Nanograss sensor for selective detection of Pseudomonas aeruginosa by pyocyanin identification in airway samples

Sensing the invisible: Ultra-low-level electrochemical detection of the microbe (Pseudomonas aeruginosa) on cobalt ferrite-doped silver nanocomposite (CoFe2O4/AgNPs) surfaces

This study introduces an efficient electrochemical method for rapidly identifying the pathogen Pseudomonas aeruginosa (P. aeruginosa), which poses threats to individuals with compromised immune systems and cystic fibrosis. Unlike conventional techniques such as polymerase chain reaction, which fails to detect modifications in the resistant properties of microbes due to environmental stress, our proposed electrochemical approach offers a promising alternative. The characterisation analyses, involving microscopic and spectroscopic methods, reveal that the nanocomposite exhibits a crystalline structure, specific atomic vibrational patterns, a cubic surface shape, and distinct elemental compositions. This sensor demonstrates exceptional detection capabilities for P. aeruginosa, with a linear range of 1-23 CFU mL-1 and a low detection limit of 4.0 × 10-3 CFU mL-1. This research not only explores novel electrochemical techniques and the CoFe2O4/AgNPs nanocomposite but also their practical implications in food science, highlighting their relevance across various food samples, water, and soil.

A paper biosensor for overcoming matrix effects interfering with the detection of sputum pyocyanin with competitive immunoassays

Detecting sputum pyocyanin (PYO) with a competitive immunoassay is a promising approach for diagnosing Pseudomonas aeruginosa respiratory infections. However, it is not possible to perform a negative control to evaluate matrix-effects in competitive immunoassays, and the highly complex sputum matrix often interferes with target detection. Here, we show that these issues are alleviated by performing competitive immunoassays with a paper biosensor. The biosensing platform consists of a paper reservoir, which contains antibody-coated gold nanoparticles, and a substrate containing a competing recognition element, which is a piece of paper modified with an albumin-antigen conjugate. Detection of PYO with a limit of detection of 4.7·10-3 µM and a dynamic range between 4.7·10-1 µM and 47.6 µM is accomplished by adding the sample to the substrate with the competing element and pressing the reservoir against it for 5 min. When tested with patient samples, the biosensor was able to qualitatively differentiate spiked from non-spiked samples, whereas ELISA did not show a clear cut-off between them. Furthermore, the relative standard deviation was lower when determining sputum with the paper-based biosensor. These features, along with a mild liquefaction step that circumvents the use of harsh chemicals or instruments, make our biosensor a good candidate for diagnosing Pseudomonas infections at the bedside through the detection of sputum PYO.

Aptasensor for the Detection of Moraxella catarrhalis Adhesin UspA2

Innovative point-of-care (PoC) diagnostic platforms are desirable to surpass the deficiencies of conventional laboratory diagnostic methods for bacterial infections and to tackle the growing antimicrobial resistance crisis. In this study, a workflow was implemented, comprising the identification of new aptamers with high affinity for the ubiquitous surface protein A2 (UspA2) of the bacterial pathogen Moraxella catarrhalis and the development of an electrochemical biosensor functionalized with the best-performing aptamer as a bioreceptor to detect UspA2. After cell-systematic evolution of ligands by exponential enrichment (cell-SELEX) was performed, next-generation sequencing was used to sequence the final aptamer pool. The most frequent aptamer sequences were further evaluated using bioinformatic tools. The two most promising aptamer candidates, Apt1 and Apt1_RC (Apt1 reverse complement), had K_d values of 214.4 and 3.4 nM, respectively. Finally, a simple and label-free electrochemical biosensor was functionalized with Apt1_RC. The aptasensor surface modifications were confirmed by impedance spectroscopy and cyclic voltammetry. The ability to detect UspA2 was evaluated by square wave voltammetry, exhibiting a linear detection range of 4.0 × 10⁴-7.0 × 10⁷ CFU mL^-1, a square correlation coefficient superior to 0.99 and a limit of detection of 4.0 × 10⁴ CFU mL^-1 at pH 5.0. The workflow described has the potential to be part of a sensitive PoC diagnostic platform to detect and quantify M. catarrhalis from biological samples.

