Analysis of infectious factors of Bacteroides fragilis in the compromised host

脆弱拟杆菌菌株YCH 46的基因组分析表明，该菌株通过广泛扩增参与多糖结合、降解和转运的基因而获得了异常高的利用多糖的能力。参与表面结构（如荚膜多糖和外膜蛋白）合成的基因的表达通过启动子的可逆DNA倒位以开关方式调节。我们确定了一个独特的27-kb的基因簇，命名为sgu（sialoglycoconjugate utilization）基因簇，它由13个基因负责的sialoglycoconjugates的吸收和降解，并位于下游区域的唾液酸酶基因（nanH 3）在B。fragilis菌株YCH 46。PCR分析表明，sgu基因簇中几乎所有的区域在B中都是保守的。fragilis菌株。转录分析的结果使分类的基因在sgu集群为三个调控单位的基础上，表达模式，以应对各种碳源。腹腔内脓肿形成的小鼠模型显示，sgu基因簇中的nanH 3、estA和estS被认为在B的脓肿形成中起重要作用。脆弱的B的限制屏障。fragilis可以通过用同源菌株的无细胞提取物在体外甲基化质粒DNA来克服。

Genomic analysis of Bacteroides fragilis strain YCH46 revealed that this strain has acquired an exceptionally high capability to utilize polysaccharides through extensive amplification of the genes involved in polysaccharide binding, degradation and transport. The expression of genes involving in the synthesis of surface architectures, such as capsular polysaccharides and outer membrane proteins are regulated in an on-off switching through reversible DNA inversions of promoters. We identified a unique 27-kb gene cluster, designated as sgu (sialoglycoconjugate utilization) gene cluster, which consists of 13 genes responsible for the uptake and degradation of sialoglycoconjugates and is located on the region downstream of the sialidase gene (nanH3) in B. fragilis strain YCH46. PCR analysis demonstrated that almost all of the regions in the sgu gene cluster were conserved among the B. fragilis strains tested. Results of transcriptional analysis enabled classification of the genes in the sgu cluster into three regulatory units on the basis of expression patterns in response to various kinds of carbon sources. A mouse model of intraabdominal abscess formation revealed that nanH3, estA, and estS in the sgu gene cluster were thought to play an important role on abscess formation of B. fragilis. The restriction barrier of B. fragilis could be overcome by methylation of plasmid DNA in vitro with a cell-free extract from the homologous strain.