Question

You must perform 3 growth curves of Staphylococcus aureus in the presence of 3 different antibiotics at 37º C. Each curve must be started by inoculating 2.4 x 107 cells of this bacterium and performed in a volume of 400 ml of fresh medium. If the absorbance value at 600nm corresponding to 2.4 x 107 cells is 0.030, how much volume (mL) of a previously grown culture with an absorbance of 0.562 should add as inoculum to each system? (present your calculations)

Answer 1

From the question, we have focused on these points- 1. Inoculum of 2.4x107 cells have been dissolved in 400ml fresh medium (we name it Solution 2) 2. Solution 2 gives OD value of 0.562 at 600nm; Let us assume that we have used 1ml cuvette to measure the OD using spectrophotometer 3. Previously grown culture (we name Solution 1) gives OD of 0.562 at 600nm

- 400 ml 1 ml solution 2 solution 2 has 2.4x107 cells has 2.4x107 = 60,000 cells 400 o.D 0.030 Using a Iml cuvette, we get OD 0.030 Bi 60 OID 60,000 cells 60,000 x0.562 1124000 cells /ml 0.030 0.562 ng = SOLUTION 1

aml (solution 1) gives o.D of 0.562 which has 1124000 cells /ml for an inoculum of 2.4x107 cells, 1124000 me 1 x2.4 x107 i. 2.4x107 cells y 1124000 [21-35 ml