Niacin assay by monitoring changes in electrical conductance caused by microbial growth

A computerized Malthus 128 H Growth Analyser was used to determine the changes in conductance produced by growth of a niacin-dependent strain of Lactobacillus plantarum ATCC 8014 in different concentrations of niacin in the growth medium. Changes in conductance varied linearly with the niacin concentration in the range 5-50 ng/ml. The time required to complete a test is inversely related to the inoculum size, and results can be obtained after 6 h.     

Reproducibility of electrical conductance assay results for the detection of salmonella

No significant differences in electrical conductance parameters were observed when multiple portions of animal proteins were examined for salmonella on three Malthus 2000 analysers. No differences were noted in the isolation rates from conductance tubes on the three analysers. Results also indicates the importance of examining multiple samples due to uneven distribution of organisms in a dry matrix.     

Detection of salmonellas in animal feeds by electrical conductance

A comparison was made between standard culture methods and electrical conductance using a Malthus AT Microbiological Analyser for the examination of animal feeds for salmonella. Conductance testing with a selenite cystine/trimethylamine-N-oxide/dulcitol medium resulted in the detection of salmonellas in 49 of 55 known positive animal feeds, 13 of 19 spiked feed samples and 36 of 47 salmonella cultures. Testing with a lysine decarboxylase/glucose medium gave significantly better results (P less than 0.05) than with selenite cystine medium but five lysine decarboxylase negative strains of salmonella were undetected. When both media were used in parallel all salmonella positive samples were detected. No difference was found between preenrichment in buffered peptone water containing trimethylamine/mannitol and that containing lysine/glucose. Positive detection criteria for selenite medium of conductance peak at greater than or equal to 500 microsiemens (microS) with a rate of change of greater than or equal to 60 microS/h or 400-499 microS with a rate of change of greater than or equal to 40 microS/h and for lysine medium with a peak of greater than or equal to 100 microS have been established. The method offers savings in media and operating costs over conventional standard culture methods, provides results within 48 h and is recommended for statutory feed monitoring purposes.     

A rapid electrical method to detect microbial growth automatically

Summary A simple electrical method has been developed which allows the direct enumeration of microorganisms in various substrates without dilution. When this method was compared with a plate count method to enumerate E. coli a correlation coefficient of –0.988 was achieved.     

Factors influencing capacitance-based monitoring of microbial growth.

Microbiological impedance devices are routinely used by food and manufacturing industries, and public health agencies to measure microbiological growth. Factors contributing to increases and decreases in capacitance at the culture medium-electrode interface are poorly understood. To objectively evaluate the effects of temperature, cell density and medium conductivity on capacitance, admittance values from an impedance device were standardized; capacitance was converted to susceptance to allow unit comparisons with conductance. Although increases in temperature increased susceptance, a linear relationship could not be established between the change of susceptance with temperature and conductance of the medium. Cell density by itself had no measureable effect on susceptance or conductance, indicating that cells did not impede the movement of ions in the medium or around the electrode. In a low conductivity medium, increases in conductance by the addition of ions resulted in a concomitant increase of susceptance values. However, in a high conductivity medium, increases in conductance resulted in little or no increase of susceptance values because ions saturated the electrode surface. Susceptance increased when Escherichia coli, Pseudomonas aeruginosa, Alcaligenes faecalis and Staphylococcus aureus were grown in high conductivity media because protons produced by metabolically active bacteria balance more charge on the electrode than other ions. Increases in susceptance due to bacterial growth and metabolism in low conductivity media were attributed to both increases in protons and ionic metabolites. These results indicate that capacitance may provide a better measure of microbial growth and metabolism than conductance.     

Hypothetical model for monitoring microbial growth by using capacitance measurements--a minireview.

