Population density profiles of nasopharyngeal carriage of 5 bacterial species in pre-school children measured using quantitative PCR offer potential insights into the dynamics of transmission

Valtyr Thors*, Begonia Morales-Aza, Grace Pidwill, Ian Vipond, Peter Muir, Adam Finn

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

21 Citations (Scopus)

Abstract

Bacterial vaccines can reduce carriage rates. Colonization is usually a binary endpoint. Real time quantitative PCR (qPCR) can quantify bacterial DNA in mucosal samples over a wide range. Using culture and single-gene species-specific qPCRs for Streptococcus pneumoniae (lytA), Streptococcus pyogenes (ntpC), Moraxella catarrhalis (ompJ), Haemophilus influenzae (hdp) and Staphylococcus aureus (nuc) and standard curves against log-phase reference strain broth cultures we described frequency and peak density distributions of carriage in nasopharyngeal swabs from 161 healthy 2–4 y old children collected into STGG broth. In general, detection by qPCR and culture was consistent. Discordance mostly occurred at lower detection thresholds of both methods, although PCR assays for S. pyogenes and S. aureus were less sensitive. Density varied across 5-7 orders of magnitude for the 5 species with the abundant species skewed toward high values (modes: S. pneumoniae log3-4, M. catarrhalis & H. influenzae log4-5 CFU/ml broth). Wide ranges of bacterial DNA concentrations in healthy children carrying these bacteria could mean that different individuals at different times vary greatly in infectiousness. Understanding the host, microbial and environmental determinants of colonization density will permit more accurate prediction of vaccine effectiveness.

Original languageEnglish
Pages (from-to)375-382
Number of pages8
JournalHuman Vaccines and Immunotherapeutics
Volume12
Issue number2
DOIs
Publication statusPublished - 1 Feb 2016

Bibliographical note

Funding Information:
Prof Finn has received research grants from GSK, AstraZeneca, Alios, Pfizer, Novartis and SPSMD and consultancy fees and speaking honoraria, all paid to his employers, from the same companies as well as Takeda. He is a member of the WHO European Technical Advisory Group of Experts on Immunisation and the UK Department of Health’s Joint Committee on Vaccination and Immunisation and subcommittees. Other authors report no conflicts of interest.

Publisher Copyright:
© 2016 Taylor & Francis Group, LLC.

Keywords

  • bacterial density
  • children
  • colonization
  • quantitative PCR

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