Compact sensor for measuring nonlinear rotational dynamics of driven magnetic microspheres with biomedical applications

The nonlinear rotation response of a magnetic particle occurs when a driving magnetic field, used to rotate the magnetic particle, exceeds a critical frequency. This type of nonlinear rotational dynamic depends on several physical parameters, such as the rotational drag that the particle experiences. Shifts in this nonlinear rotational frequency offer a dynamic approach for the detection of bacteria, measurement of their growth, their response to chemical agents, and other biomedical applications. Therefore, we have developed a stand-alone prototype device that utilizes an elegant combination of a laser diode and photodiode to monitor particle rotation.     

Extraction and partial characterisation of antioxidant pigment produced by Chryseobacterium sp. kr6

Pigments synthesised by Chryseobacterium sp. kr6 growing on feather waste were extracted and characterised. The pigment extract was characterised by KOH test, UV–vis, CIELAB colour system, HPLC-DAD-MS, FTIR and its antioxidant capacity was evaluated. A positive bathochromic shift was observed when kr6 colonies or pigment extracts were subjected to alkaline solution (20% KOH) and a λ_max at 450 nm was detected for acetone extracts, although no typical fine structure of carotenoids was detected in the electomagnetic spectra. The HPLC profile of the extracted pigment showed that the compound has three different peaks with λ_max near 450 nm. The FTIR analysis shows some principal functional groups from a flexirubin-like molecule. The pigmented compound also presents antioxidant activity evaluated by the scavenging of the ABTS radical.     

A concise review of nanoscopic aspects of bioleaching bacteria–mineral interactions

Bioleaching is a technology for the recovery of metals from minerals by means of microorganisms, which accelerate the oxidative dissolution of the mineral by regenerating ferric ions. Bioleaching processes take place at the interface of bacteria, sulfide mineral and leaching solution. The fundamental forces between a bioleaching bacterium and mineral surface are central to understanding the intricacies of interfacial phenomena, such as bacterial adhesion or detachment from minerals and the mineral dissolution. This review focuses on the current state of knowledge in the colloidal aspect of bacteria–mineral interactions, particularly for bioleaching bacteria. Special consideration is given to the microscopic structure of bacterial cells and the atomic force microscopy technique used in the quantification of fundamental interaction forces at nanoscale.     

Preliminary Evaluation of Mixed Dyes for Fingerprinting Non-Fluorescent Bacteria

Abstract

A rapid scanning fluorometer is used to obtain fluorescence spectral data characteristic of bacteria which do not readily produce fluorescent pigments. The data is generated in the form of an array of fluorescence intensity as a function of multiple excitation and emission wavelengths. Fluorescence spectral properties are introduced into the bacterial specimen using multiple dye mixtures for staining. The characteristic fluorescent fingerprints are believed to occur by preferential adsorption and reaction of bacterial cellular components with the individual dyes of the mixture. The procedure is found to be rapid and reproducible for the bacteria examined.     

Direct Determination of Bacterial Cell Viability Using Carbon Nanotubes Modified Screen‐printed Electrodes

For the early detection of bacterial infection, there is a need for rapid, sensitive, and label‐free assays. Thus, in this study, nanostrucured microbial electrochemical platform is designed to monitor the viability and cell growth of S. aureus. Using multi‐walled carbon nanotube modified screen‐printed electrodes (MWCNTs/SPE), the cyclic voltammetric measurements showed only one irreversible oxidation peak at 600 mV vs Ag/AgCl that accounts for the viable and metabolically active bacterial cells. The assay was optimized and the secreted metabolites, in the extracellular matrix, were directly detected. The peak current showed a positive correlation with viable cell numbers ranging from OD_{600 nm} of 0.1 to 1.1, indicating that the activity of live cells can be quantified. Consequently, responses of viable and non‐viable cells of S. aureus to the effects of antibiotic and respiratory chain inhibitors were determined. Thus, the proposed nanostructure‐based bacterial sensor provides a reasonable and reliable way for real‐time monitoring of live‐dead cell functions, and antibacterial profiling.     

