Construction of a glucose sensor based on a screen-printed electrode and a novel mediator pyocyanin from Pseudomonas aeruginosa

Transforming microbial pigment into therapeutic revelation: extraction and characterization of pyocyanin from Pseudomonas aeruginosa and its therapeutic potential as an antibacterial and anticancer agent

BACKGROUND

The objectives of the current study were to extract pyocyanin from Pseudomonas aeruginosa clinical isolates, characterize its chemical nature, and assess its biological activity against different bacteria and cancer cells. Due to its diverse bioactive properties, pyocyanin, being one of the virulence factors of P. aeruginosa, holds a promising, safe, and available therapeutic potential.

METHODS

30 clinical P. aeruginosa isolates were collected from different sources of infections and identified by routine methods, the VITEK 2 compact system, and 16 S rRNA. The phenazine-modifying genes (phzM, phzS) were identified using polymerase chain reaction (PCR). Pyocyanin chemical characterization included UV-Vis spectrophotometry, Fourier Transform Infra-Red spectroscopy (FTIR), Gas Chromatography-Mass Spectrometry (GC-MS), and Liquid Chromatography-Mass Spectrometry (LC-MS). The biological activity of pyocyanin was explored by determining the MIC values against different clinical bacterial strains and assessing its anticancer activity against A549, MDA-MB-231, and Caco-2 cancer cell lines using cytotoxicity, wound healing and colony forming assays.

RESULTS

All identified isolates harboured at least one of the phzM or phzS genes. The co-presence of both genes was demonstrated in 13 isolates. The UV-VIS absorbance peaks were maxima at 215, 265, 385, and 520 nm. FTIR could identify the characteristic pyocyanin functional groups, whereas both GC-MS and LC-MS elucidated the chemical formula C11H18N2O2, with a molecular weight 210. The quadri-technical analytical approaches confirmed the chemical nature of the extracted pyocyanin. The extract showed broad-spectrum antibacterial activity, with the greatest activity against Bacillus, Staphylococcus, and Streptococcus species (MICs 31.25-125 µg/mL), followed by E. coli isolates (MICs 250-1000 µg/mL). Regarding the anticancer activity, the pyocyanin extract showed IC50 values against A549, MDA-MB-231, and Caco-2 cancer cell lines of 130, 105, and 187.9 µg/mL, respectively. Furthermore, pyocyanin has markedly suppressed colony formation and migratory abilities in these cells.

CONCLUSIONS

The extracted pyocyanin has demonstrated to be a potentially effective candidate against various bacterial infections and cancers. Hence, the current findings could contribute to producing this natural compound easily through an affordable method. Nonetheless, future studies are required to investigate pyocyanin's effects in vivo and analyse the results of combining it with other traditional antibiotics or anticancer drugs.

A biomedical perspective of pyocyanin from Pseudomonas aeruginosa: its applications and challenges

Pyocyanin is a bioactive pigment produced by Pseudomonas aeruginosa. It is an important virulence factor that plays a critical role in P. aeruginosa infections as a redox-active secondary metabolite and a quorum sensing (QS) signaling molecule. Pyocyanin production from chorismic acid requires the involvement of two homologous operons, phz1 and phz2, which are activated by QS regulatory proteins. Pyocyanin inhibits the proliferation of bacterial, fungal, and mammalian cells by inducing oxidative stress due to which it acts as a potent antibacterial, antifungal, and anticancer agent. Its potential role as a neuroprotectant needs further exploration. However, pyocyanin exacerbates the damaging effects of nosocomial infections caused by P. aeruginosa in immunocompromised individuals. Further, cystic fibrosis (CF) patients are highly susceptible to persistent P. aeruginosa infections in the respiratory system. The bacterial cells form colonies and three interconnected QS networks-pqs, las, and rhl-get activated, thus stimulating the cells to produce pyocyanin which exacerbates pulmonary complications. As an opportunistic pathogen, P. aeruginosa produces pyocyanin to impede the recovery of injuries like burn wounds through its anti-proliferative activity. Moreover, pyocyanin plays a vital role in compounding P. aeruginosa infections by promoting biofilm formation. This review begins with a brief description of the characteristics of pyocyanin, its activity, and the different aspects of its production including its biosynthesis, the role of QS, and the effect of environmental factors. It then goes on to explore the potential applications of pyocyanin as a biotherapeutic molecule while also highlighting the biomedical challenges and limitations that it presents.

