Detection and differentiation of bacteria by electrical bioimpedance spectroscopy

Nitroaromatic Compounds Dictate Electrochemical Properties of Escherichia coli by Manipulating the Cellular Membrane

Nitroaromatic compounds (NACs) are generally used as starting materials and/or generated as byproducts during the manufacturing of dyes, fertilizers, and therapeutic agents. Though NACs are beneficial when used appropriately, inadequate management, disposal, and application methods have led to their introduction to bacterial ecosystems where NACs act as mutagenic agents and may even contribute to antimicrobial resistance. Many of these bacterial systems are known to have different pathways to adapt to the presence of NACs such as altering the lipid composition of cellular membranes and intracellular degradation of NACs. In general, these processes require sophisticated techniques and skilled human resources to detect the changes by conventional characterization techniques. Hence, alternative methods are needed to investigate the short-term effects of NACs on bacterial cells with better precision. Herein, we report that bacterial cells adapt to the presence of NACs initially by incorporation in the cellular membrane, which can be predicted by further altered electrical and electrochemical properties of the cells. It was observed that the whole cell bacteria were negatively charged entities that could generate varying levels of surface charges on being incubated with model NACs of biomedical importance viz. niclosamide and p-nitrophenol. Such variations were also reflected in dye entrapment assays performed by using lipidic membranes collected from NAC-treated bacterial cells after the cells. Further studies with gel electrophoresis and differential pulse voltammetry revealed the significant alterations in electrochemical properties of NAC-incubated bacterial cells. Overall, results indicate that bacterial adaptation to NACs was found to be closely linked to variations in the electrochemical properties of the bacterial cells. These outcomes advance our understanding of influences imparted by NACs during bacterial infections and might facilitate the way for developing therapies to combat antibacterial resistance in the near future.

Fluorescent carbon dots for discriminating cell types: a review

Carbon dots (CDs) are quasi-spherical carbon nanoparticles with excellent photoluminescence, good biocompatibility, favorable photostability, and easily modifiable surfaces. CDs, serving as fluorescent probes, have emerged as an ideal tool for cellular differentiation owing to their outstanding luminescence performance and tunable surface properties. In this review, we summarize the recent research progress with CDs in the differentiation of cancer/normal cells, Gram-positive/Gram-negative bacteria, and live/dead cells, as well as the cellular differences used for differentiation. Additionally, we summarize the preparation methods, raw materials, and properties of the CDs used for cell discrimination. The differentiation mechanisms and the advantages or limitations of the differentiation methods are also introduced. Finally, we propose several research challenges in this field and future research directions that require extensive investigation. It is hoped that this review will help researchers in the design of new CDs as ideal fluorescent probes for realizing diverse cell differentiation applications.

A neoteric antibacterial ceria-silver nanozyme for abiotic surfaces

Community-associated and hospital-acquired infections caused by bacteria continue to yield major global challenges to human health. Bacterial contamination on abiotic surfaces is largely spread via high-touch surfaces and contemporary standard disinfection practices show limited efficacy, resulting in unsatisfactory therapeutic outcomes. New strategies that offer non-specific and broad protection are urgently needed. Herein, we report our novel ceria-silver nanozyme engineered at a molar ratio of 5:1 and with a higher trivalent (Ce3+) surface fraction. Our results reveal potent levels of surface catalytic activity on both wet and dry surfaces, with rapid, and complete eradication of Pseudomonas aeruginosa, Staphylococcus aureus, and methicillin resistant S. aureus, in both planktonic and biofilm form. Preferential electrostatic adherence of anionic bacteria to the cationic nanozyme surface leads to a catastrophic loss in both aerobic and anaerobic respiration, DNA damage, osmodysregulation, and finally, programmed bacterial lysis. Our data reveal several unique mechanistic avenues of synergistic ceria-Ag efficacy. Ag potentially increases the presence of Ce3+ sites at the ceria-Ag interface, thereby facilitating the formation of harmful H2O2, followed by likely permeation across the cell wall. Further, a weakened Ag-induced Ce-O bond may drive electron transfer from the Ec band to O2, thereby further facilitating the selective reduction of O2 toward H2O2 formation. Ag destabilizes the surface adsorption of molecular H2O2, potentially leading to higher concentrations of free H2O2 adjacent to bacteria. To this end, our results show that H2O2 and/or NO/NO2-/NO3- are the key liberators of antibacterial activity, with a limited immediate role being offered by nanozyme-induced ROS including O2•- and OH•, and likely other light-activated radicals. A mini-pilot proof-of-concept study performed in a pediatric dental clinic setting confirms residual, and continual nanozyme antibacterial efficacy over a 28-day period. These findings open a new approach to alleviate infections caused by bacteria for use on high-touch hard surfaces.

