Name Lab Period (2 points) As a laboratory assistant you were asked to estimate
ID: 255386 • Letter: N
Question
Name Lab Period (2 points) As a laboratory assistant you were asked to estimate the total number of bacteria in the urine of a person with a urinary tract disorder. After other laboratory tests, you were left with less than 0.1 ml of urine to work with. A standardized inoculating loop (0.01 ml was available, so you transferred a loopful of the sample to 9.99 ml of a sterile saline solution. You then transferred 5 ml of this dilution into 20 ml of a new sterile saline solution. Finally, you took some of the last diluted urine solution and plated 0.01 ml and 0. ml (each in duplicate). 37 and 33 colonies were counted for the 0.01 ml plating and 309 and 34 for the 0.1 ml plating. How many bacteria were present in 1 ml of urine? 7.Explanation / Answer
We can take the minimum dilution with minimum cells (countable cells) in a plate:
Average number of bacteria in 0.01 ml plate = (37+33)/2 = 35
Here the urine is dilute by 1000times (9.99+0.01) and further 5 times dilution (5ml+20ml) =1000+5=1005 times total dilution
Therefore total number of bacterial cells in 0.01 ml of original urine =35*1005 =35,175
Therefor total number of bacteria per ml = 35,175 *100= 3517500= 3.5*106 bacteria/ml (0.01*100=1ml)
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