Upcycling of food waste streams to valuable biopigments pyocyanin and 1-hydroxyphenazine

Phenazines, including pyocyanin (PYO) and 1-hydroxyphenazine (1-HP) are extracellular secondary metabolites and multifunctional pigments of Pseudomonas aeruginosa responsible for its blue-green color. These versatile molecules are electrochemically active, involved in significant biological activities giving fitness to the host, but also recognized as antimicrobial and anticancer agents. Their wider application is still limited partly due to the cost of carbon substrate for production, which can be solved by the utilization of carbon from food waste within the biorefinery concept. In this study, a variety of food waste streams (banana peel, potato peel, potato washing, stale bread, yoghurt, processed meat, boiled eggs and mixed canteen waste) was used as sole nutrient source in submerged cultures of P. aeruginosa BK25H. Stale bread was identified as the most suitable substrate to support phenazine biopigments production and bacterial growth. This was further increased in 5-liter fermenter when on average 5.2 mg L-1 of PYO and 4.4 mg L-1 of 1-HP were purified after 24 h batch cultivations from the fermentation medium consisting of homogenized stale bread in tap water. Purified biopigments showed moderate antimicrobial activity, and showed different toxicity profiles, with PYO not being toxic against Caenorhabditis elegans, a free-living soil nematode up to 300 µg mL-1 and 1-HP showing lethal effects at 75 µg mL-1. Therefore, stale bread waste stream with minimal pretreatment should be considered as suitable biorefinery feedstock, as it can support the production of valuable biopigments such as phenazines.

Molecular and biological characterization of pyocyanin from clinical and environmental Pseudomonas aeruginosa

BACKGROUND

Pyocyanin is a secondary metabolite secreted by P. aeruginosa. It is a redox-active blue/green phenazine pigment that has various beneficial applications. The present study aims at screening the production of pyocyanin among clinical and environmental P. aeruginosa isolates in Dakahlya governorate, Egypt. Thereafter, large-scale production, purification, structure elucidation, and assessment of the biological activity of the highest pyocyanin producers were targeted.

RESULTS

Pyocyanin from the highest clinical (PsC05) and environmental (PsE02) producers were subjected to large-scale production, followed by purification using silica gel column. Pyocyanin was characterized using TLC, UV-Vis, 1 H NMR, and FTIR spectroscopy to confirm its structure and purity. Purified pyocyanin showed remarkable antimicrobial efficacy against all tested food-borne pathogens, MDR/XDR clinically isolated bacteria and C. albicans. Furthermore, it showed a substantial effect on biofilm inhibition and eradication of pre-formed biofilm against strong biofilm producing bacterial pathogens. However, it had limited antibiofilm activity against C. albicans. Pyocyanin from PsC05 had higher antioxidant and radicals scavenging activity than that from PsE02 as determined by FRAP, DPPH, and ABTS assays. Likewise, pyocyanin from PsC05 was more active against tested cancer cell lines, especially human Breast Cancer (MCF-7) and Colorectal Carcinoma (HCT-116), than that from PsE02. More importantly, it showed minimal cytotoxicity to normal cells.

CONCLUSIONS

P. aeruginosa clinical and environmental isolates produce pyocyanin pigment in varying amounts. Pyocyanin exhibits substantial anti-bacterial, and anti-fungal activity; thus, enhancing its medical applicability. It could be used to inhibit and/or eradicate biofilm from the surfaces of medical devices which is a chief source of nosocomial infections. Its antioxidant along with cytotoxic activity against cancer cell lines, make it a promising contender for use as a substitute for synthetic agents in cancer treatment.

The two faces of pyocyanin - why and how to steer its production?

