Tzipori S, Karch H, Wachsmuth K I, Robins-Browne R M, O'Brien A D, Lior H, Cohen M L, Smithers J, Levine M M
Department of Microbiology, Royal Children's Hospital, Melbourne, Australia.
Infect Immun. 1987 Dec;55(12):3117-25. doi: 10.1128/iai.55.12.3117-3125.1987.
Enterohemorrhagic Escherichia coli (EHEC) of serotype O157:H7 has two putative virulence factors: (i) a fimbrial adhesin, specified by a 60-megadalton (MDa) plasmid, and (ii) bacteriophage-specified cytotoxin(s), known as Shiga-like toxin (SLT) or verotoxin. The contribution of these factors to the pathogenesis of EHEC-induced disease in gnotobiotic piglets was examined. The bacterial strains included the following: two EHEC strains and their corresponding plasmid-cured derivatives; another EHEC isolate and its derivative which had spontaneously lost the ability to produce SLT; one E. coli K-12 transconjugatant containing a 60-MDa plasmid from an EHEC strain; two K-12 strains into which an SLT-producing phage had been transduced (one of these strains also carried a 60-MDa EHEC-derived plasmid); and the parent K-12 strain. Each strain was fed to four piglets, which were observed for diarrhea and examined for development of characteristic mucosal lesions 3 or 5 days after inoculation. All 24 piglets inoculated with the three EHEC strains and their respective derivatives (two plasmid cured and one SLT negative) showed the typical mucosal lesions of bacterial attachment: effacement of microvillous border and cell membrane dissolution culminating in destruction of surface and glandular epithelium in the cecum and colon. No such lesions were observed in 12 piglets inoculated with three strains of E. coli K-12, including the strain which carried both the 60-MDa plasmid and a phage which specified production of SLT. Moderate to severe diarrhea was observed in 16 piglets inoculated with two EHEC strains and their derivatives (one plasmid cured and one SLT negative). The third EHEC strain and its plasmid-cured derivative produced fewer typical mucosal lesions and no diarrhea. The reason for the reduced virulence of this strain was not clear. These results demonstrate that neither the 60-MDa plasmid nor the capacity to produce SLT is essential for expression of virulence by E. coli O157:H7 in gnotobiotic piglets.
血清型为O157:H7的肠出血性大肠杆菌（EHEC）有两种假定的毒力因子：（i）一种菌毛黏附素，由一个60兆道尔顿（MDa）的质粒编码；（ii）噬菌体编码的细胞毒素，即志贺样毒素（SLT）或维罗毒素。研究了这些因子对无菌仔猪EHEC诱导疾病发病机制的作用。所用细菌菌株如下：两株EHEC菌株及其相应的质粒消除衍生物；另一株EHEC分离株及其自发丧失产生SLT能力的衍生物；一株含有来自EHEC菌株的60-MDa质粒的大肠杆菌K-12转接合子；两株转导了产生SLT噬菌体的K-12菌株（其中一株还携带一个源自EHEC的60-MDa质粒）；以及亲本K-12菌株。将每种菌株喂给4头仔猪，并在接种后3天或5天观察腹泻情况，并检查特征性黏膜损伤的发展情况。接种了三株EHEC菌株及其各自衍生物（两株质粒消除和一株SLT阴性）的所有24头仔猪均出现了细菌黏附的典型黏膜损伤：微绒毛边界消失和细胞膜溶解，最终导致盲肠和结肠表面及腺上皮破坏。接种了三株大肠杆菌K-12（包括携带60-MDa质粒和指定产生SLT的噬菌体的菌株）的12头仔猪未观察到此类损伤。接种了两株EHEC菌株及其衍生物（一株质粒消除和一株SLT阴性）的16头仔猪出现了中度至重度腹泻。第三株EHEC菌株及其质粒消除衍生物产生的典型黏膜损伤较少且未出现腹泻。该菌株毒力降低的原因尚不清楚。这些结果表明，对于无菌仔猪中的大肠杆菌O157:H7，60-MDa质粒和产生SLT的能力都不是毒力表达所必需的。
