Poster Presentation Lorne Infection and Immunity 2019

Characterisation of molecular mechanisms of macrophage-mediated zinc toxicity and subversion of this antimicrobial pathway by uropathogenic E. coli   (#183)

Claudia J Stocks 1 , Minh Duy Phan 2 , Ronan Kapetanovic 1 , Alvin Lo 3 , Kate Peters 2 , Nilesh Bokil 4 , Mark A Schembri 2 , Matt J 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. Walter and Eliza Hall Institute of Medical Research, Melbourne, VIC, Australia
  4. School of Life Sciences, University of Technology, Sydney, NSW, Australia

Urinary tract infections (UTIs) are one of the most common bacterial infections worldwide. Uropathogenic E. coli (UPEC), which is the primary cause of UTIs and is also a frequent cause of sepsis, can adopt an intracellular niche to enable persistence and immune evasion. Direct zinc toxicity against intracellular bacteria has recently emerged as a novel macrophage antimicrobial pathway, however the molecular mechanisms controlling this process, as well as its role in host defence against UPEC, are not well understood. Here we show that primary human macrophages subject a globally disseminated multidrug-resistant UPEC isolate (EC958) to zinc-stress, as assessed by inducible expression of zntA, which encodes a zinc exporter selectively induced by cytotoxic zinc concentrations of this metal ion. However, in contrast to a non-pathogenic E. coli strain, UPEC genes conferring zinc resistance were not required for intramacrophage survival, suggesting that UPEC subverts the macrophage zinc toxicity pathway. To characterise mechanisms of subversion, we developed novel E. coli zinc-stress reporter strains, finding that, unlike non-pathogenic E. coli, the majority of EC958 effectively evades macrophage-mediated zinc toxicity, facilitating enhanced intramacrophage survival. In a mouse intraperitoneal challenge model, these findings were mirrored in infiltrating cells of the peritoneal cavity, with EC958, but not non-pathogenic E. coli, evading zinc toxicity and disseminating to the spleen and livers. In investigating molecular mechanisms, we found that specific host zinc transporters (the importer SLC39A8 and the exporter SLC30A1) were upregulated in infected macrophages. SLC30A1 localised to the plasma membrane and zinc-containing vesicles of the macrophage-like cell line THP-1, and inducible overexpression of this exporter enhanced bacterial clearance. Collectively, our studies reveal that UPEC effectively evades macrophage-mediated zinc toxicity and that the SLC30A1 zinc transporter is a novel component of this antimicrobial response. Modulation of this pathway may facilitate alternative, targeted treatment strategies for antibiotic-resistant bacterial pathogens.