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.