Nishio Miki, Okada Nobuhiko, Miki Tsuyoshi, Haneda Takeshi, Danbara Hirofumi
Department of Microbiology, School of Pharmaceutical Sciences, Kitasato University, 5-9-1 Shirokane, Minato-ku, Tokyo 108-8641, Japan.
Microbiology (Reading). 2005 Mar;151(Pt 3):863-873. doi: 10.1099/mic.0.27654-0.
Serum resistance is a crucial virulence factor for the development of systemic infections, including bacteraemia, by many pathogenic bacteria. Salmonella enterica serovar Choleraesuis is an important enteric pathogen that causes serious systemic infections in swine and humans. Here, it was found that, when introduced into Escherichia coli, a recombinant plasmid carrying the pagC gene from a plasmid-based genomic library of S. enterica serovar Choleraesuis conferred a high-level resistance to the bactericidal activity of pooled normal swine serum. The resistance was equal to the level conferred by rck, a gene encoding a 17 kDa outer-membrane protein which promotes the serum resistance phenotype in S. enterica serovar Typhimurium. Insertional mutagenesis of the cloned pagC gene generated a mutation that resulted in the loss of the serum resistance phenotype in E. coli. When this mutation was introduced into the chromosome of S. enterica serovar Choleraesuis by homology recombination with the wild-type allele, the resulting strain could not produce PagC, and it showed a decreased level of resistance to complement-mediated killing. The mutation could be restored by introduction of the intact pagC gene on a plasmid, but not by introduction of the point-mutated pagC gene. In addition, PagC was able to promote serum resistance in the S. enterica serovar Choleraesuis LPS mutant strain, which is highly sensitive to serum killing. Although PagC is not thought to confer serum resistance directly, these results strongly suggest that PagC is an important outer-membrane protein that plays an important role in the serum resistance of S. enterica serovar Choleraesuis.
血清抗性是许多病原菌引发包括菌血症在内的全身感染的关键毒力因子。猪霍乱沙门氏菌是一种重要的肠道病原菌，可在猪和人类中引起严重的全身感染。在此研究中发现，将携带来自猪霍乱沙门氏菌基于质粒的基因组文库中pagC基因的重组质粒导入大肠杆菌后，该大肠杆菌对混合的正常猪血清的杀菌活性具有高水平抗性。这种抗性水平与rck基因赋予的抗性相当，rck基因编码一种17 kDa的外膜蛋白，可促进鼠伤寒沙门氏菌的血清抗性表型。对克隆的pagC基因进行插入诱变产生了一个突变，导致大肠杆菌中血清抗性表型丧失。当通过与野生型等位基因进行同源重组将此突变引入猪霍乱沙门氏菌的染色体时，所得菌株无法产生PagC，并且其对补体介导的杀伤的抗性水平降低。通过在质粒上导入完整的pagC基因可恢复该突变，但导入点突变的pagC基因则无法恢复。此外，PagC能够促进对血清杀伤高度敏感的猪霍乱沙门氏菌LPS突变株的血清抗性。尽管一般认为PagC不会直接赋予血清抗性，但这些结果强烈表明，PagC是一种重要的外膜蛋白，在猪霍乱沙门氏菌的血清抗性中发挥重要作用。
