practical - MICRO

Question 1

What is the definition of “Sterile Pyuria

Answer 1

The presence of significant pyuria (pus cells) in a urine sample that shows no growth in a routine culture.

Question 2

List 5 common causes of sterile pyuria

Answer 2

-Renal tuberculosis.
-Recent antibiotic therapy.
-Non-gonococcal urethritis (e.g., Chlamydia).
-Neoplasia of the renal tract.
-Viral infection (e.g., Adenovirus).

Question 3

Q: Compare CLED agar and MacConkey’s agar based on their pH indicator and the resulting color for lactose fermenters.

Answer 3

-CLED agar
-Type :selective indicator medium
-Sugar: lactose
- Indicator: bromothymol blue
- (yellow with acidity due lactose
fermentation)
- deep green to blue in
alkaline pH.

-MacConkey’s agar
-selective indicator medium:
-Sugar: lactose
-Indicator : neutral red
-(pink with acidity due lactose
fermentation)
- pale yellow in alkaline
PH

Question 4

Describe the colony appearance of the following bacteria on CLED agar:
-E. coli
-Klebsiella species
-Proteus species
-P. aeruginosa

Answer 4

-E. coli: Yellow (lactose-fermenting) colonies.

-Klebsiella: Large, mucoid, yellow (lactose-fermenting) colonies.

-Proteus: Translucent green to blue-grey colonies (non-lactose fermenting).

-P. aeruginosa: Green colonies.

Question 5

Which of the common Gram-negative urinary pathogens is Oxidase positive?

Answer 5

Pseudomonas

Question 6

Which two organisms are Urease positive, and which is Urease negative? (From E. coli, Klebsiella, Proteus)

Answer 6

-Urease Positive: Proteus, Klebsiella.

-Urease Negative: E. coli.

Question 7

Which organism is Citrate positive, and which is Citrate negative? (From E. coli, Klebsiella)

Answer 7

-Citrate Positive: Klebsiella.

-Citrate Negative: E. coli

Question 8

Which organism produces a red ring in the Indole test

Answer 8

E. coli

Question 9

Which organism produces a yellow ring in the Indole test

Answer 9

Klebsiella

Question 10

Provide the expected results and characteristic colors for E. coli, Klebsiella, and Proteus in the following tests: Oxidase, Urease, Citrate, Indole.

Answer 10

-E. coli:
-Oxidase: Negative (No color change)
-Urease: Negative (Remains yellow)
-Citrate: Negative (Remains green)
-Indole: Positive (Red ring formation)

-Klebsiella:
-Oxidase: Negative (No color change)
-Urease: Positive (Turns pink/fuchsia)
-Citrate: Positive(Turns blue)
-Indole: Negative (Remains yellow)

-Proteus:
-Oxidase: Negative (No color change)
-Urease: Strongly Positive (Rapidly turns bright pink/fuchsia)

Question 11

• Which culture medium is most appropriate
  for isolating S. aureus from pus?

Answer 11

Mannitol salt agar

Question 12

Which test differentiates Staphylococcus
aureus from other staphylococci?

Answer 12

Coagulase test

Question 13

What are the two characteristic features of Staphylococcus aureus seen in a Gram stain from a pus sample?

Answer 13

1. Gram-positive cocci.
2. Arranged in grape-like clusters

Question 14

Describe the appearance of S. aureus colonies on Blood Agar

Answer 14

• Golden-yellow colonies, usually with β-hemolysis

Question 15

What is the key test that differentiates the entire Staphylococcus genus from Streptococcus?

Answer 15

-The Catalase test
-(Staphylococci are positive; Streptococci are negative).

Question 16

What is the single most important test to differentiate S. aureus from other staphylococci (like S. epidermidis)?

Answer 16

-The Coagulase test
-(S. aureus is positive; other staph are negative)

Question 17

What is the name of the enrichment broth used for V. cholerae, and what is its characteristic growth?

Answer 17

-Alkaline Peptone Water; it forms a surface pellicle

Question 18

What is the selective indicator medium for V. cholerae, and what is the appearance of the colonies?

Answer 18

-TCBS (Thiosulphate Citrate Bile Sucrose) agar; colonies are yellow due to sucrose fermentation.

Question 19

What is the appearance of V. cholerae on MacConkey’s agar

Answer 19

-Pale, colorless colonies (Lactose Non-Fermenter - LNF)

Question 20

• What are the results of the following biochemical tests for V. cholerae?
  -Oxidase test
  -String test
  -Indole test

Answer 20

-Oxidase: Positive
-String test: Positive
-Indole test: Positive

Question 21

What is the final confirmatory test for identifying epidemic-causing V. cholerae strains?

Answer 21

-Latex agglutination test using specific antiserum for serogroups O1 and O139.

Question 22

What is the name of the enrichment broth used for Shigella

Answer 22

Selenite broth

Question 23

What is the appearance of Shigella colonies on MacConkey’s or SS agar

Answer 23

-Pale, colorless colonies (Lactose Non-Fermenter - LNF)

Question 24

Q: Compare the selective media used for V. cholerae vs. Shigella

Answer 24

-V. cholerae: TCBS agar.

-Shigella: SS (Salmonella-Shigella) agar.