Oral Presentation BACPATH 2017

Human macrophages subject uropathogenic E. coli to a zinc toxicity antimicrobial response (#10)

Claudia Stocks 1 , Ronan Kapetanovic 1 , Min-Duy Phan 2 , Alvin Lo 2 , Nilesh Bokil 3 , Mark Schembri 2 , Matthew Sweet 1
  1. Centre for Inflammation and Disease Research, Institute for Molecular Bioscience, University of Queensland, St Lucia, QLD, Australia
  2. School of Chemistry and Biological Sciences, University of Queensland, St Lucia , QLD, Australia
  3. University of Technology, Sydney, NSW, Australia

Despite the range of strategies deployed by macrophages to eliminate invading microorganisms, several pathogens, including some strains of uropathogenic E. coli (UPEC) are able to persist within these key innate immune cells. Innate immune-mediated zinc poisoning has emerged as a novel antimicrobial pathway, however molecular mechanisms controlling this process, and its role in host defence are not well understood. Recent studies in our laboratory and others, have shown that Toll-like receptor signalling in human macrophages results in the accumulation of vesicular zinc, with intracellular bacteria being subjected to a zinc stress response. Here we show that primary human macrophages subject the clinically relevant UPEC isolate EC958 to zinc-stress, as assessed by inducible expression of zntA, which encodes a zinc exporter that is selectively induced by this metal ion. To more precisely track this response, we developed zinc-stress reporters in EC958. To do so, we generated an EC958 strain in which the zntA promoter drives mCherry expression, and confirmed the specificity of this reporter for zinc versus other metal ions. Microscopic analysis revealed substantial heterogeneity in the zinc-stress response in primary human macrophages, with only a proportion of intracellular EC958 being subjected to zinc stress. Remarkably, we found that the same population of macrophages also subject intracellular UPEC to a zinc starvation response, suggesting that the host can employ both zinc toxicity and zinc starvation as dual antimicrobial strategies against the same pathogen. In investigating mechanisms responsible, we identified specific host zinc transporters that correlated in their expression patterns with zinc toxicity (SLC39A8) and zinc starvation (SLC30A1). Using our novel zinc-stress reporter strains, we are currently investigating key host molecules involved in directing the zinc toxicity response.