Identification, prevalence and population structure of non-typable Streptococcus pneumoniae in carriage samples isolated from preschoolers attending day-care centres

Abstract

The authors aimed to get insights into the population structure of non-(sero)typable pneumococci (NTPn), a specific group of natural atypical pneumococci whose identification is often difficult, and which has remained insufficiently studied. A total of 265 presumptive NTPn, isolated between 1997 and 2003 from the nasopharynx of children, were characterized. Strains were confirmed to be pneumococci on the basis of bile solubility, and PCR detection or Southern blotting hybridization of lytA and psaA, genes ubiquitous in this species. Multilocus sequence typing (MLST) was used to exclude two isolates that gave ambiguous results. Non-typability was confirmed by the Quellung reaction using Omniserum. A total of 213 isolates were considered to be true NTPn. The molecular analysis of the true NTPn by PFGE and MLST showed that this population was genetically diverse, although a dominant cluster, accounting for 66 % of the isolates, was identified. Antimicrobial resistance was observed in most genetic backgrounds, and multidrug resistance to penicillin, erythromycin, clindamycin, tetracycline and sulfamethoxazole-trimethoprim was associated with strains belonging to the dominant cluster. Comparison with PFGE fingerprints and sequence types of large collections of serotypable strains showed that the genetic backgrounds of all but two NTPn were different from those found in serotypable strains. In addition, we found that NTPn strains with similar genetic backgrounds to those identified in our study had been isolated from disease sources in other countries. These observations seem to indicate that NTPn have diverse genetic backgrounds and may have evolved as a distinct group of pneumococcal isolates. INTRODUCTIONStreptococcus pneumoniae is a respiratory pathogen that colonizes asymptomatically the nasopharynx of humans. Although the mortality and morbidity associated with pneumococci are high, they are considered to be facultative pathogens: colonization is the rule, and disease the exception (Centers for Disease Control and Prevention, 2000).Most pneumococci are shielded by a polysaccharide capsule, a major virulence factor that hinders phagocytosis. Up to now, at least 90 different capsular types have been described (Henrichsen, 1995). The capsule can be detected by reaction with specific antisera. However, although some isolates are presumptively identified as pneumococci by routine identification tests, a negative result with type-specific antisera for the 90 serotypes is obtained. These atypical isolates are designated non-typable pneumococci (NTPn), and their correct discrimination from commensal viridans streptococci is often difficult (Carvalho et al., 2003;Hanage et al., 2005;Shayegani et al., 1982;Whatmore et al., 2000). The distinction between these closely related species is clinically important, since S. pneumoniae can cause serious disease and viridans streptococci are commensal organisms. Some NTPn have been described as extremely contagious and have been associated with pneumococcal conjunctivitis, causing ...

The Nonserotypeable Pneumococcus: Phenotypic Dynamics in the Era of Anticapsular Vaccines

“…Previous studies of NSP report a highly diverse population with a pervasive nature, an ability to cause disease, and a likely important role in pneumococcal ecology (8,23,24). Although nonencapsulated forms are less likely to cause disease, their ability for gene transfer, including the transfer of antibiotic resistance and capsular/virulence genes, is predictably high due to their capacity for an increased rate of transformation (22).…”

“…Pneumococci that lack capsule genes make up a highly diverse population that includes strains that have spread globally (8). These strains have been associated with a variety of mucosal (and, occasionally, invasive) diseases (for a review, see reference 24). Phenotypically nonencapsulated pneumococci that possess capsule genes may represent pneumococci that have lost the ability to express the capsule or strains that have temporarily ceased or downregulated capsule expression.…”

Highly Penicillin-Resistant Multidrug-Resistant Pneumococcus-Like Strains Colonizing Children in Oeiras, Portugal: Genomic Characteristics and Implications for Surveillance

“…All isolates were found to be true pneumococci that lacked a capsular operon. The isolates were genetically diverse although close to half belonged to a single lineage (39). Overall, these isolates were relatively abundant in asymptomatic carriers.…”

Temporal Trends and Molecular Epidemiology of Recently Described Serotype 6C of Streptococcus pneumoniae

“…Preparation of chromosomal DNA, restriction with SmaI endonuclease, pulsed-field gel electrophoresis (PFGE), and analysis of patterns with Bionumerics software (version 5.10; Applied Maths, Gent, Belgium) were done as previously described (15,17). Multilocus sequence typing was performed, as previously described (6), on selected strains of each PFGE cluster, choosing at least one representative of each year within each group.…”