De Rycke J, Milon A, Oswald E
Unité de recherche associée Inra/ENVT de microbiologie moléculaire, Institut national de la recherche agronomique et Ecole nationale vétérinaire, Toulouse, France.
Vet Res. 1999 Mar-Jun;30(2-3):221-33.
Necrotoxic Escherichia coli (NTEC) were originally defined as strains of E. coli producing a toxin called cytotoxic necrotising factor (CNF). Two types of CNF have been identified, each of them being genetically linked to several other specific virulence markers, a situation that allows the definition of two distinct homogeneous categories of NTEC called NTEC-1 and NTEC-2. CNF1 and CNF2 are highly homologous holoproteins containing 1,014 amino acids that exert both lethal and necrotic activities in vivo and induce multinucleation and actin stress fibres in cell cultures. The activity of CNFs on mammal cells is due to their ability to constitutively activate by deamidation the Rho proteins, a family of small GTPases that regulate the physiology of the cell cytoskeleton. In NTEC-1, the gene encoding CNF1 belongs to a pathogenicity island which also comprises the genes encoding for alpha-haemolysin and P-fimbriae. In NTEC-2 strains, CNF2 is encoded by a plasmid that also encodes, in 100% of the isolates, a new member of the cytolethal distending toxin family (CDT-III) and in about 50% of the isolates, the F17b-fimbrial adhesin that confers the ability to adhere to calf intestinal villi. The presence of CDT is also suspected in a large majority of NTEC-1 strains. NTEC-1 strains can be found in humans and in all species of domestic mammals, whereas NTEC-2 strains have only been reported in ruminants. The implication of NTEC strains has been clearly established in extra-intestinal infections of humans and animals, for instance in urinary tract infections for NTEC-1 strains. Their role in severe dysenteric syndromes, both in humans and animals, is substantiated by several clinical reports, but there is little published information on this pathogenicity in animal models of infection. The combined production of several powerful toxins (haemolysin, CNF, CDT) by NTEC strains makes them, however, potentially aggressive pathogens which deserve to be searched for on a larger scale. Moreover, NTEC-1 from man and animals appear to be highly related according to available molecular markers, which indicates that domestic animals could constitute reservoirs of NTEC strains which are pathogenic for humans.
坏死毒性大肠杆菌（NTEC）最初被定义为产生一种名为细胞毒性坏死因子（CNF）的毒素的大肠杆菌菌株。已鉴定出两种类型的CNF，它们各自在基因上与其他几种特定的毒力标记相关联，这种情况使得可以定义两种不同的NTEC同质性类别，即NTEC-1和NTEC-2。CNF1和CNF2是高度同源的全蛋白，含有1014个氨基酸，在体内发挥致死和坏死活性，并在细胞培养中诱导多核化和肌动蛋白应激纤维。CNF对哺乳动物细胞的活性归因于它们通过脱酰胺作用组成性激活Rho蛋白的能力，Rho蛋白是一类调节细胞细胞骨架生理学的小GTP酶。在NTEC-1中，编码CNF1的基因属于一个致病岛，该致病岛还包含编码α-溶血素和P菌毛的基因。在NTEC-2菌株中，CNF2由一个质粒编码，该质粒在100%的分离株中还编码细胞致死膨胀毒素家族（CDT-III）的一个新成员，在约50%的分离株中编码赋予粘附小牛肠绒毛能力的F17b菌毛粘附素。在绝大多数NTEC-1菌株中也怀疑存在CDT。NTEC-1菌株可在人类和所有家养哺乳动物物种中发现，而NTEC-2菌株仅在反刍动物中被报道。NTEC菌株在人类和动物的肠道外感染中的作用已得到明确证实，例如在NTEC-1菌株引起的尿路感染中。它们在人类和动物严重痢疾综合征中的作用得到了几份临床报告的证实，但关于这种致病性在动物感染模型中的公开信息很少。然而，NTEC菌株联合产生几种强大的毒素（溶血素、CNF、CDT），使它们成为潜在的侵袭性病原体，值得进行更广泛的搜索。此外，根据现有的分子标记，来自人和动物的NTEC-1似乎高度相关，这表明家畜可能构成对人类致病的NTEC菌株的储存库。
