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

Abstract

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.

Commercially Available Complement Component-Depleted Sera Are Unexpectedly Codepleted of Ficolin-2

“…The serotype 20A strain (AMB11) and serotype 20B strain (AMB12) were generated using ATCC 6320 (American Type Culture Collection, Manassas, VA) and CDC5931-06 (Centers for Disease Control and Prevention, Atlanta, GA), respectively, by introducing a streptomycin resistant rpsL allele using a previously described method (13). The wcjE-null strains AMB13 (serotype 20Ax) and AMB14 (serotype 20Bx) were generated from strains AMB11 and AMB12, respectively, using a previously described protocol (14). Saccharomyces cerevisiae used for MBL binding assays was a kind gift from the laboratory of Stephen Moser at the University of Alabama at Birmingham (Birmingham, AL).…”

Bacterial polysaccharides as major surface antigens: interest in O-acetyl substitutions

“…70 Subsequent structural and molecular analysis revealed that S. pneumoniae types 11E and 11A represent the two extremes of a population comprising variants, which differ by the activity of the wcjE 10 gene, and consequently by the level of expression of a 6-O-acetyl-β-D-Galp residue in their CPS repeating unit. 69 The molecular mechanisms responsible for restraining the wcjE function are not yet elucidated.…”

“…88 The occurrence of intermediate serovariants as in systems 11A/11E and 9A/9V was hypothesized. 69 In this context, the effect of CPS O-acetylation on functional antibody activity and potential cross-reactivity was questioned. A measurable antigenic difference between CPSs from type 15B and type 15C was shed to light by use of sera from individuals O-acetylation was substantiated by the absence of functional antibodies cross-reacting with type 15C in post-vaccination sera.…”

“…67 On the basis of similar, albeit more deeply investigated, findings for the types 11E and 11A from S. pneumoniae, it was proposed that types 9A and 9V correspond to two extremes of an 25 antigenic spectrum with intermediate serovariants. 69 The impact of the phenomenon on bacterial transmission, persistence and disease manifestation is not yet fully understood. 67 2 S. pneumoniae type 11E versus S. pneumoniae type 11A 30 Similarly, S. pneumoniae type 11E is thought to have materialized from S. pneumoniae type 11A in an independent wcjE evolution process.…”

The Pneumococcal Serotype 15C Capsule Is Partially O-Acetylated and Allows for Limited Evasion of 23-Valent Pneumococcal Polysaccharide Vaccine-Elicited Anti-Serotype 15B Antibodies

“…Many bacteria have membrane-bound O-acetyltransferases (MOATs) that are thought to attach O-acetyl groups to the capsular repeat unit at the end of the capsular biosynthetic process (22)(23)(24). Accordingly, the loss of MOAT-mediated O-acetylation may not disrupt global capsule biosynthesis (12,(25)(26)(27).…”