Discovery of Streptococcus pneumoniae serogroup 35 variants in Australian patients

Staples, Megan; Graham, Rikki; Hicks, Vicki; Strachan, Janet; Silva, Anders Gonçalves da; Peverall, Joanne; Wicks, V.; Jennison, Amy V.

doi:10.1016/j.cmi.2016.12.029

Cited by 9 publications

(18 citation statements)

References 15 publications

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“…After the submission of this paper, we became aware of a report from Australia describing four clinical isolates whose genetic and serological profiles match those of serotype 35D (24). In addition, the CDC Active Bacterial Core surveillance (ABCs) program has uncovered two serotype 35B wciG variants exhibiting the serology we describe for serotype 35D (Bernard Beall, CDC ABCs, personal communication).…”

Section: Discussionmentioning

confidence: 99%

Discovery of Novel Pneumococcal Serotype 35D, a Natural WciG-Deficient Variant of Serotype 35B

2017

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Pneumococcus (Streptococcus pneumoniae) remains a significant cause of morbidity and mortality, especially among those at the extremes of age. Its capsular polysaccharide is essential for systemic virulence. Over 90 serologically distinct pneumococcal capsular polysaccharides (serotypes) are recognized, but they are unequal in prevalence. Because antibodies against the capsule are protective, polysaccharide conjugate vaccines, which are constructed against the most prevalent serotypes, have caused great reductions in pneumococcal disease caused by these serotypes. In response, however, the relative prevalences of serotypes have shifted. Certain previously rare serotypes, such as serotype 35B, are increasing in prevalence. Serotype 35B is thus a likely future vaccine candidate, but due to their previous rarity, serotype 35B strains have not been scrutinized for underlying heterogeneity. We studied putative serotype 35B clinical isolates to assess the uniformity of their serological reactions. While most isolates exhibited the accepted serology of serotype 35B, one isolate failed to bind to critical serotyping reagents. We determined that the genetic basis for this aberrant serology was the presence of inactivating mutations in the O-acetyltransferase gene wciG. Complementation studies in a wciG deletion strain verified that the mutant WciG was nonfunctional, and the serology of the mutant could be restored through complementation with a construct encoding a functional WciG. Nuclear magnetic resonance studies confirmed that the capsule of the WciG-deficient isolate lacked O-acetylation but was otherwise identical to serotype 35B. As this isolate expresses a unique serology with unique biochemistry and a stable genetic basis, we named its novel capsule serotype 35D.KEYWORDS O-acetylation, Streptococcus pneumoniae, capsular polysaccharide, serogroup 35, serotype 35B, serotype 35D S treptococcus pneumoniae (pneumococcus) is an important human pathogen that can express many different polysaccharide capsules that protect the organism from opsonophagocytic killing (1). As antibodies to the capsule are protective, currently available vaccines against pneumococcus are designed to elicit antibodies to the capsule and have been highly successful in reducing the incidence of invasive pneumococcal disease (IPD). A pneumococcal polysaccharide-protein conjugate vaccine (PCV) with polysaccharide from the seven most commonly observed serotypes (PCV7) was introduced in the United States in 2000 and reduced the incidence of IPD in children younger than 5 by over 75% (2); the updated 13-valent PCV (PCV13) has reduced the incidence of IPD by an additional 64% in this age group in the United States (3). However, the protection by these vaccines is serotype specific, and their widespread implementation has brought shifts in the serotypes found in both nasopharyngeal carriage and IPD (see, e.g., reference 4).

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Section: Discussionmentioning

confidence: 99%

Discovery of Novel Pneumococcal Serotype 35D, a Natural WciG-Deficient Variant of Serotype 35B

2017

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“…The pneumococcus has a polysaccharide capsule, and 98 distinct capsular types (serotypes) have been identified based on chemical differences in their capsular repeat units (1)(2)(3). These chemical differences are mediated by genetic changes in the capsular polysaccharide synthesis (cps) operon (4) and result in different reactivities with anti-capsule antibodies.…”

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confidence: 99%

“…The genes encoding putative MOATs are found in 32 of the 98 known pneumococcal cps operons (1,2,4,(11)(12)(13)(14)(15)(16). To investigate the impact of MOATs on the biological properties of the pneumococcal capsule, we investigated serotype 33A, which has two MOATs: WciG and WcjE.…”

