# The efflux pump SugE2 involved in protection of Salmonella 4,[5],12:i:- against quaternary ammonium salts and inhibition of virulence

## TL;DR

This study shows that the SugE2 efflux pump helps Salmonella 4,[5],12:i:- resist disinfectants and influences its ability to cause infection.

## Contribution

The study identifies SugE2 as a key efflux pump involved in quaternary ammonium compound resistance and virulence in Salmonella 4,[5],12:i:-.

## Key findings

- SugE1 and SugE2 efflux pumps are essential for resistance to DDAB disinfectants in Salmonella 4,[5],12:i:-.
- Deletion of sugE2 increases bacterial adhesion, invasion, and virulence in mice models.
- Intestinal extracts induce sugE2 expression, which suppresses SPI-1 and affects infection processes.

## Abstract

Salmonella enterica serovar 4,[5],12:i:-, a monophasic variant of Salmonella Typhimurium, has emerged as a common nontyphoidal Salmonella serotype to cause human foodborne disease, exhibiting antibiotic and multidrug resistance. In this study, we identified the isolates of S. 4,[5],12:i:- resistant to quaternary ammonium compounds (QACs) disinfectants, displaying elevated minimum inhibitory concentration (MIC) values (200 μg/mL) in Mueller-Hinton (MH) broth. The efflux pump SugE1 and SugE2 could be induced by didecyldimethylammonium bromide (DDAB) and found to be indispensable for S. 4,[5],12:i:- resistance to DDAB. The Hoechst 33342 dye accumulation and reduced ethidium bromide efflux in ΔsugE1, ΔsugE2 and ΔsugE1ΔsugE2 further confirmed the efflux function of SugE1 and SugE2. Moreover, DDAB inhibited the expression of Salmonella pathogenicity island 1 (SPI-1) to decrease the adhesion and invasion ability of S. 4,[5],12:i:- in IPEC-J2 cells, whereas the deletion of sugE2 increased the adhesion and invasion ability. In an in vivo mice model, the virulence of ΔsugE2 and ΔsugE1ΔsugE2 mutant strains were enhanced and showed significantly increased bacterial loads in the liver, spleen, and cecum. The ΔsugE2 and ΔsugE1ΔsugE2 mutant strains exhibited an enhanced ability to disrupt the intestinal barrier, leading to systemic infection. Finally, we discovered that intestinal extracts could induce sugE1 and sugE2 expression, subsequently suppressing SPI-1 expression through SugE2, mediating the Salmonella intestinal infection process. In conclusion, our findings provide the pivotal role of the SugE2 efflux pump in conferring resistance to DDAB disinfectants and influencing bacterial virulence in S. 4,[5],12:i:-.

The escalating global public health concern posed by multidrug-resistant S. 4,[5],12:i:- has garnered widespread attention. The mechanisms underlying the acquisition of quaternary ammonium compound tolerance by S. 4,[5],12:i:- remain unclear. Our investigations provide significant insights into the mechanisms of QAC resistance and virulence in S. 4,[5],12:i:-, focusing on the efflux pump SugE. Our findings highlight the pivotal role of the SugE efflux pump in conferring resistance to DDAB, a widely used class of disinfectants, and also in influencing the virulence of this bacterium. Notably, our results demonstrate that intestinal extract can induce sugE2 expression and inhibit SPI-1 expression, which mediate the adhesion, invasion, and oral infection of S. 4,[5],12:i:- both in vitro and in vivo. Understanding the biological role of SugE in disinfectant resistance and virulence will aid in assessing the risks associated with targeting efflux pumps to combat Salmonella dissemination and infection.