Sansonetti P J, Kopecko D J, Formal S B
Infect Immun. 1982 Mar;35(3):852-60. doi: 10.1128/iai.35.3.852-860.1982.
Representative Shigella flexneri strains were studied to determine whether plasmids are involved in their virulence. All invasive S. flexneri strains, irrespective of serotype, were found to harbor a large plasmid of approximately 140 megadaltons in size, although some strains carried additional plasmid species. Spontaneous variants of strains of serotypes 1, 2, and 5 had lost this 140-megadalton plasmid and had concomitantly become avirulent, i.e., could neither invade HeLa cell monolayers nor produced keratoconjunctivitis in guinea pigs. To monitor plasmid transfer, the 140-megadalton plasmid of strain M90T (serotype 5) was tagged with the kanamycin resistance transposon Tn5. This tagged plasmid, pWR110, was not self-transmissible, but was mobilized by one of several different conjugative plasmids into avirulent derivatives of the heterologous serotypes 1 and 2 which had lost the comparable large plasmid. Transconjugants of both serotypes which had received pWR110 regained virulence. These data directly demonstrate that this large S. flexneri plasmid encodes or regulates some function(s) required for epithelial cell penetration.
对代表性的福氏志贺氏菌菌株进行了研究，以确定质粒是否与其毒力有关。结果发现，所有具有侵袭性的福氏志贺氏菌菌株，无论其血清型如何，均携带一个大小约为140兆道尔顿的大质粒，不过有些菌株还携带其他质粒种类。血清型1、2和5的菌株的自发变体失去了这个140兆道尔顿的质粒，并同时变得无毒力，即既不能侵袭单层Hela细胞，也不能在豚鼠中引起角膜结膜炎。为了监测质粒转移，用卡那霉素抗性转座子Tn5标记了菌株M90T（血清型5）的140兆道尔顿质粒。这个标记质粒pWR110不能自我转移，但可被几种不同的接合性质粒之一转移到已经失去类似大质粒的异源血清型1和2的无毒衍生物中。接受了pWR110的这两种血清型的接合子恢复了毒力。这些数据直接表明，这种大的福氏志贺氏菌质粒编码或调控上皮细胞穿透所需的某些功能。
