title: 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.
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.
authors.affiliation: a University of Bristol; School of Cellular and Molecular Medicine ; Bristol , UK.
authors.forename: Valtyr
authors.initials: V
authors.lastname: Thors
authors.affiliation: a University of Bristol; School of Cellular and Molecular Medicine ; Bristol , UK.
authors.forename: Begonia
authors.initials: B
authors.lastname: Morales-Aza
authors.affiliation: a University of Bristol; School of Cellular and Molecular Medicine ; Bristol , UK.
authors.forename: Grace
authors.initials: G
authors.lastname: Pidwill
authors.affiliation: b Public Health Laboratory Bristol; Public Health England ; Bristol , UK.
authors.forename: Ian
authors.initials: I
authors.lastname: Vipond
authors.affiliation: b Public Health Laboratory Bristol; Public Health England ; Bristol , UK.
authors.forename: Peter
authors.initials: P
authors.lastname: Muir
authors.affiliation: a University of Bristol; School of Cellular and Molecular Medicine ; Bristol , UK.
authors.forename: Adam
authors.initials: A
authors.lastname: Finn
mesh_terms: D002353:Carrier State / Q000382:microbiology*; D002675:Child, Preschool; D004269:DNA, Bacterial / Q000235:genetics* / Q000302:isolation & purification; D006193:Haemophilus influenzae / Q000235:genetics* / Q000302:isolation & purification; D006801:Humans; D001936:Moraxella catarrhalis / Q000235:genetics* / Q000302:isolation & purification; D009305:Nasopharynx / Q000382:microbiology*; D060888:Real-Time Polymerase Chain Reaction; D013211:Staphylococcus aureus / Q000235:genetics* / Q000302:isolation & purification; D013296:Streptococcus pneumoniae / Q000235:genetics* / Q000302:isolation & purification; D013297:Streptococcus pyogenes / Q000235:genetics* / Q000302:isolation & purification
chemical_list: D004269:DNA, Bacterial
keywords: bacterial density; children; colonization; quantitative PCR