Express all answers in Scientific Notation
Calculate the CFU/ml of a urine sample if 49 E. coli colonies were counted on TSA when
50 µl were plated on the TSA plate from a 10-6 dilution tube.
Determine the number of bacteria which must have been counted on a culture plate if 5 µl
from a dilution tube of 10-7 produced a CFU/ml of 2.0 x 1011.
A milk sample was tested for the presence of S. typhimurium. Using a 10 µl calibrated
loop a sample was taken directly from the milk and plated onto MAC and the following
day after overnight incubation 98 colonies were counted. What is the CFU/ml of the S.
typhimurium in this sample?
A local ice cream plant tested a batch of chocolate ice cream and determined that it was
contaminated with Listeria monocytogenes at 7.56 x 108 CFU/ml. If 189 colonies were
counted on the TSA plate from a sample taken from a dilution tube of 10-5. What volume
of the sample in µl from the dilution tube was actually plated on the TSA plate?
Jack, a new MLT at Scott and White Hospital was given the following information from
a patient's urine sample which had been tested for the presence of S. aureus. The urine
contained 6.4 x 107 CFU/ml S. aureus, the plate dilution was 10, and the sample had been
taken from the 10-5 dilution tube. Calculate the number of bacteria which must have been
counted on the plate and what volume of the sample in µl was actually plated to give the
above results. PS, both of these values can be calculated.