Background: Most of the proteomic studies in Escherichia coli have focussed on pathogenic strains, while very few studies have studied the commensal strains. It is important to study the commensal strains because under the selective pressure of their habitat, commensal strains might serve as reservoirs of virulent and pathogenic strains.

Objective: In this study, we have performed a comparative proteomic analysis of commensal and pathogenic strains of E. coli isolated from a major river flowing through northern India.

Methods: Proteins were resolved by two dimensional gel electrophoresis and the differentially expressed proteins were identified using matrix-assisted laser desorption ionization-time of flight mass-spectrometry (MALDI-TOF MS).

Results: Many proteins of the commensal strain showed an increased expression compared to the pathogenic strain, of which seventeen proteins were identified by MALDI-TOF MS. Functional classification of these proteins revealed that they belonged to different functional pathways like energy metabolism, nucleotide and nucleoside conversions, translation, biosynthesis of amino acids and motility and energytaxis/chemotaxis.

Conclusion: As per the best of our knowledge, this is the first report on comparative proteomic analysis of E. coli commensal and pathogenic strains of aquatic origin. Our results suggest that the increased production of these proteins might play an important role in adaptation of E. coli to a commensal/pathogenic lifestyle. However, further experiments are required to understand the precise role of these proteins in regulating the pathogenicity/commensalism of E. coli.

背景：在大肠杆菌中，大多数蛋白质组学研究都集中在致病菌株上，而很少有研究对共生菌株进行研究。研究共生菌株很重要，因为在其生境的选择压力下，共生菌株可能充当有毒力和致病性菌株的库。

目的：在这项研究中，我们对从流经印度北部的一条主要河流中分离出的大肠杆菌的共生和致病菌株进行了比较蛋白质组学分析。

方法：通过二维凝胶电泳分离蛋白质，并使用基质辅助激光解吸电离飞行时间质谱（MALDI-TOF MS）鉴定差异表达的蛋白质。

结果：与致病菌株相比，该共生菌株的许多蛋白质表达均增加，其中MALDI-TOF MS鉴定出17种蛋白质。这些蛋白质的功能分类显示它们属于不同的功能途径，例如能量代谢，核苷酸和核苷转化，翻译，氨基酸的生物合成以及动力和趋化/趋化性。

结论：据我们所知，这是对大肠杆菌共生和水生致病菌株进行比较蛋白质组学分析的第一份报告。我们的结果表明，这些蛋白质产量的增加可能在大肠杆菌适应共生/致病性生活方式中起重要作用。但是，需要进一步的实验来了解这些蛋白质在调节大肠杆菌的致病性/共性中的确切作用。