Structure of the capsular polysaccharide of pneumococcal serotype 11A reveals a novel acetylglycerol that is the structural basis for 11A subtypes

Rapid cyclic ion mobility separations of monosaccharide building blocks as a first step toward a high-throughput reaction screening platform for carbohydrate syntheses

Herein we present a new high-throughput screening method for carbohydrate syntheses based on cyclic ion mobility spectrometry-mass spectrometry (cIMS-MS)-based separations. We rapidly resolved the α/β anomers for carbohydrates with varying protecting groups after only 5 m of cIMS-MS separation and also detected their respective unwanted anomeric impurities at levels lower than 2%. All experiments were performed in 1 minute of total acquisition time demonstrating our method's high-throughput nature. Our methodology was also extended to the separation of an isomeric mixtures of two protected disaccharides illustrating its utility beyond only monosaccharides. We envision our presented workflow as a first step toward the development of a high-throughput screening platform for the rapid and sensitive detection of α/β anomeric selectivities and for trace isomeric/isobaric impurities.

Recent chemical syntheses of bacteria related oligosaccharides using modern expeditious approaches

Apart from some essential and crucial roles in life processes carbohydrates also are involved in a few detrimental courses of action related to human health, like infections by pathogenic microbes, cancer metastasis, transplanted tissue rejection, etc. Regarding management of pathogenesis by microbes, keeping in mind of multi drug-resistant bacteria and epidemic or endemic incidents, preventive measure by vaccination is the best pathway as also recommended by the WHO; by vaccination, eradication of bacterial diseases is also possible. Although some valid vaccines based on attenuated bacterial cells or isolated pure polysaccharide-antigens or the corresponding conjugates thereof are available in the market for prevention of several bacterial diseases, but these are not devoid of some disadvantages also. In order to develop improved conjugate T-cell dependent vaccines oligosaccharides related to bacterial antigens are synthesized and converted to the corresponding carrier protein conjugates. Marketed Cuban Quimi-Hib is such a vaccine being used since 2004 to resist Haemophilus influenza b infections. During nearly the past two decades research is going on worldwide for improved synthesis of bacteria related oligosaccharides or polysaccharides towards development of such semisynthetic or synthetic glycoconjugate vaccines. The present dissertation is an endeavour to encompass the recent syntheses of several pathogenic bacterial oligosaccharides or polysaccharides, made during the past ten-eleven years with special reference to modern expeditious syntheses.

Protocol for the purification of protected carbohydrates: toward coupling automated synthesis to alternate-pump recycling high-performance liquid chromatography

Given recent advances in automated oligosaccharide synthesis, analytical techniques that can be coupled to a synthetic framework are needed to not just identify but also purify to homogeneity protected carbohydrate compounds at levels of ≥99.5% purity. Herein, an alternate-pump recycling high-performance liquid chromatography (R-HPLC) method has been developed to allow purification of protected carbohydrates at levels of ≥99.5% purity.

Identification of a capsular variant and characterization of capsular acetylation in Klebsiella pneumoniae PLA-associated type K57

Klebsiella pneumoniae can cause community-acquired pyogenic liver abscess (PLA). Capsular polysaccharide (CPS) is important for its virulence. Among 79 capsular (K) types discovered thus far, K57 is often associated with PLA. Here, we report the identification of a K57 variant. Cps gene locus sequencing revealed differences between the K57 reference strain 4425/51 (Ref-K57) and a variant, the PLA isolate A1142. While Ref-K57 cps contained orf13 encoding a putative acetyltransferase, the insertion of a putative transposase-encoding gene at this position was detected in A1142. This variation was detected in other K57 clinical strains. Biochemical analyses indicated that A1142 was deficient in CPS acetylation. Genetic replacement and complementation verified that orf13 was responsible for CPS acetylation. Acetylation increased CPS immunoreactivity to antiserum and enhanced K. pneumoniae induction of pro-inflammatory cytokines through JNK and MAPK signaling. While acetylation diminished the serum resistance of bacteria, it promoted adhesion to intestinal epithelial cells possibly via increasing production of type I fimbriae. In conclusion, acetylation-mediated capsular variation in K57 was observed. Capsular acetylation contributed to the variety and antigenic diversity of CPS, influenced its biological activities, and was involved in K. pneumoniae-host interactions. These findings have implications for vaccine design and pathogenicity of K. pneumoniae.

