Abstract
BackgroundRecent studies have identified Streptococcus pneumoniae serotype 11E and serovariant 11Av among isolates previously typed as 11A by classical serotyping methods. Serotype 11E and serovariant 11Av differ from serotype 11A by having totally or partially inactive wcjE, a gene in cps locus coding for an O-acetyl transferase. Serotype 11E is rare among carriage isolates but common among invasive isolates suggesting that it survives better during invasion. Aim of this work was to investigate the epidemiology of serotype 11A in a pneumococcal collection using a new serotyping approach based on High-Resolution Magic Angle Spinning Nuclear Magnetic Resonance (HR-MAS NMR) spectroscopy to distinguish serotypes 11A and 11E.MethodsA collection of 48 (34 invasive and 14 carriage) S. pneumoniae isolates from Italy, previously identified as serotype 11A by the Quellung reaction, were investigated by wcjE sequencing, HR-MAS NMR spectroscopy and the reference flow cytometric serotyping assay (FCSA) based on monoclonal antibodies.ResultsHR-MAS NMR spectra from serotypes 11A and 11E showed different NMR peaks indicating that HR-MAS NMR could be used to distinguish these serotypes, although HR-MAS NMR could not distinguish serotype 11Av from serotype 11E unambiguously. Thirty-eight isolates were confirmed to be serotype 11A, 8 isolates with a mutated wcjE were serotype 11E, 1 isolate belonged to serovariant 11Av, and 1 isolate was a mixed population 11A/11Av. All 11E isolates were identified among invasive isolates.ConclusionsWe proved that HR-MAS NMR can be of potential use for pneumococcal serotyping. The detection of serotype 11E among invasive isolates in our collection, supports previous epidemiological studies suggesting that mutations in wcjE can represent a mechanism promoting pneumococcal survival during invasion. The discovery of a spectrum of immunochemical diversity within established serotypes should stimulate efforts to develop new serotyping approaches.
Highlights
Streptococcus pneumoniae is an important human pathogen responsible for severe life-threatening infections, including meningitis and pneumonia, especially in children and elderly people
The capsular polysaccharide (CPS), which provides a barrier against host cell-mediated phagocytosis, represents the major virulence factor of S. pneumoniae [1]
Serotype 11A is one of the most common serotypes both in human carriage and in infection [6,7] and is associated with two distinct cps alleles designated 11A-1 and 11A-2 [8]. 11A-1 corresponds to the cps allele recovered in the majority of the 11A strains sequenced so far [9,10,11], and is identical to the 11D cps locus described by Bentley et al [2], with the exception of a single nucleotide polymorphism (SNP) in wcrL, a gene coding for a putative glycosyltransferase [10,12]; 11A-2 corresponds to the cps allele reported by Bentley et al for serotype 11A [2] but is only found in a minority of serotype 11A isolates [8]
Summary
Streptococcus pneumoniae is an important human pathogen responsible for severe life-threatening infections, including meningitis and pneumonia, especially in children and elderly people. Serogroup 11 had been known to contain 5 serotypes (11F, 11A, 11B, 11C, 11D), sharing substantial homologies in the structure of the CPS, that consists of a linear tetrasaccharide backbone with different degrees of O-acetylation, and in the capsular polysaccharide synthesis locus (cps), differing mainly in O-acetyltransferase genes (wcwR, wcwC, wcjE) [5]. Serotype 11A is one of the most common serotypes both in human carriage and in infection [6,7] and is associated with two distinct cps alleles designated 11A-1 and 11A-2 [8]. Serotype 11E and serovariant 11Av differ from serotype 11A by having totally or partially inactive wcjE, a gene in cps locus coding for an O-acetyl transferase. Aim of this work was to investigate the epidemiology of serotype 11A in a pneumococcal collection using a new serotyping approach based on High-Resolution Magic Angle Spinning Nuclear Magnetic Resonance (HR-MAS NMR) spectroscopy to distinguish serotypes 11A and 11E
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