Q: A blood agar plate shows clear zones around colonies. Which formula best describes the process responsible for this observation?

$$\text{Hemoglobin} \xrightarrow{\text{Alpha toxin}} \text{Colorless products}$$

Question 1

Which property distinguishes Staphylococcus aureus from Staphylococcus epidermidis and Staphylococcus saprophyticus when grown on mannitol salt agar?

Accepted Answer

S. aureus ferments mannitol to produce acid, changing the medium color.

Question 2

A patient’s blood agar plate shows clear zones of beta hemolysis. Which bacterial property is most likely responsible for this observation?

Accepted Answer

Production of alpha toxin by Staphylococcus aureus.

Question 3

Which test would you use to differentiate Staphylococcus from Streptococcus in a clinical sample?

Accepted Answer

Catalase test: Staphylococcus is catalase positive, Streptococcus is catalase negative.

Question 4

You isolate bacteria from a fomite and observe yellow colonies on blood agar that are 2 mm in diameter and catalase positive. Which species is most likely present?

Accepted Answer

Staphylococcus aureus

Question 5

Which of the following is a correct difference between Staphylococcus and Streptococcus morphology?

Accepted Answer

Staphylococcus grows in clusters, Streptococcus grows in chains.

Question 6

A throat swab is inoculated onto a blood agar plate. After incubation, you observe small, white colonies with no hemolysis. Which organism is most likely present?

Accepted Answer

Staphylococcus epidermidis

Question 7

Which Staphylococcus species is resistant to novobiocin and does not require biotin for growth?

Accepted Answer

Staphylococcus saprophyticus

Question 8

If you observe clot formation in a serum tube after adding a bacterial culture, which enzyme is responsible and which species is most likely present?

Accepted Answer

Coagulase; Staphylococcus aureus

Question 9

Which Lancefield group is most commonly associated with Streptococcus pyogenes?

Accepted Answer

Group A

Question 10

A student swabs their nose and inoculates a blood agar plate. After incubation, the colonies are orange, catalase positive, and show beta hemolysis. Which organism is most likely present?

Accepted Answer

Staphylococcus aureus

Question 11

Which of the following best describes the role of mannitol fermentation in identifying Staphylococcus aureus?

Accepted Answer

S. aureus ferments mannitol, producing acid that changes the color of the medium.

Question 12

Which equation represents the catalase reaction used to differentiate Staphylococcus from Streptococcus?

Accepted Answer

$$2H_2O_2 \rightarrow 2H_2O + O_2$

Question 13

A blood agar plate inoculated with throat swab shows chains of Gram-positive cocci with no catalase activity. Which genus is most likely present?

Accepted Answer

Streptococcus

Question 14

Which property is shared by all three major Staphylococcus species (aureus, epidermidis, saprophyticus)?

Accepted Answer

Gram-positive cocci morphology

Question 15

A sample from a fomite is inoculated on blood agar. Colonies are white, catalase positive, and sensitive to novobiocin. Which species is most likely present?

Accepted Answer

Staphylococcus epidermidis

Question 16

Which of the following is NOT a property of Staphylococcus aureus?

Accepted Answer

Novobiocin resistance

Question 17

A blood agar plate shows clear zones around colonies. Which formula best describes the process responsible for this observation?

Accepted Answer

$$	ext{Hemoglobin} \xrightarrow{	ext{Alpha toxin}} 	ext{Colorless products}$$

Question 18

Which real-world scenario best illustrates the importance of distinguishing between Staphylococcus and Streptococcus in clinical diagnostics?

Accepted Answer

A patient with skin abscesses is treated with antibiotics targeting catalase-positive bacteria.

Question 19

Which of the following is the correct sequence for isolating Streptococcus from the throat in a laboratory setting?

Accepted Answer

Swab the back of the throat with a sterile cotton swab, then inoculate a blood agar plate.

Isolation and Identification of Staphylococcus and Streptococcus Species

스터디 가이드 - 연습 문제

학습 가이드 - 플래시카드