You are asked to determine the concentration of a bacterial culture. You take 1.

Question

You are asked to determine the concentration of a bacterial culture. You take 1.0 mL of the culture and add it to 4.0 mL ofwater(Tube #1). You then take 1.0 mL from Tube #1 and add it to 14 mL of water (Tube #2). Finally, you take 1.0 mL from Tube #2 and add it to 19 mL ofwater (Tube #3). You then spread 0.20 mL from Tube #3 onto a nutrient agar plate and incubate the plate at 37.C. After 24 hours, you count 215 colonies on the plate. (2) A. By what factor has the original culture been diluted in Tube #1? (1 point) B. By what factor has the ORIGINAL culture been diluted in Tube #27(1 point) C. By what factor has the ORIGINAL culture been diluted in Tube #37 (1 point) D. What is the concentration of the original bacterial culture? Include proper units. (S points) Sec Pages 3 o 4 Words: 492 of 530 Print Layout View 100%

Explanation / Answer

A) The orginal culture has been diluted in 1:4 ratio in test tube 1.

B) The culture of test tube 2 has been diluted in a ratio of 1:56 from test tube 1.

C) The culture of test tube 3 has been diluted in a ratio of 1:1064 from test tube 2.

D) The concentration of bacterial cells in original culture is 1143800 bacterial cells per ml of culture volume. This is obtained from Cfu calculation. CFU = Number of colonies *dilution factor / volume of culture plate. So CFU = 215 * 1064 / 0.20 = 1143800 bacterial cells per ml of culture volume.

Related Questions

Navigate

• Browse (All)
• Browse Y
• Subjects

---

---

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.