LsrR, the effector of AI-2 quorum sensing, is vital for the H2O2 stress response in mammary pathogenic Escherichia coli

Hui Wang,Lumin Yu,Jingtian Ni,Ting Xue,Fei Shang,Xiaolin Chen,Jingyi Xu,Jiawei Shen

doi:10.1186/s13567-021-00998-8

Hui Wang, Lumin Yu + Show 6 more

Open Access

https://doi.org/10.1186/s13567-021-00998-8

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Abstract

Mammary pathogenic Escherichia coli (MPEC) is an important causative agent of mastitis in dairy cows that results in reduced milk quality and production, and is responsible for severe economic losses in the dairy industry worldwide. Oxidative stress, as an imbalance between reactive oxygen species (ROS) and antioxidants, is a stress factor that is common in most bacterial habitats. The presence of ROS can damage cellular sites, including iron-sulfur clusters, cysteine and methionine protein residues, and DNA, and may cause bacterial cell death. Previous studies have reported that Autoinducer 2 (AI-2) can regulate E. coli antibiotic resistance and pathogenicity by mediating the intracellular receptor protein LsrR. This study explored the regulatory mechanism of LsrR on the H2O2 stress response in MPEC, showing that the transcript levels of lsrR significantly decreased under H2O2 stress conditions. The survival cell count of lsrR mutant XW10/pSTV28 was increased about 3080-fold when compared with that of the wild-type WT/pSTV28 in the presence of H2O2 and overexpression of lsrR (XW10/pUClsrR) resulted in a decrease in bacterial survival rates under these conditions. The β-galactosidase reporter assays showed that mutation of lsrR led to a remarkable increase in expression of the promoters of ahpCF, katG and oxyR, while lsrR-overexpressing significantly reduced the expression of ahpCF and katG. The electrophoretic mobility shift assays confirmed that LsrR could directly bind to the promoter regions of ahpCF and katG. These results revealed the important role played by LsrR in the oxidative stress response of MPEC.

Highlights

Escherichia coli is one of the main pathogenic bacteria causing clinical mastitis [1, 2]
A 1660 bp product was amplified from the wild type strain wild-type strain (WT)/pSTV28, while 1330 bp products were respectively amplified from the mutant strain XW10/ pSTV28 and the complementary strain XW10/pClsrR by using primers check-lsrR-f and check-lsrR-r (Lane 1–3)
The polymerase chain reaction (PCR) products of 100 bp were amplified from strains WT/pSTV28 and XW10/pSTV28 using primers M13-f/M13-r, and a 1094 bp product was amplified from strain XW10/pClsrR

Summary

Introduction

Escherichia coli is one of the main pathogenic bacteria causing clinical mastitis [1, 2]. Mammary pathogenic E. coli (MPEC) is a class of extraintestinal pathogenic E. coli that usually adheres to and infects dairy cow mammary epithelial cells together with other pathogens, forming biofilms. The biofilm can help pathogens to evade the host immune system and continue to multiply in the mammary gland, leading to persistent intramammary. It is generally understood that bacterial infection can trigger innate immune response [11, 12]. Once the pathogenic bacteria infect the host, they are phagocytosed by the host immune cells and macrophages and heterophile cells may produce oxidative bursts in response to pathogens [13, 14]. The rapid production of reactive oxygen species (ROS) including superoxide anions (O2−), hydrogen peroxide (H2O2)

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