Tips for Studying for the Lab Practical Exam in Microbiology
The main focus of the Lab Practical is on interpreting physical objects like test tubes and
media that you have worked with during the course of the quarter and in performing calculations
or analysis of visual results.
The test will consist of a series of stations around the room where you will stand and
work for 1-2 minutes according to the timing provided by the teacher. You will look at the
questions and write out the answers for each station on a stapled packet of pages.
When the allotted time finishes for a particular station, you must move to the next one,
even if you are not done writing. You will be allowed to revisit any station limited time after
everyone has rotated through all the questions. Except for questions that require drawing, only
your writing (complete sentences) will be considered in grading.
If you feel you are finished before the final time is called, you can submit your answer
sheet and leave the lab --you're done.
This list is not intended to cover everything that will be on the test, nor will all the things
mentioned below be on the test. This is only a guide to make sure you study some of the most
significant things. Reviewing old lab quizzes would help in studying for the final lab practical
too.
1. Review each lab we did, looking at what the purpose was. If organisms were used, from
what source did they come (e.g. environment, skin, throat)? What are typical testsused to
investigate the typical organisms from a particular source? What are the major bacterial
species found in these sources and what are their characteristics? What organisms would
you expect to see on the skin, in the respiratory system, in the colon?
2. For labs where we investigated the effects of the environment on growth, be sure you
understand how the factors we investigated enhanced or inhibited growth. These could
include things like UV light, disinfectants/antibiotics, oxygen levels, temperature, types
of nutrients, etc. How did we interpret the efficacy of inhibitory chemicals or antibiotics?
3. Know the names of all of the selective, differential, enriching, and general media we used
in lab. This includes those used to test metabolic ability. Know the abbreviations for
these media we used in class, what color they should be before inoculation and what
changes in color or growth would be expected in these media. What selective or pH dyes
are used in these media? In terms of pH dyes, we used phenol red (ferm. tubes), methyl
red (MRVP), neutral red (MacConkey), bromcresol purple (with TSY and glucose in the
Skin lab), bromthymol blue (citrate media) and brilliant green (lauryl sulfate lactose
broths in MPN).
4. Know the steps of any procedure in completing a test, like testing for acetoin, catalase,
oxidase, acid from glucose, etc.
5. The most common question on the lab practical is "What do you know about the
organisms that grew on such and such a medium" What metabolic ability did they show?
Were they probably gram positive or negative?
Tips for Studying for the Lab Practical Exam in Microbiology pg. 1
6. Be able to describe the proper technique for how to make a pure culture from a mixed
culture. What is the proper method for maintaining sterile technique during transfer.
What results from an incubation of nutrient broth where you transfered "sterile media"
into other "sterile media" asceptically or septically?
7. How did we investigate transformation and what type of growth was expected on the
plates we used. What did each sector of these plates show?
8. Know all the parts of the microscope we studied (our microscopes --- not those pictured
in the lab manual) and their functions. Be able to describe the function of immersion oil,
define resolution, and state the best wavelength of light for light microscopy. How do you
do direct staining, negative staining, wet mounts and what are the
advantages/disadvantages of each?
9. Be able to set up a series of test tubes and media in order to achieve a final dilution using
serial dilutions. Be able to write down the formula for determining cfu/ml and do the
calculations from the colony counts in a pour plate assay.
10. Be able to determine the MPN index from a presumptive test and know what comes next
in this process.
11. When would you use a shake tube, an agar deep, thioglycollate, light-proof containers,
candle jars, anaerobic jars to study organisms and why?
12. Know everything about gram staining, including names of reagents, functions, how to
make one from liquid vs solid culture, how to interpret what you see under the
microscope.
13. Some media we used: MSA, TSA, TSY+glu+bromc purple., EMB, LES, MacConkey,
tryptone broth, urea slants, sugar fermentation tubes, MRVP media (what in this?),
oxidase reagent, H2O2, agar deeps, blood agar, citrate slants, Kovacs reagent, VogesProskauer reagent, crystal violet, safranin, methylene blue, iodine, glucose salts agar.
Tips for Studying for the Lab Practical Exam in Microbiology pg. 2