Question

Explain how using the 10 square calculated result have would affect your final result for the determination of the CFU/mL in the unknown E.coli culture in the experiment Standard Plate count and Turbidimetric Methods to Enumerate the numbers of Microorganisms in a population

Answer 1

Standard plate count: This method is performed by diluting the culture several times (either by serial dilution or in ratio) in plane sterile culture media followed by plating on suitable culture plate (LB agar for E.coli) followed by incuation at 37C for overnight. Number of colonies obtained (coined as CFUs or colony forming unit) multiply by dilution factor will gives the value of number of viable cells present per ml of media. This method is more accurate as it gives count for viable cells. But it is time consuming as it requires proper dilution, plating, incubation, media preparation & calculations.

And for counting cells it should be in the range of 30-300 per plate.

Turbidimetric Method: This method involves reading cultures in quvettes using colorimeter or spectrophotometer at 600mn followed by plotting a graph of the absorbance value to a standard plot (pre-calculated or optimized by experts). Absorbance value increases based on the turbidity of the culture which gives the number of cells present in per ml. This method is quick and easy to follow and can be performed when we are counting many number of samples.

The only draw back with this method is it will not differentiate between live and dead cells as the absorbance depends on turbidity or cloudiness of the culture.