topic 3-Plate count Data,Bacterial Culture Concentration Quiz

A microbiologist plates 0.1 mL of a bacterial culture diluted by a factor of 100. After incubation, 283 colonies are observed. What is the concentration of bacteria in the original culture (CFU/mL)?

• 110,550

• 283,000

• 412,822

• 175,109

Answer explanation

To find the original concentration, multiply the number of colonies (283) by the dilution factor (100) and the volume plated (10 mL). Thus, 283 x 1000 = 283,000 CFU/mL, confirming the correct answer is 283,000.

A microbiologist plates 1.0 mL of a bacterial culture diluted by a factor of 10,000. After incubation, 36 colonies are observed. What is the concentration of bacteria in the original culture (CFU/mL)?

• 118,191

• 360,000

• 482,213

• 223,655

Answer explanation

To find the original concentration, multiply the number of colonies (36) by the dilution factor (10,000) and the volume plated (1 mL). Thus, 36 x 10,000 = 360,000 CFU/mL, making 360,000 the correct answer.

A microbiologist plates 0.5 mL of a bacterial culture diluted by a factor of 10,000. After incubation, 135 colonies are observed. What is the concentration of bacteria in the original culture (CFU/mL)?

• 1,791,978

• 3,579,489

• 2,700,000

• 667,846

Answer explanation

To find the original concentration, multiply the number of colonies (135) by the dilution factor (10,000) and divide by the volume plated (0.5 mL). This gives 135 x 10,000 / 0.5 = 2,700,000 CFU/mL.

A microbiologist plates 0.1 mL of a bacterial culture diluted by a factor of 10,000. After incubation, 292 colonies are observed. What is the concentration of bacteria in the original culture (CFU/mL)?

• 29,200,000

• 11,318,434

• 43,629,134

• 21,526,404

Answer explanation

To find the original concentration, multiply the number of colonies (292) by the dilution factor (10,000) and then divide by the volume plated (0.1 mL). This gives 292 x 10,000 / 0.1 = 29,200,000 CFU/mL.

A microbiologist plates 0.2 mL of a bacterial culture diluted by a factor of 10,000. After incubation, 30 colonies are observed. What is the concentration of bacteria in the original culture (CFU/mL)?

• 337,234

• 1,500,000

• 1,086,250

• 1,792,596

Answer explanation

To find the original concentration, multiply the number of colonies (30) by the dilution factor (10,000) and divide by the volume plated (0.2 mL). Thus, (30 x 10,000) / 0.2 = 1,500,000 CFU/mL.

A microbiologist plates 0.2 mL of a bacterial culture diluted by a factor of 100. After incubation, 68 colonies are observed. What is the concentration of bacteria in the original culture (CFU/mL)?

• 34,000

• 42,149

• 21,263

• 6,583

Answer explanation

To find the original concentration, multiply the number of colonies (68) by the dilution factor (100) and divide by the volume plated (0.2 mL). Thus, (68 * 100) / 0.2 = 34,000 CFU/mL, which is the correct answer.

A microbiologist plates 0.5 mL of a bacterial culture diluted by a factor of 1,000. After incubation, 288 colonies are observed. What is the concentration of bacteria in the original culture (CFU/mL)?

• 197,712

• 383,755

• 801,848

• 576,000

Answer explanation

To find the original concentration, multiply the number of colonies (288) by the dilution factor (1000) and divide by the volume plated (0.5 mL). Thus, (288 x 1000) / 0.5 = 576,000 CFU/mL.

A microbiologist plates 0.2 mL of a bacterial culture diluted by a factor of 10,000. After incubation, 256 colonies are observed. What is the concentration of bacteria in the original culture (CFU/mL)?

• 1,425,689

• 18,450,032

• 12,800,000

• 6,842,993

Answer explanation

To find the original concentration, multiply the number of colonies (256) by the dilution factor (10,000) and divide by the volume plated (0.2 mL). This gives 256 x 10,000 / 0.2 = 12,800,000 CFU/mL.

A microbiologist plates 0.2 mL of a bacterial culture diluted by a factor of 100. After incubation, 138 colonies are observed. What is the concentration of bacteria in the original culture (CFU/mL)?

• 99,894

• 36,233

• 69,000

• 11,175

Answer explanation

To find the original concentration, calculate: (138 colonies / 0.2 mL) * 100 (dilution factor) = 69,000 CFU/mL. Thus, the concentration of bacteria in the original culture is 69,000 CFU/mL.

A microbiologist plates 0.2 mL of a bacterial culture diluted by a factor of 10,000. After incubation, 245 colonies are observed. What is the concentration of bacteria in the original culture (CFU/mL)?

• 12,250,000

• 16,134,330

• 9,096,252

• 2,122,987

Answer explanation

To find the original concentration, multiply the number of colonies (245) by the dilution factor (10,000) and divide by the volume plated (0.2 mL). This gives 245 x 10,000 / 0.2 = 12,250,000 CFU/mL.