Biochemical, Genetic, and Serological Characterization of Two Capsule Subtypes among Streptococcus pneumoniae Serotype 20 Strains

Calix, Juan J.; Porambo, Richard J.; Brady, Allison M.; Larson, Thomas R.; Yother, Janet; Abeygunwardana, Chitrananda; Nahm, Moon H.

doi:10.1074/jbc.m112.380451

Cited by 134 publications

(103 citation statements)

References 27 publications

(45 reference statements)

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“…Based on our studies with 11A, 11E, and 11Av, we propose that pneumococcal serotypes 9V and 9A also form two extremes of an antigenic spectrum with intermediate serovariants. Indeed, intermediate serovariants may exist in multiple serogroups, considering that wcjE and wcjE-like O-acetyltransferase genes (i.e., wciG, wciZ, wciX, wcyO, and wcyH) are encoded in the cps loci of multiple serogroups (10,14). These include a few cases in which gene inactivation putatively results in loss of capsule O-acetylation and…”

Section: Discussionmentioning

confidence: 99%

“…We purified capsule PS from the following strains: MNZ2293-A, MNZ2293-C, 3102-06, MNZ264, JC03, JC04, JC12, and JC13. Capsule PS purification was performed as described previously (10). Briefly, PS was obtained by ethanol precipitation from autolyzed bacterial cultures and purified by ion exchange and size exclusion chromatography.…”

Section: Pneumococcal Clinical Isolatesmentioning

confidence: 99%

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Spectrum of Pneumococcal Serotype 11A Variants Results from Incomplete Loss of Capsule O -Acetylation

Calix

Brady

et al. 2014

J Clin Microbiol

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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 ␤-galactose-6-O-acetylation (␤Gal6OAc) mediated by the capsule synthesis gene wcjE, while 11E strains contain loss-of-function mutations in wcjE and completely lack the expression of ␤Gal6OAc. 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 ␤Gal6OAc on 11Av capsule polysaccharide. Furthermore, the transformation of strains with wcjE alleles from 11Av strains was sufficient to restore partial ␤Gal6OAc 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.

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Section: Discussionmentioning

confidence: 99%

Section: Pneumococcal Clinical Isolatesmentioning

confidence: 99%

Spectrum of Pneumococcal Serotype 11A Variants Results from Incomplete Loss of Capsule O -Acetylation

Calix

Brady

et al. 2014

J Clin Microbiol

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“…The chemical composition and linkages between polysaccharide subunits distinguish one capsular serotype from another (10)(11)(12)(13)(14)(15)(24)(25)(26)(27)(28). All serotypes, except for types 3 and 37, are synthesized in a Wzx flippase/Wzy polymerase-dependent fashion (1,25,29,30).…”

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confidence: 99%

Mutations in Pneumococcal cpsE Generated via In Vitro Serial Passaging Reveal a Potential Mechanism of Reduced Encapsulation Utilized by a Conjunctival Isolate

et al. 2015

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The polysaccharide capsule of Streptococcus pneumoniae is required for nasopharyngeal colonization and for invasive disease in the lungs, blood, and meninges. In contrast, the vast majority of conjunctival isolates are acapsular. The first serotype-specific gene in the capsule operon, cpsE, encodes the initiating glycosyltransferase and is one of the few serotype-specific genes that can tolerate null mutations. This report characterizes a spontaneously arising TIGR4 mutant exhibiting a reduced capsule, caused by a 6-nucleotide duplication in cpsE which results in duplication of Ala and Ile at positions 45 and 46. This strain (AI45dup) possessed more exposed phosphorylcholine and was hypersusceptible to C3 complement deposition compared to the wild type. Accordingly, the mutant was significantly better at forming abiotic biofilms and binding epithelial cells in vitro but was avirulent in a sepsis model. In vitro serial passaging of the wild-type strain failed to reproduce the AI45dup mutation but instead led to a variety of mutants with reduced capsule harboring single nucleotide polymorphisms (SNPs) in cpsE. A single passage in the sepsis model after high-dose inoculation readily yielded revertants of AI45dup with restored wild-type capsule level, but the majority of SNP alleles of cpsE could not revert, suppress, or bypass. Analysis of cpsE in conjunctival isolates revealed a strain with a single missense mutation at amino acid position 377, which was responsible for reduced encapsulation. This study supports the hypothesis that spontaneous, nonreverting mutations in cpsE serve as a form of adaptive mutation by providing a selective advantage to S. pneumoniae in niches where expression of capsule is detrimental. IMPORTANCEWhile the capsule of Streptococcus pneumoniae is required for colonization and invasive disease, most conjunctival isolates are acapsular by virtue of deletion of the entire capsular operon. We show that spontaneous acapsular mutants isolated in vitro harbor mostly nonrevertible single nucleotide polymorphism (SNP) null mutations in cpsE, encoding the initiating glycosyltransferase. From a small collection of acapsular conjunctival isolates, we identified one strain with a complete capsular operon but containing a SNP in cpsE that we show is responsible for the acapsular phenotype. We propose that acapsular conjunctival isolates may arise initially from such nonreverting SNP null mutations in cpsE, which can be followed later by deletion of portions or all of the cps operon. Streptococcus pneumoniae (the pneumococcus) is a Gram-positive bacterium that is frequently found as a commensal organism of the human nasopharynx. However, depending on the site of dissemination, it can also cause various invasive diseases, including pneumonia, otitis media, sepsis, and meningitis (1-4). One critical pneumococcal virulence factor is the capsular polysaccharide (capsule), of which over 90 different serotypes have been characterized. The capsule has many important immune evasion functions, including...