The ambiguous nature of pyocyanin was noted quite early after its discovery. This substance is a recognized Pseudomonas aeruginosa virulence factor that causes problems in cystic fibrosis, wound healing, and microbiologically induced corrosion. However, it can also be a potent chemical with potential use in a wide variety of technologies and applications, e.g. green energy production in microbial fuel cells, biocontrol in agriculture, therapy in medicine, or environmental protection. In this mini-review, we shortly describe the properties of pyocyanin, its role in the physiology of Pseudomonas and show the ever-growing interest in it. We also summarize the possible ways of modulating pyocyanin production. We underline different approaches of the researchers that aim either at lowering or increasing pyocyanin production by using different culturing methods, chemical additives, physical factors (e.g. electromagnetic field), or genetic engineering techniques. The review aims to present the ambiguous character of pyocyanin, underline its potential, and signalize the possible further research directions.

Rapid differentiation of antibiotic-susceptible and -resistant bacteria through mediated extracellular electron transfer

Conventional methods for testing antibiotic susceptibility rely on bacterial growth on agar plates (diffusion assays) or in liquid culture (microdilution assays). These time-consuming assays use population growth as a proxy for cellular respiration. Herein we propose to use mediated extracellular electron transfer as a rapid and direct method to classify antibiotic-susceptible and -resistant bacteria. We tested antibiotics with diverse mechanisms of action (ciprofloxacin, imipenem, oxacillin, or tobramycin) with four important nosocomial pathogens (Acinetobacter baumannii, Staphylococcus aureus, Escherichia coli, and Klebsiella pneumoniae) by adding the bacterial culture to a custom-designed electrochemical cell with a glassy-carbon electrode and growth media supplemented with a soluble electron transfer mediator, phenazine methosulfate (PMS). During cell respiration, liberated electrons reduce PMS, which is then oxidized on the electrode surface, and current is recorded. Using this novel approach, we were able to consistently classify strains as antibiotic-resistant or -susceptible in <90 min for methodology development and <150 min for blinded tests.

Biomarker imprinted magnetic core-shell nanoparticles for rapid, culture free detection of pathogenic bacteria

Rapid and selective detection of microorganisms in complex biological systems draws huge attention to address the rising issue of antimicrobial resistance. Diagnostics based on the identification of whole microorganisms are laborious, time-consuming and costly, thus alternative strategies for early clinical diagnosis include biomarker based microbial detection. This paper describes a low-cost, easy-to-use method for the detection of Pseudomonas aeruginosa infections by specifically identifying a biomarker pyocyanin, using surface-molecularly imprinted nanoparticles or "plastibodies". The selective nanopockets are created by templating pyocyanin onto 20 nm allyl-functionalized magnetic nanoparticles coated with a thin layer of the acrylamide-based polymer. This functional material with an impressive imprinting factor (IF) of 5 and a binding capacity of ∼2.5 mg g-1 of polymers can be directly applied for the detection of bacteria in complex biological samples based on the presence of pyocyanin. These MIPs are highly selective and sensitive to pyocyanin and can consistently bind with pyocyanin in repeated use. Finally, the facile and efficient capture of pyocyanin has versatile applications ranging from biomarker based culture free detection of P. aeruginosa to monitoring of the therapeutic regime, in addition to developing a new class of antibiotics.

Electrochemical Detection of Multianalyte Biomarkers in Wound Healing Efficacy

The targeted diagnosis and effective treatments of chronic skin wounds remain a healthcare burden, requiring the development of sensors for real-time monitoring of wound healing activity. Herein, we describe an adaptable method for the fabrication of carbon ultramicroelectrode arrays (CUAs) on flexible substrates with the goal to utilize this sensor as a wearable device to monitor chronic wounds. As a proof-of-concept study, we demonstrate the electrochemical detection of three electroactive analytes as biomarkers for wound healing state in simulated wound media on flexible CUAs. Notably, to follow pathogenic responses, we characterize analytical figures of merit for identification and monitoring of bacterial warfare toxin pyocyanin (PYO) secreted by the opportunistic human pathogen Pseudomonas aeruginosa. We also demonstrate the detection of uric acid (UA) and nitric oxide (NO^•), which are signaling molecules indicative of wound healing and immune responses, respectively. The electrochemically determined limit of detection (LOD) and linear dynamic range (LDR) for PYO, UA, and NO^• fall within the clinically relevant concentrations. Additionally, we demonstrate the successful use of flexible CUAs for quantitative, electrochemical detection of PYO from P. aeruginosa strains and cellular NO^• from immune cells in the wound matrix. Moreover, we present an electrochemical examination of the interaction between PYO and NO^•, providing insight into pathogen-host responses. Finally, the effects of the antimicrobial agent, silver (Ag⁺), on P. aeruginosa PYO production rates are investigated on flexible CUAs. Our electrochemical results show that the addition of Ag⁺ to P. aeruginosa in wound simulant decreases PYO secretion rates.

