Bacterial virulence regulation through soluble peptidoglycan fragments sensing and response: knowledge gaps and therapeutic potential

Abstract

Given the growing clinical-epidemiological threat posed by the phenomenon of antibiotic resistance, new therapeutic options are urgently needed, especially against top nosocomial pathogens such as those within the ESKAPE group. In this scenario, research is pushed to explore therapeutic alternatives and, among these, those oriented towards reducing bacterial pathogenic power could pose encouraging options. However, the first step in developing these anti-virulence weapons is to find weak points in the bacterial biology to be attacked with the goal of dampening pathogenesis. In this regard, during the last decades some studies have directly/indirectly suggested that certain soluble peptidoglycan-derived fragments display virulence-regulatory capacities, likely through similar mechanisms to those followed to regulate the production of several β-lactamases: binding to specific transcriptional regulators and/or sensing/activation of two-component systems. These data suggest the existence of intra- and also inter-cellular peptidoglycan-derived signaling capable of impacting bacterial behavior and hence likely exploitable from the therapeutic perspective. Using the well-known phenomenon of peptidoglycan metabolism-linked β-lactamase regulation as a starting point, we gather and integrate the studies connecting soluble peptidoglycan sensing with fitness/virulence regulation in Gram-negatives, dissecting the gaps in current knowledge that need filling to enable potential therapeutic strategy development, a topic which is also finally discussed.

Transferable AmpCs in Klebsiella pneumoniae : interplay with peptidoglycan recycling, mechanisms of hyperproduction, and virulence implications

“…Therefore, based on previous publications ( 56 – 60 ) and our results, we believe that the mildly reduced virulence of Kp52.145RΔAG TC (DHA-1) and Kp52.145RΔAG pUCP-DHA-1 transformant could lean on a greater parallel peptidoglycanase activity of DHA-1 compared to that of CMY-2, which seems devoid of significant associated burdens even when overproduced ( Fig. 1 and 2 ).…”

“…In this regard, some studies have shown that the production of certain β-lactamases (e.g., some OXA-2-derived extended spectrum variants) entails dramatic biological costs and virulence attenuations in P. aeruginosa, while similar outputs have been obtained for other gram-negatives. These effects have been proposed to be likely mediated by residual activities of β-lactamases on peptidoglycan and/or muropeptide-based regulatory networks ( 40 , 56 – 60 ). In this study, we wanted to decipher whether or not the production of acquired AmpCs could impair K. pneumoniae pathogenic power in a similar way.…”

“…1 and 2 ). In fact, the existence of a residual peptidoglycan-degrading power reminiscent of an alleged PBP ascendance for certain β-lactamases has been proposed, mostly in terms of peptidase activity ( 56 – 60 ). Accordingly, DHA-1 residual activity would then entail a measurable attenuation in bacterial virulence but only in the situation of energy/metabolic alteration linked to peptidoglycan recycling blockade, which would unmask the mild negative effects linked to this β-lactamase.…”

“…Accordingly, DHA-1 residual activity would then entail a measurable attenuation in bacterial virulence but only in the situation of energy/metabolic alteration linked to peptidoglycan recycling blockade, which would unmask the mild negative effects linked to this β-lactamase. However, whether the alleged peptidoglycan-degrading power of DHA-1 is directed at (i) the entire murein sacculus weakening its structure (already likely debilitated by the lack of recycling) and dampening cell viability/resistance against peptidoglycan-targeting immunity, and/or (ii) a network of muropeptides linked to recycling, signaling, and virulence modulation are possibilities that cannot be validated for the time being ( 56 – 60 ). In any case, our results suggest that even in a peptidoglycan recycling-blocked state, the burden of DHA-1 expression is quite low, at least compared to other β-lactamases, accompanied by dramatic impairments in parameters such as motility, biofilm formation, growth rate, invasiveness, intracellular survival, mortality in animal models, etc.…”

Minimalist Tetrazine N-Acetyl Muramic Acid Probes for Rapid and Efficient Labeling of Commensal and Pathogenic Peptidoglycans in Living Bacterial Culture and During Macrophage Invasion

“…aeruginosa infection, including biofilm formation cell-secreted factors, as well as several anatomical structures, including pili, flagella, and LPS . These factors all serve as potential drug targets for improved treatment modalities where new antibiotics are desperately needed to combat these bacteria in the clinic. − It is well known that these bacteria, like others, are able to shed and remodel their PG structures; however, few studies have been able to distinguish PG as a definitive virulence factor during infection. − Additionally, current investigations examining the dynamic changes in PG topology and architecture during infection involve the use of denaturing methods to isolate PG for downstream assaying. − Here, we sought to utilize our fast and robust minimal tetrazine probe to execute dynamic in situ labeling of the PG anatomy in live bacteria to serve as a platform for many potential downstream applications. Previous attempts to label these species resulted in either low incorporation, high background, or unusual morphology and nonspecific labeling when labeled with SPAAC. , Use of the new HTz-NAM and aTCO-SiR labeling strategy resulted in markedly improved labeling and notably less background in the NAM-treated sample in P. putida (Figure A, SI Figures 33 and 34).…”