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The type 2 capsule locus of Streptococcus pneumoniae.

ABSTRACT: The type 2 capsule locus of Streptococcus pneumoniae was characterized in Avery's strain D39, which is the parent strain of the standard transformation recipients currently used in pneumococcal research and is largely used as a virulent strain in studies on the pathogenesis of pneumococcal infections. The capsule locus was sequenced by using a 21.7-kb PCR fragment from the D39 genome as a template. Sequence data analysis showed the presence of 18 open reading frames, 17 of which have the same direction of transcription and all of which are potentially involved in capsule biosynthesis. It was also shown that R36A and R6, which are unencapsulated (rough) derivatives of D39, carry a 7,504-bp deletion involving nine capsule genes.

SUBMITTER: Iannelli F

PROVIDER: S-EPMC93698 | biostudies-literature | 1999 Apr

REPOSITORIES: biostudies-literature

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The type 2 capsule locus of Streptococcus pneumoniae.

Iannelli F F Pearce B J BJ Pozzi G G

Journal of bacteriology 19990401 8

The type 2 capsule locus of Streptococcus pneumoniae was characterized in Avery's strain D39, which is the parent strain of the standard transformation recipients currently used in pneumococcal research and is largely used as a virulent strain in studies on the pathogenesis of pneumococcal infections. The capsule locus was sequenced by using a 21.7-kb PCR fragment from the D39 genome as a template. Sequence data analysis showed the presence of 18 open reading frames, 17 of which have the same di ...[more]

PMID: 10198036

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Project description:The polysaccharide capsule of Streptococcus pneumoniae defines over ninety serotypes, which differ in their carriage prevalence and invasiveness for poorly understood reasons. Recently, an inverse correlation between carriage prevalence and oligosaccharide structure of a given capsule has been described. Our previous work suggested a link between serotype and growth in vitro. Here we investigate whether capsule production interferes with growth in vitro and whether this predicts carriage prevalence in vivo. Eighty-one capsule switch mutants were constructed representing nine different serotypes, five of low (4, 7F, 14, 15, 18C) and four of high carriage prevalence (6B, 9V, 19F, 23F). Growth (length of lag phase, maximum optical density) of wildtype strains, nontypeable mutants and capsule switch mutants was studied in nutrient-restricted Lacks medium (MLM) and in rich undefined brain heart infusion broth supplemented with 5% foetal calf serum (BHI+FCS). In MLM growth phenotype depended on, and was transferred with, capsule operon type. Colonization efficiency of mouse nasopharynx also depended on, and was transferred with, capsule operon type. Capsule production interfered with growth, which correlated inversely with serotype-specific carriage prevalence. Serotypes with better growth and higher carriage prevalence produced thicker capsules (by electron microscopy, FITC-dextran exclusion assays and HPLC) than serotypes with delayed growth and low carriage prevalence. However, expression of cpsA, the first capsule gene, (by quantitative RT-PCR) correlated inversely with capsule thickness. Energy spent for capsule production (incorporation of H3-glucose) relative to amount of capsule produced was higher for serotypes with low carriage prevalence. Experiments in BHI+FCS showed overall better bacterial growth and more capsule production than growth in MLM and differences between serotypes were no longer apparent. Production of polysaccharide capsule in S. pneumoniae interferes with growth in nutrient-limiting conditions probably by competition for energy against the central metabolism. Serotype-specific nasopharyngeal carriage prevalence in vivo is predicted by the growth phenotype.

Project description:The capsular polysaccharide (CPS) of Streptococcus pneumoniae is characterized by its diversity, as it has over 95 known serotypes, and the variation in its thickness as it surrounds an organism. While within-host effects of CPS have been studied in detail, there is no information about its contribution to host-to-host transmission. In this study, we used an infant mouse model of intralitter transmission, together with isogenic capsule switch and cps promoter switch constructs, to explore the effects of CPS type and amount. The determining factor in the transmission rate in this model is the number of pneumococci shed in nasal secretions by colonized hosts. Two of seven capsule switch constructs showed reduced shedding. These constructs were unimpaired in colonization and expressed capsules similar in size to those of the wild-type strain. A cps promoter switch mutant expressing ~50% of wild-type amounts of CPS also displayed reduced shedding without a defect in colonization. Since shedding from the mucosal surface may require escape from mucus entrapment, a mucin-binding assay was used to compare capsule switch and cps promoter switch mutants. The CPS type or amount constructs that shed poorly were bound more robustly by immobilized mucin. These capsule switch and cps promoter switch constructs with increased mucin-binding affinity and reduced shedding also had lower rates of pup-to-pup transmission. Our results demonstrate that CPS type and amount affect transmission dynamics and may contribute to the marked differences in prevalence among pneumococcal types.IMPORTANCEStreptococcus pneumoniae, a leading cause of morbidity and mortality, is readily transmitted, especially among young children. Its structurally and antigenically diverse capsular polysaccharide is the target of currently licensed pneumococcal vaccines. Epidemiology studies show that only a subset of the >95 distinct serotypes are prevalent in the human population, suggesting that certain capsular polysaccharide types might be more likely to be transmitted within the community. Herein, we used an infant mouse model to show that both capsule type and amount are important determinants in the spread of pneumococci from host to host. Transmission rates correlate with those capsule types that are better at escaping mucus entrapment, a key step in exiting the host upper respiratory tract. Hence, our study provides a better mechanistic understanding of why certain pneumococcal serotypes are more common in the human population.

Dataset Information

The type 2 capsule locus of Streptococcus pneumoniae.

Publications

The type 2 capsule locus of Streptococcus pneumoniae.

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