Novel antimicrobial peptide prevents C. rodentium infection in C57BL/6 mice by enhancing acid-induced pathogen killing

Potentiation of Antibiotics by a Novel Antimicrobial Peptide against Shiga Toxin Producing E. coli O157:H7

Infection with Shiga toxin-producing Escherichia coli (STEC) results in hemorrhagic colitis and can lead to life-threatening sequelae including hemolytic uremic syndrome (HUS). Conventional treatment is intravenous fluid volume expansion. Antibiotic treatment is contraindicated, due in part to the elevated risk of HUS related to increased Shiga toxin (Stx) release associated with some antibiotics. Given the lack of effective strategies and the increasing number of STEC outbreaks, new treatment approaches are critically needed. In this study, we used an antimicrobial peptide wrwycr, previously shown to enhance STEC killing without increasing Stx production, in combination with antibiotic treatments. Checkerboard and time-kill assays were used to assess peptide wrwycr-antibiotic combinations for synergistic STEC killing. Cytotoxicity and real-time PCR were used to evaluate Stx production and stx expression, respectively, associated with these combinations. The synergistic combinations that showed rapid killing, no growth recovery and minimal Stx production were peptide wrwycr-kanamycin/gentamicin. Transmission electron microscopy revealed striking differences in bacterial cell morphology associated with various treatments. This study provides proof of principle for the design of an antibiotic-peptide wrwycr combination effective in killing STEC without enhancing release of Shiga toxins. It also offers a strategy for the repurposing of antibiotics for treatment of STEC infection.

Dps Protects Enterohemorrhagic Escherichia coli against Acid-Induced Antimicrobial Peptide Killing

Dps, a DNA-binding protein from starved cells in Escherichia coli, is part of the bacterial defense system that protects DNA against various cellular stresses. Our lab previously demonstrated that a novel antimicrobial peptide, WRWYCR, enhances acid-induced killing of enterohemorrhagic Escherichia coli (EHEC) and ameliorates infection in a Citrobacter rodentium mouse model of EHEC infection. WRWYCR has previously been shown to compromise DNA damage repair and to increase chelatable iron within the cell. These findings, combined with the effects of peptide and acid stress on DNA damage, suggest a key defense role for Dps in peptide-induced killing of EHEC. The goal of this study is to evaluate the role of Dps in peptide-induced killing of EHEC through survival assays and flow cytometric analyses of DNA damage and hydroxyl radical formation. Our results demonstrate that disruption of the dps gene in stationary-phase EHEC O157:H7 cells, but not in exponential-phase cells, enhances acid-, peptide-, and peptide-acid-induced killing relative to that of wild-type (WT) EHEC. Using flow cytometric analysis, we have also demonstrated increased levels of hydroxyl radicals in peptide-treated wild-type EHEC relative to those in the untreated control. Disruption of the dps gene further increases this. These findings indicate that peptide treatment of EHEC enhances the formation of hydroxyl radicals, likely through the Fenton reaction, thereby contributing to the killing action of the peptide, and that dps protects against peptide killing of EHEC. This study provides important insights into peptide WRWYCR-mediated killing of EHEC, which could be exploited in the development of more effective antimicrobials.IMPORTANCE The research presented in this paper explores the role of the DNA-binding protein Dps as a key defense mechanism of enterohemorrhagic Escherichia coli (EHEC) strains in protecting against killing by the novel antimicrobial peptide WRWYCR. Our results demonstrate that Dps protects against peptide-induced killing of EHEC through direct protection against acid stress and hydroxyl radical formation, both of which are mechanisms targeted by the antimicrobial peptide. This study provides important insights into peptide WRWYCR-mediated killing of EHEC, which could be exploited in the development of more effective antimicrobials through specific targeting of Dps in order to allow a more potent response to the antimicrobial WRWYCR.