712. Diffocins: Precision Anti-Infectives Targeting Clostridium difficile with Potential for Prophylactic and Therapeutic Use
Session: Poster Abstract Session: Antimicrobials: Novel Agents
Friday, October 4, 2013
Room: The Moscone Center: Poster Hall C
Background: Traditional broad-spectrum antibiotics have historically exhibited miraculous life-saving effects.  However, the unintended, adverse consequences of their use are now apparent: broad-spread antibiotic resistance and lasting damage to the host’s GI microbiota.  Opportunistic pathogens, such as Clostridium difficile, take advantage of the damage to proliferate and cause C. difficile infections (CDIs).  We have identified novel high-molecular weight bacteriocins, termed Diffocins, that act as bactericidal agents against C. difficile.  Diffocins are analogous to R-type pyocins from Pseudomonas aeruginosa, except they derive from and specifically target C. difficile strains.

Methods: A Diffocin gene cluster was cloned from C. difficile and expressed in Bacillus subtilis. Engineered Diffocins were constructed by replacing the natural receptor binding protein (RBP) with RBPs from C. difficile bacteriophages and prophages. The killing spectra and stability of the Diffocins were determined via in vitro bactericidal assays.  The in vivo efficacy of Diffocins was evaluated in a C57Bl/6 mouse model of CDI caused by strain CD630 spores. Microbial pharmacodynamic and RBP target identification studies are ongoing.

Results: Using phage RBPs, we are able to re-target Diffocins to kill specific strains of C. difficile, including the “hypervirulent” 027 ribotype. Interestingly, the engineered Diffocins have wider killing spectra than the host ranges of RBP-donor phages. Compared to natural Diffocins, engineered Diffocins are more thermally stable, less pH sensitive, and remained active during passage through the mouse GI tract.  Preliminary in vivo data show that repeated oral dosing of Diffocin to mice can reduce fecal shedding ~20-fold in the first 24 hrs post challenge.

Conclusion: We believe that engineered Diffocins represent a new wave of precision anti-infective medicines. These bactericidal agents will not spread antibacterial resistance to non-target (already-insensitive) organisms and are highly unlikely to cause collateral damage to the microbiota. In addition, their greater stability, ability to evade phage immunity mechanisms, and inability to replicate give them advantages over phage and other bacteriocin prophylactic and therapeutic agents.

Dana Gebhart, Dean Scholl, Ph.D. and Gregory Govoni, Ph. D., AvidBiotics Corp., South San Francisco, CA


D. Gebhart, Avidbiotics: Employee and Shareholder, Salary

D. Scholl, Avidbiotics: Employee and Shareholder, Salary

G. Govoni, AvidBiotics Corp.: Employee and Shareholder, Salary

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