Capsule type of Streptococcus pneumoniae determines growth phenotype.
Capsule type of Streptococcus pneumoniae determines growth phenotype.
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DOI：
10.1371/journal.ppat.1002574
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发表时间：
2012
期刊：
影响因子：
6.7
通讯作者：
Mühlemann K
中科院分区：
文献类型：
--
作者：
Hathaway LJ;Brugger SD;Morand B;Bangert M;Rotzetter JU;Hauser C;Graber WA;Gore S;Kadioglu A;Mühlemann K
肺炎链球菌的多糖荚膜定义了超过90种血清型，这些血清型在它们的携带流行性和侵袭性方面存在差异，原因尚不清楚。最近，已经描述了给定胶囊的携带流行率和寡糖结构之间的负相关性。我们以前的工作表明血清型和体外生长之间的联系。在这里，我们调查胶囊生产是否干扰体外生长，这是否预示着在体内携带流行。构建了代表9种不同血清型的81个胶囊转换突变体，5个低携带流行率（4、7 F、14、15、18 C）和4个高携带流行率（6 B、9V、19 F、23 F）。在营养限制性Lacks培养基（MLM）和补充有5%胎牛血清（BHI+FCS）的丰富不确定脑心浸液肉汤中研究了野生型菌株、不可分型突变体和胶囊转换突变体的生长（滞后期长度、最大光密度）。在MLM生长表型依赖于，并转移，胶囊操纵子类型。小鼠鼻咽部的定殖效率也依赖于囊操纵子类型，并随囊操纵子类型转移。胶囊生产干扰生长，这与特定类型的携带率呈负相关。具有更好的生长和更高的携带率的血清型比具有延迟生长和低携带率的血清型产生更厚的胶囊（通过电子显微镜、FITC-葡聚糖排除测定和HPLC）。然而，表达的cpsA，第一个胶囊基因，（通过定量RT-PCR）与胶囊厚度呈负相关。对于携带率低的血清型，胶囊生产（掺入H3-葡萄糖）相对于胶囊生产量的能量消耗较高。在BHI+FCS中的实验显示总体上比在MLM中的生长更好的细菌生长和更多的荚膜产生，并且血清型之间的差异不再明显。用S.在营养限制条件下，肺炎杆菌可能通过与中枢代谢竞争能量来干扰生长。通过生长表型预测体内血清型特异性鼻咽携带率。 肺炎链球菌是导致脑膜炎、肺炎和菌血症等严重人类感染的原因，也是儿童中耳炎（耳部感染）的常见原因。然而，它们通常无害地存在于婴儿鼻咽中。长期以来，人们一直观察到围绕细菌的多糖胶囊类型与无害的定植和侵袭性疾病之间存在关联。在这里，我们建议，对于细菌来说成本高昂的胶囊类型以较低的数量生产，并且它们的生产限制了细菌在营养限制条件下的生长。相比之下，具有需要较少能量的胶囊的细菌可以产生更多的胶囊并更成功地生长。这也许可以解释为什么S。具有某些荚膜类型的肺炎球菌可以是鼻咽的有效长期定殖者，而其它球菌需要更丰富的营养环境才能生长，因此最常与侵袭性疾病相关。当考虑在未来疫苗中靶向哪种胶囊类型时，该信息可能有用。
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. Streptococcus pneumoniae bacteria are responsible for serious human infections including meningitis, pneumonia and bacteraemia and are a common cause of otitis media (ear infection) in children. However, they most often reside harmlessly in the infant nasopharynx. An association has long been observed between the type of polysaccharide capsule surrounding the bacteria and harmless colonization versus invasive disease. Here we suggest that capsule types that are costly for the bacteria to make are produced in lower quantities and their production limits the growth of the bacteria in nutrient-restricted conditions. In contrast, bacteria with capsules that require less energy can produce more capsule and grow more successfully. This may be an explanation for why S. pneumoniae with certain capsule types can be effective long-term colonizers of the nasopharynx while others need a richer nutritional environment to flourish and so are most often associated with invasive disease. This information may be of use when considering which capsules types to target in future vaccines.
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