title: Detection of Streptococcus pneumoniae strain cocolonization in the nasopharynx.
abstract: Colonization with more than one distinct strain of the same species, also termed cocolonization, is a prerequisite for horizontal gene transfer between pneumococcal strains that may lead to change of the capsular serotype. Capsule switch has become an important issue since the introduction of conjugated pneumococcal polysaccharide vaccines. There is, however, a lack of techniques to detect multiple colonization by S. pneumoniae strains directly in nasopharyngeal samples. Two hundred eighty-seven nasopharyngeal swabs collected during the prevaccine era within a nationwide surveillance program were analyzed by a novel technique for the detection of cocolonization, based on PCR amplification of a noncoding region adjacent to the pneumolysin gene (plyNCR) and restriction fragment length polymorphism (RFLP) analysis. The numbers of strains and their relative abundance in cocolonized samples were determined by terminal RFLP. The pneumococcal carriage rate found by PCR was 51.6%, compared to 40.0% found by culture. Cocolonization was present in 9.5% (10/105) of samples, most (9/10) of which contained two strains in a ratio of between 1:1 and 17:1. Five of the 10 cocolonized samples showed combinations of vaccine types only (n = 2) or combinations of nonvaccine types only (n = 3). Carriers of multiple pneumococcal strains had received recent antibiotic treatment more often than those colonized with a single strain (33% versus 9%, P = 0.025). This new technique allows for the rapid and economical study of pneumococcal cocolonization in nasopharyngeal swabs. It will be valuable for the surveillance of S. pneumoniae epidemiology under vaccine selection pressure.
authors.affiliation: Institute for Infectious Diseases, University of Bern, Friedbühlstrasse 51, CH-3010 Bern, Switzerland.
authors.forename: Silvio D
authors.initials: SD
authors.lastname: Brugger
authors.forename: Lucy J
authors.initials: LJ
authors.lastname: Hathaway
authors.forename: Kathrin
authors.initials: K
authors.lastname: Mühlemann
mesh_terms: D015373:Bacterial Typing Techniques / Q000379:methods*; D002353:Carrier State / Q000382:microbiology*; D002648:Child; D002675:Child, Preschool; D016000:Cluster Analysis; D016172:DNA Fingerprinting; D004269:DNA, Bacterial / Q000235:genetics; D021901:DNA, Intergenic; D005838:Genotype; D006801:Humans; D007223:Infant; D009305:Nasopharynx / Q000382:microbiology*; D011008:Pneumococcal Infections / Q000453:epidemiology / Q000382:microbiology*; D016133:Polymerase Chain Reaction / Q000379:methods*; D012150:Polymorphism, Restriction Fragment Length; D015995:Prevalence; D012680:Sensitivity and Specificity; D013296:Streptococcus pneumoniae / Q000145:classification* / Q000235:genetics / Q000302:isolation & purification
chemical_list: D004269:DNA, Bacterial; D021901:DNA, Intergenic