Fill in the blanks: (3 pts for each blank)
7. Decarboxylases are inducible enzymes. They are induced in the presence of the substrate,
provided the environment is both ____________________ and __________________
8. KIA tubes offer important information in identification of microorganisms.
A black color in this reaction is indicative of _________________.
The chemical name of the black precipitate is ____________________________
9. In agarose gel electrophoresis, DNA fragments move towards the
_______________ electrode, because the DNA fragments are ___________________ charged.
10. At the end of Hfr X F- conjugation, the donor strain is ___________, and
the recipient is _________________
11. A patient’s blood causes NO hemagglutination with anti-A, anti-B or
anti-Rh antisera. The patient’s blood type is _______________________ ; and the patient’s blood contains
12. Simon’s citrate agar uses __________________ as the source of carbon.
Organisms capable of using this carbon source turn the agar ________________ (write down the color).
13. “Phenylalanine deaminase” test, uses _______________________ (name
the reagent). A positive reaction is indicated by the appearance of a
Short answers: Please be precise in your answers.
14. (8 pts) You have a chemically defined medium containing only a buffered
carbon source. Could you use this medium to enrich for any particular group of microorganisms?
If “Yes” which property of the organism allows it to do so.
If “No”, then why not?
15. (10pts) Mention 5 characteristics of enterics.
16. (4 pts) Briefly describe the difference between beta and gamma hemolysis.
17. (9 pts) Name a medium that you used in the lab to select for Gram positive
microorganisms. Which component(s) of this medium allowed it to be selective for Gram positive microorganisms?
18. (10 pts) Why is it important to read your KIA tube’s results within 18 to 24
hours? (Be brief and complete in your answer. Make sure you mention the
problems both associated with early reading as well as those due to late
19. (9 pts) Explain and interpret the following observation:
A student wrote down the following results for the KIA tube:
+ / - / +
20. (5 pts) Besides Gram staining and morphological differences,
Staphylococcus aureus and Streptococcus fecalis can be distinguished from one other by _________________ test.
21. (10 pts) What is the function of the indicator strain in plaque assay?
How would the amount of indicator influence the assay?
22. (5 pts) What is the main difference between a cell that is an Hfr and one that is F+.
23. (10 pts) At 25°C Serratia marcescens appears red, where as at 37°C it is colorless.
Is this a result of adaptation or mutation? How can you confirm this?
24. (15 pts) The following biochemical pathways describe three mutants having
a defect at three different steps. Use the information given below, to fill in the blanks.
Mutant 1: A------>B------>C------>D---X--->E
Mutant 2: A--X-->B------>C------>D-------->E
Mutant 3: A------>B------>C--X-->D------->E
List ALL the mutants that Mutant 1 can crossfeed: _______________
List ALL the mutants that Mutant 2 can crossfeed: _______________
List ALL the mutants that Mutant 3 can crossfeed: _______________
25. (12 pts) What will be the genotype of the recombinants obtained as a result
of conjugation between an Hfr (leu +, his -, and tetracycline sen) and an F-
(leu -, his + and tetracycline resistant)?
Fill in the table below to show which of these organisms will grow on which medium.
(F-, Hfr and/or recombinants)
Relevant genotype of the recombinants: _________________________
||ORGANISM(S) EXPECTED TO GROW
|Minimal medium (M.M.)
leu + tetracycline
|Complete medium (TSA)
26. (10 pts) You need to find out the titer of a “Stock” solution of bacteriophage
T7. To accomplish this, you made serial dilutions and used 0.1 ml of diluted
phage solutions (from each tube) for the plaque assay. Next day you counted
50 plaques from the 10-3 dilution tube. (Show your calculations)
Titer of the phage “Stock” is __________________________ (Use appropriate
27. (6 pts) What is the importance of serotyping in microbiology labs in the
28. (5 Points) How are DNA bands visualized on an agarose gel after
electrophoresis? (Mention how it was done in your gel electrophoresis lab)
29. (5 pts)
What is the main difference between agglutination and flocculation?
What is the purpose of the Widal test?