Question 1

Which of the following features is a major virulence factor of Staphylococcus aureus that allows it to evade phagocytosis by the host immune system?

Accepted Answer

Production of protein A

Question 2

A patient presents with a rapidly spreading skin infection characterized by redness, swelling, and pus formation. Laboratory analysis reveals Gram-positive cocci in clusters. Which organism is most likely responsible, and what is a key enzyme it produces to facilitate tissue invasion?

Accepted Answer

Staphylococcus aureus; coagulase

Question 3

Which of the following best differentiates Staphylococcus from Streptococcus in a laboratory setting?

Accepted Answer

Catalase test result

Question 4

A newborn develops meningitis. The causative agent is a Gram-positive coccus that is beta-hemolytic and belongs to Lancefield group B. Which organism is most likely responsible?

Accepted Answer

Streptococcus agalactiae

Question 5

Which of the following bacteria is most commonly associated with the formation of pseudomembranous colitis following antibiotic therapy?

Accepted Answer

Clostridium difficile

Question 6

A patient presents with muscle spasms and lockjaw after stepping on a rusty nail. Which Gram-positive bacterium is responsible, and what is the mechanism of its toxin?

Accepted Answer

Clostridium tetani; inhibits inhibitory neurotransmitter release

Question 7

Which of the following is a unique characteristic of Mycoplasma pneumoniae compared to other Gram-positive bacteria listed in the chapter?

Accepted Answer

It lacks a cell wall

Question 8

A laboratory technician is asked to classify a Streptococcus isolate using the Lancefield grouping system. What is the basis for this classification?

Accepted Answer

Presence of specific cell wall carbohydrates

Question 9

Which Gram-positive bacterium is responsible for causing anthrax, and what is a key feature of its pathogenesis?

Accepted Answer

Bacillus anthracis; production of a poly-D-glutamic acid capsule

Question 10

A patient with a history of unpasteurized cheese consumption develops meningitis. The causative agent is a Gram-positive rod capable of growth at low temperatures and intracellular movement. Which organism is most likely responsible?

Accepted Answer

Listeria monocytogenes

Question 11

Which of the following statements about Enterococcus faecalis is correct?

Accepted Answer

It is a common cause of urinary tract infections in hospitalized patients

Question 12

A child presents with a sore throat, fever, and a grayish pseudomembrane in the throat. Which Gram-positive bacterium is most likely responsible, and what is the major virulence factor?

Accepted Answer

Corynebacterium diphtheriae; diphtheria toxin

Question 13

Which of the following best explains why Mycobacterium tuberculosis is resistant to many common antibiotics?

Accepted Answer

It has a waxy cell wall rich in mycolic acids

Question 14

A patient develops flaccid paralysis after eating improperly canned food. Which Gram-positive bacterium is responsible, and what is the mechanism of its toxin?

Accepted Answer

Clostridium botulinum; blocks acetylcholine release at neuromuscular junctions

Question 15

Which of the following is the most effective method for preventing neonatal infection with Streptococcus agalactiae?

Accepted Answer

Screening pregnant women and administering intrapartum antibiotics

Question 16

A patient with a history of chronic cough, night sweats, and weight loss is found to have acid-fast bacilli in a sputum sample. Which bacterium is most likely responsible, and what is a key feature of its cell wall?

Accepted Answer

Mycobacterium tuberculosis; mycolic acid-rich cell wall

Question 17

Which of the following Gram-positive bacteria is most likely to cause gas gangrene in a patient with a deep, contaminated wound, and what is a key virulence factor?

Accepted Answer

Clostridium perfringens; alpha toxin

Question 18

A 5-year-old child develops a sandpaper-like rash and a 'strawberry' tongue following a sore throat. Which Gram-positive bacterium is responsible, and what is the likely toxin involved?

Accepted Answer

Streptococcus pyogenes; erythrogenic toxin

Question 19

Which of the following best describes the transmission route of Listeria monocytogenes leading to human infection?

Accepted Answer

Ingestion of contaminated food products

Question 20

A patient is diagnosed with leprosy. Which bacterium is responsible, and what is a unique feature of its pathogenesis?

Accepted Answer

Mycobacterium leprae; infects peripheral nerves and skin

Pathogenic Gram-Positive Bacteria: Structure, Virulence, and Disease

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