Solution-Based Ultra-Sensitive Surface-Enhanced Raman Scattering Detection of the Toxin Bacterial Biomarker Pyocyanin in Biological Fluids Using Sharp-Branched Gold Nanostars

There is a critical need for sensitive rapid point-of-care detection of bacterial infection biomarkers in complex biological fluids with minimal sample preparation, which can improve early-stage diagnosis and prevent several bacterial infections and fatal diseases. A solution-based surface-enhanced Raman scattering (SERS) detection platform has long been sought after for low cost, rapid, and on-site detection of analyte molecules, but current methods still exhibit poor sensitivity. In this study, we have tuned the morphology of the surfactant-free gold nanostars (GNSs) to achieve sharp protruding spikes for maximum SERS enhancement. We have controlled the GNS spike morphologies and optimized SERS performance in the solution phase using para-mercaptobenzoic acid as an SERS probe. To illustrate the potential for point-of-care applications, we have utilized a portable Raman instrument for measurements. For pathogenic agent sensing applications, we demonstrated rapid and sensitive detection of the toxin biomarker pyocyanin (PYO) used as the bacterial biomarker model system. Pyocyanin is a toxic compound produced and secreted by the common water-borne Gram-negative bacterium Pseudomonas aeruginosa, a pathogen known for advanced antibiotic resistance and association with serious diseases such as ventilator-associated pneumonia and cystic fibrosis. The limit of detection (LOD) achieved for PYO was 0.05 nM using sharp branched GNSs. Furthermore, as a proof of strategy, this SERS detection of PYO was performed directly in drinking water, human saliva, and human urine without any sample treatment pre-purification, achieving an LOD of 0.05 nM for drinking water and 0.4 nM for human saliva and urine. This work provides a proof-of-principle demonstration for the high sensitivity detection of the bacterial toxin biomarker with minimal sample preparation: the "mix and detect" detection of the GNS platform is simple, robust, and rapid, taking only 1-2 min for each measurement. Overall, our SERS detection platform shows great potential for point-of-need sensing and point-of-care diagnostics in biological fluids.

Label-free multimodal imaging of infected Galleria mellonella larvae

Non-linear imaging modalities have enabled us to obtain unique morpho-chemical insights into the tissue architecture of various biological model organisms in a label-free manner. However, these imaging techniques have so far not been applied to analyze the Galleria mellonella infection model. This study utilizes for the first time the strength of multimodal imaging techniques to explore infection-related changes in the Galleria mellonella larvae due to massive E. faecalis bacterial infection. Multimodal imaging techniques such as fluorescent lifetime imaging (FLIM), coherent anti-Stokes Raman scattering (CARS), two-photon excited fluorescence (TPEF), and second harmonic generation (SHG) were implemented in conjunction with histological HE images to analyze infection-associated tissue damage. The changes in the larvae in response to the infection, such as melanization, vacuolization, nodule formation, and hemocyte infiltration as a defense mechanism of insects against microbial pathogens, were visualized after Enterococcus faecalis was administered. Furthermore, multimodal imaging served for the analysis of implant-associated biofilm infections by visualizing biofilm adherence on medical stainless steel and ePTFE implants within the larvae. Our results suggest that infection-related changes as well as the integrity of the tissue of G. mellonella larvae can be studied with high morphological and chemical contrast in a label-free manner.

Electrochemical Sensors Based on MoSx -Functionalized Laser-Induced Graphene for Real-Time Monitoring of Phenazines Produced by Pseudomonas aeruginosa

Pseudomonas aeruginosa (P. aeruginosa) is an opportunistic pathogen causing infections in blood and implanted devices. Traditional identification methods take more than 24 h to produce results. Molecular biology methods expedite detection, but require an advanced skill set. To address these challenges, this work demonstrates functionalization of laser-induced graphene (LIG) for developing flexible electrochemical sensors for P. aeruginosa based on phenazines. Electrodeposition as a facile approach is used to functionalize LIG with molybdenum polysulfide (MoSx ). The sensor's limit of detection (LOD), sensitivity, and specificity are determined in broth, agar, and wound simulating medium (WSM). Control experiments with Escherichia coli, which does not produce phenazines, demonstrate specificity of sensors for P. aeruginosa. The LOD for pyocyanin (PYO) and phenazine-1-carboxylic acid (PCA) is 0.19 × 10-6  and 1.2 × 10-6  m, respectively. Furthermore, the highly stable sensors enable real-time monitoring of P. aeruginosa biofilms over several days. Comparing square wave voltammetry data over time shows time-dependent generation of phenazines. In particular, two configurations-"Normal" and "Flipped"-are studied, showing that the phenazines time dynamics vary depending on how cells interact with sensors. The reported results demonstrate the potential of the developed sensors for integration with wound dressings for early diagnosis of P. aeruginosa infection.

