Using a Chemical Genetic Screen to Enhance Our Understanding of the Antibacterial Properties of Silver

It is essential to understand the mechanisms by which a toxicant is capable of poisoning the bacterial cell. The mechanism of action of many biocides and toxins, including numerous ubiquitous compounds, is not fully understood. For example, despite the widespread clinical and commercial use of silver (Ag), the mechanisms describing how this metal poisons bacterial cells remains incomplete. To advance our understanding surrounding the antimicrobial action of Ag, we performed a chemical genetic screen of a mutant library of Escherichia coli—the Keio collection, in order to identify Ag sensitive or resistant deletion strains. Indeed, our findings corroborate many previously established mechanisms that describe the antibacterial effects of Ag, such as the disruption of iron-sulfur clusters containing proteins and certain cellular redox enzymes. However, the data presented here demonstrates that the activity of Ag within the bacterial cell is more extensive, encompassing genes involved in cell wall maintenance, quinone metabolism and sulfur assimilation. Altogether, this study provides further insight into the antimicrobial mechanism of Ag and the physiological adaption of E. coli to this metal

Comparing the mechanisms of metal action in bacteria: insight into novel genes involved in silver, gallium and copper resistance and toxicity in Escherichia coli

It is fundamental to understand the mechanisms by which a toxicant is capable of poisoning the bacterial cell or resistance is developed. The mechanisms of actions of many antimicrobials such as metal-based compounds are not fully understood, yet, the development of these agents continues. Despite the essentiality of metals in the biochemistry of life, both non-essential and essential metals have been used as antimicrobials for agricultural and medical purposes for thousands of years. Applications include wound dressings, nanoparticles, antiseptic formulations, combination treatments, polymers and nanocomposites, among many more. Many of these have proven to be effective at controlling and eradicating microbial populations at low concentrations. Currently, studies in this field largely focus attention on developing new formulations and utilities for metal-based antimicrobials. The identity of the cellular targets that are involved in metal resistance and toxicity are known to a lesser degree. This current knowledge gap potentiates the progression of antimicrobial resistance since there is an incomplete understanding of metal action in microorganisms. Previous studies that have directed efforts toward these fundamental questions have failed to provide a comprehensive depiction of the global cellular effects of metal exposure; the literature is often replete with contradicting reports. Based on the aforementioned, we sought to answer the fundamental question – how do the mechanisms of metal toxicity and resistance compare in bacteria? We observed that the efficacies of metal ions varied between bacterial species and isolates of the same species. By means of the Keio collection, this comparison was validated by demonstrating that silver, copper and gallium act differently in Escherichia coli. Here, we presented a list of novel resistant and sensitive gene hits that may be involved in metal action. These experiments were performed under sublethal prolonged metal exposure, rather than acute shock. Resistance mechanisms range from efflux, iron-sulfur cluster maintenance, DNA repair, nucleotide biosynthesis to tRNA modification, and sensitive pathways include biomolecule import, NAD+ synthesis, amino acid biosynthesis, sulfur assimilation, electron transport, carbon metabolism and outer membrane maintenance, amongst others. To mitigate the improper use of metal-based antimicrobials, it is imperative that we understand precisely how these agents are able to eradicate bacterial cells and what are the accompanying mechanisms of resistance, particularly as development and use expands

Specificity in the Susceptibilities of Escherichia coli, Pseudomonas aeruginosa and Staphylococcus aureus Clinical Isolates to Six Metal Antimicrobials

In response to the occurrence of antibiotic resistance, there has been rapid developments in the field of metal-based antimicrobials. Although it is largely assumed that metals provide broad-spectrum microbial efficacy, studies have shown that this is not always the case. Therefore, in this study, we compared the susceptibilities of 93 clinical isolates belonging to the species Escherichia coli, Pseudomonas aeruginosa and Staphylococcus aureus against six metals, namely aluminum, copper, gallium, nickel, silver and zinc. To provide qualitative comparative information, the resulting zones of growth inhibition were compared to the minimal inhibitory concentrations of three indicator strains E. coli ATCC 25922, P. aeruginosa ATCC 27853 and S. aureus ATCC 25923. Here, we demonstrate that the metal efficacies were species- and isolate-specific. Only several isolates were either resistant or sensitive to all of the six metals, with great variability found between isolates. However, the greatest degree of similarity was found with the E. coli isolates. In contrast, the susceptibilities of the remaining two collections, S. aureus and P. aeruginosa, were more highly dispersed. Using this information, we have shown that metals are not equal in their efficacies. Hence, their use should be tailored against a particular microorganism and care should be taken to ensure the use of the correct concentration

The efficacy of different antimicrobial metals at preventing the formation of, and eradicating bacterial biofilms of pathogenic indicator strains.

