<i>Kingella kingae</i> Expresses Four Structurally Distinct Polysaccharide Capsules That Differ in Their Correlation with Invasive Disease

Kingella kingae is an encapsulated gram-negative organism that is a common cause of osteoarticular infections in young children. In earlier work, we identified a glycosyltransferase gene called csaA that is necessary for synthesis of the [3)-β-GalpNAc-(1→5)-β-Kdop-(2→] polysaccharide capsule (type a) in K. kingae strain 269–492. In the current study, we analyzed a large collection of invasive and carrier isolates from Israel and found that csaA was present in only 47% of the isolates. Further examination of this collection using primers based on the sequence that flanks csaA revealed three additional gene clusters (designated the csb, csc, and csd loci), all encoding predicted glycosyltransferases. The csb locus contains the csbA, csbB, and csbC genes and is associated with a capsule that is a polymer of [6)-α-GlcpNAc-(1→5)-β-(8-OAc)Kdop-(2→] (type b). The csc locus contains the cscA, cscB, and cscC genes and is associated with a capsule that is a polymer of [3)-β-Ribf-(1→2)-β-Ribf-(1→2)-β-Ribf-(1→4)-β-Kdop-(2→] (type c). The csd locus contains the csdA, csdB, and csdC genes and is associated with a capsule that is a polymer of [P-(O→3)[β-Galp-(1→4)]-β-GlcpNAc-(1→3)-α-GlcpNAc-1-] (type d). Introduction of the csa, csb, csc, and csd loci into strain KK01Δcsa, a strain 269–492 derivative that lacks the native csaA gene, was sufficient to produce the type a capsule, type b capsule, type c capsule, and type d capsule, respectively, indicating that these loci are solely responsible for determining capsule type in K. kingae. Further analysis demonstrated that 96% of the invasive isolates express either the type a or type b capsule and that a disproportionate percentage of carrier isolates express the type c or type d capsule. These results establish that there are at least four structurally distinct K. kingae capsule types and suggest that capsule type plays an important role in promoting K. kingae invasive disease.金氏国王菌（Kingella kingae）是一种带荚膜的革兰氏阴性微生物，为幼儿骨关节感染的常见致病菌。在既往研究中，我们于金氏国王菌269–492菌株中鉴定出一种名为csaA的糖基转移酶基因，该基因是其[3)-β-GalpNAc-(1→5)-β-Kdop-(2→]多糖荚膜（a型）合成的必需基因。本研究中，我们对以色列收集的大量侵袭性分离株与定植分离株进行了分析，发现仅47%的分离株携带csaA基因。利用靶向csaA侧翼序列的引物对该分离株群开展进一步检测，我们发现了另外3个基因簇（分别命名为csb、csc及csd基因座），三者均编码预测的糖基转移酶。csb基因座包含csbA、csbB及csbC基因，其关联的荚膜为[6)-α-GlcpNAc-(1→5)-β-(8-OAc)Kdop-(2→]聚合物（b型荚膜）。csc基因座包含cscA、cscB及cscC基因，其关联的荚膜为[3)-β-Ribf-(1→2)-β-Ribf-(1→2)-β-Ribf-(1→4)-β-Kdop-(2→]聚合物（c型荚膜）。csd基因座包含csdA、csdB及csdC基因，其关联的荚膜为[P-(O→3)[β-Galp-(1→4)]-β-GlcpNAc-(1→3)-α-GlcpNAc-1-]聚合物（d型荚膜）。将csa、csb、csc及csd基因座分别导入缺失天然csaA基因的269–492菌株衍生株KK01Δcsa后，即可分别合成a型、b型、c型及d型荚膜，证实这些基因座可独立决定金氏国王菌的荚膜类型。进一步分析显示，96%的侵袭性分离株表达a型或b型荚膜，而定植分离株中表达c型或d型荚膜的比例显著偏高。上述结果证实金氏国王菌至少存在4种结构迥异的荚膜类型，并提示荚膜类型在促进金氏国王菌侵袭性疾病发生中具有重要作用。