Microbiological impedance devices are used routinely by food and manufacturing industries, and public health agencies to measure microbial growth and metabolism. In this paper a hypothetical model explaining the effects of microbial growth and metabolism on capacitance at electrode-medium interfaces, that can be supported by fundamental theories and principles of electrochemistry, is presented. This model provides a framework to interpret changes in capacitance during microbial growth and metabolism and can be used to generate and test hypotheses on factors (i.e., temperature, microbial cell density, microbial growth and medium conductivity) contributing to increases or decreases in capacitance.     

A microprocessor-controlled photometer for monitoring microbial growth in multi-welled plates

Multi-welled microtitre plates provide a convenient means of handling 'large block' multifactorial experiments with microbial cultures. An inexpensive instrument, termed a 'Biophotometer', has been designed to monitor microbial growth in each well, by transmitted light measurements. Optional microcomputer control is employed to facilitate scanning of plates and data handling. A unique method for agitating cultures is incorporated into the system. Typical results are presented to illustrate the versatility of this system.     

A microprocessor-controlled photometer for monitoring microbial growth in multi-welled plates

Multi-welled microtitre plates provide a convenient means of handling 'large block' multifactorial experiments with microbial cultures. An inexpensive instrument, termed a 'Biophotometer', has been designed to monitor microbial growth in each well, by transmitted light measurements. Optional microcomputer control is employed to facilitate scanning of plates and data handling. A unique method for agitating cultures is incorporated into the system. Typical results are presented to illustrate the versatility of this system.     

Dynamic monitoring of changes in endothelial cell-substrate adhesiveness during leukocyte adhesion by microelectrical impedance assay

Adhesion of leukocytes to endothelial cells in inflammation processes leads to changes of endothelial cellsubstrate adhesiveness, and understanding of such changes will provide us with important information of inflammation processes. In this study, we used a noninvasive biosensor system referred to as real-time cell electronic sensor （RT-CES） system to monitor the changes in endothelial cell-substrate adhesiveness induced by human monoblastic cell line U937 cell adhesion in a dynamic and quantitative manner. This assay, which is based on cell-substrate impedance readout, is able to monitor transient changes in cell- substrate adhesiveness as a result of U937 cell adhesion. The U937 cell adhesion to endothelial cells was induced by lipopolysaccharide （LPS） in a dose-dependent manner. Although the number of adherent U937 cells to the endothelial cells was verified by a standard assay, the adhesiveness of endothelial cells after addition of U937 cells was monitored by the RT-CES system. Furthermore, focal adhesion kinase protein decrease and F-actin rearrangement in endothelial cells were observed after addition of U937 cells. Our results indicated that the adhesion of U937 cells to LPS-treated endothelial cells reduced the substrate, and such infiltration of leukocytes. the cell adhesiveness to reduction might facilitate     

Application of rapid enzyme assay techniques for monitoring of microbial water quality

Rapid enzyme assay techniques based on direct measurement of beta-d-galactosidase (GALase) or beta-d-glucuronidase (GLUase) activity without selective cultivation are used for rapid estimation of the level of coliform bacteria and Escherichia coli in water samples. Reported detection limits using fluorogenic substrates correspond to culturable target bacteria concentrations that can be appropriate within present guidelines for recreational waters. The rapidity, that is detection within one hour, compromises the specificity of the assay; enzyme activity contributions from other than target bacteria need to be considered, particularly at low levels of target bacteria. Enzyme activities are more persistent than the culturability of target bacteria to environmental and disinfection stress, thus water samples may express enzyme activities of both culturable and viable non-culturable cells.     

Structural changes in the muscle thin filament during contractions caused by single and double electrical pulses

In order to investigate the structural changes of the myofilaments involved in the phenomenon of summation in skeletal muscle contraction, we studied small-angle x-ray intensity changes during twitches of frog skeletal muscle elicited by either a single or a double stimulus at 16 °C. The separation of the pulses in the double-pulse stimulation was either 15 or 30 ms. The peak tension was more than doubled by the second stimulus. The equatorial (1,0) intensity, which decreased upon the first stimulus, further decreased with the second stimulus, indicating that more cross-bridges are formed. The meridional reflections from troponin at 1/38.5 and 1/19.2 nm^− 1 were affected only slightly by the second stimulus, showing that attachment of a small number of myosin heads to actin can make a cooperative structural change. In overstretched muscle, the intensity increase of the troponin reflection in response to the second stimulus was smaller than that to the first stimulus. These results show that the summation is not due to an increased Ca binding to troponin and further suggest a highly cooperative nature of the structural changes in the thin filament that are related to the regulation of contraction.     

