Synergistic Antibacterial and Antibiofilm Activity of the MreB Inhibitor A22 Hydrochloride in Combination with Conventional Antibiotics against Pseudomonas aeruginosa and Escherichia coli Clinical Isolates

Mirani

et al. 2022

Cells

The present study discusses a biofilm-positive P. aeruginosa isolate that survives at pH levels ranging from 4.0 to 9.0. The biofilm consortia were colonized with different phenotypes i.e., planktonic, slow-growing and metabolically inactive small colony variants (SCVs). The lower base of the consortia was occupied by SCVs. These cells were strongly attached to solid surfaces and interconnected through a network of nanotubes. Nanotubes were observed at the stationary phase of biofilm indwellers and were more prominent after applying weight to the consortia. The scanning electron micrographs indicated that the nanotubes are polar appendages with intraspecies connectivity. The micrographs indicated variations in physical dimensions (length, width, and height) and a considerable reduction in volume due to weight pressure. A total of 35 cells were randomly selected. The mean volume of cells before the application of weight was 0.288µm3, which was reduced to 0.144 µm3 after the application of weight. It was observed that a single cell may produce as many as six nanotubes, connected simultaneously to six neighbouring cells in different directions. The in-depth analysis confirmed that these structures were the intra-species connecting tools as no free nanotubes were found. Furthermore, after the application of weight, cells incapable of producing nanotubes were wiped out and the surface was covered by nanotube producers. This suggests that the nanotubes give a selective advantage to the cells to resist harsh environmental conditions and weight pressure. After the removal of weight and proper supply of nutrients, these phenotypes reverted to normal planktonic lifestyles. It is concluded that the nanotubes are not merely the phenomenon of dying cells; rather they are a connectivity tool which helps connected cells to tolerate and resist environmental stress.

Section: Discussionsupporting

confidence: 52%

Nanotubes Formation in P. aeruginosa

Mirani

et al. 2022

Cells

“… 69 − 77 Furthermore, synergists that specifically engage with Gram-negative targets and subsequently cause OM disruption as a secondary effect are not discussed in this Review. 78 − 86 …”

mentioning

confidence: 99%

“…As for Gram-positive specific antibiotics whose activity is potentiated by OM-disrupting synergists, we have chosen to focus on clinically used agents that are most commonly evaluated for synergy with OM disrupters: erythromycin, rifampicin, vancomycin, and novobiocin. , This criterion has, for example, led to the exclusion of OM-disrupting agents for which synergy was reported with macrolide antibiotics other than erythromycin. − Also, while the specific media conditions used in antibacterial assays can strongly influence the outcome of synergy studies, for the sake of brevity, we do not include this level of detail here and instead provide clear referencing of the original studies wherein such information can be found. In addition, to further streamline the Review, synergists for which an OM-disrupting mechanism was not clearly demonstrated are not here discussed in detail. − Furthermore, synergists that specifically engage with Gram-negative targets and subsequently cause OM disruption as a secondary effect are not discussed in this Review. − …”

mentioning

confidence: 99%

Synergy by Perturbing the Gram-Negative Outer Membrane: Opening the Door for Gram-Positive Specific Antibiotics

Wesseling

Martin

2022

ACS Infect. Dis.

New approaches to target antibacterial agents toward Gram-negative bacteria are key, given the rise of antibiotic resistance. Since the discovery of polymyxin B nonapeptide as a potent Gram-negative outer membrane (OM)-permeabilizing synergist in the early 1980s, a vast amount of literature on such synergists has been published. This Review addresses a range of peptide-based and small organic compounds that disrupt the OM to elicit a synergistic effect with antibiotics that are otherwise inactive toward Gram-negative bacteria, with synergy defined as a fractional inhibitory concentration index (FICI) of <0.5. Another requirement for the inclusion of the synergists here covered is their potentiation of a specific set of clinically used antibiotics: erythromycin, rifampicin, novobiocin, or vancomycin. In addition, we have focused on those synergists with reported activity against Gram-negative members of the ESKAPE family of pathogens namely, Escherichia coli , Pseudomonas aeruginosa , Klebsiella pneumoniae , and/or Acinetobacter baumannii . In cases where the FICI values were not directly reported in the primary literature but could be calculated from the published data, we have done so, allowing for more direct comparison of potency with other synergists. We also address the hemolytic activity of the various OM-disrupting synergists reported in the literature, an effect that is often downplayed but is of key importance in assessing the selectivity of such compounds for Gram-negative bacteria.

“…For example, in bacteria, the MreB actin-like protein is important for virulence, motility, and cell wall stability. Small molecule inhibitors disrupting MreB cytoskeletal protein have potent antibacterial properties against major rod-shaped pathogens including P. aeruginosa, K. pneumonia, Salmonella and pathogenic E. coli 17,18,59 . In the case of eukaryotes, actin mediates tumor-relevant processes, including cell migration, invasion, metastasis, and signal transduction pathways implicated in tumorigenesis 17 .…”

Section: Discussionmentioning

confidence: 99%

Probing the Molecular Interactions of A22 with Prokaryotic Actin MreB and Eukaryotic Actin: A Computational and Experimental Study

Kumar,

Kukal,

Marepalli

et al. 2024

Preprint

Actin is a major cytoskeletal system that mediates the intricate organization of macromolecules within cells. The bacterial cytoskeletal protein MreB is a prokaryotic actin-like protein governing cell shape and intracellular organization in many rod-shaped bacteria including pathogens. MreB stands as a target for antibiotic development, and compounds like A22 and its analogue, MP265, are identified as potent inhibitors of MreB. The bacterial actin MreB shares structural homology with eukaryotic actin, despite lacking sequence similarity. It is currently not clear whether small molecules that inhibit MreB can act on the eukaryotic actin due to their structural similarity. In this study, we investigate the molecular interactions between A22 and both MreB and eukaryotic actin through molecular dynamics approach. Employing MD simulations and free energy calculations with an all-atom model, we unveil robust A22-MreB interaction and substantial binding affinity with eukaryotic actin. Experimental assays reveal A22's toxicity to eukaryotic cells, including yeast and human glioblastoma cells. Microscopy analysis demonstrates profound effects of A22 on actin organization in human glioblastoma cells. Overall, this integrative computational and experimental study advances our understanding of A22's mode of action and highlights its potential as a versatile tool for probing actin dynamics and as a candidate for therapeutic intervention in pathological conditions like cancer.