Effects of PCV7 and PCV13 on invasive pneumococcal disease and carriage in Stockholm, Sweden

The effects of pneumococcal conjugated vaccines (PCVs) need to be investigated. In Stockholm County, Sweden, PCV7 was introduced in the childhood immunisation programme in 2007 and changed to PCV13 in 2010.Over 90% of all invasive isolates during 2005-2014 (n=2336) and carriage isolates, 260 before and 647 after vaccine introduction, were characterised by serotyping, molecular typing and antibiotic susceptibility, and serotype diversity was calculated. Clinical information was collected for children and adults with invasive pneumococcal disease (IPD).The IPD incidence decreased post-PCV7, but not post-PCV13, in vaccinated children. Beneficial herd effects were seen in older children and adults, but not in the elderly. The herd protection was more pronounced post-PCV7 than post-PCV13. PCV7 serotypes decreased. IPD caused by PCV13 serotypes 3 and 19A increased post-PCV7. Post-PCV13, serotypes 6A and 19A, but not serotype 3, decreased. The serotype distribution changed in carriage and IPD to nonvaccine types, also in nonvaccinated populations. Expansion of non-PCV13 serotypes was largest following PCV13 introduction. Serotype diversity increased and nonvaccine clones emerged, such as CC433 (serotype 22F) in IPD and CC62 (serotype 11A) in carriage. In young children, meningitis, septicaemia and severe rhinosinusitis, but not bacteraemic pneumonia, decreased.Pneumococcal vaccination leads to expansion of new or minor serotypes/clones, also in nonvaccinated populations.

Pneumococcal Capsules and Their Types: Past, Present, and Future

Streptococcus pneumoniae (the pneumococcus) is an important human pathogen. Its virulence is largely due to its polysaccharide capsule, which shields it from the host immune system, and because of this, the capsule has been extensively studied. Studies of the capsule led to the identification of DNA as the genetic material, identification of many different capsular serotypes, and identification of the serotype-specific nature of protection by adaptive immunity. Recent studies have led to the determination of capsular polysaccharide structures for many serotypes using advanced analytical technologies, complete elucidation of genetic basis for the capsular types, and the development of highly effective pneumococcal conjugate vaccines. Conjugate vaccine use has altered the serotype distribution by either serotype replacement or switching, and this has increased the need to serotype pneumococci. Due to great advances in molecular technologies and our understanding of the pneumococcal genome, molecular approaches have become powerful tools to predict pneumococcal serotypes. In addition, more-precise and -efficient serotyping methods that directly detect polysaccharide structures are emerging. These improvements in our capabilities will greatly enhance future investigations of pneumococcal epidemiology and diseases and the biology of colonization and innate immunity to pneumococcal capsules.

Enzymatic modifications of exopolysaccharides enhance bacterial persistence

Biofilms are surface-attached communities of bacterial cells embedded in a self-produced matrix that are found ubiquitously in nature. The biofilm matrix is composed of various extracellular polymeric substances, which confer advantages to the encapsulated bacteria by protecting them from eradication. The matrix composition varies between species and is dependent on the environmental niche that the bacteria inhabit. Exopolysaccharides (EPS) play a variety of important roles in biofilm formation in numerous bacterial species. The ability of bacteria to thrive in a broad range of environmental settings is reflected in part by the structural diversity of the EPS produced both within individual bacterial strains as well as by different species. This variability is achieved through polymerization of distinct sugar moieties into homo- or hetero-polymers, as well as post-polymerization modification of the polysaccharide. Specific enzymes that are unique to the production of each polymer can transfer or remove non-carbohydrate moieties, or in other cases, epimerize the sugar units. These modifications alter the physicochemical properties of the polymer, which in turn can affect bacterial pathogenicity, virulence, and environmental adaptability. Herein, we review the diversity of modifications that the EPS alginate, the Pel polysaccharide, Vibrio polysaccharide, cepacian, glycosaminoglycans, and poly-N-acetyl-glucosamine undergo during biosynthesis. These are EPS produced by human pathogenic bacteria for which studies have begun to unravel the effect modifications have on their physicochemical and biological properties. The biological advantages these polymer modifications confer to the bacteria that produce them will be discussed. The expanding list of identified modifications will allow future efforts to focus on linking these modifications to specific biosynthetic genes and biofilm phenotypes.