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“…The pneumococcal capsule constitutes an important virulence factor and provides protection against the host immune response (2). More than 90 known encapsulated serotypes have been identified (3) based on the composition of their capsular polysaccharides (CPS). Pneumococcal infections show a broad spectrum of clinical presentations, from nasopharyngeal colonization to invasive pneumococcal disease (IPD), depending on host factors and the causative serotype (4).…”

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confidence: 99%

Association between Serotype-Specific Antibody Response and Serotype Characteristics in Patients with Pneumococcal Pneumonia, with Special Reference to Degree of Encapsulation and Invasive Potential

Athlin

Kaltoft

Slotved

et al. 2014

Clin. Vaccine Immunol.

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We studied the immunoglobulin (Ig) response to causative serotype-specific capsular polysaccharides in adult pneumococcal pneumonia patients. The serotypes were grouped according to their degree of encapsulation and invasive potential. Seventy patients with pneumococcal pneumonia, 20 of whom were bacteremic, were prospectively studied. All pneumococcal isolates from the patients were serotyped, and the Ig titers to the homologous serotype were determined in acute-and convalescent-phase sera using a serotype-specific enzyme-linked immunosorbent assay. The Ig titers were lower in bacteremic cases than in nonbacteremic cases (P < 0.042). The Ig titer ratio (convalescent/acute titer) was >2 in 33 patients, 1 to 1.99 in 20 patients, and <1 in 17 patients. Patients >65 years old had a lower median Ig titer ratio than did younger patients (P < 0.031). The patients with serotypes with a thin capsule (1, 4, 7F, 9N, 9V, and 14) and medium/high invasive potential (1, 4, 7F, 9N, 9V, 14, and 18C) had higher Ig titer ratios than did patients with serotypes with a thick capsule (3, 6B, 11A, 18C, 19A, 19F, and 23F) and low invasive potential (3, 6B, 19A, 19F, and 23F) (P < 0.05 for both comparisons after adjustment for age). Ig titer ratios of <1 were predominantly noted in patients with serotypes with a thick capsule. In 8 patients with pneumococcal DNA detected in plasma, the three patients with the highest DNA load had the lowest Ig titer ratios. In conclusion, a high antibody response was associated with serotypes with a thin capsule and medium/high invasive potential, although a low antibody response was associated with serotypes with a thick capsule and a high pneumococcal plasma load.

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Biochemical, Genetic, and Serological Characterization of Two Capsule Subtypes among Streptococcus pneumoniae Serotype 20 Strains

Cited by 134 publications

References 27 publications

Spectrum of Pneumococcal Serotype 11A Variants Results from Incomplete Loss of Capsule O -Acetylation

Spectrum of Pneumococcal Serotype 11A Variants Results from Incomplete Loss of Capsule O -Acetylation

Mutations in Pneumococcal cpsE Generated via In Vitro Serial Passaging Reveal a Potential Mechanism of Reduced Encapsulation Utilized by a Conjunctival Isolate

Association between Serotype-Specific Antibody Response and Serotype Characteristics in Patients with Pneumococcal Pneumonia, with Special Reference to Degree of Encapsulation and Invasive Potential

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