An overnight culture of Serratia marcescens is used as a sample. One ml of the c

Question

An overnight culture of Serratia marcescens is used as a sample. One ml of the culture is added to a bottle containing 99 ml of culture media. This dilution is mixed well, and one ml of the diluted culture is mixed in 9 ml of culture media. This second dilution is diluted by three successive 1/10 dilutions. The last dilution is used for plating, and 0.1 ml is plated on nutrient agar. After incubation, 100 colonies are counted on the plate. How many colony-forming units (CFUs) were present per ml of Serratia marcescens culture?

Explanation / Answer

1ml of culture is added to the 99 ml of the culture media ,total dilution if we add 1 ml to 99 ml is 100 ml of culture media ,1 ml of culture to 100ml of culture media which is equal to 1/100 ml .

for this we are adding 1 ml of 1/100 dilution to 9 ml of the culture media it becomes 1/1000 ml dilution ,this is diluted 3 times to 1/10 dilutions so in total it becomes three times of 1/100 dilutions .

so if we multiply the dilution we get ;

1/100 * 1/1000*1/100* 1/100* 1/100 which is equal to 1/1011 is the diluted factor added to plate .

CFU s, the number of diluted is 0.1 ml is added to plate it beomes 1/10 of a ml ,the total dilution becomes one one of a million [1/1 /1011] it becomes 1011.

number of colonies will be ;

100 *10 11 which is equal to 1.00 *1013 CFU s /ml

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