Evaluation of Blood-Brain-Barrier Permeability, Neurotoxicity, and Potential Cognitive Impairment by Pseudomonas aeruginosa’s Virulence Factor Pyocyanin

Pyocyanin (PCN) is a redox-active secondary metabolite produced by Pseudomonas aeruginosa as its primary virulence factor. Several studies have reported the cytotoxic potential of PCN and its role during infection establishment and progression. Considering its ability to diffuse through biological membranes, it is hypothesized that PCN can gain entry into the brain and induce oxidative stress across the blood-brain barrier (BBB), ultimately contributing towards reactive oxygen species (ROS) mediated neurodegeneration. Potential roles of PCN in the central nervous system (CNS) have never been evaluated, hence the study aimed to evaluate PCN's probable penetration into CNS through blood-brain barrier (BBB) using both in silico and in vivo (Balb/c mice) approaches and the impact of ROS generation via commonly used tests: Morris water maze test, novel object recognition, elevated plus maze test, and tail suspension test. Furthermore, evidence for ROS generation in the brain was assessed using glutathione S-transferase assay. PCN demonstrated BBB permeability albeit in minute quantities. A significant hike was observed in ROS generation (P < 0.0001) along with changes in behavior indicating PCN permeability across BBB and potentially affecting cognitive functions. This is the first study exploring the potential role of PCN in influencing the cognitive functions of test animals.

Modern Analytical Techniques for Detection of Bacteria in Surface and Wastewaters

Contamination of surface waters with pathogens as well as all diseases associated with such events are a significant concern worldwide. In recent decades, there has been a growing interest in developing analytical methods with good performance for the detection of this category of contaminants. The most important analytical methods applied for the determination of bacteria in waters are traditional ones (such as bacterial culturing methods, enzyme-linked immunoassay, polymerase chain reaction, and loop-mediated isothermal amplification) and advanced alternative methods (such as spectrometry, chromatography, capillary electrophoresis, surface-enhanced Raman scattering, and magnetic field-assisted and hyphenated techniques). In addition, optical and electrochemical sensors have gained much attention as essential alternatives for the conventional detection of bacteria. The large number of available methods have been materialized by many publications in this field aimed to ensure the control of water quality in water resources. This study represents a critical synthesis of the literature regarding the latest analytical methods covering comparative aspects of pathogen contamination of water resources. All these aspects are presented as representative examples, focusing on two important bacteria with essential implications on the health of the population, namely Pseudomonas aeruginosa and Escherichia coli.

Gold nanoparticle-based immunochromatographic assay for detection Pseudomonas aeruginosa in water and food samples

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An ICA was developed for P. aeruginosa detection.

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The ICA strip showed a limit of detection of 2.41 × 10⁴ CFU/mL.

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The ICA could be applied to detect P. aeruginosa in water and food samples.

Pseudomonas aeruginosa (P. aeruginosa) is the common infection-causing bacterial pathogen. Conventional methods for the detection of P. aeruginosa are time-consuming, and therefore, a more rapid analytical method is required. Here, monoclonal antibodies (Mabs) against P. aeruginosa (CICC 10419) were prepared and based on paired Mabs, an immunochromatographic assay (ICA) was developed. The ICA strip showed a limit of detection of 2.41 × 10⁴ CFU/mL and the linear range of detection was 3.13 × 10⁴-1.0 × 10⁶ CFU/mL. No cross-reactivity was observed when other common Gram-negative and Gram-positive bacteria were used. The analytical performance of the ICA strip indicated that the developed ICA had good specificity and stability. Moreover, the feasibility of the ICA strip was verified by detecting P. aeruginosa (CICC 10419) in spiked water and food samples. The ICA strip could detect samples contaminated with a low-level of P. aeruginosa (CICC 10419) after 8 h enrichment.

