Question

1. Capsular Staining. Some bacterial cells are enclosed with an extracellular gel-like layer that occurs outside the cell wall. Capsules are pathogenic factors that also function in attachment. If the capsule stain is not properly prepared the gel-like material may shrink and will not be seen during microscopy. Which of the following is INCORRECT?

1. a capsular stain was used to prepare Klebsiella pneumonia slides for microcopy
2. the smear is air-dried
3. the smear was heat fixed
4. all the above are incorrect
5. none of the above are incorrect

2. Differential Staining requires the use of more than one chemical stain. QUESTION: The Gram Stain is a NOT a Differential Stain. T or F

3. Motility in bacteria can be determined using which of the following methods
   1. Wet mount
   2. Flagella stain and wet mount
   3. Wet mount and SIM media
   4. Wet mount, flagella, stain, or SIM media
4. Biochemical Procedures that use selective & differential media identify:

1. the shape and arrangement of bacteria
2. the microscopic properties of bacteria
3. enzymatic properties of bacteria
4. the size characteristics of bacteria

5. In a SIM test, one SIM tube was inoculated with two unknown bacteria. The results were then used to identify both bacteria. T or F

6. Selective Medium support the growth of one type of organism and inhibits the growth of another. T or F

7. Sulfide, Indole, Motility (SIM): Bacteria that have the enzyme tryptophanase, can convert the amino acid tryptophan to indole. Indole reacts with Kovac’s reagent to form a Black Color. T or F

8. GROWTH ON EMB & MAC: Which Observations are INCORRECT?

1. both EMB and MAC contain dyes that inhibits gram-positive bacteria.
2. both EMB and MAC differentiate gram negative organisms based on their ability to ferment lactose
3. both EMB and MAC indicate that the pH becomes basic (alkaline) because of fermentation
4. all the above are incorrect
5. none of the above

9. GROWTH On MSA (7.5% NaCl). Which Observations are CORRECT?
   1.    MSA is selective for Staphylococci
   2. Staphylococci species are Gram +
   3.     MSA is differential based on acid production
   4. Acid production on MSA changes the phenol red (acid indictor) to yellow
   5.    All the above

10. Blood Agar is differential with respect to Hemolysis. Which of the following is CORRECT?
    1. hemolytic enzymes are produced in produced hemolysis
    2. Beta (ß) hemolysis and results in the complete breakdown of the RBCs
    3. Alpha (a) hemolysis Partial destruction of the RBCs leads to a greenish brown color
    4. Gamma(γ)hemolysis causes no damage to the RBCs
    5. all the above are correct

11. Blood Agar Plates have the enzyme catalase. We use blood agar to determine whether an unknown bacterium is catalase positive. T or F

12. Differential and/or Selective Media include EMB, MSA, MAC, Blood Agar Plates, Simmons Citrate & SIM Tubes. Regarding what was observed on these media, which is CORRECT?
    1.     a change in color on any of those media means we are looking at the result of enzyme activity
    2.   acid production, or no -acid production indicate the presence or absence of specific enzymes
    3.     all the above are correct
    4.   none of the above are correct

13. A pH sensitive dye (in media) responds to acid production with a change in color, and
    1. MacConkey (MAC) media turns reddish
    2. Eosin Methylene Blue (EMB) agar media inoculated with Escherichia coli produces a green metallic sheen
    3. Mannitol-salt agar (MSA) turns yellow
    4. all the above
    5. none of the above

14. Page 284 of Benson’s summaries some “characteristics of common Gram-positive and Gram-negative bacterial Species.”. The Table identifies a list of Gram (-) bacteria that are all catalase +. Which of the following makes sense?
    1.    the catalase test can be used to categorize bacteria., i.e. they can be categorized as catalase (+ or -)
    2. the catalase test alone could be used to identify a specific Gram (-) bacteria on that list
    3.   all the above makes sense
    4. none of the above makes sense

Answer 1

1. Which of the following is INCORRECT?

Incorrect statement is - the smear was heat fixed.

Capsule stain is a type of differential stain, which uses acidic and basic dyes to stain background & bacterial cells respectively, so that presence of capsule is easily visualized. Here we are identifying the bacteria by observing the capsule. When it is heat fixed, this will cause the capsule to shrink or be destroyed.  Only air-dry is enough.

2. The Gram Stain is a NOT a Differential Stain. T or F?

It is false statement. Differential Staining requires the use of more than one chemical stain. In gram staining, first Cells are stained with crystal violet dye. After the use of decolorizer, another dye, weakly water soluble safranin is used. So gram stain is a differential stain.

It is used to differentiate between gram positive organisms and gram negative organisms. Hence, it is a differential stain.

3. Motility in bacteria can be determined using which of the following methods?

Answer :Wet mount, flagella stain, or SIM media

These 3 technique is used to find the motility of bacteria.

In a wet mount, the specimen (Here bacteria) is placed in a drop of water or other liquid held between the slide and the cover slip by surface tension. This method is commonly used for studying the movement and behavior of living micro organism including bacteria.

Flagella stain is used to visualize the presence and arrangement of flagella for the presumptive identification of motile bacterial species. In bacteria flagella is used for the movement. So the presence of flagella indicates its motility.

SIM (Sulfur, Indole, Motility) media is used for the differentiation of microorganisms on the basis of hydrogen sulfide production, indole production, and motility in a laboratory setting.

4. Biochemical Procedures that use selective & differential media identify.

Answer : The size and characteristics of bacteria.

Selective media generally allow the growth of only selected microorganisms and stopping the growth of or altogether killing non-desired organisms.

Differential media (indicator media) distinguish one microorganism type from another growing on the same media. For example differentiate the gram positive and gram negative bacteria.

5. Selective Medium support the growth of one type of organism and inhibits the growth of another.

This statement is correct. Selective media generally allow the growth of only selected microorganisms and stopping the growth of or altogether killing non-desired organisms.