Chloride-inducible expression vector for delivery of antimicrobial peptides targeting antibiotic-resistant Enterococcus faecium

Antibiotic-resistant enterococcal infections are a major concern in hospitals where patients with compromised immunity are readily infected. Enterococcus faecium bacteria are of particular interest as these pathogens account for over 80% of vancomycinresistant enterococcal infections. Antimicrobial peptides (AMPs) produced at the site of infection by engineered bacteria may offer a potential alternative to traditional antibiotics for the treatment of resistant bacteria such as E. faecium. For this mode of delivery to be effective, it is essential to identify a suitable protein expression system that can be used in the desired delivery bacterium. In this study, we describe a promising chloride-inducible promoter and its application in the bacterial delivery of AMPs from Lactococcus lactis to reduce counts of E. faecium bacteria in vitro. Reporter gene studies show that at chloride concentrations found within the human intestines, the chloride-inducible promoter exhibits high levels of protein expression compared to those of the commonly used nisin-inducible promoter. These results indicate that this system is powerful and would not require the exogenous administration of an inducer molecule. In its application for AMP production against E. faecium in vitro, L. lactis producing AMPs under the chloride promoter rapidly decreased E. faecium counts by nearly 10,000-fold. As an extension of this application, we also demonstrate the potential in using this type of delivery system in combination with traditional antibiotics to slow the development of resistance. Collectively, this study shows the promise of using a chloride-inducible promoter for the bacterial delivery of AMPs in the body for the treatment of vancomycin-resistant enterococci (VRE) and other antibiotic-resistant bacteria.