Gu Congcong, Xue Tao, Xu Tingting, Gao Song, Jiao Xin'an, Liu Xiufan
Key Laboratory of Animal Infectious Disease of Agriculture Ministry, College of Veterinary Medicine, Yangzhou University, Yangzhou 225009, China.
Wei Sheng Wu Xue Bao. 2011 May;51(5):676-83.
In order to investigate the distribution of Shiga toxin-producing Escherichia coli (STEC) among healthy sheep in a farm and the pathogenicity to mice and Vero cells of these STEC isolates.
We used polymerase chain reaction (PCR) to detect genes of eaeA, stx1, stx2, hlyA, which had been developed in this laboratory previously, combing the selective cultivation and Chrom-Agar (CA) O157 plates to isolate STEC strains.
A total of 107 STEC strains were isolated in a sheep farm during six visits from August, 2008 to January, 2009. The isolation rate was 19.8% (107/550). These isolates belonged to 41 O serotypes and 60 O: H serotypes, except that 21 were O non-typable and 1 was rough. 093 was the common serotype. Some isolates such as O5, O91, O103, which are reported in other countries originated from healthy sheep were also isolated in this study. Stx2 positive rate was higher than that of stxl. 50% lethal dose assay in mice indicated the pathogenicity of isolates was low and none of the 3 tested isolates caused mice death. We selected 107 stx gene positive STEC strains to induce the lambdoid bacteriophages. The results showed that 71 out of 107 isolates formed plagues, while 28 did not after induction. Detection of Shiga toxins for three tested isolates in Vero cell assay indicated one stx gene positive strain lacked the toxigenicity to Vero cells.
Sheep are the natural reservoirs of STEC and they are healthy to carry STEC. Although these STEC isolates experience low pathogenicity to mice, they are potential threat to human health. Shiga toxin gene positive were not equal to production of Shiga toxins, so we need to further study the Shiga toxin expression and regulation mechanism.
调查某养殖场健康绵羊中产志贺毒素大肠杆菌（STEC）的分布情况以及这些STEC分离株对小鼠和Vero细胞的致病性。
我们采用聚合酶链反应（PCR）检测先前在本实验室开发的eaeA、stx1、stx2、hlyA基因，结合选择性培养和Chrom - Agar（CA）O157平板分离STEC菌株。
在2008年8月至2009年1月的六次走访中，某养羊场共分离出107株STEC菌株。分离率为19.8%（107/550）。这些分离株属于41种O血清型和60种O:H血清型，其中21株为O非分型，1株为粗糙型。093是常见血清型。本研究还分离出了其他国家报道的一些源自健康绵羊的分离株，如O5、O91、O103。stx2阳性率高于stx1。小鼠半数致死剂量试验表明分离株的致病性较低，所检测的3株分离株均未导致小鼠死亡。我们选取107株stx基因阳性的STEC菌株诱导λ噬菌体。结果显示，107株分离株中有71株诱导后形成噬菌斑，28株未形成。对3株检测分离株进行Vero细胞试验检测志贺毒素，结果表明1株stx基因阳性菌株对Vero细胞缺乏产毒性。
绵羊是STEC的天然宿主，它们携带STEC但健康。尽管这些STEC分离株对小鼠致病性较低，但对人类健康仍有潜在威胁。志贺毒素基因阳性并不等同于产生志贺毒素，因此我们需要进一步研究志贺毒素的表达及调控机制。