Low invasiveness of pneumococcal serotype 11A is linked to ficolin-2 recognition of O-acetylated capsule epitopes and lectin complement pathway activation

BACKGROUND

The divergent epidemiological behavior of Streptococcus pneumoniae serotypes suggests that serotype-specific features such as capsule O-acetylation influence the propensity of a strain to cause invasive pneumococcal disease (IPD). We hypothesize that innate host factors mediate the observed negative association between IPD and the serotype 11A (ST11A) capsule O-acetyltransferase gene, wcjE.

METHODS

We evaluated the ability of ficolin-2, an initiator of the lectin complement pathway that was previously shown to bind ST11A pneumococci, to recognize and mediate complement-dependent opsonophagocytosis of different pneumococcal serotypes. We supplemented findings with an epidemiological meta-analysis comparing invasiveness of the 30 most prevalent pneumococcal serotypes.

RESULTS

Ficolin-2 bound ST11A capsule polysaccharide and other wcjE-containing pneumococcal serotypes, except ST9V and ST20B. Ficolin-2 did not bind wcjE-null serotypes, including the wcjE-null variant of ST11A, ST11E. We observed C1q-independent complement deposition and phagocytic killing of pneumococci expressing ST11A but not those expressing ST11E. Inhibition of ficolin-2 binding abrogated ST11A-associated complement deposition and phagocytosis. In children, invasiveness of ST11A was the lowest among serotypes tested in our meta-analysis, while ST9V was among the highest.

CONCLUSIONS

Ficolin-2 mediates serum protection by recognizing specific O-acetylated epitopes of pneumococcal capsule polysaccharides, exemplifying a novel host-microbe interaction that innately offers serotype-specific immunity to IPD.

Identification of Streptococcus pneumoniae serotype 11E, serovariant 11Av and mixed populations by high-resolution magic angle spinning nuclear magnetic resonance (HR-MAS NMR) spectroscopy and flow cytometric serotyping assay (FCSA)

Background

Recent studies have identified Streptococcus pneumoniae serotype 11E and serovariant 11Av among isolates previously typed as 11A by classical serotyping methods. Serotype 11E and serovariant 11Av differ from serotype 11A by having totally or partially inactive wcjE, a gene in cps locus coding for an O-acetyl transferase. Serotype 11E is rare among carriage isolates but common among invasive isolates suggesting that it survives better during invasion. Aim of this work was to investigate the epidemiology of serotype 11A in a pneumococcal collection using a new serotyping approach based on High-Resolution Magic Angle Spinning Nuclear Magnetic Resonance (HR-MAS NMR) spectroscopy to distinguish serotypes 11A and 11E.

Methods

A collection of 48 (34 invasive and 14 carriage) S. pneumoniae isolates from Italy, previously identified as serotype 11A by the Quellung reaction, were investigated by wcjE sequencing, HR-MAS NMR spectroscopy and the reference flow cytometric serotyping assay (FCSA) based on monoclonal antibodies.

Results

HR-MAS NMR spectra from serotypes 11A and 11E showed different NMR peaks indicating that HR-MAS NMR could be used to distinguish these serotypes, although HR-MAS NMR could not distinguish serotype 11Av from serotype 11E unambiguously. Thirty-eight isolates were confirmed to be serotype 11A, 8 isolates with a mutated wcjE were serotype 11E, 1 isolate belonged to serovariant 11Av, and 1 isolate was a mixed population 11A/11Av. All 11E isolates were identified among invasive isolates.