Oxidized cholesterol exacerbates toll-like receptor 4 expression and activity in the hearts of rats with myocardial infarction

Introduction: The present study examined the effects of high cholesterol and high oxidized-cholesterol diets on the myocardial expression of TLR4 and pro-inflammatory cytokine in rats.

Methods: Male Wistar rats were allocated into 6 groups and fed with a normal diet, cholesterol, and oxidized-cholesterol rich diets with or without isoproterenol-induced myocardial infarction. TLR4 and MyD 88 expression and levels tumor necrosis factor alpha (TNF-α) and interleukin 6 (IL-6) were measured in the heart and serum.

Results: Oxidized cholesterol-fed animals had higher serum levels of oxidized low-density lipoprotein (LDL) (263 ± 13 ng/dL) than the cholesterol-fed animals (98 ± 8 ng/dL; P < 0.001). A high level of oxidized-LDL caused fibrotic cell formation and enhanced neutrophil infiltration in the absence of MI. Both cholesterol and oxidized-cholesterol upregulated TLR4 mRNA expression and increased TNF-α and IL-6 production in the hearts of rats with MI. In rats fed with oxidized-cholesterol the serum and myocardial levels of TNF-α (653 ± 42 pg/mL, 1375 ± 121 pg/100 mg, respectively) were higher than MI group (358±24 pg/mL, P < 0.001 and 885 ± 56 pg/100 mg, P < 0.01). A significant correlation was seen between TLR4 expression and infarct size.

Conclusion: These findings suggest that cardiac TLR4 is preferentially upregulated by oxidized cholesterol in rats. Oxidized cholesterol may have a critical role in cardiac toxicity in the absence of pathological conditions.

Isolation and characterization of nutrient dependent pyocyanin from Pseudomonas aeruginosa and its dye and agrochemical properties

Pyocyanin is a blue green phenazine pigment produced in large quantities by active cultures of Pseudomonas aeruginosa, with advantageous applications in medicine, agriculture and for the environment. Hence, in the present study, a potent bacterium was isolated from agricultural soil and was identified morphologically and by 16S rRNA sequencing as P. aeruginosa (isolate KU_BIO2). When the influence of nutrient supplements in both King’s A and Nutrient media as amended was investigated, an enhanced pyocyanin production of 2.56 µg ml⁻¹ was achieved in King’s A medium amended with soya bean followed by 1.702 µg ml⁻¹ of pyocyanin from the nutrient medium amended with sweet potato. Purified pyocyanin was characterized by UV-Vis Spectrophotometer and Fourier-Transform Infrared spectroscopy (FTIR). Furthermore, Liquid Chromatography Mass Spectrum (LCMS) and Nuclear Magnetic Resonance (NMR) confirmed its mass value at 211 and as N-CH₃ protons resonating at 3.363 ppm as a singlet respectively. The isolated pyocyanin displayed remarkable dye property by inducing color change in cotton cloth from white to pink. Lastly, the antifungal activity of test pyocyanin showed inhibition of growth of rice blast fungus, Magnaporthe grisea and bacterial blight of rice, Xanthomonas oryzae at concentrations of 150 and 200 ppm, respectively. Thus, this investigation provides evidence for diverse actions of pyocyanin which are nutrient dependent and are capable of acting on a large scale, by utilizing microbes existing in agriculture wastes, and thus could be used as an alternative source in the making of natural textile dyes with strong durability and a broad spectrum of ecofriendly agrochemicals.

