USA300 and USA500 Clonal Lineages of Staphylococcus aureus Do Not Produce a Capsular Polysaccharide Due to Conserved Mutations in the cap5 Locus
USA300 and USA500 Clonal Lineages of Staphylococcus aureus Do Not Produce a Capsular Polysaccharide Due to Conserved Mutations in the cap5 Locus
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DOI：
10.1128/mbio.02585-14
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发表时间：
2015-03-01
期刊：
影响因子：
6.4
通讯作者：
Daum, Robert S.
中科院分区：
文献类型：
--
作者：
Boyle-Vavra, Susan;Li, Xue;Daum, Robert S.
表面囊囊多糖（CP）是一种毒力因子，已在几种针对细菌病原体的成功疫苗中用作抗原。尽管两种含有CP抗原的多组分疫苗正在临床试验中，但尚未对金黄色葡萄球菌获得疫苗的许可。在这项研究中，我们评估了美国300耐甲氧西林的金黄色葡萄球菌（MRSA）分离株的CP生产，这些分离株已成为美国主要与社区相关的MRSA克隆。我们发现所有167个USA300 MRSA和50个USA300甲氧西林易感链球菌（MSSA）分离株均为CP阴性（CP-）。此外，所有16个USA500分离株（假定为USA300的祖细胞谱系）也均为CP-。对146个CP-USA300 MRSA分离株的全基因组序列分析表明，与Newman菌株相比，它们都带有一个带有4个保守突变的CAP5基因座。遗传互补实验表明，其中三个突变（在CAP5启动子中，CAP5D核苷酸994和CAP5E核苷酸223）在USA300中消融的CP产生，该CAP5E75 ASP位于同酶结合域中的CAP5E75 ASP对于Capsule的生产至关重要。除三个USA300 MSSA分离株外，所有其他CAP5突变都在USA300 MRSA分离株中都具有相同的四个CAP5突变。大多数具有USA500脉冲型的分离株都携带了这四个USA300特异性突变中的三个，这表明第四个突变发生在USA300谱系中。对我们USA300分离株的CAP基因座以及来自41种其他序列类型的公开基因组的系统发育分析表明，在USA300和USA500隔离的共同祖先中，在金黄色葡萄球菌中出现了USA300特异性CAP5突变。从那时起，它已经迅速传播，现在引起了与医疗保健相关的感染。这项研究表明，CP阴性（CP-）表型持续存在于USA300分离株之间，并且是这种非常成功的MRSA谱系的普遍和特征性状。重要的是要注意，仅由CP抗原组成的疫苗在美国人群中不太可能表现出很高的疗效，在美国人群中，大约一半的MRSA分离株包含USA300。此外，将USA300菌株转化为CP阳性（CP+）表型的转化不太可能在体内或体外，因为它需要重新恢复3个突变。我们还确定，USA300 MSSA分离株和USA500分离株是CP-，并为USA300和USA500谱系的演变提供了新的见解。
The surface capsular polysaccharide (CP) is a virulence factor that has been used as an antigen in several successful vaccines against bacterial pathogens. A vaccine has not yet been licensed against Staphylococcus aureus, although two multicomponent vaccines that contain CP antigens are in clinical trials. In this study, we evaluated CP production in USA300 methicillin-resistant S. aureus (MRSA) isolates that have become the predominant community-associated MRSA clones in the United States. We found that all 167 USA300 MRSA and 50 USA300 methicillin-susceptible S. aureus (MSSA) isolates were CP negative (CP-). Moreover, all 16 USA500 isolates, which have been postulated to be the progenitor lineage of USA300, were also CP-. Whole-genome sequence analysis of 146 CP- USA300 MRSA isolates revealed they all carry a cap5 locus with 4 conserved mutations compared with strain Newman. Genetic complementation experiments revealed that three of these mutations (in the cap5 promoter, cap5D nucleotide 994, and cap5E nucleotide 223) ablated CP production in USA300 and that Cap5E75 Asp, located in the coenzyme-binding domain, is essential for capsule production. All but three USA300 MSSA isolates had the same four cap5 mutations found in USA300 MRSA isolates. Most isolates with a USA500 pulsotype carried three of these four USA300-specific mutations, suggesting the fourth mutation occurred in the USA300 lineage. Phylogenetic analysis of the cap loci of our USA300 isolates as well as publicly available genomes from 41 other sequence types revealed that the USA300-specific cap5 mutations arose sequentially in S. aureus in a common ancestor of USA300 and USA500 isolates.IMPORTANCE The USA300 MRSA clone emerged as a community-associated pathogen in the United States nearly 20 years ago. Since then, it has rapidly disseminated and now causes health care-associated infections. This study shows that the CP-negative (CP-) phenotype has persisted among USA300 isolates and is a universal and characteristic trait of this highly successful MRSA lineage. It is important to note that a vaccine consisting solely of CP antigens would not likely demonstrate high efficacy in the U.S. population, where about half of MRSA isolates comprise USA300. Moreover, conversion of a USA300 strain to a CP-positive (CP+) phenotype is unlikely in vivo or in vitro since it would require the reversion of 3 mutations. We have also established that USA300 MSSA isolates and USA500 isolates are CP- and provide new insight into the evolution of the USA300 and USA500 lineages.