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confidence: 99%

Position of O-Acetylation within the Capsular Repeat Unit Impacts the Biological Properties of Pneumococcal Serotypes 33A and 33F

et al. 2017

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Streptococcus pneumoniae (pneumococcus) produces many capsule types that differ in their abilities to evade host immune recognition. To explain these serotypedependent protective capacities, many studies have investigated capsular thickness or the interaction of the capsule with complement proteins, but the effects of small chemical modifications of the capsule on its function have not been studied. One small chemical modification found frequently among pneumococcal capsules is O-acetylation. Pneumococcal serotype 33A has two membrane-bound O-acetyltransferase genes, wciG and wcjE. A 33A wcjE-deficient variant, 33F, occurs naturally and is increasing in prevalence in the wake of widespread conjugate vaccine use, but no wciG-deficient variants have been reported. To study the biological consequence of the loss of O-acetylation, we created wciG-deficient variants in both serotypes 33A and 33F, which we named 33X1 (ΔwciG) and 33X2 (ΔwciG ΔwcjE). Serotypes 33X1 and 33X2 express novel capsule types based on serological and biochemical analyses. We found that loss of WcjE-mediated O-acetylation appears not to affect cell wall shielding, since serotypes 33A and 33F exhibit comparable nonspecific opsonophagocytic killing, biofilm production, and adhesion to nasopharyngeal cells, though serotype 33F survived short-term drying better than serotype 33A. Loss of WciG-mediated O-acetylation in serotypes 33X1 and 33X2, however, resulted in a phenotype resembling that of nonencapsulated strains: increased cell wall accessibility, increased nonspecific opsonophagocytic killing, enhanced biofilm formation, and increased adhesion to nasopharyngeal cells. We conclude that WciG-mediated, but not WcjE-mediated, O-acetylation is important for producing protective capsules in 33A and that small chemical changes to the capsule can drastically affect its biological properties.KEYWORDS O-acetyltransferase, O-acetylation, capsular diversity, pneumococcal vaccine, capsular polysaccharide, serotype S treptococcus pneumoniae (pneumococcus) is an important human pathogen that can colonize the nasopharynx asymptomatically and disseminate opportunistically to cause pneumonia, meningitis, septicemia, and otitis media. The pneumococcus has a polysaccharide capsule, and 98 distinct capsular types (serotypes) have been identified based on chemical differences in their capsular repeat units (1-3). These chemical differences are mediated by genetic changes in the capsular polysaccharide synthesis (cps) operon (4) and result in different reactivities with anti-capsule antibodies. The capsule is essential for pneumococcal virulence (5), since it shelters pneumococci from complement fixation and opsonophagocytosis (6). However, differences in capsule type have been shown to affect complement fixation and virulence (7).

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“…For example, WcjE-positive and -negative pairs have been observed in serogroups 9, 11, and 33 (11,21). wciG is carried by 13 serotypes, including serotype 42 and every member of serogroup 35 (11), and wciG functionality differentiates serotype 35B from the recently identified serotype 35D (3,22). Thus, wciG functionality may be an as-yet-unexplored mechanism of significantly increasing capsule diversity among pneumococci.…”

Section: -H 1-c 2-h 2-c 3-h 3-c 4-h 4-c 5-h 5-c 6-h 6-c 35c (Smentioning

confidence: 99%

WciG O -Acetyltransferase Functionality Differentiates Pneumococcal Serotypes 35C and 42

et al. 2017

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Streptococcus pneumoniae expresses capsular polysaccharides (CPSs) to protect itself from opsonophagocytic killing. The genes responsible for capsules synthesized by the Wzy-dependent mechanism, which accounts for 96 of the 98 known pneumococcal capsule types, are in a chromosomal region known as the cps locus. The nucleotide sequence in this region has been determined for all serotypes. In contrast, not all CPS structures have been defined. The structure of the serotype 35C polysaccharide was recently reported, but the presence of O-acetyltransferase genes in the serotype 35C cps locus suggested that it could be incomplete, as the reported structure contains no O-acetylation. In addition, the genetic distinction of serotype 35C from the closely related serotype 42 was unclear, as their reported cps loci are nearly identical. To clarify these discrepancies, we obtained serotype 35C and 42 clinical and reference isolates and studied their serological and genetic properties, as well as the structures of CPSs purified from reference isolates. We demonstrated that the Oacetyltransferase WciG was functional in serotype 35C but nonfunctional in serotype 42 due to a deletion in wciG. Serotype 35C was O-acetylated at the 5-and 6-positions of 3-␤-galactofuranose, as well as the 2-position of 6-␤-galactofuranose. However, serotype 42 has only O-acetylation at 3-␤-galactofuranose, an observation consistent with its loss of WciG functionality, which is associated with O-acetylation at the 2-position and subsequent reaction with typing antiserum 35a. These findings provide a comprehensive view of the genetic, biochemical structural, and serological bases of serotypes 35C and 42.

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Discovery of Streptococcus pneumoniae serogroup 35 variants in Australian patients

Abstract: This is the first published report on the incidence and capsular gene characteristics of a S. pneumoniae 35B variant.

Cited by 9 publications

References 15 publications

Discovery of Novel Pneumococcal Serotype 35D, a Natural WciG-Deficient Variant of Serotype 35B

Discovery of Novel Pneumococcal Serotype 35D, a Natural WciG-Deficient Variant of Serotype 35B

Position of O-Acetylation within the Capsular Repeat Unit Impacts the Biological Properties of Pneumococcal Serotypes 33A and 33F

WciG O -Acetyltransferase Functionality Differentiates Pneumococcal Serotypes 35C and 42

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