The Role of Copper and Zinc Toxicity in Innate Immune Defense against Bacterial Pathogens

Zinc (Zn) and copper (Cu) are essential for optimal innate immune function, and nutritional deficiency in either metal leads to increased susceptibility to bacterial infection. Recently, the decreased survival of bacterial pathogens with impaired Cu and/or Zn detoxification systems in phagocytes and animal models of infection has been reported. Consequently, a model has emerged in which the host utilizes Cu and/or Zn intoxication to reduce the intracellular survival of pathogens. This review describes and assesses the potential role for Cu and Zn intoxication in innate immune function and their direct bactericidal function

The role of zinc acquisition and zinc tolerance in group A streptococcal infection

Zinc plays an important role in host innate immune function. However, the innate immune system also utilizes zinc starvation ('nutritional immunity') to combat infections. Here, we investigate the role of zinc import and export in protection of(Group A; GAS), a Gram-positive bacterial pathogen responsible for a wide spectrum of human diseases, against challenge from host innate immune defence. In order to determine the role of GAS zinc import and export during infection, we utilized the zinc import (Δ) and export (Δ) deletion mutants in competition with wild-type in bothandvirulence models. We demonstrate that nutritional immunity is deployed extracellularly while zinc toxicity is utilized upon phagocytosis of GAS by neutrophils. We also show that lysosomes and azurophilic granules in neutrophils contain zinc stores for use against intracellular pathogens

Molecular analysis of type 3 fimbrial genes from Escherichia coli, Klebsiella and Citrobacter species

Background: Catheter-associated urinary tract infection (CAUTI) is the most common nosocomial infection in the United States and is caused by a range of uropathogens. Biofilm formation by uropathogens that cause CAUTI is often mediated by cell surface structures such as fimbriae. In this study, we characterised the genes encoding type 3 fimbriae from CAUTI strains of Escherichia coli, Klebsiella pneumoniae, Klebsiella oxytoca, Citrobacter koseri and Citrobacter freundii

Chemical Synergy between Ionophore PBT2 and Zinc Reverses Antibiotic Resistance.

The World Health Organization reports that antibiotic-resistant pathogens represent an imminent global health disaster for the 21st century. Gram-positive superbugs threaten to breach last-line antibiotic treatment, and the pharmaceutical industry antibiotic development pipeline is waning. Here we report the synergy between ionophore-induced physiological stress in Gram-positive bacteria and antibiotic treatment. PBT2 is a safe-for-human-use zinc ionophore that has progressed to phase 2 clinical trials for Alzheimer's and Huntington's disease treatment. In combination with zinc, PBT2 exhibits antibacterial activity and disrupts cellular homeostasis in erythromycin-resistant group A Streptococcus (GAS), methicillin-resistant Staphylococcus aureus (MRSA), and vancomycin-resistant Enterococcus (VRE). We were unable to select for mutants resistant to PBT2-zinc treatment. While ineffective alone against resistant bacteria, several clinically relevant antibiotics act synergistically with PBT2-zinc to enhance killing of these Gram-positive pathogens. These data represent a new paradigm whereby disruption of bacterial metal homeostasis reverses antibiotic-resistant phenotypes in a number of priority human bacterial pathogens.IMPORTANCE The rise of bacterial antibiotic resistance coupled with a reduction in new antibiotic development has placed significant burdens on global health care. Resistant bacterial pathogens such as methicillin-resistant Staphylococcus aureus and vancomycin-resistant Enterococcus are leading causes of community- and hospital-acquired infection and present a significant clinical challenge. These pathogens have acquired resistance to broad classes of antimicrobials. Furthermore, Streptococcus pyogenes, a significant disease agent among Indigenous Australians, has now acquired resistance to several antibiotic classes. With a rise in antibiotic resistance and reduction in new antibiotic discovery, it is imperative to investigate alternative therapeutic regimens that complement the use of current antibiotic treatment strategies. As stated by the WHO Director-General, "On current trends, common diseases may become untreatable. Doctors facing patients will have to say, Sorry, there is nothing I can do for you.

The contribution of X-linked coding variation to severe developmental disorders

Abstract: Over 130 X-linked genes have been robustly associated with developmental disorders, and X-linked causes have been hypothesised to underlie the higher developmental disorder rates in males. Here, we evaluate the burden of X-linked coding variation in 11,044 developmental disorder patients, and find a similar rate of X-linked causes in males and females (6.0% and 6.9%, respectively), indicating that such variants do not account for the 1.4-fold male bias. We develop an improved strategy to detect X-linked developmental disorders and identify 23 significant genes, all of which were previously known, consistent with our inference that the vast majority of the X-linked burden is in known developmental disorder-associated genes. Importantly, we estimate that, in male probands, only 13% of inherited rare missense variants in known developmental disorder-associated genes are likely to be pathogenic. Our results demonstrate that statistical analysis of large datasets can refine our understanding of modes of inheritance for individual X-linked disorders

