Total yield is obtained by multiplying the DNA concentration by the final total purified sample volume.ĭNA yield (µg) = DNA concentration × total sample volume (ml) To ensure the numbers are useful, the A 260 reading should be within the instrument's linear range (generally 0.1–1.0).ĭNA concentration is estimated by measuring the absorbance at 260nm, adjusting the A 260 measurement for turbidity (measured by absorbance at 320nm), multiplying by the dilution factor, and using the relationship that an A 260 of 1.0 = 50µg/ml pure dsDNA.Ĭoncentration (µg/ml) = (A 260 reading – A 320 reading) × dilution factor × 50µg/ml Absorbance readings are performed at 260nm (A 260) where DNA absorbs light most strongly, and the number generated allows one to estimate the concentration of the solution. All that is needed for the absorbance method is a spectrophotometer equipped with a UV lamp, UV-transparent cuvettes (depending on the instrument) and a solution of purified DNA. Although it could be argued that fluorescence measurement is easier, absorbance measurement is simple, and requires commonly available laboratory equipment. that is DNase negative.The most common technique to determine DNA yield and purity is measurement of absorbance. Serratia marcescens (Serratia fonticola is the only Serratia sp. Decant the excess hydrochloric acid, then examine the box within 5 minutes against a dark background. AFTER INCUBATION: If the DNase medium does not contain a color indicator: Flood the dish with 1N hydrochloric acid and Let the dish stand for a few minutes to allow the reagent to adsorb.You will make a single line down the center of the box (if you are using 2 species of staphylococci, you can split the box in half and pass each organism down one side).◈ Principle : When toluidine blue O (TBO) is added, a complex forms with the DNA, which changes structure when the DNA is hydrolyzed, resulting in a bright pink color. marcescens from other members of the KES division: Klebsiella, Enterobacter, Serratia. "A" and "B" DNase test positive, "C" DNase test negativeĭescribed by Schreier, originally designed to easily and quickly differentiate S.
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