Tóth István, Hérault Fréderique, Beutin Lothar, Oswald Eric
Veterinary Medical Research Institute of the Hungarian Academy of Sciences, Budapest, Hungary.
J Clin Microbiol. 2003 Sep;41(9):4285-91. doi: 10.1128/JCM.41.9.4285-4291.2003.
Three types of cytolethal distending toxin (CDT), namely, CDT-I, CDT-II, and CDT-III, have been described in Escherichia coli. Using primers designed for the detection of sequences common to the cdtB genes, we analyzed by PCR a set of 21 CDT-producing E. coli strains of intestinal and extraintestinal origins isolated from human and different animal species in several European countries and in the United States. On the basis of the existing differences in the cdtB genes, cdt-I-, cdt-II-, and cdt-III-specific primer pairs were designed and used for cdt typing. These new primers successfully differentiated all of the previously described cdt genes. Six strains proved to be cdt-I; eight strains proved to be cdt-III. However, none of the type I-, II-, and III-specific primers generated amplicons from six CDT(+) strains, suggesting the existence of a new cdt variant. Sequence analysis of the amplicons from two untypeable genes confirmed the existence of a new cdt variant that we called cdt-IV. Using the new specific primers, cdt-IV was detected in human, porcine, and poultry strains of intestinal and extraintestinal origins. To validate all sets of cdt specific primers, a group of 353 human E. coli strains isolated in Hungary was then investigated for the presence of cdt genes. This included 190 strains isolated from patients with urinary tract infections (UTI), 51 strains isolated from other (nonurinary) extraintestinal infections, and 112 intestinal strains isolated from healthy individuals. Of 190 UTI strains, 15 (7.9%) had cdt genes. Of 51 non-UTI extraintestinal strains 3 (5.9%) contained the cdt gene, and 1 (0.9%) of 112 healthy intestinal strains was PCR positive. Five strains proved to be cdt-I, and fourteen strains proved to be cdt-IV. The CDT-producing extraintestinal strains belonged to a wide variety of serogroups, including O2, O6, O75, and O170. In conclusion, we have developed a new PCR typing system for CDT able to detect a new CDT variant present in pathogenic E. coli strains obtained from animals and humans.
在大肠杆菌中已发现三种细胞致死性膨胀毒素（CDT），即CDT-I、CDT-II和CDT-III。我们使用针对cdtB基因共同序列检测设计的引物，通过聚合酶链反应（PCR）分析了一组21株产生CDT的大肠杆菌菌株，这些菌株分离自几个欧洲国家和美国的人类及不同动物物种，包括肠道来源和肠外来源。基于cdtB基因现有的差异，设计了cdt-I、cdt-II和cdt-III特异性引物对，并用于CDT分型。这些新引物成功区分了所有先前描述的cdt基因。六株菌株被鉴定为cdt-I型；八株菌株被鉴定为cdt-III型。然而，I型、II型和III型特异性引物均未从六株CDT（+）菌株中扩增出产物，这表明存在一种新的cdt变体。对两个无法分型的基因的扩增产物进行序列分析，证实了一种新的cdt变体的存在，我们将其命名为cdt-IV。使用新的特异性引物，在人类、猪和家禽的肠道及肠外来源菌株中检测到了cdt-IV。为了验证所有的cdt特异性引物组，随后对匈牙利分离的一组353株人类大肠杆菌菌株进行了cdt基因检测。这包括从尿路感染（UTI）患者中分离的190株菌株、从其他（非泌尿系统）肠外感染中分离的51株菌株以及从健康个体中分离的112株肠道菌株。在190株UTI菌株中，15株（7.9%）含有cdt基因。在51株非UTI肠外菌株中，3株（5.9%）含有cdt基因，在112株健康肠道菌株中有1株（0.9%）PCR检测呈阳性。五株菌株被鉴定为cdt-I型，十四株菌株被鉴定为cdt-IV型。产生CDT的肠外菌株属于多种血清群，包括O2、O6、O75和O170。总之，我们开发了一种新的用于CDT的PCR分型系统，能够检测从动物和人类分离的致病性大肠杆菌菌株中存在的一种新的CDT变体。
