Abstract
It has been known for centuries that copper is toxic to bacteria. Within the host innate immune system,
engulfed bacteria are exposed to high levels of copper within the phagolysosome of macrophages. As a
response to counteract this tool used by the innate immune system, bacteria have evolved export systems to
pump out copper that enter the bacterial cell. Studying how pathogens respond to this copper stress will help
us devise novel antimicrobial strategies. Our model organism, Streptococcus pneumoniae, is a leading cause
of meningitis, otitis media, pneumonia, and sepsis worldwide. In response to macrophage-derived copper
stress, S. pneumoniae upregulates the cop operon locus, which serves to export copper out from the bacterial
cell. Enhancing copper stress above a bacterium’s export capacity can be a mechanism for a novel
antimicrobial. Copper chelating compounds that direct copper to macrophages for uptake and use within the
phagolysosome will enhance copper stress. A recently developed antifungal, 8-hydroxychloroquine (8-HQ),
utilizes copper chelation and uptake into macrophages to enhance killing efficiency. Following screening of
several known copper chelators and compounds with similar structural elements, our lab has identified several
candidate chelating compounds to test for antimicrobial efficacy. I hypothesize that similar copper chelating
compounds enhance kill bacteria and enhance host macrophage killing of engulfed pathogens by
increasing the intra-macrophage copper concentration. Current gaps in our knowledge include how
pathogens respond to the copper stress induced by these chelating compounds and whether compounds work
in vitro and in vivo. To test this hypothesis, I will first define the copper affinity of chelating compounds and the
subsequent change in intra-bacterial Cu2+ concentration. Findings from this aim assess whether chelating
compounds increase bacterial Cu2+ concentration or increase its intracellular availability. Additionally, I will
determine how S. pneumoniae respond to copper stress induced by copper chelating compounds. Findings
from this aim will characterize how copper stress is induced by these copper chelating compounds. Lastly, I will
determine the role of macrophages in antimicrobial efficacy of our identified synergistic copper chelating
compounds. Findings from this aim will show antimicrobial efficacy to be macrophage-dependent or
macrophage-independent. While most commercially available antimicrobials target bacterial DNA transcription
or mRNA translation, our research in this proposed study will employ the long-known principle of copper
toxicity for an under-utilized purpose.