Question 1

A 7-year-old child presents with a sore throat and fever. A throat swab is collected from the posterior pharynx and inoculated onto a blood agar plate. After incubation, beta-hemolytic colonies are observed. Which organism is most likely responsible for these findings?

Accepted Answer

Streptococcus pyogenes

Question 2

Which of the following best describes the proper method for collecting a nasopharyngeal specimen to diagnose Bordetella pertussis infection?

Accepted Answer

Use a flexible thin wire swab guided into the nares to the posterior pharynx

Question 3

A sputum sample is evaluated using Bartlett’s classification. The Gram stain shows numerous neutrophils and few squamous epithelial cells per low power field. What does this indicate about the specimen?

Accepted Answer

It is likely a good quality specimen indicating infection

Question 4

Which of the following urine collection methods is LEAST likely to yield a specimen suitable for diagnosing a urinary tract infection (UTI)?

Accepted Answer

Random voided urine

Question 5

A urine culture is performed using a 1 $\mu$L calibrated inoculating loop. After 24 hours, 200 colonies are counted on the plate. What is the colony-forming unit (CFU) per mL in the original urine sample?

Accepted Answer

$2.0 	imes 10^5$ CFU/mL

Question 6

A patient’s urine sample is dark yellow and cloudy with a slightly fruity odor. Which of the following is the most likely explanation for these findings?

Accepted Answer

The patient is dehydrated and may have a urinary tract infection

Question 7

Which of the following best explains why blood cultures are collected from two sites at least one hour apart?

Accepted Answer

To increase the likelihood of detecting intermittent bacteremia

Question 8

A cerebrospinal fluid (CSF) sample is collected for microbiological analysis. Which of the following organisms is a fastidious pathogen that requires chocolate agar and incubation at 37$^\circ$C for optimal growth?

Accepted Answer

Neisseria meningitidis

Question 9

A male patient presents with a painful, purulent urethral exudate. Which of the following is the most appropriate selective media for isolating the likely causative organism?

Accepted Answer

Modified Thayer Martin (MTM) agar

Question 10

A wound specimen is collected from a deep pressure ulcer in a nursing home patient. Which of the following is the preferred method for specimen collection to minimize contamination and maximize diagnostic yield?

Accepted Answer

Needle aspirate of purulent material

Question 11

A Gram stain of a clinical specimen reveals numerous neutrophils and gram-positive cocci in clusters. Which preliminary biochemical test would best differentiate Staphylococcus from Streptococcus species?

Accepted Answer

Catalase test

Question 12

Which of the following media is both selective and differential, and is used to isolate and differentiate lactose fermenting gram-negative bacteria from non-lactose fermenters?

Accepted Answer

MacConkey agar

Question 13

A clinical laboratory is attempting to isolate Neisseria gonorrhoeae from a genital specimen. Which of the following best explains the use of Modified Thayer Martin (MTM) media in this context?

Accepted Answer

MTM contains antibiotics that inhibit the growth of most bacteria except Neisseria gonorrhoeae

Question 14

A stool sample is plated on Hektoen Enteric (HE) agar. Which of the following best describes the purpose of this medium?

Accepted Answer

To inhibit normal flora and enhance isolation of stool pathogens

Question 15

A laboratory technician is preparing a culture for a suspected case of Proteus vulgaris. To prevent swarming and obtain regular colonies, which of the following should be added to the chocolate agar plate?

Accepted Answer

$0.5\%$ sodium citrate

Question 16

A clinical isolate produces a green metallic sheen on Eosin Methylene Blue (EMB) agar. Which organism is most likely responsible for this appearance?

Accepted Answer

Escherichia coli

Question 17

Which of the following best describes the principle of the catalase test and its clinical significance?

Accepted Answer

Hydrogen peroxide is converted to water and oxygen, and bubbling indicates a positive result, differentiating Staphylococcus (positive) from Streptococcus (negative)

Question 18

A spot indole test is performed on a lactose fermenting, gram-negative rod isolated from a urine culture. The test yields a pink/red color. Which of the following is the most likely organism?

Accepted Answer

Escherichia coli

Question 19

A clinical specimen is inoculated onto blood agar and incubated at 35$^\circ$C in a CO$_2$ incubator. After 24 hours, colonies with complete clearing around them are observed. What type of hemolysis is this, and which organism is most likely to produce it?

Accepted Answer

Beta hemolysis; Streptococcus pyogenes

Question 20

A laboratory is using thioglycollate broth to culture a wound specimen. Which of the following best explains the purpose of this medium?

Accepted Answer

To differentiate between aerobes and anaerobes based on their growth location in the tube

Clinical Microbiology: Specimen Collection, Processing, and Identification

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