12/21/2023 0 Comments Best macro lens for iphone x![]() ![]() ![]() By measuring the position of a few colonies in the cone and utilizing the derived probability function, the total number of colonies in the entire cone can be computed with high precision. Analytically, we find this probability to be proportional to the squared perpendicular distance of the colony to the cone tip. Intuitively, the probability of a colony forming at the tip of the cone is less than near the base due to differences in the cross-sectional area. GVA calculates the CFUs in a sample on the basis of the axial position of embedded colonies that form in a cone. Here we developed a viability assay called the geometric viability assay (GVA). However, none of these approaches combines the simplicity, low cost, dynamic range and versatility of simply diluting cells and then growing drops on solid media as first proposed in ref. The most commercially successful alternative to the CFU assay is the spiral plater method 16 which deposits the sample in an Archimedes spiral on a solid medium plate. Previous approaches to increase the scale of viability measurements include (1) increasing the speed with robotic liquid handling and imaging 1, 4, 13, (2) decreasing the amount of pipetting by using viability stains 14 or microfluidics 15 or (3) using cell growth to estimate the initial number of viable cells post-treatment 3. However, measuring viability across numerous conditions using the CFU assay is time- and resource-intensive while generating a substantial amount of plastic waste 4, 12. Viability measurements are critical in numerous contexts spanning food safety 7, functional genomics 8, 9, 10 and drug discovery against persister cells 2, 11. The CFU assay combines simplicity with readily available reagents to achieve an enormous dynamic range, commonly measuring between 1 and 100,000,000 viable cells in a sample. The colony-forming unit (CFU) assay is the gold standard for enumerating viable cells in microbiology labs around the world 1, 2, 3, 4, 5, 6. The ease and low cost of GVA evinces that it can replace existing viability assays and enable viability measurements at previously impractical scales. Laborious CFU experiments such as checkerboard assays, treatment time-courses and drug screens against slow-growing cells are simplified by GVA. GVA is compatible with Gram-positive and Gram-negative planktonic bacteria ( Escherichia coli, Pseudomonas aeruginosa and Bacillus subtilis), biofilms and fungi ( Saccharomyces cerevisiae). GVA computes a sample’s viable cell count on the basis of the distribution of embedded colonies growing inside a pipette tip. Here we describe the geometric viability assay (GVA) that replicates CFU measurements over 6 orders of magnitude while reducing over 10-fold the time and consumables required. The colony-forming unit (CFU) assay has remained the gold standard to measure viability across disciplines, but it is time-intensive and resource-consuming. ![]() Counting viable cells is a universal practice in microbiology. ![]()
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