de Sablet Thibaut, Bertin Yolande, Vareille Marjolaine, Girardeau Jean-Pierre, Garrivier Annie, Gobert Alain P, Martin Christine
INRA, UR454 Unité de Microbiologie, 63122 St-Genès-Champanelle, France.
Microbiology (Reading). 2008 Jan;154(Pt 1):176-186. doi: 10.1099/mic.0.2007/009704-0.
Only a subset of Shiga toxin (Stx)-producing Escherichia coli (STEC) are human pathogens, but the characteristics that account for differences in pathogenicity are not well understood. In this study, we investigated the distribution of the stx variants coding for Stx2 and its variants in highly virulent STEC of seropathotype A and low-pathogenic STEC of seropathotype C. We analysed and compared transcription of the corresponding genes, production of Shiga toxins, and stx-phage release in basal as well as in induced conditions. We found that the stx(2) variant was mainly associated with strains of seropathotype A, whereas most of the strains of seropathotype C possessed the stx(2-vhb) variant, which was frequently associated with stx(2), stx(2-vha) or stx(2c). Levels of stx(2) and stx(2)-related mRNA were higher in strains belonging to seropathotype A and in those strains of seropathotype C that express the stx(2) variant than in the remaining strains of seropathotype C. The stx(2-vhb) genes were the least expressed, in basal as well as in induced conditions, and in many cases did not seem to be carried by an inducible prophage. A clear correlation was observed between stx mRNA levels and stx-phage DNA in the culture supernatants, suggesting that most stx(2)-related genes are expressed only when they are carried by a phage. In conclusion, some relationship between stx(2)-related gene expression in vitro and the seropathotype of the STEC strains was observed. A higher expression of the stx(2) gene and a higher release of its product, in basal as well as in induced conditions, was observed in pathogenic strains of seropathotype A. A subset of strains of seropathotype C shows the same characteristics and could be a high risk to human health.
只有一部分产志贺毒素（Stx）的大肠杆菌（STEC）是人类病原体，但导致致病性差异的特征尚未完全明确。在本研究中，我们调查了编码Stx2及其变体的stx变体在血清型A的高毒力STEC和血清型C的低致病性STEC中的分布情况。我们分析并比较了相应基因的转录、志贺毒素的产生以及在基础条件和诱导条件下stx噬菌体的释放情况。我们发现stx(2)变体主要与血清型A的菌株相关，而大多数血清型C的菌株拥有stx(2-vhb)变体，该变体常与stx(2)、stx(2-vha)或stx(2c)相关。血清型A的菌株以及表达stx(2)变体的血清型C的菌株中，stx(2)和stx(2)相关mRNA的水平高于血清型C的其余菌株。在基础条件和诱导条件下，stx(2-vhb)基因的表达最少，并且在许多情况下似乎不是由可诱导噬菌体携带。在培养上清液中观察到stx mRNA水平与stx噬菌体DNA之间存在明显的相关性，这表明大多数stx(2)相关基因只有在由噬菌体携带时才会表达。总之，观察到了体外stx(2)相关基因表达与STEC菌株血清型之间的某种关系。在血清型A的致病菌株中，无论是在基础条件还是诱导条件下，都观察到stx(2)基因的更高表达及其产物的更高释放。血清型C的一部分菌株表现出相同的特征，可能对人类健康构成高风险。
