Lack of AcrB efflux function confers loss of virulence on Salmonella enterica serovar Typhimurium

Research output: Contribution to journalArticlepeer-review

Authors

  • Barbara Chirullo
  • Jonathan Betts
  • Roberto M La Ragione
  • Alasdair Ivens
  • Vito Ricci
  • Timothy J Opperman

External organisations

  • Institute of Microbiology and Infection, College of Medical and Dental Sciences, The University of Birmingham, Birmingham, United Kingdom.
  • Unit of Prophylaxis and Control of Bacterial Zoonoses, Department of Veterinary Public Health and Food Safety, Istituto Superiore di Sanità, Rome, Italy.
  • School of Veterinary Medicine, Faculty of Health and Medical Sciences, University of Surrey, Guildford, United Kingdom.
  • Centre for Immunity, Infection and Evolution, University of Edinburgh, Edinburgh, United Kingdom.
  • Microbiotix, Inc., Anti-Infectives R&D, Worcester, Massachusetts, USA.

Abstract

AcrAB-TolC is the paradigm resistance-nodulation-division (RND) multidrug resistance efflux system in Gram-negative bacteria, with AcrB being the pump protein in this complex. We constructed a nonfunctional AcrB mutant by replacing D408, a highly conserved residue essential for proton translocation. Western blotting confirmed that the AcrB D408A mutant had the same native level of expression of AcrB as the parental strain. The mutant had no growth deficiencies in rich or minimal medium. However, compared with wild-type SL1344, the mutant had increased accumulation of Hoechst 33342 dye and decreased efflux of ethidium bromide and was multidrug hypersusceptible. The D408A mutant was attenuated in vivo in mouse and Galleria mellonella models and showed significantly reduced invasion into intestinal epithelial cells and macrophages in vitro. A dose-dependent inhibition of invasion was also observed when two different efflux pump inhibitors were added to the wild-type strain during infection of epithelial cells. RNA sequencing (RNA-seq) revealed downregulation of bacterial factors necessary for infection, including those in the Salmonella pathogenicity islands 1, 2, and 4; quorum sensing genes; and phoPQ. Several general stress response genes were upregulated, probably due to retention of noxious molecules inside the bacterium. Unlike loss of AcrB protein, loss of efflux function did not induce overexpression of other RND efflux pumps. Our data suggest that gene deletion mutants are unsuitable for studying membrane transporters and, importantly, that inhibitors of AcrB efflux function will not induce expression of other RND pumps.

Details

Original languageEnglish
Article numbere00968-17
JournalmBio
Volume8
Issue number4
Publication statusPublished - 18 Jul 2017

Keywords

  • AcrB, SPI, Salmonella, Salmonella pathogenicity island, efflux, motility, transcriptome, virulence