Serial Dilutions, Direct Counting of Bacteria, and UTIs - Lab Practical 4

Is making serial dilutions a direct or indirect method of counting cells?

• Direct counting

What does it mean if bacteria are viable?

• The bacteria are able to grow and multiply

What is the spreading tool called?

• A hockey stick

What is SPC an abbreviation for?

• Standard plate counts

What is CFUs an abbreviation for?

• Colony forming units

From a serial dilution, know how many CFUs should be on the plate to determine an accurate estimate of the number of bacteria in the original sample

• 30-300 CFU

Be able to identify from a series of agar plates, the best one to count

• Know if the growth is classified as heavy, intermediate, or scant

Be able to do the math to determine the CFUs/ml in an original sample given the CFUs on the plate, the dilution, an if 1 mL or 0.1 mL was used

• #CFU x dilution factor

• If 1 mL was plated, don’t do anything with that number

• If 0.1 mL was plated, multiply this number by 10

Are bacteria normally found in the urine (clean catch sample)?

• Yes

What is the threshold limit (CFUs/mL in the urine specimen) to diagnose a UTI?

• 100,000 CFU/mL

Determine the CFUs in a urine specimen by doing the same math and compare that number to the threshold to determine if the person has a UTI

• Remember the CFUs/mL in the urine specimen must be over the threshold

Who is more prone to UTI’s, male or females? Why (two reasons)?

• Women

  • Women have a shorter urethra

  • Their urethra is closer to the anus