细菌接合性耐药质粒与毒力关系的研究

The Relationship between Bacterial Conjugal R Plasmid and Virulence

目的 研究伤寒菌接合性耐药质粒ｐＲＳＴ９８ 与宿主菌毒力的关系。方法 用伤寒菌同源染色体的含ｐＲＳＴ９８ 野生株、消除ｐＲＳＴ９８ 菌株及ｐＲＳＴ９８ 重新导入消除菌株后，检测它们在人、兔及豚鼠血清中抵抗力的改变。将ｐＲＳＴ９８ 导入不含质粒的鼠伤寒无毒株ＲＩＡ，比较接合子ｐＲＳＴ９８／ＲＩＡ 与含一毒力质粒的鼠伤寒毒株ＳＲ－ １１ 及ＲＩＡ在体外对Ｈｅｐ－ ２ 、ＣＨＯ 和ＨｅＬａ 细胞的粘附、侵袭能力；经口感染小鼠观察３ 种菌在体内播散、繁殖及引起所在脏器的病理改变，并经腹腔感染测定对小鼠的半数致死量。结果 携带ｐＲＳＴ９８ 的菌株在血清中的抵抗力显著高于无此质粒菌株（ Ｐ＜ ０ ．０５）；ｐＲＳＴ９８ 在体外不影响宿主菌对上述３ 种细胞的粘附、侵袭力，但能使携带该质粒的ｐＲＳＴ９８／ＲＩＡ在小鼠肠系膜淋巴结、脾和肝脏的活菌数显著增加（ Ｐ＜ ０．０５） ，并引起相应的病理变化；腹腔注射小鼠ＬＤ５０ 比ＲＩＡ降低１０００ 倍（Ｐ＜ ０．０１） 。结论 伤寒菌耐药质粒ｐＲＳＴ９８ 具有多效性，不但能编码对药物的抗性，同时还能使宿主菌的毒力增强。

Object A group IncC R plasmid from S.typhi (pR ST98 ) encoding resistance to antimicrobial agents was investigated whether the R plasmid could increase the virulence of its host bacteria.Method The association of pR ST98 with resistance to the bactericidal activity of human,rabbit and guiner pig serum (NHS,NRS and GPS) was studied in chromosomally isogenic strains of S.typhi, i.e.,plasmid-containing wild type strain STpR ST98 ,plasmid-cured strain ST(R -),and plasmid-reintroduced into the cured strain pR ST98 /ST(R -).The pathogensis of pR ST98 was examined by transfer the R plasmid into an avirulent,plasmid-free strain of Salmonella typhimurium RIA.The in vitro role of the conjugant pR ST98 /RIA in the adhesive and invasive of the Hep-2,CHO and HeLa cells was examined and murine typhoid infection was employed to assess the effect of the pR ST98 on the virulence of the infecting agent in vivo by oral inoculation of strain RIA,pR ST98 /RIA and SR-11, a representative virulent strain of S.typhimurium harbored a 100kb virulence plasmid,to mice.The virulence of pR ST98 /RIA as determined by intraperitoneal 50% lethaldose was also compared with that of RIA and SR-11.Results ①The presence of pR ST98 correlated with resistance to serum.The absence of the plasmid increased sensitivity to serum,whereas the reintroduction of the plasmid to the cell resulted in the restoration of resistance to serum;②pR ST98 did not affect the ability of S.typhimurium to adhere to and invade the three cells;③The number of viable bacteria of SR-11 and pR ST98 /RIA in mesenteric lymph nodes,spleen and liver were great and histopathological changes were sever,while those with RIA were low and none or moderate;④The mice were killed by 100 CFU of SR-11 and pR ST98 /RIA injected ip,whereas they survived ip challenge with 10 5 CFU of RIA,reflected the significantly lower titeer of LD 50 .Conclusions pR ST98 carried not only genes for drug resistance,but also genes for virulence phenotypes,such as serum resistance and restore mouse virulence to a plasmid-free and avirulent S.typhimurium RIA.