Conclusions

We proved that HR-MAS NMR can be of potential use for pneumococcal serotyping. The detection of serotype 11E among invasive isolates in our collection, supports previous epidemiological studies suggesting that mutations in wcjE can represent a mechanism promoting pneumococcal survival during invasion. The discovery of a spectrum of immunochemical diversity within established serotypes should stimulate efforts to develop new serotyping approaches.

Spectrum of pneumococcal serotype 11A variants results from incomplete loss of capsule O-acetylation

Streptococcus pneumoniae is a significant bacterial pathogen that expresses >90 capsule serotypes. Conventional serotyping methods assume that each serotype is a genetically and antigenically distinct entity; however, recent investigations have revealed pneumococcal isolates that cannot be unambiguously serotyped because they share the properties of more than one serotype. Here, we employed a novel serotyping method and NMR spectroscopy to examine clinical isolates sharing properties of serotypes 11A and 11E. These ambiguous clinical isolates were provisionally named 11A variant (11Av) isolates. Serotype 11A pneumococci characteristically express capsule β-galactose-6-O-acetylation (βGal6OAc) mediated by the capsule synthesis gene wcjE, while 11E strains contain loss-of-function mutations in wcjE and completely lack the expression of βGal6OAc. Although 11Av isolates also contained mutated wcjE alleles, 11Av clinical isolates were composed of antigenically homogeneous bacteria expressing reduced amounts of 11A-specific capsule antigen. NMR data confirmed reduced but detectable amounts of βGal6OAc on 11Av capsule polysaccharide. Furthermore, the transformation of strains with wcjE alleles from 11Av strains was sufficient to restore partial βGal6OAc in an 11E background. We conclude that, instead of being distinct entities, serotypes 11A and 11E represent two extremes of an antigenic spectrum resulting from variable capsule O-acetylation secondary to heterologous wcjE mutations. These findings challenge whether all clinically relevant pneumococci can be definitively categorized into distinct serotypes.

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.

Structural characterization of Streptococcus pneumoniae serotype 9A capsule polysaccharide reveals role of glycosyl 6-O-acetyltransferase wcjE in serotype 9V capsule biosynthesis and immunogenicity

The putative capsule O-acetyltransferase gene wcjE is highly conserved across various Streptococcus pneumoniae serotypes, but the role of the gene in capsule biosynthesis and bacterial fitness remains largely unclear. Isolates expressing pneumococcal serotype 9A arise from precursors expressing wcjE-associated serotype 9V through loss-of-function mutation to wcjE. To define the biosynthetic role of 9V wcjE, we characterized the structure and serological properties of serotype 9V and 9A capsule polysaccharide (PS). NMR data revealed that both 9V and 9A PS are composed of an identical pentasaccharide repeat unit, as reported previously. However, in sharp contrast to previous studies on 9A PS being devoid of any O-acetylation, we identified O-acetylation of α-glucuronic acid and α-glucose in 9A PS. In addition, 9V PS also contained -CH(2) O-acetylation of β-N-acetylmannosamine, a modification that disappeared following in vitro recombinatorial deletion of wcjE. We also show that serotyping sera and monoclonal antibodies specific for 9V and 9A bound capsule PS in an O-acetate-dependent manner. Furthermore, IgG and to a lesser extent IgM from human donors immunized with serotype 9V PS displayed stronger binding to 9V compared with 9A PS. We conclude that serotype 9V wcjE mediates 6-O-acetylation of β-N-acetylmannosamine. This PS modification can be selectively targeted by antibodies in immunized individuals, identifying a potential selective advantage for wcjE inactivation and serotype 9A emergence.

