Riccardin C derivatives cause cell leakage in Staphylococcus aureus

Area of Science:

• Microbiology
• Medicinal Chemistry
• Biochemistry

Background:

• Methicillin-resistant Staphylococcus aureus (MRSA) poses a significant clinical challenge due to its resistance to conventional antimicrobial agents.
• Synthetic macrocyclic bis(bibenzyl) derivatives, inspired by natural compounds from liverworts, have demonstrated anti-MRSA activity, but their mechanisms of action remain largely unelucidated.
• Understanding the precise mechanisms is crucial for developing novel therapeutic strategies against resistant bacterial strains.

Purpose of the Study:

• To elucidate the action mechanism of the synthetic macrocyclic bis(bibenzyl) compound RC-112 and its partial structure IDPO-9 against MRSA.
• To differentiate the mechanisms of action between RC-112 and IDPO-9 and identify potential resistance pathways.

Main Methods:

• Bactericidal and bacteriostatic assays were performed to assess the effects of RC-112 and IDPO-9 on MRSA survival.
• Mutant selection and whole-genome sequencing were employed to identify resistance mechanisms.
• Ethidium uptake and outflow experiments were conducted to evaluate membrane permeability changes.
• Transmission electron microscopy (TEM) was used to visualize cellular structural alterations.
• Intracellular ion concentrations (Na+, K+) were measured following compound treatment.

Main Results:

• RC-112 demonstrated bactericidal activity against MRSA, while IDPO-9 exhibited bacteriostatic effects.
• IDPO-9-resistant mutants showed cross-resistance to triclosan, indicating mutations in the fabI gene (enoyl-acyl carrier protein reductase).
• RC-112 treatment led to increased uptake of ethidium and propidium, and facilitated ethidium outflow, suggesting compromised membrane integrity.
• TEM revealed intracellular lamellar mesosomal-like structures in RC-112 treated cells.
• RC-112 significantly altered intracellular Na+ and K+ concentrations, indicating disruption of ion homeostasis.

Conclusions:

• RC-112 enhances the permeability of the MRSA cell membrane, leading to cell death.
• The mechanism of action for IDPO-9 differs from RC-112 and involves the fabI gene, a known target for other antimicrobials.
• These findings provide critical insights into the distinct mechanisms of action of macrocyclic bis(bibenzyl) derivatives, paving the way for the development of new anti-MRSA agents.