The Pseudomonas aeruginosa CreBC Two-Component System Plays a Major Role in the Response to β-Lactams, Fitness, Biofilm Growth, and Global Regulation

Abstract

bPseudomonas aeruginosa is a ubiquitous versatile environmental microorganism with a remarkable ability to grow under diverse environmental conditions. Moreover, P. aeruginosa is responsible for life-threatening infections in immunocompromised and cystic fibrosis patients, as the extraordinary capacity of this pathogen to develop antimicrobial resistance dramatically limits our therapeutic arsenal. Its large genome carries an outstanding number of genes belonging to regulatory systems, including multiple two-component sensor-regulator systems that modulate the response to the different environmental stimuli. Here, we show that one of two systems, designated CreBC (carbon source responsive) and BlrAB (␤-lactam resistance), might be of particular relevance. We first identified the stimuli triggering the activation of the CreBC system, which specifically responds to penicillin-binding protein 4 (PBP4) inhibition by certain ␤-lactam antibiotics. Second, through an analysis of a large comprehensive collection of mutants, we demonstrate an intricate interconnection between the CreBC system, the peptidoglycan recycling pathway, and the expression of the concerning chromosomal ␤-lactamase AmpC. Third, we show that the CreBC system, and particularly its effector inner membrane protein CreD, plays a major role in bacterial fitness and biofilm development, especially in the presence of subinhibitory concentrations of ␤-lactams. Finally, global transcriptomics reveals broad regulatory functions of CreBC in basic physiological aspects, particularly anaerobic respiration, in both the presence and absence of antibiotics. Therefore, the CreBC system is envisaged as a potentially interesting target for improving the efficacy of ␤-lactams against P. aeruginosa infections.

Complex Regulation Pathways of AmpC-Mediated β-Lactam Resistance in Enterobacter cloacae Complex

“…This mechanism of regulation radically diverges from that described in the P. aeruginosa model, where the inactivation of PBP4 leads to a constitutive ampC overexpression (23). In this last species, the role of PBP4 in the ampC induction process is linked to the activation of the CreBC two-component system that, in turn, plays a crucial role in ␤-lactam resistance (58). Such a regulatory system has not been found in the genome of ECL13047, and this may explain why regulatory pathways of ampC expression are, in part, different from those of P. aeruginosa.…”

Cell-wall recycling and synthesis in Escherichia coli and Pseudomonas aeruginosa – their role in the development of resistance

“…The inactivation of dacB (PBP4) leads to an increased expression of creBC, creD and ampC. The increased expression of ampC is accompanied by elevated MIC of b-lactams, which reverts to wild-type levels upon deletion of creBC [226]. The association of creBC and b-lactam resistance was seen only in dacB mutants and not with other mutations that confer high resistance, namely ampD, ampDh2 and ampDh3 [216].…”

“…The association of creBC and b-lactam resistance was seen only in dacB mutants and not with other mutations that confer high resistance, namely ampD, ampDh2 and ampDh3 [216]. Moreover, these resistance phenotypes regulated through creBC were lost in the absence of NagZ and AmpG [207,216,226] (Table 3). Although the interplay of the cellwall recycling components, ampC expression and the creBCcreD system is found to regulate b-lactam resistance, the underlying details remain to be elucidated.…”

“…E. coli CreB was also found to regulate the expression of Aeromonas hydrophila b-lactamase [225]. This two-component system in P. aeruginosa plays a pivotal role in b-lactam resistance and bacterial fitness [226,227]. The inactivation of dacB (PBP4) leads to an increased expression of creBC, creD and ampC.…”

Interplay among Membrane-Bound Lytic Transglycosylase D1, the CreBC Two-Component Regulatory System, the AmpNG-AmpD I -NagZ-AmpR Regulatory Circuit, and L1/L2 β-Lactamase Expression in Stenotrophomonas maltophilia

“…In addition, the CreBC (BlrAB) twocomponent system (TCS) has also been reported to be associated with ␤-lactam resistance in P. aeruginosa (9). PBP 4 (encoded by dacB) inactivated by particular ␤-lactams (e.g., cefoxitin) or mutations in dacB itself increases the level of resistance to ␤-lactams in a CreBC (BlrAB)-and AmpR-dependent manner (9,10).…”