SEP 13, 2018 1:30 PM PDT

Mechanisms of Antimicrobial Bioconversion by Environmental and Host-Associated Bacteria

Speaker
  • Pathology and Immunology Postdoctoral Scholar, Dantas Lab, Washington University in St. Louis
    Biography
      Dr. Crofts is currently a post-doctoral scholar at Washington University in St. Louis working with Dr. Gautam Dantas. One focus of his research has been the metabolic fate of antibiotics in the environment, a project that ties together antibiotic resistance and bacterial metabolism. A second focus is how early life antibiotic therapy alters the developing human gut microbiota in infants as well as the host immune system using a gnotobiotic mouse model I have developed. A third focus has been studying how the human microbiome interacts with pharmaceuticals and other xenobiotics, with a focus on the mechanisms underlying drug toxicity. Prior to this he received his Ph.D. in Microbiology from the University of California, Berkeley, working with Dr. Michi Taga studying how bacterial producers of vitamin B12 analogs use enzyme-substrate specificity to avoid incorporating incorrect lower ligands from their environment. He began his career earning joint B.S. degrees in Molecular and Cellular Biology and Chemistry from the University of Illinois, where he completed an honor's research project on T-cell receptor specificity in the lab of Dr. David Kranz.

      He is looking forward to starting next fall at Northwestern University as a Research Assistant Professor, where he will continue to focus on understanding how the gut microbiota affects the efficacy and toxicity of pharmaceuticals, including small molecules and biologics, as well as study how microbiota in the environment respond to and modify/degrade antimicrobials.

    Abstract

    The soil microbiome can produce, resist, or degrade antibiotics and even catabolize them. Resistance genes are widely distributed in the soil and may act as a reservoir for pathogen antibiotic resistance. Work done in the Dantas lab has identified high diversity of genes encoding antibiotic resistance across all antibiotic classes, but generally these genes are not at great risk of mobilization to pathogens. However, the sub-group of resistant, culturable Proteobacteria show both resistance to high concentrations of antibiotics and resistance across many antibiotic classes. These highly resistant Proteobacteria are related to human pathogens, and show evidence of increased horizontal gene transfer of resistance genes. Interestingly, many of these Proteobacteria are not only antibiotic resistant, they have also been found to be capable of antibiotic catabolism. Little is known about the enzymes, mechanisms, and pathways involved in antibiotic catabolism. We describe a pathway for penicillin catabolism in four strains of Proteobacteria. Genomic and transcriptomic sequencing revealed β -lactamase, amidase, and phenylacetic acid catabolon upregulation. Knocking out part of the phenylacetic acid catabolon or an apparent penicillin utilization operon (put) resulted in loss of penicillin catabolism in one isolate. A hydrolase from the put operon was found to degrade in vitro benzylpenicilloic acid, the β -lactamase penicillin product. To test the generality of this strategy, an Escherichia coli strain was engineered to co-express a β -lactamase and a penicillin amidase or the put operon, enabling it to grow using penicillin or benzylpenicilloic acid, respectively. Elucidation of additional pathways may allow bioremediation of antibiotic-contaminated soils and discovery of antibiotic-remodeling enzymes with industrial utility.

    Learning Objectives: 

    1. Antibiotics and pharmaceuticals are not privileged molecules, they can be modified or catabolized by microbes. 
    2. Metabolism of these molecules in unexpected ways can impact human health.


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