Departamento de Genética, Facultad de Biología, Universidad de Sevilla, Apartado 1095, Seville 41080, Spain.
Plasmid. 2011 Mar;65(2):169-75. doi: 10.1016/j.plasmid.2010.12.001. Epub 2010 Dec 8.
Strains ATCC 14028 and SL1344 of Salmonella enterica serovar Typhimurium are more virulent than LT2 in the BALB/c mouse model. Virulence plasmid swapping between strains ATCC 14208, LT2, and SL1344 does not alter their competitive indexes during mouse infection, indicating that the three plasmids are functionally equivalent, and that their contribution to virulence is independent from the host background. Strains ATCC 14028 and LT2 are more efficient than SL1344 as conjugal donors of the virulence plasmid. Virulence plasmid swapping indicates that reduced ability of conjugal transfer is a property of the SL1344 plasmid, not of the host strain. An A→V amino acid substitution in the TraG protein appears to be the major cause that reduces conjugal transfer in the virulence plasmid of SL1344. Additional sequence differences in the tra operon are found between the SL1344 plasmid and the ATCC 14028 and LT2 plasmids. Divergence in the tra operon may reflect the occurrence of genetic drift either after laboratory domestication or in the environment. The latter might provide evidence that possession of conjugal transfer functions is a neutral trait in Salmonella populations, a view consistent with the abundance of Salmonella isolates whose virulence plasmids are non-conjugative.
肠沙门氏菌血清型鼠伤寒亚种 ATCC 14028 和 SL1344 菌株比 LT2 菌株在 BALB/c 小鼠模型中具有更强的毒力。在小鼠感染过程中，菌株 ATCC 14208、LT2 和 SL1344 之间的毒力质粒交换并没有改变它们的竞争指数，这表明这三个质粒在功能上是等效的，并且它们对毒力的贡献与宿主背景无关。菌株 ATCC 14028 和 LT2 作为毒力质粒的共轭供体比 SL1344 更有效。毒力质粒交换表明，共轭转移能力的降低是 SL1344 质粒的特性，而不是宿主菌株的特性。TraG 蛋白中的 A→V 氨基酸取代似乎是降低 SL1344 毒力质粒共轭转移的主要原因。在 SL1344 质粒与 ATCC 14028 和 LT2 质粒之间，还发现了 tra 操纵子中的其他序列差异。tra 操纵子的差异可能反映了实验室驯化或环境中遗传漂变的发生。后者可能提供了证据，表明拥有共轭转移功能是沙门氏菌群体中的中性特征，这一观点与大量非共轭性毒力质粒的沙门氏菌分离株的存在相一致。
