If the standards have low OD values this could be caused by adding the reagents in the wrong order. It is critical to add reagent A first, mix, and then add reagent B. The color reaction is time and temperature dependent. The 30 minute incubation time is for room temperature (25°C). If the temperature is lower, you have to incubate longer to obtain the same OD values.
We have not tested feces samples ourselves and are not aware of any publications using this kit with stool samples, but believe it should work: We would suggest homogenizing the feces sample in a neutral buffer (e.g. PBS), urease is water soluble and will dissolve. Depending on the consistence of the sample, I would suggest starting with a 10:1 ratio of buffer to sample and homogenize the sample, e.g. by sonication. Then filter the sample to remove all larger particulates. After that, if necessary, add a centrifugation step (5 min at 15,000 x g) to remove smaller particulates. Only clear supernatant should be used in the assay.
Use 0.5 g soil. Add 0.3 mL of 0.4mm glass beads, 500 µL of buffer. Vortex on high speed for 2 minutes, then centrifuge for 2 min at 12000 rpm, use 100 µL of the clear fluid and incubate with substrate at 37°C for 3 hours.
Joerger RD, et al (2020) Effect of sodium bisulfate amendments on bacterial populations in broiler litter. Poultry Science.;99(11):5560-5571. Assay: Urease in chicken litter.
Wei, T., et al (2020). Chinese yellow rice wine processing with reduced ethyl carbamate formation by deleting transcriptional regulator dal80p in saccharomyces cerevisiae. Molecules (Basel, Switzerland), 25(16). Assay: Urease in yeast cells.
Liu, Q. W., Liu, Q. Y., Li, J. Y., Wei, L., Ren, K. K., Zhang, X. C. & Xin, H. B. (2018). Therapeutic efficiency of human amniotic epithelial stem cell-derived functional hepatocyte-like cells in mice with acute hepatic failure. Stem cell research & therapy, 9(1), 321. Assay: Urease in human urine.
Wu, D (2015). Constitutive expression of the DUR1, 2 gene in an industrial yeast strain to minimize ethyl carbamate production during Chinese rice wine fermentation. FEMS Microbiology Letters 363(1): fnv214. Assay: Urease.
Zhang, T. et al (2015). Development of an Agrobacterium-mediated transformation system for the cold-adapted fungi Pseudogymnoascus destructans and P. pannorum. Fungal Genetics and Biology 81: 73-81. Assay: urease in fungus.
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