The use of 1H-31P GHMBC and covariance NMR to unambiguously determine phosphate ester linkages in complex polysaccharide mixtures

Poly- and oligo-saccharides are commonly employed as antigens in many vaccines. These antigens contain phosphoester structural elements that are crucial to the antigenicity, and hence the effectiveness of the vaccine. Nuclear Magnetic Resonance (NMR) is a powerful tool for the site-specific identification of phosphoesters in saccharides. We describe here two advances in the characterization of phosphoesters in saccharides: (1) the use of (1)H-(31)P GHMBC to determine the site-specific identity of phosphoester moieties in heterogeneous mixtures and (2) the use of Unsymmetrical/Generalized Indirect Covariance (U/GIC) to calculate a carbon-phosphorus 2D spectrum. The sensitivity of the (1)H-(31)P GHMBC is far greater than the "standard" (1)H-(31)P GHSQC and allows long-range (3-5)J(HP) couplings to be readily detected. This is the first example to be reported of using U/GIC to calculate a carbon-phosphorus spectrum. The U/GIC processing affords, in many cases, a fivefold to tenfold or greater increase in signal-to-noise ratios in the calculated spectrum. When coupled with the high sensitivity of (1)H-(31)P HMBC, U/GIC processing allows the complete and unambiguous assignments of phosphoester moieties present in heterogeneous samples at levels of ~5% (or less) of the total sample, expanding the breadth of samples that NMR can be used to analyze. This new analytical technique is generally applicable to any NMR-observable phosphoester.

Development of an automated and multiplexed serotyping assay for Streptococcus pneumoniae

Streptococcus pneumoniae expresses more than 90 capsule types, and currently available pneumococcal vaccines are designed to provide serotype-specific protection. Consequently, serotyping of pneumococcal isolates is important for determining the serotypes to be included in pneumococcal vaccines and to monitor their efficacy. Yet serotyping of pneumococcal isolates has remained a significant technical challenge. By multiplexing many assays, we have now developed a simple yet comprehensive serotyping assay system that can not only identify all known pneumococcal serotypes but also subdivide nontypeable (NT) isolates into those with or without the conventional capsule locus. We have developed this assay system to require only six key reagents: two are used in one multiplex inhibition-type immunoassay, and four are required in two multiplex PCR-based assays. The assay system is largely automated by a seamless combination of monoclonal antibody-based and PCR-based multiplex assays using the flow cytometric bead array technology from Luminex. The assay system has been validated with a panel of pneumococci expressing all known pneumococcal serotypes and was found to be easily transferable to another laboratory.

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.

BgaA acts as an adhesin to mediate attachment of some pneumococcal strains to human epithelial cells

Streptococcus pneumoniae colonization of the respiratory tract is an essential precursor for pneumococcal disease. To colonize efficiently, bacteria must adhere to the epithelial-cell surface. S. pneumoniae possesses surface-associated exoglycosidases that are capable of sequentially deglycosylating human glycans. Two exoglycosidases, neuraminidase (NanA) and β-galactosidase (BgaA), have previously been shown to contribute to S. pneumoniae adherence to human epithelial cells, as deletion of either of these genes results in reduced adherence. It has been suggested that these enzymes may modulate adherence by cleaving sugars to reveal a receptor on host cells. Pretreatment of epithelial cells with exogenous neuraminidase restores the adherence of a nanA mutant, whereas pretreatment with β-galactosidase does not restore the adherence of a bgaA mutant. These data suggest that BgaA may not function to reveal a receptor, and implicate an alternative role for BgaA in adherence. Here we demonstrate that β-galactosidase activity is not required for BgaA-mediated adherence. Addition of recombinant BgaA (rBgaA) to adherence assays and pretreatment of epithelial cells with rBgaA both significantly reduced the level of adherence of the parental strain, but not the BgaA mutant. One possible explanation of these data is that BgaA is acting as an adhesin and that rBgaA is binding to the receptor, preventing bacterial binding. A bead-binding assay demonstrated that BgaA can bind directly to human epithelial cells, supporting the hypothesis that BgaA is an adhesin. Preliminary characterization of the epithelial-cell receptor suggests that it is a glycan in the context of a glycosphingolipid. To further establish the relevance of this adherence mechanism, we demonstrated that BgaA-mediated adherence contributed to adherence of a recent clinical isolate to primary human epithelial cells. Together, these data suggest a novel role for BgaA as an adhesin and suggest that this mechanism could contribute to adherence of at least some pneumococcal strains in vivo.