Conjugative Plasmid Transfer and Adhesion Dynamics in an Escherichia coli Biofilm▿ †

A conjugative plasmid from the catheter-associated urinary tract infection strain Escherichia coli MS2027 was sequenced and annotated. This 42,644-bp plasmid, designated pMAS2027, contains 58 putative genes and is most closely related to plasmids belonging to incompatibility group X (IncX1). Plasmid pMAS2027 encodes two important virulence factors: type 3 fimbriae and a type IV secretion (T4S) system. Type 3 fimbriae, recently found to be functionally expressed in E. coli, played an important role in biofilm formation. Biofilm formation by E. coli MS2027 was specifically due to expression of type 3 fimbriae and not the T4S system. The T4S system, however, accounted for the conjugative ability of pMAS2027 and enabled a non-biofilm-forming strain to grow as part of a mixed biofilm following acquisition of this plasmid. Thus, the importance of conjugation as a mechanism to spread biofilm determinants was demonstrated. Conjugation may represent an important mechanism by which type 3 fimbria genes are transferred among the Enterobacteriaceae that cause device-related infections in nosocomial settings

Transition Metal Homeostasis in Streptococcus pyogenes and Streptococcus pneumoniae

Trace metals such as Fe, Mn, Zn and Cu are essential for various biological functions including proper innate immune function. The host immune system has complicated and coordinated mechanisms in place to either starve and/or overload invading pathogens with various metals to combat the infection. Here, we discuss the roles of Fe, Mn and Zn in terms of nutritional immunity, and also the roles of Cu and Zn in metal overload in relation to the physiology and pathogenesis of two human streptococcal species, Streptococcus pneumoniae and Streptococcus pyogenes. S. pneumoniae is a major human pathogen that is carried asymptomatically in the nasopharynx by up to 70% of the population; however, transition to internal sites can cause a range of diseases such as pneumonia, otitis media, meningitis and bacteraemia. S. pyogenes is a human pathogen responsible for diseases ranging from pharyngitis and impetigo, to severe invasive infections. Both species have overlapping capacity with respect to metal acquisition, export and regulation and how metal homeostasis relates to their virulence and ability to invade and survive within the host. It is becoming more apparent that metals have an important role to play in the control of infection, and with further investigations, it could lead to the potential use of metals in novel antimicrobial therapies

An antimicrobial role for zinc in innate immune defence against group A streptococcus

Background. Zinc plays an important role in human immunity, and it is known that zinc deficiency in the host is linked to increased susceptibility to bacterial infection. In this study, we investigate the role of zinc efflux in the pathogenesis of Streptococcus pyogenes (group A Streptococcus [GAS]), a human pathogen responsible for superficial infections, such as pharyngitis and impetigo, and severe invasive infections. Methods. The clinically important M1T1 wild-type strain was used in this study, and isogenic mutants were constructed with deletions in the czcD gene (Spy0653; which encodes a putative zinc efflux pump) and adjacent gczA gene (Spy0654; which encodes a putative zinc-dependent activator of czcD).Wild-type, isogenic mutants and complemented strains were tested for resistance against zinc stress, intracellular zinc accumulation, and virulence. Results. Both czcD and gczA mutants exhibited increased sensitivity to zinc. Transcriptional analyses indicate that GczA upregulates czcD in response to zinc. Both mutants displayed increased susceptibility to human neutrophil killing and reduced virulence in a murine infection model. Furthermore, we showed that neutrophils mobilize zinc in response to GAS. Conclusions. These data indicate that the innate immune system may use zinc as an antimicrobial agent and that zinc efflux is an important contributor to GAS pathogenesis

Group A Streptococcus co-ordinates manganese import and iron efflux in response to hydrogen peroxide stress

Bacterial pathogens encounter a variety of adverse physiological conditions during infection, including metal starvation, metal overload and oxidative stress. Here we demonstrate that group A Streptococcus (GAS) utilizes Mn(II) import via MtsABC during conditions of hydrogen peroxide stress to optimally metallate the superoxide dismutase, SodA, with Mn. MtsABC expression is controlled by the DtxR-family metalloregulator MtsR, which also regulates expression of Fe uptake systems in GAS. Our results indicate that the SodA in GAS requires Mn for full activity and has lower activity when it contains Fe. As a consequence, under conditions of hydrogen peroxide stress where Fe is elevated we observed that the PerR-regulated Fe(II) efflux system PmtA was required to reduce intracellular Fe, thus protecting SodA from becoming mismetallated. Our findings demonstrate the coordinate action of MtsR-regulated Mn(II) import by MtsABC and PerR-regulated Fe(II) efflux by PmtA to ensure appropriate Mn(II) metallation of SodA for optimal superoxide dismutase function