Document Type

Dissertation

Degree

Doctor of Philosophy

Major

Biology, Molecular and Cellular Biology

Date of Defense

12-12-2021

Graduate Advisor

George Gokel, Ph.D.

Committee

Eike Bauer

Lon Chubiz

Xeumin Wang

Abstract

Antibiotic resistance has become a world-wide health care crisis. In 2013 there were 50,000 deaths in U.S. and EU, associated with hospital acquired bacterial infections. This problem is exacerbated by the lack of new antibiotics in development. Here, we report that synthetic amphiphiles represent a new class of adjuvants that rescue antibiotic potency against multidrug resistant bacteria. Hydraphiles are amphiphiles, designed and synthesized in Gokel lab, that show many of the same properties as protein ion channels. Hydraphiles were previously shown to have antimicrobial activity against Escherichia coli, Bacillus subtilis and Saccharomyces cerevisiae. Here, we report that hydraphiles recover the activity of tetracycline and fluoroquinolones (ciprofloxacin, norfloxacin) against E. coli, Klebsiella pneumoniae, Staphylococcus aureus bacteria. At sub-lethal concentrations, hydraphiles do not inhibit bacterial growth, show synergy with existing antibiotics and transport K+ ions. Controls confirmed that the structure and function of hydraphiles are critical for its activity. Our investigation shows that hydraphiles can inhibit antibiotic efflux pumps and increase the bacterial membrane permeability. The outer membranes of Gram negative bacteria provide for an attractive target for antibiotic development. We showed that benzyl C14 hydraphile localize in the cell membrane of E. coli and human embryonic kidney (HEK-293) cells. However, hydraphile only increases the permeability of bacterial membranes. An advantage of this approach is that bacteria cannot readily develop resistance to membrane-active amphiphiles as observed with benzyl C14 hydraphiles. Our results show that hydraphiles inhibited the activity of norA efflux pump in S. aureus. As a result, the accumulation of the substrate/antibiotic increases in the S. aureus cytoplasm. This increases the antibiotic potency. At sub-lethal concentration of benzyl C14 hydraphile, the survival of three different mammalian cells was 80-100%. Overall, we report a novel adjuvant platform that could be used to rescue the efficacy of existing antibiotics for the treatment of life-threatening bacterial infections.

Available for download on Sunday, December 12, 2021

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