Sensing of Salivary Glucose Using Nano-Structured Biosensors

The anxiety and pain associated with frequent finger pricking has always been troublesome for diabetics measuring blood glucose (BG) in their daily lives. For this reason, a reliable glucose monitoring system that allows noninvasive measurements is highly desirable. Our main objective is to develop a biosensor that can detect low-level glucose in saliva (physiological range 0.5–20 mg/dL). Salivary glucose (SG) sensors were built using a layer-by-layer self-assembly of single-walled carbon nanotubes, chitosan, gold nanoparticles, and glucose oxidase onto a screen-printed platinum electrode. An electrochemical method was utilized for the quantitative detection of glucose in both buffer solution and saliva samples. A standard spectrophotometric technique was used as a reference method to validate the glucose content of each sample. The disposable glucose sensors have a detection limit of 0.41 mg/dL, a sensitivity of 0.24 μA·s·dL·mg⁻¹, a linear range of 0.5–20 mg/dL in buffer solution, and a response time of 30 s. A study of 10 healthy subjects was conducted, and SG levels between 1.1 to 10.1 mg/dL were successfully detected. The results revealed that the noninvasive SG monitoring could be an alternative for diabetes self-management at home. This paper is not intended to replace regular BG tests, but to study SG itself as an indicator for the quality of diabetes care. It can potentially help patients control and monitor their health conditions, enabling them to comply with prescribed treatments for diabetes.

Elucidation of Enzymatic Mechanism of Phenazine Biosynthetic Protein PhzF Using QM/MM and MD Simulations

The phenazine biosynthetic pathway is of considerable importance for the pharmaceutical industry. The pathway produces two products: phenazine-1,6-dicarboxylic acid and phenazine-1-carboxylic acid. PhzF is an isomerase that catalyzes trans-2,3-dihydro-3-hydroxyanthranilic acid isomerization and plays an essential role in the phenazine biosynthetic pathway. Although the PhzF crystal structure has been determined recently, an understanding of the detailed catalytic mechanism and the roles of key catalytic residues are still lacking. In this study, a computational strategy using a combination of molecular modeling, molecular dynamics simulations, and quantum mechanics/molecular mechanics simulations was used to elucidate these important issues. The Apo enzyme, enzyme-substrate complexes with negatively charged Glu45, enzyme-transition state analog inhibitor complexes with neutral Glu45, and enzyme-product complexes with negatively charged Glu45 structures were optimized and modeled using a 200 ns molecular dynamics simulation. Residues such as Gly73, His74, Asp208, Gly212, Ser213, and water, which play important roles in ligand binding and the isomerization reaction, were comprehensively investigated. Our results suggest that the Glu45 residue at the active site of PhzF acts as a general base/acid catalyst during proton transfer. This study provides new insights into the detailed catalytic mechanism of PhzF and the results have important implications for PhzF modification.

Pyocyanin induced in vitro oxidative damage and its toxicity level in human, fish and insect cell lines for its selective biological applications

Pyocyanin is a redox active phenazine pigment produced by Pseudomonas aeruginosa, with broad antibiotic activity having pharmacological, aquaculture, agriculture and industrial applications. In the present work cytotoxicity induced by pyocyanin is demonstrated in a human embryonic lung epithelial cell line (L-132), a rainbow trout gonad cell line (RTG-2) and a Spodoptera frugiperda pupal ovarian cell line (Sf9). For toxicity evaluation, cellular morphology, mitochondrial function (XTT), membrane leakage of lactate dehydrogenase, neutral red uptake, affinity of electrostatic binding of protein with sulforhodamine B dyes, glucose metabolism, and reactive oxygen species, were assessed. Results showed that higher pyocyanin concentration is required for eliciting cytotoxicity in L-132, RTG-2 and Sf9. The microscopic studies demonstrated that the cell lines exposed to pyocyanin at higher concentrations alone showed morphological changes such as clumping and necrosis. Among the three cell lines L-132 showed the highest response to pyocyanin than the others. In short, pyocyanin application at concentrations ranging from 5 to 10 mg l(-1) were not having any pathological effect in eukaryotic systems and can be used as drug of choice in aquaculture against vibrios in lieu of conventional antibiotics and as biocontrol agent against fungal and bacterial pathogens in agriculture. This is besides its industrial and pharmacological applications.

