Liu K, Knabel S J, Dudley E G
Department of Food Science, The Pennsylvania State University, University Park, PA 16802, USA.
Appl Environ Microbiol. 2009 Sep;75(18):5853-62. doi: 10.1128/AEM.00859-09. Epub 2009 Jul 24.
DNA sequence-based molecular subtyping methods such as multilocus sequence typing (MLST) are commonly used to generate phylogenetic inferences for monomorphic pathogens. The development of an effective MLST scheme for subtyping Escherichia coli O157:H7 has been hindered in the past due to the lack of sequence variation found within analyzed housekeeping and virulence genes. A recent study suggested that rhs genes are under strong positive selection pressure, and therefore in this study we analyzed these genes within a diverse collection of E. coli O157:H7 strains for sequence variability. Eighteen O157:H7 strains from lineages I and II and 15 O157:H7 strains from eight clades were included. Examination of these rhs genes revealed 44 polymorphic loci (PL) and 10 sequence types (STs) among the 18 lineage strains and 280 PL and 12 STs among the 15 clade strains. Phylogenetic analysis using rhs genes generally grouped strains according to their known lineage and clade classifications. These findings also suggested that O157:H7 strains from clades 6 and 8 fall into lineage I/II and that strains of clades 1, 2, 3, and 4 fall into lineage I. Additionally, unique markers were found in rhsA and rhsJ that might be used to define clade 8 and clade 6. Therefore, rhs genes may be useful markers for phylogenetic analysis of E. coli O157:H7.
基于DNA序列的分子分型方法，如多位点序列分型（MLST），通常用于对单态病原体进行系统发育推断。过去，由于在所分析的管家基因和毒力基因中缺乏序列变异，阻碍了开发一种有效的用于大肠杆菌O157:H7分型的MLST方案。最近的一项研究表明，rhs基因受到强烈的正选择压力，因此在本研究中，我们分析了不同大肠杆菌O157:H7菌株集合中的这些基因的序列变异性。纳入了来自谱系I和II的18株O157:H7菌株以及来自八个进化枝的15株O157:H7菌株。对这些rhs基因的检测显示，在18株谱系菌株中发现了44个多态性位点（PL）和10种序列类型（ST），在15株进化枝菌株中发现了280个PL和12种ST。使用rhs基因进行的系统发育分析通常根据其已知的谱系和进化枝分类对菌株进行分组。这些发现还表明，来自进化枝6和8的O157:H7菌株属于谱系I/II，而来自进化枝1、2、3和4的菌株属于谱系I。此外，在rhsA和rhsJ中发现了可能用于定义进化枝8和进化枝6的独特标记。因此，rhs基因可能是用于大肠杆菌O157:H7系统发育分析的有用标记。
