Date of Award

Summer 8-15-2018

Author's School

Graduate School of Arts and Sciences

Author's Department

Biology & Biomedical Sciences (Molecular Genetics & Genomics)

Degree Name

Doctor of Philosophy (PhD)

Degree Type




A Mechanism of Antimicrobial Resistance and a Mitigation Strategy


Christopher Bulow

Doctor of Philosophy in Biology and Biomedical Sciences

Molecular Genetics and Genomics

Washington University in St. Louis, 2018

Professor Gautam Dantas, Chair

The ability to treat infections, perform surgery, and administer immunosuppressants and chemotherapy depends on effective antibiotics. The emergence and spread of antimicrobial resistance is far outpacing the development of new therapies1-3 threatening to thrust medicine into a post-antibiotic era4. Many mechanisms of antimicrobial action and of antimicrobial resistance remain poorly understood as drug development struggles to keep pace. As resistance develops, the human gut serves as a reservoir and provides ample opportunities for resistance gene transmission between commensal and pathogenic bacteria5-11. Once resistant organisms colonize the gut, they can persist for extended durations even without continued antimicrobial exposure6-12. New approaches are necessary to prevent or reverse colonization with resistant organisms. This work takes two important steps to addressing the antimicrobial resistance crisis: 1) Understanding an antimicrobial mechanism of action and a corresponding mechanism of resistance and 2) Developing an approach to prevent or reverse colonization of human hosts with resistant organisms.

Daptomycin, a broad spectrum antibiotic used for treating multi-drug resistant Gram-positive infections, is experiencing clinical failure against important infectious agents including Corynebacterium striatum, an opportunistic pathogen and skin commensal. The recent transition of daptomycin to generic status is projected to dramatically increase availability, use, and clinical failure. Here we confirm the genetic mechanism of high-level daptomycin resistance (HLDR, MIC > 256 g/mL) in C. striatum, which evolved within a patient during daptomycin therapy. This work demonstrates that loss of function mutation in pgsA2 and the loss of membrane PG is necessary and sufficient to produce high-level resistance to daptomycin in C. striatum. This elimination of PG and the absence of additional compensatory changes support the conclusion that PG is the target of daptomycin. This work highlights the importance of understanding how different bacterial species respond to lipopeptide antibiotics. Drugs that target membrane components may vary in efficacy by species due to differing abilities of species to alter or remove various membrane components.

Strategies to prevent infection by multidrug-resistant organisms (MDROs) are scarce; however, autologous fecal microbiota transplantation (autoFMT) may limit gastrointestinal MDRO expansion. AutoFMT involves banking oneճ feces during a healthy state for later use in restoring gut microbiota following perturbation. In this pilot clinical trial involving 10 healthy participants, autoFMT was safe and well tolerated in the ten participants evaluated. The trial also evaluated the effects of amoxicillin-clavulanic acid (amox/clav) exposure and the ability of autoFMT to restore the microbiome. Both autoFMT and saline control restored metabolic capacity and resistance gene levels, but additional work is necessary to determine its ability to restore phylogeny. Importantly, metabolic capacity was perturbed following amox/clav even in cases where gross phylogeny remained unchanged.


English (en)

Chair and Committee

Gautam Dantas

Committee Members

Gautam Dantas, Megan Baldridge, Michael Brent, Carey-Ann Burnham,


Permanent URL: 2018-08-15