Chapter 30: Lab Skills Test
Basic microbiology lab skills are an essential aspect of this course. You
will be tested on six important techniques:
- Aseptic technique: broth-to-broth transfer (7
- Streak plate technique: separate a mixed culture (8 points)
- Preparation of pure cultures: from your streak plate (5 points)
- Staining: Gram stain of a mixed culture (7
- Microscopy: Find and focus on bacterial cells
- Pipetting: Accurate transfer of liquids (6 points)
The lab skills test will be held over several lab days as indicated on the
Aseptic technique: You will be
given two sterile TSB (broth) tubes.
- Label both tubes with your initials and your lab section (LA, LB, LC)
- Perform an aseptic transfer of a loopful of broth from the first tube to
the second tube. You may narrate out loud is you wish.
- Upon completion, you will be informed of any missed steps. The tubes will
be incubated to check for contamination.
Streak plate technique: You will be given
a sterile TSA plate and a broth mixture of two bacteria (Staphylococcus aureus
and Escherichia coli).
- Label your TSA plate with your name, lab section, and "mix"
- Perform a streak plate technique using a loopful of the mix broth
- Your plate will be incubated for 2-5 days and graded based on the
Pure culture technique: You will use your
streak plate and 2 sterile TSA slants
- Label your two slants "SA" and "EC"
(plus: name, lab section)
- Aseptically transfer a colony of each bacterium to its respective slant
- The slants will be incubated and graded based on growth and purity
Gram staining: You will be given a slide
and a mixed broth culture of E. coli and S. aureus
- Prepare a heat-fixed bacterial smear using the mixed broth
- Gram-stain your slide
- You will be graded based on how clear and distinct the stained smear
appears under the microscope
Miscroscopy: You will use a prepared slide
- Bring your specimen into focus on low power.
- Bring the specimen into focus on oil immersion
- Correctly adjust the microscope controls (focus, light level, diaphragm)
- Identify parts of the microscope as instructed
Pipetting: You will be given a beaker of
water and a pipette with a pipette pump
- Correctly identify the pipette
- Accurately pipette a given volume of water (e.g. 8.0 ml) into a plastic dish
- Your accuracy will be checked by weighing the dish (1 ml water = 1.00
- Correctly use a micropipettor
© 2003 - 2017 Josť de Ondarza, Ph.D.