Sue David, Fink Daniel, Wiedmann Martin, Boor Kathryn J
Department of Food Science, Cornell University, Ithaca, NY 14853, USA.
Department of Statistical Science, Cornell University, Ithaca, NY 14853, USA.
Microbiology (Reading). 2004 Nov;150(Pt 11):3843-3855. doi: 10.1099/mic.0.27257-0.
Listeria monocytogenes must overcome a variety of stress conditions in the host digestive tract to cause foodborne infections. The alternative sigma factor sigma(B), encoded by sigB, is responsible for regulating transcription of several L. monocytogenes virulence and stress-response genes, including genes that contribute to establishment of gastrointestinal infections. A quantitative RT-PCR assay was used to measure mRNA transcript accumulation for the virulence genes inlA and bsh, the stress-response genes opuCA and lmo0669 (encoding a carnitine transporter and an oxidoreductase, respectively) and the housekeeping gene rpoB. Assays were conducted on mid-exponential phase L. monocytogenes cells exposed to conditions reflecting osmotic (0.3 M NaCl) or acid (pH 4.5) conditions typical for the human intestinal lumen. In exponential-phase cells, as well as under osmotic and acid stress, inlA, opuCA and bsh showed significantly lower absolute expression levels in a L. monocytogenes DeltasigB null mutant compared to wild-type. A statistical model that normalized target gene expression relative to rpoB showed that accumulation of inlA, opuCA and bsh transcripts was significantly increased in the wild-type strain within 5 min of acid and osmotic stress exposure; lmo0669 transcript accumulation increased significantly only after acid exposure. It was concluded that sigma(B) is essential for rapid induction of the tested stress-response and virulence genes under conditions typically encountered during gastrointestinal passage. As inlA, bsh and opuCA are critical for gastrointestinal infections in animal models, the data also suggest that sigma(B) contributes to the ability of L. monocytogenes to cause foodborne infections.
单核细胞增生李斯特菌必须克服宿主消化道中的多种应激条件才能引发食源性感染。由sigB编码的替代σ因子σ(B)负责调控多个单核细胞增生李斯特菌毒力和应激反应基因的转录，包括有助于胃肠道感染建立的基因。采用定量逆转录聚合酶链反应（RT-PCR）分析法来测定毒力基因inlA和bsh、应激反应基因opuCA和lmo0669（分别编码一种肉碱转运蛋白和一种氧化还原酶）以及管家基因rpoB的mRNA转录本积累情况。对处于指数中期的单核细胞增生李斯特菌细胞进行分析，这些细胞暴露于反映人类肠腔典型渗透压（0.3 M NaCl）或酸性（pH 4.5）条件的环境中。在指数期细胞以及渗透压和酸性应激条件下，与野生型相比，单核细胞增生李斯特菌ΔsigB基因缺失突变体中的inlA、opuCA和bsh显示出明显更低的绝对表达水平。一个将靶基因表达相对于rpoB进行标准化的统计模型表明，在酸性和渗透压应激暴露5分钟内，野生型菌株中inlA、opuCA和bsh转录本的积累显著增加；仅在酸性暴露后，lmo0669转录本的积累才显著增加。得出的结论是，σ(B)对于在胃肠道通过过程中通常遇到的条件下快速诱导所测试的应激反应和毒力基因至关重要。由于inlA、bsh和opuCA对动物模型中的胃肠道感染至关重要，这些数据还表明σ(B)有助于单核细胞增生李斯特菌引发食源性感染的能力。