BacteSign: Building a Findable, Accessible, Interoperable, and Reusable (FAIR) Database for Universal Bacterial Identification

With the increasing incidence of diverse global bacterial outbreaks, it is important to build an immutable decentralized database that can capture regional changes in bacterial resistance with time. Herein, we investigate the use of a rapid 3D printed µbiochamber with a laser-ablated interdigitated electrode developed for biofilm analysis of Pseudomonas aeruginosa, Acinetobacter baumannii and Bacillus subtilis using electrochemical biological impedance spectroscopy (EBIS) across a 48 h spectrum, along with novel ladder-based minimum inhibitory concentration (MIC) stencil tests against oxytetracycline, kanamycin, penicillin G and streptomycin. Furthermore, in this investigation, a search query database has been built demonstrating the deterministic nature of the bacterial strains with real and imaginary impedance, phase, and capacitance, showing increased bacterial specification selectivity in the 9772.37 Hz range.

In situ detection and viability assessment of target microorganisms

Rapid detection and viability assessment of pathogenic microorganisms, without the need for pre-enrichment steps, is critical in clinical microbiology, food safety, environmental quality assessment, and biosecurity. We demonstrate a powerful analytical concept and the related platform that enable in situ rapid detection, separation, sensitive quantification, and viability assessment of targeted microorganisms (bacteria and fungi) from minimally processed samples. This is based on a novel integration of magneto-affine selection and electrical impedance assay. The entire process, from capture to measurement, is executed using controlled magnetic fields to manipulate magnetic particles (MPs)-microbe affinity-based clusters, in a compact, portable setup equipped with cost-effective, single-use chambers. The system was tested for non-invasive in situ evaluation of model bacteria (Escherichia coli) and fungi (Saccharomyces cerevisiae) within clinically relevant concentration ranges, and it was demonstrated amenable for both commercial and custom MPs, proving its high versatility. The high capture efficiency, the ability to provide analytic results within 30 min directly from unprocessed samples (buffer and synthetic urine), and the high sensitivity in distinguishing live and dead cells in dynamic exposures represent significant advancements over existing assays and recommend the system as a screening tool for pathogen presence and antimicrobial susceptibility in clinical and environmental samples.

DEPIS: A combined dielectrophoresis and impedance spectroscopy platform for rapid cell viability and antimicrobial susceptibility analysis

Antimicrobial resistance (AMR) is caused by inappropriate or excessive antibiotic consumption. Early diagnosis of bacterial infections can greatly curb empirical treatment and thus AMR. Current diagnostic procedures are time-consuming as they rely on gene amplification and cell culture techniques that are inherently limited by the doubling rate of the involved species. Further, biochemical methods for species identification and antibiotic susceptibility testing for drug/dose effectiveness take several days and are non-scalable. We report a real-time, label-free approach called DEPIS that combines dielectrophoresis (DEP) for bacterial enrichment and impedance spectroscopy (IS) for cell viability analysis under 60 min. Target bacteria are captured on interdigitated electrodes using DEP (30 min) and their antibiotic-induced stress response is measured using IS (another 30 min). This principle is used to generate minimum bactericidal concentration (MBC) plots by measuring impedance change due to ionic release by dying bacteria in a low conductivity buffer. The results are rapid since they rely on cell death rather than cell growth which is an intrinsically slower process. The results are also highly specific and work across all bactericidal antibiotics studied, irrespective of their cellular target or drug action mechanism. More importantly, preliminary results with clinical isolates show that methicillin-susceptible Staphylococcus aureus (MSSA) can easily be differentiated from methicillin-resistant S. aureus (MRSA) under 1 h. This rapid cell analyses approach can aid in faster diagnosis of bacterial infections and benefit the clinical decision-making process for antibiotic treatment, addressing the critical issue of AMR.