Improved sandwich-hybridization assay for an electrical DNA-chip-based monitoring of bioprocess-relevant marker genes

Recently, it was shown that electrical DNA-chips in connection with a magnetic bead-based sandwich-hybridization assay can be a suitable alternative for the analysis of gene expression by monitoring the respective mRNA levels. In this study, we established an improved assay which allowed for a significantly shortened but sensitive detection of specific mRNAs. These improvements include the change to a solution-based sandwich-hybridization and the rearrangement of the used oligonucleotide probes. The introduction of a second labeled detection probe further increased the hybridization signals and, in turn, leads to a substantial time reduction of the detection protocol. The presented solution-based sandwich-hybridization protocol for the electrochemical detection of specific mRNAs requires about 60 min and the whole procedure, including sampling, cell disruption, and RNA isolation, approx. 80 min. The assay of this study was verified by nutrient-limited growth experiments and the analysis of selected starvation marker genes of the industrial host Bacillus licheniformis. The expression profiles determined with the electrical chip and the optimized protocol were, in most cases, comparable with the profiles determined by real-time RT-PCR measurements.     

An explosion caused by microbial hydrogen formation

Summary A gas phase explosion in a storage tower with semichemical pulp at a paper mill has possibly been caused by combustion of a mixture of hydrogen and air. The hydrogen was formed by microorganisms in the pulp. Ignition may be due to electric sparks in connection with an electric field in the mist above the pulp.     

Proton conductance caused by long-chain fatty acids in phospholipid bilayer membranes

Summary Mechanisms of proton conductance (G _H) were investigated in phospholipid bilayer membranes containing long-chain fatty acids (lauric, myristic, palmitic, oleic or phytanic). Membranes were formed from diphytanoyl phosphatidylcholine in decane plus chlorodecane (usually 30% vol/vol). Fatty acids were added either to the aqueous phase or to the membrane-forming solution. Proton conductance was calculated from the steadystate total conductance and the H⁺ diffusion potential produced by a transmembrane pH gradient. Fatty acids causedG _H to increase in proportion to the first power of the fatty acid concentration. TheG _H induced by fatty acids was inhibited by phloretin, low pH and serum albumin.G _H was increased by chlorodecane, and the voltage dependence ofG _H was superlinear. The results suggest that fatty acids act as simple (A^– type) proton carriers. The membrane: water partition coefficient (K _p ) and adsorption coefficient () were estimated by finding the membrane and aqueous fatty acid concentrations which gave identical values ofG _H. For palmitic and oleic acidsK _p was about 10⁵ and was about 10^–2 cm. The A^– translocation or flip-flop rate (k _a ) was estimated from the value ofG _H and the fatty acid concentration in the membrane, assuming that A^– translocation was the rate limiting step in H⁺ transport. Thek _A 's were about 10^–4 sec^–1, slower than classical weak-acid uncouplers by a factor of 10⁵. Although long-chain fatty acids are relatively inefficient H⁺ carriers, they may cause significant biological H⁺ conductance when present in the membrane at high concentrations, e.g., in ischemia, hypoxia, hormonally induced lipolysis, or certain hereditary disorders, e.g., Refsum's (phytanic acid storage) disease.     

Real-time monitoring of a microbial electrolysis cell using an electrical equivalent circuit model

Bioprocess and Biosystems Engineering - Efforts in developing microbial electrolysis cells (MECs) resulted in several novel approaches for wastewater treatment and bioelectrosynthesis....