Uncovering the role of polyamines in bacterial survival and antibiotic resistance

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Bacteria encounter many chemicals in their extracellular milieu. Conceivably, these chemicals collectively affect cellular responses influencing bacterial survival and antibiotic resistance. Such effects are typically undetected in standard in vitro assays, often overlooking critical virulence and antibiotic resistance phenotypes. A prominent class of such chemicals is polyamines being ubiquitous in the environment and overproduced by plant and animal cells during infection. High concentrations of polyamines kill bacteria. Yet, before reaching lethal levels, polyamines make bacteria either more resistant or susceptible to many antibiotics, thereby changing the efficacy of these drugs. The overall goal of my NSERC research program is to understand how polyamines interact with bacteria influencing their survival and adaptation under stress. The proposed research advances my earlier work that identified the role of polyamines in antibiotic resistance and harnesses high-throughput chemical genomics approaches to study bacterial responses at the whole-genome level. I hypothesize that bacteria use previously unrecognized mechanisms to withstand high polyamine concentrations. Further, I hypothesize that polyamines modulate the bacterial responses to antibiotics through interaction with specific cellular targets and that antibiotic exposure triggers regulatory cascades linking polyamine production to the antibiotic response. To address these hypotheses, I propose three parallel and complementary work packages to achieve three specific objectives of this discovery grant: 1. Study how model Gram-positive and Gram-negative bacteria tolerate high concentrations of polyamines. 2. Determine the mechanisms by which polyamines mediate altered responses to antibiotics. 3. Characterize the regulatory networks underpinning polyamine role in response to antibiotics. My lab will use a whole-genomic approach to interrogate thousands of mutants, each harboring single gene deletions, profiling their responses to polyamines and polyamine-antibiotic combos. We will also construct a reporter library to measure the expression of polyamine biosynthetic enzymes when exposed to antibiotics. We will use S. aureus and E. coli as representatives of Gram-positive polyamine non-producer and Gram-negative polyamine-producer bacteria, respectively. Through this systems approach, we will formulate new hypotheses that will allow us to undertake detailed analyses using conventional biochemical and molecular biology methods providing mechanistic insights into the bacterial responses to polyamines and antibiotic resistance. Together, my research program addresses a significant knowledge gap in understanding the importance of polyamines in bacterial survival and antibiotic resistance. The discoveries generated from this program will pave the way for future applications to fight superbugs and will have tangible benefits to the healthcare systems, agriculture, and the biotech sectors.