The bile salt glycocholate induces global changes in gene and protein expression and activates virulence in enterotoxigenic Escherichia coli

Enrique Joffre,Matilda Nicklasson,Åsa Sjöling,Sandra Álvarez-Carretero,Baoli Zhu,Xue Xiao,Lei Sun,Intawat Nookaew

doi:10.1038/s41598-018-36414-z

Abstract

Pathogenic bacteria use specific host factors to modulate virulence and stress responses during infection. We found previously that the host factor bile and the bile component glyco-conjugated cholate (NaGCH, sodium glycocholate) upregulate the colonization factor CS5 in enterotoxigenic Escherichia coli (ETEC). To further understand the global regulatory effects of bile and NaGCH, we performed Illumina RNA-Seq and found that crude bile and NaGCH altered the expression of 61 genes in CS5 + CS6 ETEC isolates. The most striking finding was high induction of the CS5 operon (csfA-F), its putative transcription factor csvR, and the putative ETEC virulence factor cexE. iTRAQ-coupled LC-MS/MS proteomic analyses verified induction of the plasmid-borne virulence proteins CS5 and CexE and also showed that NaGCH affected the expression of bacterial membrane proteins. Furthermore, NaGCH induced bacteria to aggregate, increased their adherence to epithelial cells, and reduced their motility. Our results indicate that CS5 + CS6 ETEC use NaGCH present in the small intestine as a signal to initiate colonization of the epithelium.

Highlights

Enterotoxigenic Escherichia coli (ETEC) is one of the most common bacterial causes of acute watery diarrhea in the developing world, both among children under five years old and in indigenous adults or travelers to endemic regions[1]
Two enterotoxigenic Escherichia coli (ETEC) clinical isolates, E1777 and E2265, each expressing the virulence factors labile toxin (LT), STh, coli surface antigen 5 (CS5), and coli surface antigen 6 (CS6) were analyzed by RNA-Seq for their transcriptional response to bile (0.15%) and the bile component NaGCH (0.2%)
Among these 61 genes, we found 3 expression patterns: 35 genes were induced by bile and/or NaGCH; 17 genes were repressed by bile and/or NaGCH; and 9 genes were not affected or were downregulated by bile, but upregulated by NaGCH (Fig. 1a)

Summary

Introduction

Enterotoxigenic Escherichia coli (ETEC) is one of the most common bacterial causes of acute watery diarrhea in the developing world, both among children under five years old and in indigenous adults or travelers to endemic regions[1]. Bile and some of its individual components, such as the major primary bile salt cholate and the secondary bile salt deoxycholate, as well as the conjugated primary salts taurocholate and glycocholate[16], are known inducers of virulence in bacterial enteropathogens such as ETEC, V. cholerae, enteropathogenic E. coli (EPEC), Campylobacter jejuni, and Shigella spp[17,18,19,20,21,22]. Because it is a detergent, bile is involved in the host antimicrobial defense, making it one of the most intriguing host signals affecting virulence. We employed a whole- transcriptome and -proteome approach using RNA sequencing and iTRAQ-coupled LC-MS/MS technology

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