1. Sample Comprehensive Laboratory exam
BIO 2420
Intro to Microbiology
Sample Comprehensive Laboratory exam
Created by R. Rohde

2. Identify the gram reaction seen at the pointer.
Cocci
diplococci
Identify the gram reaction seen at the pointer.
Identify the morphology (shape).
Identify the arrangement.

3. Identify the staining technique.
Capsule
Adhesion/Protection from phagocytosis
Acidic dyes are negatively charged and will adhere to the positively charged glass allowing for the capsule to be visualized.
Identify the staining technique.
What is the purpose of the white structure seen at the pointer.
13. Why is an acidic dye used for this technique?

4. Identify the staining technique.
Gram stain
Iodine is a mordant that firmly fixes the primary dye, crystal violet, to the G+ cells
Staphylococci
Staphylococcus aureus
Identify the staining technique.
Identify the purpose of iodine in this technique.
Name the primary morphology seen in the slide.
Name the most likely Genus and species seen in this image.

5. 23. What is the purpose of this method?
Streak plate
Isolation of single pure colonies of bacteria
22. Identify the method.
23. What is the purpose of this method?

6. 36. Identify which tube illustrated a non-motile organism.
(Klebsiella and Shigella are both non-motile G- enterics) A B C
36. Identify which tube illustrated a non-motile organism.

7. 37. Identify microscope part # 1 38. What is the magnification of
39. Identify microscope part # 6 that is
labeled 10X.
What is the magnification when
using the oil immersion objective lens?
Ocular
10X
Low pwr objective
1000X

8. Identify the bacteria that is found on plate A.
Identify the bacteria that is found to produce the green/blue pigment seen
in image B.
35. Between these two bacteria (A and B), which one produces a soluble pigment?
Serratia marcescens
Pseudomonas aeruginosa
P. aeruginosa

9. A&B
Casease
Identify which sector(s) is/are positive for the breakdown of the milk protein
casein.
2. Name the enzyme that is present when a bacteria can breakdown this protein.

10. 14. In the nitrate reduction test shown above, what two reagents were added to
determine if nitrate reductase is present?
2nd reagent
What 3rd reagent must be added to the inconclusive tube above to determine if nitrate
has been totally reduced?
If the inconclusive tube stays the same color as above after this reagent (#16 answer)
is added, what does that outcome mean?

11. Identify the amino acid that is the substrate in this test.
Indole (Kovac’s reagent is added for detection)
Tryptophan
E. coli
Identify the end-product that has been produced in the tube on the right.
Identify the amino acid that is the substrate in this test.
For which bacteria, is this test a presumptive test (positive indicator)?

12. Name the pH indicator in this test. What is the purpose of this test?
Citrate
Bromothymol blue
Determine if citrate is utilized as a carbon source
Name the test.
Name the pH indicator in this test.
What is the purpose of this test?

13. You have been given a sample of urine to determine whether or not
it’s likely to be a urinary tract infection (UTI). The only information you know
is that you have a gram negative rod in the urine that “swarms” on agar. The
only biochem test you have available in the lab is the urea test and it turns up positive.
Based on this information, what is the most likely organism that is causing this UTI?
Proteus spp.

14. Based on the observations with hemolytic activity and bacitracin,
Streptococcus pyogenes (beta hemolytic and bacitracin susceptible)
Based on the observations with hemolytic activity and bacitracin,
identify the genus and species most likely isolated on this plate.

15. Which family of bacteria is the IMViC test useful for most often?
The following results were noted for the IMViC test (+, +, -, -). Based
on these results, what is the identification of the most likely gram-negative
enteric that we’ve studied in our lab?
47 and 48. If the IMViC results were reversed (-, -, +, +), which two likely gram-
negative enterics would you suspect based on our labs?
49. Which simple test could one use to differentiate between these two bacteria?
Enterobacteriaceae
E. Coli
Klebsiella & Enterobacter
Motility (Klebsiella is non-motile while Enterobacter is motile)

16. Name which bacteria is positive for this test
The culture turned purple within 15 seconds of adding the oxidase reagent to the swab. Is this a positive or negative test?
Name which bacteria is positive for this test
that also is assachrolytic and produces a bluish-
green pigment.
Positive
Pseudomonas aeruginosa

17. 9. Identify this selective and differential media that allows for
Differentiation between Staph. aureus and Staph. epidermidis.
Name which sector you would find S. aureus.
Name the ingredient that makes this plate “selective”.
Why is sector “1” turning yellow?
Mannitol salt agar
Sector 1
Salt allows halophiles to be selected on the plate
Fermentation of mannitol (ph idicator turns yellow in presence of acid)

18. What does EMB stand for in this test?
Eosin methylene blue G+
While EMB allows for differentiation of lactose fermenters from non-lactose fermenters, E.coli (and other coliforms) often give a “green sheen” appearance.
What does EMB stand for in this test?
Which bacteria are inhibited on this plate?
Name the bacteria isolated on the above plate.

19. Identify which disk the bacteria is totally resistant to.
SSS (triple sulfa)
P (penicillin)
Mixed culture (contamination) and resistant bacteria
Identify which disk the bacteria is totally resistant to.
Identify which disk the bacteria is most susceptible to.
29 & 30. Name 2 reasons for the colonies seen in the inhibition zone at
the arrow.

20. An enteric culture gave the following results: gram positive cocci,
Gamma/alpha hemolytic, bacitracin negative, optochin negative,
Bile esculin slant tube entirely black, 6.5% NaCl broth turbid.
Based on the results above, name the genus and species of the most
likely bacteria.
Name the beta-hemolytic, gram positive bacteria that is found in
the Group B streptococcus organisms.
A skin swab gave the following results: gram positive cocci,
Catalase positive, halophile, ferments mannitol. Based on these results,
name the most likely genus and species.
Enterococcus faecalis
Streptococcus agalactiae
Staphylococcus aureus

21. On this Hektoen enteric media (HE), are the isolated colonies
Non-lactose fermenters (NLF)
H2S production (black centers in colonies)
Salmonella typhimurium
On this Hektoen enteric media (HE), are the isolated colonies
LF’s or NLF’s?
What other characteristic is observed with the isolated colonies?
Name one bacteria that would give this result.

22. 8. Identify by genus and species.
Trichuris trichuiria (whipworm egg)
8. Identify by genus and species.

23. Identify this protozoan that can cause dysentery from drinking
trophozoite
cyst
Identify this protozoan that can cause dysentery from drinking
non-purified water when camping, etc.
13. What class does this protozoan belong to?
Giardia lamblia
Flagellates

24. Identify this flagellate protozoan (genus only).
Trypanosoma spp.
blood
Identify this flagellate protozoan (genus only).
27. Name the type of specimen (urine, etc.) one would have to
acquire to view this microbe.

25. Identify the helminth (Genus & species that produces this egg.)
Enterobius vermicularis
Cellophane tape prep via the perianal region (females worms lay eggs at night which causes itching, usually fecal oral transmission among young)
Identify the helminth (Genus & species that produces this egg.)
It is the #1 roundworm infection in the USA.
Specifically, how would one obtain a sample of these eggs to ID
them for a clinical diagnosis?

26. Identify this microbe by genus. Name the class?
Rhizopus spp.
Zygomycetes
Identify this microbe by genus.
Name the class?