Affiliation:
1. Department of Biomedicine, Aarhus University, Aarhus, Denmark
2. Beijing Pediatric Research Institute, Beijing Children’s Hospital, Capital Medical University, Xicheng District, Beijing, People’s Republic of China
3. Department of Microbiology and Immunology, Institute for Genome Sciences, University of Maryland School of Medicine, Baltimore, Maryland, USA
Abstract
ABSTRACT
Expression of a capsular polysaccharide is considered a hallmark of most invasive species of bacteria, including
Streptococcus pneumoniae
, in which the capsule is among the principal virulence factors and is the basis for successful vaccines. Consequently, it was previously assumed that capsule production distinguishes
S. pneumoniae
from closely related commensals of the mitis group streptococci. Based on antigenic and genetic analyses of 187 mitis group streptococci, including 90 recognized serotypes of
S. pneumoniae
, we demonstrated capsule production by the Wzy/Wzx pathway in 74% of 66
S. mitis
strains and in virtually all tested strains of
S. oralis
(subspecies
oralis
,
dentisani
, and
tigurinus
) and
S. infantis
. Additional analyses of genomes of
S. cristatus
,
S. parasanguinis
,
S. australis
,
S. sanguinis
,
S. gordonii
,
S. anginosus
,
S. intermedius
, and
S. constellatus
revealed complete capsular biosynthesis (
cps
) loci in all strains tested. Truncated
cps
loci were detected in three strains of
S. pseudopneumoniae
, in 26% of
S. mitis
strains, and in a single
S. oralis
strain. The level of sequence identities of
cps
locus genes confirmed that the structural polymorphism of capsular polysaccharides in
S. pneumoniae
evolved by import of
cps
fragments from commensal
Streptococcus
species, resulting in a mosaic of genes of different origins. The demonstrated antigenic identity of at least eight of the numerous capsular polysaccharide structures expressed by commensal streptococci with recognized serotypes of
S. pneumoniae
raises concerns about potential misidentifications in addition to important questions concerning the consequences for vaccination and host-parasite relationships both for the commensals and for the pathogen.
IMPORTANCE
Expression of a capsular polysaccharide is among the principal virulence factors of
Streptococcus pneumoniae
and is the basis for successful vaccines against infections caused by this important pathogen. Contrasting with previous assumptions, this study showed that expression of capsular polysaccharides by the same genetic mechanisms is a general property of closely related species of streptococci that form a significant part of our commensal microbiota. The demonstrated antigenic identity of many capsular polysaccharides expressed by commensal streptococci and
S. pneumoniae
raises important questions concerning the consequences for vaccination and host-parasite relationships both for the commensals and the pathogen.
Funder
Danish Council for Independent Research
Publisher
American Society for Microbiology
Cited by
81 articles.
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