title: Decrease in pneumococcal co-colonization following vaccination with the seven-valent pneumococcal conjugate vaccine.
abstract: Understanding the epidemiology of pneumococcal co-colonization is important for monitoring vaccine effectiveness and the occurrence of horizontal gene transfer between pneumococcal strains. In this study we aimed to evaluate the impact of the seven-valent pneumococcal conjugate vaccine (PCV7) on pneumococcal co-colonization among Portuguese children. Nasopharyngeal samples from children up to 6 years old yielding a pneumococcal culture were clustered into three groups: pre-vaccine era (n = 173), unvaccinated children of the vaccine era (n = 169), and fully vaccinated children (4 doses; n = 150). Co-colonization, serotype identification, and relative serotype abundance were detected by analysis of DNA of the total bacterial growth of the primary culture plate using the plyNCR-RFLP method and a molecular serotyping microarray-based strategy. The plyNCR-RFLP method detected an overall co-colonization rate of 20.1%. Microarray analysis confirmed the plyNCR-RFLP results. Vaccination status was the only factor found to be significantly associated with co-colonization: co-colonization rates were significantly lower (p = 0.004; Fisher's exact test) among fully vaccinated children (8.0%) than among children from the pre-PCV7 era (17.3%) or unvaccinated children of the PCV7 era (18.3%). In the PCV7 era there were significantly less non-vaccine type (NVT) co-colonization events than would be expected based on the NVT distribution observed in the pre-PCV7 era (p = 0.024). In conclusion, vaccination with PCV7 resulted in a lower co-colonization rate due to an asymmetric distribution between NVTs found in single and co-colonized samples. We propose that some NVTs prevalent in the PCV7 era are more competitive than others, hampering their co-existence in the same niche. This result may have important implications since a decrease in co-colonization events is expected to translate in decreased opportunities for horizontal gene transfer, hindering pneumococcal evolution events such as acquisition of antibiotic resistance determinants or capsular switch. This might represent a novel potential benefit of conjugate vaccines.
authors.affiliation: Laboratory of Molecular Microbiology of Human Pathogens, Instituto de Tecnologia Química e Biológica, Universidade Nova de Lisboa, Oeiras, Portugal.
authors.forename: Carina
authors.initials: C
authors.lastname: Valente
authors.forename: Jason
authors.initials: J
authors.lastname: Hinds
authors.forename: Francisco
authors.initials: F
authors.lastname: Pinto
authors.forename: Silvio D
authors.initials: SD
authors.lastname: Brugger
authors.forename: Katherine
authors.initials: K
authors.lastname: Gould
authors.forename: Kathrin
authors.initials: K
authors.lastname: Mühlemann
authors.forename: Hermínia
authors.initials: H
authors.lastname: de Lencastre
authors.forename: Raquel
authors.initials: R
authors.lastname: Sá-Leão
mesh_terms: D002648:Child; D002675:Child, Preschool; D015169:Colony Count, Microbial; D000069443:Heptavalent Pneumococcal Conjugate Vaccine; D006801:Humans; D007223:Infant; D015999:Multivariate Analysis; D020411:Oligonucleotide Array Sequence Analysis; D022242:Pneumococcal Vaccines / Q000276:immunology*; D012150:Polymorphism, Restriction Fragment Length; D015203:Reproducibility of Results; D012307:Risk Factors; D012703:Serotyping; D013296:Streptococcus pneumoniae / Q000145:classification / Q000254:growth & development* / Q000276:immunology* / Q000302:isolation & purification; D014611:Vaccination
chemical_list: D000069443:Heptavalent Pneumococcal Conjugate Vaccine; D022242:Pneumococcal Vaccines