Microbial Evolution Laboratory, National Food Safety and Toxicology Center, 165 Food Safety and Toxicology Building, Michigan State University, East Lansing, MI 48824, USA.
Appl Environ Microbiol. 2010 Jan;76(1):60-8. doi: 10.1128/AEM.01666-09. Epub 2009 Oct 30.
Escherichia coli O157:H7 strains can be classified into different genotypes based on the presence of specific Shiga toxin-encoding bacteriophage insertion sites. Certain O157:H7 genotypes predominate among human clinical cases (clinical genotypes), while others are more frequently found in bovines (bovine-biased genotypes). To determine whether inherent differences in gene expression explain the variation in infectivity of these genotypes, we compared the expression patterns of clinical genotype 1 strains with those of bovine-biased genotype 5 strains using microarrays. Important O157:H7 virulence factors, including locus of enterocyte effacement genes, the enterohemolysin, and several pO157 genes, showed increased expression in the clinical versus bovine-biased genotypes. In contrast, genes essential for acid resistance (e.g., gadA, gadB, and gadC) and stress fitness were upregulated in bovine-biased genotype 5 strains. Increased expression of acid resistance genes was confirmed functionally using a model stomach assay, in which strains of bovine-biased genotype 5 had a 2-fold-higher survival rate than strains of clinical genotype 1. Overall, these results suggest that the increased prevalence of O157:H7 illness caused by clinical genotype 1 strains is due in part to the overexpression of key virulence genes. The bovine-biased genotype 5 strains, however, are more resistant to adverse environmental conditions, a characteristic that likely facilitates O157:H7 colonization of bovines.
大肠杆菌 O157:H7 菌株可以根据特定的志贺毒素编码噬菌体插入位点的存在进行不同的基因型分类。某些 O157:H7 基因型在人类临床病例中占主导地位（临床基因型），而其他基因型则更常见于牛（牛偏向基因型）。为了确定基因表达的固有差异是否解释了这些基因型的感染力差异，我们使用微阵列比较了临床基因型 1 株和牛偏向基因型 5 株的表达模式。包括肠上皮细胞 effacement 基因座、肠溶血素和几个 pO157 基因在内的重要 O157:H7 毒力因子在临床株与牛偏向株中的表达均增加。相比之下，对于酸抗性（例如 gadA、gadB 和 gadC）和应激适应性至关重要的基因在牛偏向基因型 5 株中上调。通过模型胃试验证实了酸抗性基因上调的功能，牛偏向基因型 5 株的存活率比临床基因型 1 株高 2 倍。总的来说，这些结果表明，由临床基因型 1 株引起的 O157:H7 疾病的高发部分原因是关键毒力基因的过度表达。然而，牛偏向基因型 5 株对不利的环境条件具有更强的抵抗力，这种特征可能有助于 O157:H7 对牛的定植。
