Prevention of hemoglobin interference on the formazan reaction

Potential Application of the WST-8-mPMS Assay for Rapid Viable Microorganism Detection

To ensure clean drinking water, viable pathogens in water must be rapidly and efficiently screened. The traditional culture or spread-plate process-the conventional standard for bacterial detection-is laborious, time-consuming, and unsuitable for rapid detection. Therefore, we developed a colorimetric assay for rapid microorganism detection using a metabolism-based approach. The reaction between a viable microorganism and the combination of 2-(2-methoxy-4-nitrophenyl)-3-(4-nitrophenyl)-5-(2,4-disulfophenyl)-2H-tetrazolium sodium salt (WST-8) and 1-methoxy-5-methylphenazinium methyl sulfate (mPMS) results in a color change. In combination with a microplate reader, WST-8-mPMS reactivity was leveraged to develop a colorimetric assay for the rapid detection of various bacteria. The detection limit of the WST-8-mPMS assay for both gram-negative and gram-positive bacteria was evaluated. This WST-8-mPMS assay can be used to perform colorimetrical semi-quantitative detection of various bacterial strains in buffers or culture media within 1 h without incubation before the reaction. The easy-to-use, robust, rapid, and sensitive nature of this novel assay demonstrates its potential for practical and medical use for microorganism detection.

Detection of Microorganisms in Body Fluids via MTT-PMS Assay

Early detection of microorganisms is essential for the management of infectious diseases. However, this is challenging, as traditional culture methods are labor-intensive and time-consuming. The 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide-phenazine methosulfate (MTT-PMS) assay has been used to evaluate the metabolic activity in live cells and can thus be used for detecting living microorganisms. With the addition of NaOH and Tris-EDTA, the same approach can be accelerated (within 15 min) and used for the quick detection of common bacterial pathogens. The assay results can be evaluated colorimetrically or semi-quantitatively. Here, the quick detection by MTT-PMS assay was further investigated. The assay had a detection limit of approximately 104 CFU/mL. In clinical evaluations, we used the MTT-PMS assay to detect clinical samples and bacteriuria (>105 CFU/mL). The negative predictive value of the MTT-PMS assay for determining bacteriuria was 79.59% but was 100% when the interference of abnormal blood was excluded. Thus, the MTT-PMS assay might be a potential "rule-out" tool for bacterial detection in clinical samples, at a cost of approximately USD 1 per test. Owing to its low cost, rapid results, and easy-to-use characteristics, the MTT-PMS assay may be a potential tool for microorganism detection.

A novel assay for triglycerides using glycerol dehydrogenase and a water-soluble formazan dye, WST-8

Background

The glycerol-3-phosphate (GPO)-peroxidase (POD) chromogenic method is one of the most widely used methods to assay triglycerides. However, it is well known that peroxidase is affected by reducing agents, and recently, it has been reported that some materials affect its activity. Moreover, there is a high possibility of non-specific reaction, as the method uses many enzymes. Against this background, we developed a simpler assay method for triglycerides without using peroxidase.

Methods

Triglycerides were hydrolysed to glycerol and fatty acids by lipoprotein lipase followed by the oxidation of glycerol to dihydroxyacetone with simultaneous production of NADH by glycerol dehydrogenase. To overcome incomplete conversion of glycerol to dihydroxyacetone by glycerol dehydrogenase at equilibrium, we added 2-(2-methoxy-4-nitrophenyl)-3–(4-nitrophenyl)-5–(2,4-disulfophenyl)-2 H-tetrazolium monosodium salt (WST-8) to the reaction mixture to remove NADH, allowing the reaction to complete while showing stoichiometric production of reduced WST-8.

Results

The reaction was linear up to 6.4 mmol/L. The mean intra-assay ( n = 20) and inter-assay ( n = 20) imprecision, as determined by replicate analysis of three pooled human serum samples with different triglyceride concentrations, were 1.1–2.3% and 1.1–1.5% coefficient of variation (%CV), respectively. No interference by 2.5 g/L haemoglobin, 65  μmol/L free bilirubin and 359  μmol/L conjugated bilirubin was observed. The equation obtained in comparison with that by the GPO-POD method including endogenous glycerol-eliminating step was: y = 1.0002x + 0.0395 mmol/L; r = 0.999; Sy/x = 0.049 mmol/L; n = 97.

Conclusion

Our method is an accurate, yet simpler and more sensitive for the quantitative analysis of triglycerides.

Hibernating little brown myotis (Myotis lucifugus) show variable immunological responses to white-nose syndrome

White-nose syndrome (WNS) is an emerging infectious disease devastating hibernating North American bat populations that is caused by the psychrophilic fungus Geomyces destructans. Previous histopathological analysis demonstrated little evidence of inflammatory responses in infected bats, however few studies have compared other aspects of immune function between WNS-affected and unaffected bats. We collected bats from confirmed WNS-affected and unaffected sites during the winter of 2008–2009 and compared estimates of their circulating levels of total leukocytes, total immunoglobulins, cytokines and total antioxidants. Bats from affected and unaffected sites did not differ in their total circulating immunoglobulin levels, but significantly higher leukocyte counts were observed in bats from affected sites and particularly in affected bats with elevated body temperatures (above 20°C). Bats from WNS-affected sites exhibited significantly lower antioxidant activity and levels of interleukin-4 (IL-4), a cytokine that induces T cell differentiation. Within affected sites only, bats exhibiting visible fungal infections had significantly lower antioxidant activity and levels of IL-4 compared to bats without visible fungal infections. Overall, bats hibernating in WNS-affected sites showed immunological changes that may be evident of attempted defense against G. destructans. Observed changes, specifically elevated circulating leukocytes, may also be related to the documented changes in thermoregulatory behaviors of affected bats (i.e. increased frequencies in arousal from torpor). Alterations in immune function may reflect expensive energetic costs associated with these processes and intrinsic qualities of the immunocapability of hibernating bats to clear fungal infections. Additionally, lowered antioxidant activity indicates a possible imbalance in the pro- versus antioxidant system, may reflect oxidative tissue damage, and should be investigated as a contributor to WNS-associated morbidity and mortality.