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2016 ; 7
(2
): e01792
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Nonencapsulated Streptococcus pneumoniae: Emergence and Pathogenesis
#MMPMID27006456
Keller LE
; Robinson DA
; McDaniel LS
mBio
2016[Mar]; 7
(2
): e01792
PMID27006456
show ga
While significant protection from pneumococcal disease has been achieved by the
use of polysaccharide and polysaccharide-protein conjugate vaccines,
capsule-independent protection has been limited by serotype replacement along
with disease caused by nonencapsulatedStreptococcus pneumoniae(NESp). NESp
strains compose approximately 3% to 19% of asymptomatic carriage isolates and
harbor multiple antibiotic resistance genes. Surface proteins unique to NESp
enhance colonization and virulence despite the lack of a capsule even though the
capsule has been thought to be required for pneumococcal pathogenesis. Genes for
pneumococcal surface proteins replace the capsular polysaccharide (cps) locus in
some NESp isolates, and these proteins aid in pneumococcal colonization and
otitis media (OM). NESp strains have been isolated from patients with invasive
and noninvasive pneumococcal disease, but noninvasive diseases, specifically,
conjunctivitis (85%) and OM (8%), are of higher prevalence. Conjunctival strains
are commonly of the so-called classical NESp lineages defined by multilocus
sequence types (STs) ST344 and ST448, while sporadic NESp lineages such as ST1106
are more commonly isolated from patients with other diseases. Interestingly,
sporadic lineages have significantly higher rates of recombination than classical
lineages. Higher rates of recombination can lead to increased acquisition of
antibiotic resistance and virulence factors, increasing the risk of disease and
hindering treatment. NESp strains are a significant proportion of the
pneumococcal population, can cause disease, and may be increasing in prevalence
in the population due to effects on the pneumococcal niche caused by pneumococcal
vaccines. Current vaccines are ineffective against NESp, and further research is
necessary to develop vaccines effective against both encapsulated and
nonencapsulated pneumococci.