Pohl Mary Ann, Wiedmann Martin, Nightingale Kendra K
Department of Food Science, Cornell University, Ithaca, NY 14853, USA.
Am J Vet Res. 2006 Apr;67(4):616-26. doi: 10.2460/ajvr.67.4.616.
To determine whether specific strains of Listeria monocytogenes, as determined by genetic characteristics and virulence phenotypes, were associated with distinct clinical manifestations of listeriosis in cattle and thus may potentially have tissue specificity.
32 cattle.
DNA sequence data for the virulence genes actAand inlAwere used to infer the phylogeny of L. monocytogenes and to test for positive selection. Isolates were screened for the presence or absence of internalin genes and assigned an internalin profile. Plaquing assays were performed to determine the relative cytopathogenicity of each isolate. Categorical data analyses were performed to describe associations among L. monocytogenes genotypes, virulence phenotypes, and clinical manifestations of listeriosis.
Results confirmed that L. monocytogenes represents 2 deeply separated evolutionary lineages. Genes actA and inlA contained amino acid sites under positive selection, and specific residues at some sites were associated with lineage and manifestation of listeriosis. Whereas lineage I was clonal and predominantly composed of isolates from cases of encephalitis, lineage II was more genetically diverse and equally represented by isolates from cases of encephalitis versus septicemia and fetal infection. Lineage I isolates also had greater cytopathogenicity in vitro, compared with lineage II isolates.
Results indicated that L. monocytogenes virulence genes underwent positive selection that is consistent with the diversification of 2 evolutionary lineages: lineage I is clonal and associated with encephalitis, and lineage II is more genetically diverse and equally likely to cause both major forms of listeriosis in cattle.
根据遗传特征和毒力表型确定特定的单核细胞增生李斯特菌菌株是否与牛李斯特菌病的不同临床表现相关，从而可能具有组织特异性。
32头牛。
使用毒力基因actA和inlA的DNA序列数据推断单核细胞增生李斯特菌的系统发育并测试正选择。筛选分离株是否存在内化素基因并确定内化素谱。进行噬斑测定以确定每个分离株的相对细胞致病性。进行分类数据分析以描述单核细胞增生李斯特菌基因型、毒力表型和李斯特菌病临床表现之间的关联。
结果证实单核细胞增生李斯特菌代表2个深度分离的进化谱系。基因actA和inlA包含处于正选择下的氨基酸位点，并且某些位点的特定残基与李斯特菌病的谱系和表现相关。谱系I是克隆性的，主要由脑炎病例的分离株组成，而谱系II的遗传多样性更高，脑炎病例与败血症和胎儿感染病例的分离株数量相当。与谱系II分离株相比，谱系I分离株在体外也具有更大的细胞致病性。
结果表明，单核细胞增生李斯特菌毒力基因经历了正选择，这与2个进化谱系的多样化一致：谱系I是克隆性的，与脑炎相关，谱系II的遗传多样性更高，同样可能导致牛李斯特菌病的两种主要形式。
