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Abstract：
Two patients with acute gastroenteritis tested positive for Shiga toxin-producing Escherichia coli (STEC) by polymerase chain reaction (PCR), and both strains carried the Shiga toxin 2 encoding gene. Since routine culture using CHROMagar STEC failed to recover these isolates, immunomagnetic separation (IMS) targeting the top six non-O157:H7 serotypes was used for isolate recovery. After two subsequent IMS runs, the STEC strains were isolated from trypticase soy broth with and without overnight enrichment for runs 1 and 2, respectively. Serotyping based on whole-genome sequencing revealed that both patients carried the strain O166:H15 STEC with the stx2 gene. Hence, the magnetic beads used in IMS appeared to have cross-reactivity with other E. coli serotypes. When the STEC isolates from both stools were cultured on CHROMagar STEC and sheep blood agar (BAP), two distinct colony sizes were apparent after overnight incubation. The small and large colonies were picked and separately cultured on both media, and colony growth was observed for 2 weeks at room temperature after an initial overnight incubation at 37°C. After 1 week, the colonies showed concentric ring structures with a darker center and a lighter surrounding on CHROMagar STEC and a \"fried egg\"-resembling structure with a raised circular center and a flat surrounding on BAP. Both colony types remained morphologically different on CHROMagar STEC throughout the 15 days. However, on BAP, their appearance was comparable by day 7.
OBJECTIVE: Shiga toxin-producing E. coli (STEC) infections can lead to severe complications such as bloody diarrhea and hemolytic uremic syndrome (HUS), especially in young children and the elderly. Strains that carry the shiga toxin 2 gene (stx2), such as O157:H7, have been mostly linked with severe disease outcomes. In recent years, outbreaks caused by non-O157:H7 strains have increased. E. coli O166:H15 has been previously reported causing a gastroenteritis outbreak in 1996 as a non-STEC strain, however the O166:H15 serotype we recovered carried the stx2 gene. It was particularly challenging to isolate this strain from stools by culture. Consequently, we tested immunomagnetic separation for the STEC recovery, which was a novel approach on clinical stools. Virulence genes were included for the characterization of these isolates.
OBJECTIVE: Shiga toxin-producing E. coli (STEC) infections can lead to severe complications such as bloody diarrhea and hemolytic uremic syndrome (HUS), especially in young children and the elderly. Strains that carry the shiga toxin 2 gene (stx2), such as O157:H7, have been mostly linked with severe disease outcomes. In recent years, outbreaks caused by non-O157:H7 strains have increased. E. coli O166:H15 has been previously reported causing a gastroenteritis outbreak in 1996 as a non-STEC strain, however the O166:H15 serotype we recovered carried the stx2 gene. It was particularly challenging to isolate this strain from stools by culture. Consequently, we tested immunomagnetic separation for the STEC recovery, which was a novel approach on clinical stools. Virulence genes were included for the characterization of these isolates.
摘要：
两名急性胃肠炎患者通过聚合酶链反应（PCR）检测出产志贺毒素的大肠杆菌（STEC）呈阳性，两种菌株都携带志贺毒素2编码基因。由于使用CHROMagarSTEC的常规培养无法恢复这些分离株，针对前六种非O157:H7血清型的免疫磁性分离(IMS)用于分离物回收。随后运行两次IMS后，从胰蛋白酶大豆肉汤中分离STEC菌株,分别在运行1和2中进行和不进行过夜富集。基于全基因组测序的血清分型显示，两名患者均携带具有stx2基因的O166：H15STEC菌株。因此，IMS中使用的磁珠似乎与其他大肠杆菌血清型具有交叉反应性。当从两种粪便中分离的STEC在CHROMagarSTEC和绵羊血琼脂（BAP）上培养时，过夜孵育后,两种不同的菌落大小是明显的。挑取小菌落和大菌落，在两种培养基上分别培养，在37°C下初始过夜孵育后，在室温下观察到菌落生长2周。1周后,菌落在CHROMagarSTEC上显示出同心环结构，中心较暗，周围较浅，在BAP上显示出类似“煎蛋”的结构，中心凸起，周围平坦。在整个15天的CHROMagarSTEC上，两种菌落类型在形态上保持不同。然而,在BAP上，到第7天，它们的外观相当。
目的：产志贺毒素大肠杆菌（STEC）感染可导致严重的并发症，如血性腹泻和溶血性尿毒综合征（HUS），尤其是幼儿和老人。携带志贺毒素2基因（stx2）的菌株，如O157:H7，主要与严重的疾病结局有关。近年来,非O157:H7菌株引起的疫情有所增加。大肠杆菌O166:H15以前曾被报道在1996年作为非STEC菌株引起肠胃炎爆发，然而，我们恢复的O166：H15血清型携带stx2基因。通过培养从粪便中分离该菌株是特别具有挑战性的。因此,我们测试了免疫磁性分离的STEC回收率，这是临床大便的一种新方法。包括毒力基因用于表征这些分离株。
目的：产志贺毒素大肠杆菌（STEC）感染可导致严重的并发症，如血性腹泻和溶血性尿毒综合征（HUS），尤其是幼儿和老人。携带志贺毒素2基因（stx2）的菌株，如O157:H7，主要与严重的疾病结局有关。近年来,非O157:H7菌株引起的疫情有所增加。大肠杆菌O166:H15以前曾被报道在1996年作为非STEC菌株引起肠胃炎爆发，然而，我们恢复的O166：H15血清型携带stx2基因。通过培养从粪便中分离该菌株是特别具有挑战性的。因此,我们测试了免疫磁性分离的STEC回收率，这是临床大便的一种新方法。包括毒力基因用于表征这些分离株。
