Research Center for Food Safety, Graduate School of Agricultural and Life Sciences, The University of Tokyo, Yayoi 1-1-1, Bunkyo-ku, Tokyo 113-8657, Japan.
Department of Microbiology, Juntendo University School of Medicine, Hongo 2-1-1, Bunkyo-ku, Tokyo 113-8421, Japan.
FEMS Microbiol Lett. 2021 Jul 9;368(13). doi: 10.1093/femsle/fnab083.
The capsule (cap) of Streptococcus suis is an anti-phagocytic element and is one of the major virulence factors. However, we have found cap-positive and cap-negative isolates in porcine endocarditis. Here, we compared genome sequences of multiple cap-negative isolates with those of a cap-positive isolate from a single endocarditis. Cap-positive and cap-negative isolates from the same pig were phylogenetically closest compared with those from other pigs. Some of cap-negative isolates from the same pig showed different mutations in capsular polysaccharide synthesis (cps) genes, suggesting that these isolates arisen in pigs after infection. Different mutations in whole-genomes were also found among isolates with identical mutations in cps genes, indicating that mutations in cps genes and the whole-genome occurred independently. Since cap-negative isolates are rarely found in lesions of other diseases, these results suggest that endocarditis lesions may simply favored cap-negative mutants to survive the niches, leading to their persistence in the lesions.
猪链球菌荚膜（Cap）是一种抗吞噬素，是主要的毒力因子之一。然而，我们在猪心内膜炎中发现了荚膜阳性和荚膜阴性分离株。在这里，我们比较了多个荚膜阴性分离株与来自单个心内膜炎的荚膜阳性分离株的基因组序列。与来自其他猪的分离株相比，来自同一猪的荚膜阳性和荚膜阴性分离株在系统发育上最为接近。来自同一猪的一些荚膜阴性分离株在荚膜多糖合成（cps）基因中显示出不同的突变，表明这些分离株在感染后出现在猪体内。在 cps 基因具有相同突变的分离株中也发现了整个基因组的不同突变，表明 cps 基因和整个基因组的突变是独立发生的。由于荚膜阴性分离株在其他疾病的病变中很少被发现，这些结果表明心内膜炎病变可能只是有利于荚膜阴性突变体在小生境中存活，从而导致它们在病变中持续存在。
