biosynthetic cps regions, ranging in size from 15 to 34 kb, from selected C. jejuni strains of HS:1, HS:19, HS:23, HS:36, HS:23/36 and HS:41 serotypes. Comparison of the determined cps sequences of the HS:1, HS:19 and HS:41 strains with the sequenced strain, NCTC11168 (HS:2), provides evidence for multiple mechanisms of structural variation including exchange of capsular genes and entire clusters by horizontal transfer, gene duplication, deletion, fusion and contingency gene variation. In contrast, the HS:23, HS:36 and HS:23/36 cps sequences were highly conserved. We report the first detailed structural analysis of 81-176 (HS:23/36) and G1 (HS:1) and refine the previous structural interpretations of the HS:19, HS:23, HS:36 and HS:41 serostrains. For the first time, we demonstrate the commonality and function of a second heptose biosynthetic pathway for Campylobacter CPS independent of the pathway for lipooligosaccharide (LOS) biosynthesis and identify a novel heptosyltransferase utilized by this alternate pathway. Furthermore, we show the retention of two functional heptose isomerases in Campylobacter and the sharing of a phosphatase for both LOS and CPS heptose biosynthesis.     

Population pattern of pneumococci with lower susceptibility to penicillin and prospects of antipneumococcal vaccination to control antibiotic resistance distribution

Large-scale antipneumococcal vaccination is followed by changes in the serotype composition and level of antibiotic resistance in pneumococci. The aim of the study was to evaluate the serotype composition and population pattern of pneumococci with lower susceptibility to penicillin before large-scale antipneumococcal vaccination. Among 260 Streptococcus pneumoniae strains isolated in the Russian Federation within 2003-2007, serotypes 23F (37.2%) and 19F (13.9%) were the most frequent ones. 19.3% of the isolates belonged to serogroup 6, 3.6% of the isolates each belonged to serotype 3 and serogroup 18, 4.9% of the isolates belonged to serotype 14 and 2.2% of the isolates belonged to serotype 19A. 66.8% of the isolates belonged to serotypes of the 7-valent conjugated pneumococcal vaccine, 67.3 and 82.1% of the isolates belonged to the 10- and 13-valent conjugated pneumococcal vaccines respectively. The isolates with lower susceptibility to penicillin were characterized by significant clonality and 56.9% of them belonged to 4 global clonal complexes (CC81, CC156, CC320 and CC315). Inclusion of the conjugated antipneumococcal vaccine to the National Vaccination Time-Table of the Russian Federation could promote lower levels of antibiotic resistance in pneumococci.     

Streptococcus pneumoniae Serotype 11D Has a Bispecific Glycosyltransferase and Expresses Two Different Capsular Polysaccharide Repeating Units

Streptococcus pneumoniae (pneumococcus) expresses a capsular polysaccharide (CPS) that protects against host immunity and is synthesized by enzymes in the capsular polysaccharide synthesis (cps) locus. Serogroup 11 has six members (11A to -E) and the CPS structure of all members has been solved, except for serotype 11D. The cps loci of 11A and 11D differ by one codon (N112S) in wcrL, which putatively encodes a glycosyltransferase that adds the fourth sugar of the CPS repeating unit (RU). Gas chromatography and nuclear magnetic resonance analysis revealed that 11A and 11D PSs contain identical CPS RUs that contain αGlc as the fourth sugar. However, ∼25% of 11D CPS RUs contain instead αGlcNAc as the fourth sugar, suggesting that 11D wcrL encodes a bispecific glycosyltransferase. To test the hypothesis that codon 112 of WcrL determines enzyme specificity, and therefore the fourth sugar in the RU, we generated three isogenic pneumococcal strains with 11A cps loci containing wcrL encoding Ser-112 (MBO128) or Ala-112 (MBO130). MBO128 was serologically and biochemically identical to serotype 11D. MBO130 has a unique serologic profile; has as much αGlcNAc as 11F, 11B, and 11C CPS do; and may represent a new serotype. These findings demonstrate how pneumococci alter their CPS structure and their immunologic properties with a minimal genetic change.     

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.     

Characterization of the O-antigen gene clusters of Yersinia pseudotuberculosis and the cryptic O-antigen gene cluster of Yersinia pestis shows that the plague bacillus is most closely related to and has evolved from Y. pseudotuberculosis serotype O:1b

One of the most virulent and feared bacterial pathogens is Yersinia pestis, the aetiologic agent of bubonic plague. Characterization of the O-antigen gene clusters of 21 serotypes of Yersinia pseudotuberculosis and the cryptic O-antigen gene cluster of Y. pestis showed that the plague bacillus is most closely related to and has evolved from Y. pseudotuberculosis serotype O:1b. The nucleotide sequences of both gene clusters (about 20.5 kb each) were determined and compared to identify the differences that caused the silencing of the Y. pestis gene cluster. At the nucleotide sequence level, the loci were 98.9% identical and, of the 17 biosynthetic genes identified from the O:1b gene cluster, five were inactivated in the Y. pestis cluster, four by insertions or deletions of one nucleotide and one by a deletion of 62 nucleotides. Apparently, the expression of the O-antigen is not beneficial for the virulence or to the lifestyle of Y. pestis and, therefore, as one step in the evolution of Y. pestis, the O-antigen gene cluster was inactivated.     

Emerging,Non-PCV13 Serotypes 11A and 35B of Streptococcus pneumoniae Show High Potential for Biofilm Formation In Vitro

Background

Since the use of pneumococcal conjugate vaccines PCV7 and PCV13 in children became widespread, invasive pneumococcal disease (IPD) has dramatically decreased. Nevertheless, there has been a rise in incidence of Streptococcus pneumoniae non-vaccine serotypes (NVT) colonising the human nasopharynx. Nasopharyngeal colonisation, an essential step in the development of S. pneumoniae-induced IPD, is associated with biofilm formation. Although the capsule is the main pneumococcal virulence factor, the formation of pneumococcal biofilms might, in fact, be limited by the presence of capsular polysaccharide (CPS).

Methodology/Principal Findings

We used clinical isolates of 16 emerging, non-PCV13 serotypes as well as isogenic transformants of the same serotypes. The biofilm formation capacity of isogenic transformants expressing CPSs from NVT was evaluated in vitro to ascertain whether this trait can be used to predict the emergence of NVT. Fourteen out of 16 NVT analysed were not good biofilm formers, presumably because of the presence of CPS. In contrast, serotypes 11A and 35B formed ≥45% of the biofilm produced by the non-encapsulated M11 strain.

Conclusions/Significance

This study suggest that emerging, NVT serotypes 11A and 35B deserve a close surveillance.