Changes in toxin production of environmental Pseudomonas aeruginosa isolates exposed to sub-inhibitory concentrations of three common antibiotics

Pseudomonas aeruginosa is an environmental pathogen that can cause severe infections in immunocompromised patients. P. aeruginosa infections are typically treated with multiple antibiotics including tobramycin, ciprofloxacin, and meropenem. However, antibiotics do not always entirely clear the bacteria from the infection site, where they may remain virulent. This is because the effective antibiotic concentration and diffusion in vitro may differ from the in vivo environment in patients. Therefore, it is important to understand the effect of non-lethal sub-inhibitory antibiotic concentrations on bacterial phenotype. Here, we investigate if sub-inhibitory antimicrobial concentrations cause alterations in bacterial virulence factor production using pyocyanin as a model toxin. We tested this using the aforementioned antibiotics on 10 environmental P. aeruginosa strains. Using on-the-spot electrochemical screening, we were able to directly quantify changes in production of pyocyanin in a measurement time of 17 seconds. Upon selecting 3 representative strains to further test the effects of sub-minimum inhibitory concentration (MICs), we found that pyocyanin production changed significantly when the bacteria were exposed to 10-fold MIC of the 3 antibiotics tested, and this was strain specific. A series of biologically relevant measured pyocyanin concentrations were also used to assess the effects of increased virulence on a culture of epithelial cells. We found a decreased viability of the epithelial cells when incubated with biologically relevant pyocyanin concentrations. This suggests that the antibiotic-induced virulence also is a value worth being enclosed in regular testing of pathogens.

How Bacterial Adaptation to Cystic Fibrosis Environment Shapes Interactions Between Pseudomonas aeruginosa and Staphylococcus aureus

Pseudomonas aeruginosa and Staphylococcus aureus are the two most prevalent bacteria species in the lungs of cystic fibrosis (CF) patients and are associated with poor clinical outcomes. Co-infection by the two species is a frequent situation that promotes their interaction. The ability of P. aeruginosa to outperform S. aureus has been widely described, and this competitive interaction was, for a long time, the only one considered. More recently, several studies have described that the two species are able to coexist. This change in relationship is linked to the evolution of bacterial strains in the lungs. This review attempts to decipher how bacterial adaptation to the CF environment can induce a change in the type of interaction and promote coexisting interaction between P. aeruginosa and S. aureus. The impact of coexistence on the establishment and maintenance of a chronic infection will also be presented, by considering the latest research on the subject.

Pathogen detection with electrochemical biosensors: Advantages, challenges and future perspectives

Detection of pathogens, e.g., bacteria and viruses, is still a big challenge in analytical medicine due to their vast number and variety. Developing strategies for rapid, inexpensive, specific, and sensitive detection of the pathogens using nanomaterials, integrating with microfluidics devices, amplification methods, or even combining these strategies have received significant attention. Especially, after the health-threatening COVID-19 outbreak, rapid and sensitive detection of pathogens became very critical. Detection of pathogens could be realized with electrochemical, optical, mass sensitive, or thermal methods. Among them, electrochemical methods are very promising by bringing different advantages, i.e., they exhibit more versatile detection schemes and real-time quantification as well as label-free measurements, which provides a broader application perspective. In this review, we discuss the recent advances for the detection of bacteria and viruses using electrochemical biosensors. Moreover, electrochemical biosensors for pathogen detection were broadly reviewed in terms of analyte, bio-recognition and transduction elements. Different fabrication techniques, detection principles, and applications of various pathogens with the electrochemical biosensors were also discussed.

Electrochemical Detection of Pyocyanin as a Biomarker for Pseudomonas aeruginosa: A Focused Review

Pseudomonas aeruginosa (PA) is a pathogen that is recognized for its advanced antibiotic resistance and its association with serious diseases such as ventilator-associated pneumonia and cystic fibrosis. The ability to rapidly detect the presence of pathogenic bacteria in patient samples is crucial for the immediate eradication of the infection. Pyocyanin is one of PA’s virulence factors used to establish infections. Pyocyanin promotes virulence by interfering in numerous cellular functions in host cells due to its redox-activity. Fortunately, the redox-active nature of pyocyanin makes it ideal for detection with simple electrochemical techniques without sample pretreatment or sensor functionalization. The previous decade has seen an increased interest in the electrochemical detection of pyocyanin either as an indicator of the presence of PA in samples or as a tool for quantifying PA virulence. This review provides the first overview of the advances in electrochemical detection of pyocyanin and offers an input regarding the future directions in the field.