Stability of Serotypes during Nasopharyngeal Carriage of Streptococcus
pneumoniae
Emma Meats,1 Angela B. Brueggemann,2 Mark C.
Enright,3 Karen Sleeman,4 David T. Griffiths,2
Derrick W. Crook,2 and Brian G. Spratt1*
Department of Infectious Disease Epidemiology, Faculty of Medicine, Imperial
College London, St. Mary's Hospital Campus, London W2 1PG,1 Oxford
Vaccine Group, University Department of Paediatrics,4 Academic
Department of Microbiology and Infectious Disease, John Radcliffe Hospital,
University of Oxford, Oxford OX3 9DU,2 Department of Biology and
Biochemistry, University of Bath, Bath BA2 7AY, United Kingdom3
Received 15 July 2002/ Returned for modification 14 September 2002/ Accepted
6 October 2002
Serotype changes among natural isolates of Streptococcus
pneumoniaeare well documented and occur by recombinational
exchanges atthe capsular biosynthetic locus. However, the frequency
withwhich this phenomenon occurs within the nasopharynx of childrenis not clear and is likely to be highest in the nasopharynxof
children, who have high rates of pneumococcal carriage. Abirth
cohort of 100 infants was studied, and pneumococci wererecovered
from nasopharyngeal samples taken at monthly intervalsduring the
first 6 months of life and then at 2-monthly intervalsuntil the age
of 2 years. Among the 1,353 nasopharyngeal sampleswere 523 that
contained presumptive pneumococci, and three coloniesfrom each were
serotyped. A total of 333 isolates, includingall isolates of
differing serotypes from the same child, werecharacterized by
multilocus sequence typing. Sixty-eight childrencarried multiple
serotypes during the first 2 years of life.Two children carried a
typeable and a nonserotypeable pneumococcusof identical genotype,
and five children carried geneticallyindistinguishable isolates of
serotypes 15B and 15C. These isolateswere considered, respectively,
to be due to loss of capsuleexpression and the known ability of
serotype 15B and 15C pneumococcito interconvert by loss or gain of
an acetyl group on the capsularpolysaccharide. In all other cases,
isolates from the same childrenthat differed in serotype also
differed in genotype, indicatingthe acquisition of a different
pneumococcal strain rather thana change in capsular type. There was
therefore no evidence inthis study for any change of serotype due to
recombinationalreplacements at the capsular locus among the
pneumococci carriedwithin the nasopharynges of the children.
* Corresponding author. Mailing address: Department of
Infectious Disease Epidemiology, Faculty of Medicine, Imperial College London,
St. Mary's Hospital Campus, Norfolk Place, London W2 1PG, United Kingdom. Phone:
44 20 7594 3629. Fax: 44 20 7594 3693. E-mail:
b.spratt@ic.ac.uk.
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