Salmonella Typhimurium stbC mutant. Salmonella enterica subsp. enterica serovar Typhimurium str. LT2

Salmonella enterica serotype Typhimurium produces a variety of fimbrial appendages, among which the type 1 fimbriae is the most common type. In vitro static broth culture favors S. Typhimurium to produce type 1 fimbriae, while solid agar inhibits its expression. A transposon inserted in the stbC gene, which would encode an usher protein for Stb fimbriae of a non-flagellar S. Typhimurium LB5010 strain, conferred it to agglutinate yeast cells on both cultures, and was mannose-sensitive. Reverse transcription polymerase chain reaction (RT-PCR) revealed that the expression of the fimbrial major subunit gene fimA, and fimZ, a positive regulator gene of fimA, were both increased in the stbC mutant strain when grown on LB agar; fimW, a repressor gene of fimA, exhibited lower expression. Flagella were observed in the stbC mutant and this phenotype was correlated with the motile phenotype detected by MSRV agar medium and reaction with flagella antiserum. Microarray data and RT-PCR also indicated that the expression of three genes, motA, motB, and cheM, was enhanced in the stbC mutant. The S. Typhimurium stbC mutant was resistant to a variety of antibiotics, consistent with the finding that expression of yhcQ and ramA, two genes involved in multidrug resistance, was enhanced. A complementation test revealed that transforming a recombinant plasmid possessing the coding sequence of the stbC gene restored the mannose-sensitive agglutination phenotype to the stbC mutant much as that in the parental S. Typhimurium LB5010 strain, indicating the possibility of an interplay of different fimbrial systems in coordinating their expression. Key Words: Salmonella enterica serotype Typhimurium, fimbriae, type 1 fimbriae, stbC, transposon, multidrug resistant, flagella Overall design: RNA transcript of Salmonella Typhimurium LB5010 strain comparing wild-type with stbC mutant. Two-cindition experiment, wild-type vs. stbC mutant strain.

肠炎沙门氏菌鼠伤寒血清型（Salmonella enterica serotype Typhimurium）可产生多种菌毛附属结构，其中1型菌毛（type 1 fimbriae）最为常见。体外静态肉汤培养有利于该菌株表达1型菌毛，而固体琼脂培养基则会抑制其表达。将转座子（transposon）插入无鞭毛的鼠伤寒沙门氏菌LB5010菌株的stbC基因（该基因编码Stb菌毛的usher蛋白（usher protein））后，突变株在两种培养条件下均能凝集酵母细胞，且该凝集效应具有甘露糖敏感性（mannose-sensitive）。

逆转录聚合酶链反应（Reverse transcription polymerase chain reaction, RT-PCR）结果显示，在LB琼脂培养基上培养时，stbC突变株中菌毛主要亚基基因fimA以及fimA的正调控基因fimZ的表达水平均显著上调；而fimA的阻遏基因fimW的表达水平则显著下调。stbC突变株可观察到鞭毛（flagella），该表型与通过MSRV琼脂培养基（MSRV agar medium）检测到的运动表型（motile phenotype）以及抗鞭毛血清反应结果一致。基因芯片（Microarray）数据与RT-PCR结果均表明，stbC突变株中motA、motB及cheM三个基因的表达水平均得到增强。鼠伤寒沙门氏菌stbC突变株对多种抗生素具有耐药性，这与多重耐药（multidrug resistance）相关基因yhcQ和ramA的表达上调结果相符。互补试验（complementation test）结果显示，将携带stbC基因编码序列（coding sequence）的重组质粒（recombinant plasmid）转化至stbC突变株后，可恢复其甘露糖敏感性凝集表型，该表型与亲本鼠伤寒沙门氏菌LB5010菌株一致，提示不同菌毛系统之间可能存在相互作用以协调其表达。

关键词：肠炎沙门氏菌鼠伤寒血清型，菌毛，1型菌毛，stbC，转座子，多重耐药，鞭毛
实验设计概述：对比鼠伤寒沙门氏菌LB5010野生型菌株与stbC突变株的RNA转录本。本实验采用双条件设计，即野生型菌株与stbC突变株的对照实验。