Repurposing azithromycin and rifampicin against Gram-negative pathogens by combination with peptide potentiators

Area of Science:

• Microbiology
• Drug Discovery
• Antimicrobial Resistance

Background:

• Gram-negative bacteria possess intrinsic resistance to many antibiotics due to their cell envelope barrier.
• Multidrug-resistant (MDR) Gram-negative pathogens pose a significant global health threat.
• Novel strategies are needed to overcome antibiotic resistance in these bacteria.

Purpose of the Study:

• To identify peptides that can restore antibiotic susceptibility in MDR Gram-negative bacteria.
• To evaluate the synergistic potential of identified peptides with existing antibiotics.
• To assess the safety and efficacy of peptide-antibiotic combinations.

Main Methods:

• Pairwise screening of 34 peptides with four antibiotics against Gram-negative bacteria.
• Testing synergistic activity with azithromycin and clindamycin in MDR strains.
• Synthesizing and evaluating all-d analogues of promising peptides for antibacterial activity and cytotoxicity.

Main Results:

• Four peptides were identified that conferred susceptibility to rifampicin or erythromycin in *Escherichia coli*.
• The identified peptides showed synergy with azithromycin and potentiated clindamycin in MDR *E. coli* and *Klebsiella pneumoniae*.
• All-d analogues (D1 and D2) retained synergistic activity and exhibited low cytotoxicity, inhibiting growth of clinical strains in combination with azithromycin and rifampicin.

Conclusions:

• Combinatorial screening of peptides and antibiotics at low concentrations is an effective strategy for identifying new therapeutic combinations.
• The identified peptide-antibiotic combinations show potential for repurposing azithromycin and rifampicin against Gram-negative pathogens.
• Further in vivo studies are warranted to validate these findings for clinical application.