Mutations Associated with Reduced Surotomycin Susceptibility in Clostridium difficile and Enterococcus Species

Abstract

bClostridium difficile infection (CDI) is an urgent public health concern causing considerable clinical and economic burdens. CDI can be treated with antibiotics, but recurrence of the disease following successful treatment of the initial episode often occurs. Surotomycin is a rapidly bactericidal cyclic lipopeptide antibiotic that is in clinical trials for CDI treatment and that has demonstrated superiority over vancomycin in preventing CDI relapse. Surotomycin is a structural analogue of the membraneactive antibiotic daptomycin. Previously, we utilized in vitro serial passage experiments to derive C. difficile strains with reduced surotomycin susceptibilities. The parent strains used included ATCC 700057 and clinical isolates from the restriction endonuclease analysis (REA) groups BI and K. Serial passage experiments were also performed with vancomycin-resistant and vancomycin-susceptible Enterococcus faecium and Enterococcus faecalis. The goal of this study is to identify mutations associated with reduced surotomycin susceptibility in C. difficile and enterococci. Illumina sequence data generated for the parent strains and serial passage isolates were compared. We identified nonsynonymous mutations in genes coding for cardiolipin synthase in C. difficile ATCC 700057, enoyl-(acyl carrier protein) reductase II (FabK) and cell division protein FtsH2 in C. difficile REA type BI, and a PadR family transcriptional regulator in C. difficile REA type K. Among the 4 enterococcal strain pairs, 20 mutations were identified, and those mutations overlap those associated with daptomycin resistance. These data give insight into the mechanism of action of surotomycin against C. difficile, possible mechanisms for resistance emergence during clinical use, and the potential impacts of surotomycin therapy on intestinal enterococci. C lostridium difficile is a Gram-positive anaerobic spore-forming bacterium and a causative agent of health care-associated infections (HAIs). C. difficile infection (CDI; alternatively called C. difficile-associated diarrhea) can occur after disruption of the normal microbiota of the gastrointestinal (GI) tract, thereby decreasing colonization resistance and allowing for C. difficile outgrowth (1). Toxin production by C. difficile can lead to severe disease. Over the last two decades, the incidence of CDI has increased dramatically, especially among elderly health care patients (1-3). A recent Centers for Disease Control and Prevention report on antibiotic resistance threats in the United States classifies C. difficile as an urgent public health threat, as it causes an estimated 250,000 infections per year, leading to an estimated 14,000 deaths and at least $1 billion in medical costs (2).CDI can be treated with antibiotics, but recurrence can occur after a successful therapy and is a persistent concern (3). Vancomycin, metronidazole, and the recently FDA-approved drug fidaxomicin are used to treat CDI (1, 3, 4). Surotomycin (CB-183,315) is a cyclic lipopeptide antibiotic and daptomycin analogue that...

Chlorhexidine Induces VanA-Type Vancomycin Resistance Genes in Enterococci

“…E. faecium genomic DNA (gDNA) was isolated using a previously published protocol (31). Electroporation of E. faecium is described in the supplemental material.…”

Antibacterials Developed to Target a Single Organism: Mechanisms and Frequencies of Reduced Susceptibility to the Novel Anti-Clostridium difficileCompounds Fidaxomicin and LFF571

“…Recently, Adams et al reported that the serial passage of C. difficile in subinhibitory concentrations of the phase III CDI compound surotomycin resulted in mutants with an eight-to16-fold shift in susceptibility to both surotomycin and daptomycin, the clinically used natural product antibiotic from which surotomycin is derived (Adams et al 2015). In addition, surotomycin also selected for mutants of Enterococcus faecium and E. faecalis that are cross-resistant to daptomycin (Mascio et al 2014).…”

Discovery and development of surotomycin for the treatment of Clostridium difficile

“…Serial passage studies were also performed on enterococci isolates. In general, the surotomycin susceptibility of vancomycin-sensitive and -resistant enterococci remained relatively unchanged over the 15-day passage; however, some mutants with MICs of up to 16 μg/mL were identified [1]. Low rates of spontaneous resistance and MICs well below the intestinal concentration of surotomycin suggest that the emergence of C. difficile and enterococci resistance with surotomycin treatment should be a rare event.…”