Question

A Student takes a sample from a table top in the student lounge using a sterile swab. She then cleans the table with water and paper towels and samples the table again. She cultures the sample on nutrient agar in a 37C incubator for 24 hours. The student counted 600 colony forming units on the sample plate collected from the table before it was cleaned and 150CFUs on the sample collected after the table was wiped off. What was the percent reduction of bacterial CFUs on the table due to the paper and water cleaning method? Show calculations. H: DV: IV: +contol -contol

Answer 1

Number of bacteria before cleaning = 600 CFU

Number of bacteria after cleaning = 150 CFU

Percent reduction in CFU = (CFU before cleaning - CFU after cleaning) / (CFU before cleaning) × 100

= (600 - 150) / (600) × 100

= 450 / 600 × 100

= 75 %

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