Pseudomonas aeruginosa can be detected in a polymicrobial competition model using impedance spectroscopy with a novel biosensor

Electrochemical Impedance Spectroscopy (EIS) is a powerful technique that can be used to elicit information about an electrode interface. In this article, we highlight six principal processes by which the presence of microorganisms can affect impedance and show how one of these--the production of electroactive metabolites--changes the impedance signature of culture media containing Pseudomonas aeruginosa. EIS, was used in conjunction with a low cost screen printed carbon sensor to detect the presence of P. aeruginosa when grown in isolation or as part of a polymicrobial infection with Staphylococcus aureus. By comparing the electrode to a starting measurement, we were able to identify an impedance signature characteristic of P. aeruginosa. Furthermore, we are able to show that one of the changes in the impedance signature is due to pyocyanin and associated phenazine compounds. The findings of this study indicate that it might be possible to develop a low cost sensor for the detection of P. aeruginosa in important point of care diagnostic applications. In particular, we suggest that a development of the device described here could be used in a polymicrobial clinical sample such as sputum from a CF patient to detect P. aeruginosa.

Production of rhamnolipid biosurfactants by Pseudomonas aeruginosa DS10-129 in a microfluidic bioreactor

A low-cost microBR (microbioreactor) made from PTFE [poly(tetrafluoroethylene)] was used to cultivate a model organism, Pseudomonas aeruginosa DS10-129. The progress of bioprocessing was monitored by comparing the growth of the organism in a microBR, a conventional bench scale bioreactor and a shake flask. Under the microBR conditions, the organism produced 23 mg/ml of pyocyanin that had antimicrobial effects against Bacillus subtilis, Staphylococcus aureus, Staphylococcus epidermidis, Pseudomonas teessidea and Pseudomonas clemancea. Furthermore, it produced a total of 106 microg/ml of effective biosurfactants consisting of dirhamnolipids (RL2) and monorhamnolipids (RL1). The biosurfactants reduced the surface tension of distilled water from 72 to 27.9 mN/m and emulsified kerosene by 71.30%. The pyocyanin and rhamnolipids were produced during the exponential and stationary phases of growth respectively. The results of the microBR were comparable to those obtained using conventional scale methods.

GidA posttranscriptionally regulates rhl quorum sensing in Pseudomonas aeruginosa

The opportunistic pathogen Pseudomonas aeruginosa utilizes two interconnected acyl-homoserine lactone quorum-sensing (acyl-HSL QS) systems, LasRI and RhlRI, to regulate the expression of hundreds of genes. The QS circuitry itself is integrated into a complex network of regulation by other factors. However, our understanding of this network is still unlikely to be complete, as a comprehensive, saturating approach to identifying regulatory components has never been attempted. Here, we utilized a nonredundant P. aeruginosa PA14 transposon library to identify additional genes that regulate QS at the level of LasRI/RhlRI. We initially screened all 5,459 mutants for loss of function in one QS-controlled trait (skim milk proteolysis) and then rescreened attenuated candidates for defects in other QS phenotypes (LasA protease, rhamnolipid, and pyocyanin production) to exclude mutants defective in functions other than QS. We identified several known and novel genes, but only two novel genes, gidA and pcnB, affected all of the traits assayed. We characterized gidA, which exhibited the most striking QS phenotypes, further. This gene is predicted to encode a conserved flavin adenine dinucleotide-binding protein involved in tRNA modification. Inactivation of the gene primarily affected rhlR-dependent QS phenotypes such as LasA, pyocyanin, and rhamnolipid production. GidA affected RhlR protein but not transcript levels and also had no impact on LasR and acyl-HSL production. Overexpression of rhlR in a gidA mutant partially restored QS-dependent phenotypes. Taken together, these results indicate that GidA selectively controls QS gene expression posttranscriptionally via RhlR-dependent and -independent pathways.