A new pneumococcal serotype, 11E, has a variably inactivated wcjE gene

Recently, 2 serologically and biochemically distinct subtypes-11Aalpha and 11Abeta-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 11Abeta phenotype. Directed disruption of wcjE in vitro in an 11Aalpha strain switched the strain to the 11Abeta phenotype, confirming the role played by the gene in the divergence between the subtypes. Furthermore, sequences from 7 11Abeta 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 11Aalpha subtype as serotype 11A and the 11Abeta subtype as 11E, a new serotype. Our findings also suggest that the diversity of pneumococcal capsules is much greater than was previously recognized.

Identification of 3-O-acetylglycerol, a novel structural element in bacterial polysaccharides

We have discovered a novel bacterial polysaccharide structural element, 3-O-acetylglycerol, in the Streptococcus pneumoniae ST11A polysaccharide: This moiety was elucidated through a combination of homonuclear and heteronuclear 1D and 2D NMR experiments using (1)H, (13)C, and (31)P in various combinations. The 3-O-acetylglycerol moiety is substoichiometrically O-acetylated in ST11A; yet, key connectivities that unequivocally show O-acetylation at the glycerol are provided by the long-range correlations from the acetate methyl groups to the glycerol in the (1)H-(13)C HMBC spectrum. Additionally, we clarify the (1)H-(31)P assignments previously presented.

Genetic diversity of the pneumococcal capsule: implications for molecular-based serotyping

Streptococcus pneumoniae remains an important pathogen despite licensure of a seven-valent pneumococcal protein conjugate vaccine. As a result, serotyping strains remains of paramount importance to both assess the effectiveness of current vaccines and closely monitor for the emergence of nonvaccine strains. Given the limitations of the quellung reaction, both molecularand immunology-based serotyping methods have been pursued. Currently, the most promising assay combines an immunologic assay with multiplex PCR of serotype-specific genes. The key limitation with a molecular-based assay is the plasticity of the pneumococcus, as capsular transformation or point mutations could easily result in serotype misclassification. Based on the currently available techniques, a comprehensive immunology-based assay appears to be the most promising alternative to the quellung reaction. In the future, assays that utilize high-throughput sequencing technology and/or matrix-assisted laser desorption ionization–time-of-flight mass spectrometry (MALDI–TOF MS) could lead to a novel pneumococcal serotyping method.

Evaluation of the specificity of pneumococcal polysaccharide enzyme-linked immunosorbent assay and the effect of serum adsorption based on standard pneumococcal serogroup- or serotype-specific rabbit antisera

Worldwide, Streptococcus pneumoniae (pneumococcus) is a major cause of morbidity and mortality, especially in infants and elderly people. Pneumococcal capsular polysaccharides are well characterized, and more than 90 different serotypes have been identified. Serotype-specific antibodies against the capsular polysaccharide are produced during infection. Detection of antibodies against pneumococci by enzyme-linked immunosorbent assay (ELISA) is performed according to WHO guidelines, using antigens provided by ATCC. However, testing the ELISA for specificity is challenging due to the difficulty in obtaining human naïve serum with pneumococcal antibodies as well as human serum with antibodies against a single serotype. The application of well-defined serotype-specific sera produced in animals to evaluate the specificity of the ATCC antigens and the effect of adsorption with cell wall and 22F polysaccharides has not been performed before, to our knowledge. In this study, the specificity of ATCC antigens (serotypes 4, 6B, 9V, 14, 18C, 19F, and 23F) was tested by using commercial serotype-, serogroup-, and pool-specific pneumococcal rabbit antisera.