INSERM U722 and Université Paris 13, Paris, France.
BMC Microbiol. 2009 Dec 29;9:273. doi: 10.1186/1471-2180-9-273.
Previous studies have established a correlation between electrophoretic polymorphism of esterase B, and virulence and phylogeny of Escherichia coli. Strains belonging to the phylogenetic group B2 are more frequently implicated in extraintestinal infections and include esterase B2 variants, whereas phylogenetic groups A, B1 and D contain less virulent strains and include esterase B1 variants. We investigated esterase B as a marker of phylogeny and/or virulence, in a thorough analysis of the esterase B-encoding gene.
We identified the gene encoding esterase B as the acetyl-esterase gene (aes) using gene disruption. The analysis of aes nucleotide sequences in a panel of 78 reference strains, including the E. coli reference (ECOR) strains, demonstrated that the gene is under purifying selection. The phylogenetic tree reconstructed from aes sequences showed a strong correlation with the species phylogenetic history, based on multi-locus sequence typing using six housekeeping genes. The unambiguous distinction between variants B1 and B2 by electrophoresis was consistent with Aes amino-acid sequence analysis and protein modelling, which showed that substituted amino acids in the two esterase B variants occurred mostly at different sites on the protein surface. Studies in an experimental mouse model of septicaemia using mutant strains did not reveal a direct link between aes and extraintestinal virulence. Moreover, we did not find any genes in the chromosomal region of aes to be associated with virulence.
Our findings suggest that aes does not play a direct role in the virulence of E. coli extraintestinal infection. However, this gene acts as a powerful marker of phylogeny, illustrating the extensive divergence of B2 phylogenetic group strains from the rest of the species.
先前的研究已经证实了酯酶 B 的电泳多态性与大肠杆菌的毒力和系统发育之间存在相关性。属于 B2 进化群的菌株更频繁地与肠外感染有关，包括酯酶 B2 变体，而 A、B1 和 D 进化群包含的毒力较弱的菌株包括酯酶 B1 变体。我们研究了酯酶 B 作为进化和/或毒力的标记物，对编码酯酶 B 的基因进行了全面分析。
我们使用基因敲除的方法确定了编码酯酶 B 的基因是乙酰酯酶基因(aes)。在包括大肠杆菌参考菌株（ECOR 株）在内的 78 个参考菌株的 aes 基因核苷酸序列分析中，我们发现该基因受到纯化选择的影响。根据 6 个管家基因的多位点序列分型，从 aes 序列重建的系统发育树与物种系统发育史有很强的相关性。通过电泳对 B1 和 B2 变体进行的明确区分与 aes 氨基酸序列分析和蛋白质建模一致，这表明两种酯酶 B 变体中的取代氨基酸主要发生在蛋白质表面的不同部位。使用突变菌株在实验性败血症小鼠模型中的研究并未显示 aes 与肠外毒力之间存在直接联系。此外，我们在 aes 染色体区域没有发现任何与毒力相关的基因。
我们的研究结果表明，aes 并不直接参与大肠杆菌肠外感染的毒力。然而，该基因是进化的有力标记物，说明了 B2 进化群菌株与其他菌株之间的广泛分歧。
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