Question

Which method of measuring microbial growth would give you a better estimate of the total number of living cells in a sample, a plate count or turbidity? Why?,

Answer 1

Plate count method gives better results of microbial count.

In plate count method, sample is diluted up to specific dilution factor and pour over sterile nutrient agar plate. Living cells in sample grows into colonies during incubation period. We can count number of colonies after incubation. Because single colony arises from single cell. After measuring colonies we can calculate colony forming unit per ml of sample(cfu/ml). We get viable cell count

If we use turbidity method for measurements of living cells it may give false results. Because in this method observed turbidity in test tube . Turbidity is due to growth of organism but all Organisms are living or some killed it is not determined by visual detection.

Another point is that we can not calculate no. Of colonies as plate count method but by by using spectrophotometer we can calculate percentage of transmission or absorbance and can be determine growth of cells. But we can not calculate only viable cells (living cells) by turbidity method.