Comparative proteomic analysis of B. cenocepacia using two-dimensional liquid separations coupled with mass spectrometry

Burkholderia cenocepacia is an important respiratory pathogen in persons with cystic fibrosis. We compared the proteomes of clinical and environmental isolates of B. cenocepacia by using a 2D liquid separation method coupled with mass spectrometry. Proteome maps of four B. cenocepacia isolates were generated. In the first dimension, 5 mg of protein from each isolate was fractionated by chromatofocusing (CF) in the range of pH 4.0-7.0. In the second dimension, each CF fraction was separated by NPS-RP-HPLC. Results of the 2D liquid separation were visualized as 2D UV maps, which allowed direct comparison of proteomes with high resolution and reproducibility. From the proteomic comparison of the four isolates, 38 of 96 differentially abundant proteins were identified by peptide mass fingerprinting and MS/MS sequence analysis using a partially annotated B. cenocepacia protein database. Many of the identified proteins in the clinical isolates are involved in gene translation and bacterial virulence such as transmissibility, resistance, and quorum sensing.     

Paper-based chromatic toxicity bioassay by analysis of bacterial ferricyanide reduction

Water quality assessment requires a continuous and strict analysis of samples to guarantee compliance with established standards. Nowadays, the increasing number of pollutants and their synergistic effects lead to the development general toxicity bioassays capable to analyse water pollution as a whole. Current general toxicity methods, e.g. Microtox^®, rely on long operation protocols, the use of complex and expensive instrumentation and sample pre-treatment, which should be transported to the laboratory for analysis. These requirements delay sample analysis and hence, the response to avoid an environmental catastrophe. In an attempt to solve it, a fast (15 min) and low-cost toxicity bioassay based on the chromatic changes associated to bacterial ferricyanide reduction is here presented. E. coli cells (used as model bacteria) were stably trapped on low-cost paper matrices (cellulose-based paper discs, PDs) and remained viable for long times (1 month at −20 °C). Apart from bacterial carrier, paper matrices also acted as a fluidic element, allowing fluid management without the need of external pumps. Bioassay evaluation was performed using copper as model toxic agent. Chromatic changes associated to bacterial ferricyanide reduction were determined by three different transduction methods, i.e. (i) optical reflectometry (as reference method), (ii) image analysis and (iii) visual inspection. In all cases, bioassay results (in terms of half maximal effective concentrations, EC₅₀) were in agreement with already reported data, confirming the good performance of the bioassay. The validation of the bioassay was performed by analysis of real samples from natural sources, which were analysed and compared with a reference method (i.e. Microtox). Obtained results showed agreement for about 70% of toxic samples and 80% of non-toxic samples, which may validate the use of this simple and quick protocol in the determination of general toxicity. The minimum instrumentation requirements and the simplicity of the bioassay open the possibility of in-situ water toxicity assessment with a fast and low-cost protocol.     

Electropermeabilization responses in Gram-positive and Gram-negative bacteria

Effects of 3-kJ kg^?1 nanosecond pulsed electric fields (PEFs) on cellular permeabilization of Salmonella enterica and Staphylococcus aureus were observed. It was seen that bacterial responses depend on both the electrical pulse attribute and the cell plasma membrane structure. For traditional permeabilization, the responses involved the thickness of the peptidoglycan layer where a maximum of 2.5 log reduction in S. enterica population was achieved. Meanwhile, in the area of selective permeabilization, it showed insignificant reduction in both pathogens. Such inactivation mechanisms were described through the behavior of potential across plasma membrane and intracellular organelles by PSPICE simulations incorporating PEF-cell interaction model.     

Bacterial wetting agents working in colonization of bacteria on surface environments

Bacteria are very small and highly susceptible to the effects of intermolecular forces. Especially, bacteria living on solid-air interfaces are under a strong influence from the surface tension of water. During studies of bacteria which prefer to live on surfaces, we noted that some species of bacteria (e.g. Serratia marcescens) secrete large amounts of wetting agents (e.g. serrawettins). Therefore, we isolated mutants defective in the production of wetting agents and examined the physiological functions of these wetting agents by comparing the behavior of wild types and mutants on surface environments. In terms of accessibility to the water-repelling surfaces and spreading growth on solid media. mutants demonstrated inferior abilities in comparison with wild types. Thus, the ability of S. marcescens to form a giant fractal colony through nutrient-diffusion-limited growth processes was shown to be defective in the serrawettinless mutants. In the locomotion of flagellated bacteria on surfaces, the bacteria seem to overcome various restrictive intermolecular forces. In contrast to swimming in a liquid, a single bacterium alone was unable to translocate on a surface. By video-microscopic analyses, the cooperative multicellular behavior of bacteria was clearly demonstrated. The remarkable effects of wetting agents on such microbial swarming behavior on surfaces were also disclosed.