Stability of Serotypes during Nasopharyngeal Carriage of Streptococcus pneumoniae

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http://jcm.asm.org/cgi/content/abstract/41/1/386

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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. Spratt^1*

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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