Microbio cell growth dilution question Please show all steps

Microbio cell growth dilution question. Please show all steps! Thank you.

You have a sample of bacteria and perform the following dilution set:

Take 1 ml of original sample and add to 9 ml of diluent (tube A).

From tube A remove 1 ml and add to 9 ml of diluent (tube B).        

From tube B remove 1 ml and add to 9 ml of diluent (tube C)

From tube C remove 1 ml and add to 9 ml of diluent (tube D)

From tube D remove 1 ml and plate the entire sample on tryptic soy agar.

If 145 colonies grow on the plate, what was the concentration of bacteria in the original sample?

Solution

Ans. On agar plate you found 145 colonies indicate 145 individual bacterian initially. you have taken 1 ml from tube D. so tube D conatians 10 ml. now multuply 145 colonies with 10 ml. that means each ml of D contains 145 bacterian.

Calcu;ation:

1 mL of tube D =145 colonies. that means 145 bacterian. so 10 ml of tube D conatins 1450 bacteria( 145X10)

1mL of Tube C =1450 bacterian. total 10mL of tube C=14500 bacterian(1450X10)

1mL of tube B=14500 bacterian. total 10 mL of tube B=145000 bacterian (14500X10)

1ml of tube A =145000 bacterian. total 10mL of tube A= 1450000 (14500X10)

initially you have taken 1mL original sample and diluted into 10 mL by adding 9mL which does not contains any bacterian.

Finally your 1 mL of original sample contains 1450000 bacterian.,