The emergence of multidrug resistant pathogens and the prevalence of biofilm-related infections have generated a demand for alternative antimicrobial therapies. Metals have not been explored in adequate detail for their capacity to combat infectious disease. Metal compounds can now be found in textiles, medical devices, and disinfectants – yet, we know little about their efficacy against specific pathogens. To help fill this knowledge gap, we report on the antimicrobial and antibiofilm activity of seven metals; silver, copper, titanium, gallium, nickel, aluminum and zinc against three bacterial strains, Pseudomonas aeruginosa, Staphylococcus aureus, and Escherichia coli. In order to evaluate the capacity of metal ions to prevent the growth of, and eradicate biofilms and planktonic cells, bacterial cultures were inoculated in the Calgary Biofilm Device (MBEC™) in the presence the metal salts. Copper, gallium, and titanium were capable of preventing planktonic and biofilm growth, and eradicating established biofilms of all tested strains. Further, we observed that the efficacies of the other tested metal salts displayed variable efficacy against the tested strains. Further, contrary to the enhanced resistance anticipated from bacterial biofilms, particular metal salts were observed to be more effective against biofilm communities versus planktonic cells. In this study, we have demonstrated that the identity of the bacterial strain must be considered prior to treatment with a particular metal ion. Consequently, as the use of metal ions as antimicrobial agents to fight multidrug resistant and biofilm related infections increases, we must aim for more selective deployment in a given infectious setting.NSERC, AIHS,Ye

Specificity in the Susceptibilities of <i>Escherichia coli</i>, <i>Pseudomonas aeruginosa</i> and <i>Staphylococcus aureus</i> Clinical Isolates to Six Metal Antimicrobials

In response to the occurrence of antibiotic resistance, there has been rapid developments in the field of metal-based antimicrobials. Although it is largely assumed that metals provide broad-spectrum microbial efficacy, studies have shown that this is not always the case. Therefore, in this study, we compared the susceptibilities of 93 clinical isolates belonging to the species Escherichia coli, Pseudomonas aeruginosa and Staphylococcus aureus against six metals, namely aluminum, copper, gallium, nickel, silver and zinc. To provide qualitative comparative information, the resulting zones of growth inhibition were compared to the minimal inhibitory concentrations of three indicator strains E. coli ATCC 25922, P. aeruginosa ATCC 27853 and S. aureus ATCC 25923. Here, we demonstrate that the metal efficacies were species- and isolate-specific. Only several isolates were either resistant or sensitive to all of the six metals, with great variability found between isolates. However, the greatest degree of similarity was found with the E. coli isolates. In contrast, the susceptibilities of the remaining two collections, S. aureus and P. aeruginosa, were more highly dispersed. Using this information, we have shown that metals are not equal in their efficacies. Hence, their use should be tailored against a particular microorganism and care should be taken to ensure the use of the correct concentration

Using a Chemical Genetic Screen to Enhance Our Understanding of the Antimicrobial Properties of Gallium against Escherichia coli

The diagnostic and therapeutic agent gallium offers multiple clinical and commercial uses including the treatment of cancer and the localization of tumors, among others. Further, this metal has been proven to be an effective antimicrobial agent against a number of microbes. Despite the latter, the fundamental mechanisms of gallium action have yet to be fully identified and understood. To further the development of this antimicrobial, it is imperative that we understand the mechanisms by which gallium interacts with cells. As a result, we screened the Escherichia coli Keio mutant collection as a means of identifying the genes that are implicated in prolonged gallium toxicity or resistance and mapped their biological processes to their respective cellular system. We discovered that the deletion of genes functioning in response to oxidative stress, DNA or iron–sulfur cluster repair, and nucleotide biosynthesis were sensitive to gallium, while Ga resistance comprised of genes involved in iron/siderophore import, amino acid biosynthesis and cell envelope maintenance. Altogether, our explanations of these findings offer further insight into the mechanisms of gallium toxicity and resistance in E. coli

MOESM1 of Development and characterization of microsatellite markers in the African forest elephant (Loxodonta cyclotis)

Additional file 1. Additional material

Using a Chemical Genetic Screen to Enhance Our Understanding of the Antibacterial Properties of Silver

It is essential to understand the mechanisms by which a toxicant is capable of poisoning the bacterial cell. The mechanism of action of many biocides and toxins, including numerous ubiquitous compounds, is not fully understood. For example, despite the widespread clinical and commercial use of silver (Ag), the mechanisms describing how this metal poisons bacterial cells remains incomplete. To advance our understanding surrounding the antimicrobial action of Ag, we performed a chemical genetic screen of a mutant library of Escherichia coli&mdash;the Keio collection, in order to identify Ag sensitive or resistant deletion strains. Indeed, our findings corroborate many previously established mechanisms that describe the antibacterial effects of Ag, such as the disruption of iron-sulfur clusters containing proteins and certain cellular redox enzymes. However, the data presented here demonstrates that the activity of Ag within the bacterial cell is more extensive, encompassing genes involved in cell wall maintenance, quinone metabolism and sulfur assimilation. Altogether, this study provides further insight into the antimicrobial mechanism of Ag and the physiological adaption of E. coli to this metal

Silver oxynitrate – an efficacious compound for the prevention and eradication of dual-species biofilms

<p>Preventing and eradicating biofilms remains a challenge in clinical and industrial settings. Recently, the present authors demonstrated that silver oxynitrate (Ag₇NO₁₁) prevented and eradicated single-species planktonic and biofilm populations of numerous microbes at lower concentrations than other silver (Ag) compounds. Here, the antimicrobial and anti-biofilm efficacy of Ag₇NO₁₁ is elaborated by testing its <i>in vitro</i> activity against combinations of dual-species, planktonic and biofilm populations of <i>Escherichia coli</i>, <i>Staphylococcus aureus</i> and <i>Pseudomonas aeruginosa</i>. As further evidence emerges that multispecies bacterial communities are more common in the environment than their single-species counterparts, this study reinforces the diverse applicability of the minimal biofilm eradication concentration (MBEC™) assay for testing antimicrobial compounds against biofilms. Furthermore, this study demonstrated that Ag₇NO₁₁ had enhanced antimicrobial and anti-biofilm activity compared to copper sulfate (CuSO₄) and silver nitrate (AgNO₃) against the tested bacterial species.</p