Mechanism of Action
Bac1: Cyclic Disulfide Membrane Disruption
Bac1 is a 12-residue cyclic AMP with one disulfide bond. It disrupts bacterial membranes by inserting the hydrophobic face of the ring structure into the lipid bilayer. The cyclic structure provides proteolytic resistance compared to linear AMPs. Activity is primarily against Gram-negative bacteria, with limited Gram-positive coverage.
Bac7: Proline-Rich Intracellular Killing
Bac7 is a 60-residue proline-rich AMP. Its N-terminal fragment Bac7(1-35) enters bacteria via SbmA and YjiL transporters and kills intracellularly by binding to the 70S ribosome, specifically inhibiting translation elongation. This ribosome-targeting mechanism is distinct from all conventional antibiotic classes and notably lacks cross-resistance with existing antibiotics. MDR bacteria retain susceptibility to Bac7(1-35) since they do not downregulate the uptake transporters.
Research Summary
MDR Gram-Negative Activity
PreclinicalBac7(1-35) kills carbapenem-resistant Klebsiella pneumoniae, NDM-1-producing E. coli, and MDR Salmonella strains at MIC values comparable to or better than last-resort antibiotics colistin and polymyxin B, but through a different mechanism. The intracellular ribosome-targeting mechanism means typical resistance mechanisms (efflux pumps, porin loss, lipid A modification) do not confer resistance. In vivo efficacy has been demonstrated in murine infection models.
Resistance Barrier Analysis
PreclinicalSerial passage studies with Bac7(1-35) show markedly slower resistance development compared to conventional antibiotics. Resistance mutants selected under laboratory conditions have reduced fitness and virulence, and resistance occurs predominantly through downregulation of SbmA, which itself attenuates pathogen virulence. This intrinsic resistance barrier is a key advantage for clinical development.
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Research Protocols
| Goal | Dose | Frequency | Route |
|---|---|---|---|
| MDR Gram-negative (in vitro) | 1-8 uM MIC (Bac7 1-35) | Single exposure | Direct application |
| In vivo infection (mouse) | 5-20 mg/kg | Twice daily | IV / IP (research) |
No human protocols. All data from preclinical models.
Interactions
Safety Profile
Bac7(1-35) shows low hemolytic activity and minimal mammalian cell toxicity in preclinical studies. The SbmA-dependent uptake mechanism is absent in mammalian cells, providing a natural selectivity mechanism. Renal and hepatic safety profiles appear favorable in acute animal studies. No human clinical data.
References
- [1]Gennaro R, et al. (2002). Proline-rich antibacterial peptides from animals: backbone structure, bioactivities and prediction of activity. Curr Protein Pept Sci, 3(6), 679-698.
- [2]Mardirossian M, et al. (2014). The host defense peptide Bac7(1-35) binds to bacterial ribosomal proteins. Chem Biol, 21(12), 1639-1647.