Poster Presentation BacPath 13: Molecular Analysis of Bacterial Pathogens Conference 2015

An antimicrobial role for zinc in innate immune defense against Group A Streptococcus (#130)

Cheryl-Lynn Y. Ong 1 , Mark J. Walker 1 , Alastair G. McEwan 1
  1. School of Chemistry and Molecular Biosciences, Australian Infectious Diseases Research Centre, The University of Queensland, St Lucia, QLD, Australia

Zinc deficiency is associated with increased susceptibility to bacterial infection, although the way in which zinc exerts its effect is not fully understood. We have investigated the role of zinc in innate immune defense against Group A Streptococcus (GAS), a Gram-positive bacterial pathogen responsible for a wide spectrum of human diseases. We analyzed the clinically important GAS M1T1 strain, and the phenotypes of two isogenic mutants and corresponding complemented mutants. The targeted GAS czcD gene encodes for a zinc efflux pump and the adjacent gczA gene encodes the zinc-dependent activator of czcD expression. Compared to the wild-type, both mutants exhibited reduced ability to grow in the presence of zinc and increased accumulation of internal zinc. We also demonstrate that zinc efflux plays a critical role in GAS pathogenesis, as both mutants displayed increased susceptibility to killing by human neutrophils and reduced virulence in a murine infection model. Furthermore, we show that neutrophils utilize intracellular zinc poisoning as a mechanism to eliminate the invading GAS cells and that GAS-infected mice had increased zinc in the blood and at the sites of infection. We have also demonstrated the mechanisms by which zinc exerts its toxic effect in GAS. As such, zinc efflux is an important contributor to GAS pathogenesis and zinc may play a direct antibacterial role in innate immune defense against infection. To date, our data has provided new insight into the potential use of zinc as therapeutics against bacterial infections.