Pyocyanin Production by Pseudomonas aeruginosa Confers Resistance to Ionic Silver

Abstract

Silver in its ionic form (Ag ؉ ), but not the bulk metal (Ag 0 ), is toxic to microbial life forms and has been used for many years in the treatment of wound infections. The prevalence of bacterial resistance to silver is considered low due to the nonspecific nature of its toxicity. However, the recent increased use of silver as an antimicrobial agent for medical, consumer, and industrial products has raised concern that widespread silver resistance may emerge. Pseudomonas aeruginosa is a common pathogen that produces pyocyanin, a redox toxin and a reductant for molecular oxygen and ferric (Fe 3؉ ) ions. The objective of this study was to determine whether pyocyanin reduces Ag ؉ to Ag 0 , which may contribute to silver resistance due to lower bioavailability of the cation. Using surface plasmon resonance spectroscopy and scanning electron microscopy, pyocyanin was confirmed to be a reductant for Ag ؉ , forming Ag 0 nanoparticles and reducing the bioavailability of free Ag ؉ by >95% within minutes. Similarly, a pyocyanin-producing strain of P. aeruginosa (PA14) reduced Ag ؉ but not a pyocyanin-deficient (⌬phzM) strain of the bacterium. Challenge of each strain with Ag ؉ (as AgNO 3 ) gave MICs of 20 and 5 g/ml for the PA14 and ⌬phzM strains, respectively. Removal of pyocyanin from the medium strain PA14 was grown in or its addition to the medium that ⌬phzM mutant was grown in gave MICs of 5 and 20 g/ml, respectively. Clinical isolates demonstrated similar pyocyanin-dependent resistance to Ag ؉ . We conclude that pseudomonal silver resistance exists independently of previously recognized intracellular mechanisms and may be more prevalent than previously considered.

Acylase‐containing polyurethane coatings with anti‐biofilm activity

“…The samples were centrifuged at 4500 rpm for 5 min to separate the organic phase from the aqueous phase. After separation, the absorbance of organic phase was measured at 695 nm (e ¼ 5816 M À1 cm À1 ) to quantify pyocyanin levels (Essar et al, 1990;Muller and Merrett, 2014;Ng et al, 2011;Sarkisova et al, 2005). Escherichia coli BL21 DE3, which does not secrete pyocyanin, was used as a negative control.…”

Visible Light Plasmon Excitation of Silver Nanoparticles Against Antibiotic-ResistantPseudomonas aeruginosa

“…It has also been shown that high doses of blue light treatment inhibited the activity of pyocyanin, staphylolysin, pseudolysin and other proteases (37, 39). Furthermore, it has been demonstrated that pyocyanin confers on P. aeruginosa resistance to ionic silver (49). It is thus possible that pyocyanin inhibition by LED floodlight contributes to the bactericidal effect of AgNPs on P. aeruginosa and diminishes the virulence of the surviving bacteria.…”

Bioactivity of pyocyanin of Pseudomonas aeruginosa clinical isolates against a variety of human pathogenic bacteria and fungi species

“…A zwitterions that canenterbiological membranes, pyocyanin can directly accept electrons from reducing agents such asNADPH and reduced glutathione ( Figure 1) and endure redox cycling using oxygen as an electron acceptor resulting in the generation of the reactive oxygen species (ROS), particularly hydrogen peroxide, with resulting induction of oxidative stress and disturbance of intracellular redox homeostasis [5]. Therefore, the important mechanisms of pyocyanin to prokaryotic and eukaryotic cells are related to inhibition cellular respiration [6] Pseudomonas spp.…”

“…are also capable of producing organic volatiles, whose in vitro antifungal nature has been demonstrated against Phytophthora- Conclusions: Antimicrobial activity of pyocyanin was more observed against Gram-positive than Gram-negative bacteria, but mostly similar against all fungi (molds and yeast). Cefotaxime was the most active antimicrobial drug against all P. aeruginosa isolates Figure 1: Chemical structure of reduced and oxidized forms of pyocyanin and mechanizm [5]. vignae in cowpea [7].…”