Novel Insight into the Effects of CpxR on Salmonella enteritidis Cells during the Chlorhexidine Treatment and Non-Stressful Growing Conditions

Abstract

The development and spread of antibiotics and biocides resistance is a significant global challenge. To find a solution for this emerging problem, the discovery of novel bacterial cellular targets and the critical pathways associated with antimicrobial resistance is needed. In the present study, we investigated the role of the two most critical envelope stress response regulators, RpoE and CpxR, on the physiology and susceptibility of growing Salmonella enterica serovar enteritidis cells using the polycationic antimicrobial agent, chlorhexidine (CHX). It was shown that deletion of the cpxR gene significantly increased the susceptibility of this organism, whereas deletion of the rpoE gene had no effect on the pathogen’s susceptibility to this antiseptic. It has been shown that a lack of the CpxR regulator induces multifaceted stress responses not only in the envelope but also in the cytosol, further affecting the key biomolecules, including DNA, RNA, and proteins. We showed that alterations in cellular trafficking and most of the stress responses are associated with a dysfunctional CpxR regulator during exponential growth phase, indicating that these physiological changes are intrinsically associated with the lack of the CpxR regulator. In contrast, induction of type II toxin-antitoxin systems and decrease of abundances of enzymes and proteins associated with the recycling of muropeptides and resistance to polymixin and cationic antimicrobial peptides were specific responses of the ∆cpxR mutant to the CHX treatment. Overall, our study provides insight into the effects of CpxR on the physiology of S. Enteritidis cells during the exponential growth phase and CHX treatment, which may point to potential cellular targets for the development of an effective antimicrobial agent.

Gram-negative bacteria resist antimicrobial agents by a DzrR-mediated envelope stress response

“…In P . aeruginosa , the stimulated expression of MexCD-OprM in the presence of chlorhexidine and chlorpromazine is RpoE-dependent [ 5 ], while in Salmonella enterica serovar enteritidis ATCC 13,076, it is Cpx ESR that responds to chlorhexidine and triggers the expression of a range of membrane-associated proteins [ 8 ]. In view of these findings, we tested whether RpoE, Cpx, and other three well established ESRs were associated with the zeamine-induced desAB expression.…”

“…Envelope stress response (ESR) mechanisms are crucial for maintenance of bacterial envelope homeostasis by activating protective mechanisms against envelope-damaging stresses [ 1 ]. Five widespread ESRs, i.e., Bae, Cpx, RpoE (σ E ), Rcs, and Psp, have been identified in Escherichia coli and other bacterial species upon exposure to envelope-targeting antimicrobial agents [ 1 , 2 ], such as vancomycin [ 3 ], β-lactam antibiotics [ 4 ], chlorhexidine [ 5 – 8 ], chlorpromazine [ 6 , 7 ], and polymyxin B [ 9 , 10 ]. These reported ESR mechanisms are mainly through maintaining the compositions of cell envelope [ 2 , 11 ], and activating the expression of RND efflux pumps [ 12 – 14 ].…”

Targeting the Holy Triangle of Quorum Sensing, Biofilm Formation, and Antibiotic Resistance in Pathogenic Bacteria

“…The Cpx stress response mediated by the two-component sensor histidine kinase CpxA and the cytoplasmic response regulator CpxR confers resistance to aminoglycoside antibiotics [477], hydroxyurea [477], cationic antimicrobial peptides [420,423], β-lactams [211,403], and chlorhexidine [478], besides being implicated in virulence [479] and biofilm formation [480,481] (Figure 10). The Cpx TCS senses periplasmic or inner membrane protein misfolding and accumulation resulting in the upregulation of the periplasmic protease DegP and degradation of the misfolded proteins [482].…”