Q: Which of the following equations best represents the calculation of bacterial load in a food sample, given colony-forming units (CFU) and dilution factor?

$$\text{Bacterial Load} = \text{CFU} \times \text{Dilution Factor}$$

Question 1

Which of the following is a major structural feature that allows Staphylococcus aureus to evade phagocytosis by binding to immunoglobulin G (IgG) and inhibiting opsonization?

Accepted Answer

Protein A

Question 2

A patient presents with symptoms of food poisoning after consuming contaminated food. Which toxin produced by Staphylococcus aureus is most likely responsible for these symptoms?

Accepted Answer

Enterotoxin

Question 3

Which enzyme produced by Staphylococcus aureus allows it to dissolve fibrin threads in blood clots, facilitating its escape from clots?

Accepted Answer

Staphylokinase

Question 4

A Gram-positive bacterium is isolated from a patient’s skin infection. It is non-motile, catalase positive, and forms grape-like clusters. Which species is most likely responsible?

Accepted Answer

Staphylococcus aureus

Question 5

Which of the following virulence factors is present in Staphylococcus aureus but absent in Staphylococcus epidermidis?

Accepted Answer

Protein A

Question 6

A patient develops osteomyelitis after a traumatic wound. Which pathogen is most commonly associated with this condition and what is the primary mechanism of infection?

Accepted Answer

Staphylococcus aureus via bacteremia or direct wound contamination

Question 7

Which of the following best explains why methicillin-resistant Staphylococcus aureus (MRSA) is difficult to treat?

Accepted Answer

It produces β-lactamase, which breaks down β-lactam antibiotics

Question 8

Which of the following is a distinguishing feature of Streptococcus pyogenes that contributes to its ability to evade the host immune system?

Accepted Answer

M protein destabilizes complement and interferes with opsonization

Question 9

A child presents with a strawberry-red tongue and a widespread rash following pharyngitis. Which toxin is responsible for these symptoms?

Accepted Answer

Erythrogenic (pyrogenic) toxin

Question 10

Which of the following diseases is most likely to result from antibodies bound to streptococcal antigens accumulating in the glomeruli of the kidneys?

Accepted Answer

Glomerulonephritis

Question 11

Which of the following is the most effective method for preventing healthcare-associated Staphylococcus infections?

Accepted Answer

Hand antisepsis and aseptic techniques

Question 12

Which enzyme produced by Streptococcus pyogenes decreases inflammation and limits recruitment of leukocytes by breaking down C5a?

Accepted Answer

C5a peptidase

Question 13

A newborn develops bacteremia and meningitis shortly after birth. Which pathogen is most likely responsible, and what is a key preventive measure?

Accepted Answer

Streptococcus agalactiae; prophylactic penicillin during childbirth

Question 14

Which of the following is a characteristic of Viridans group streptococci?

Accepted Answer

Alpha-hemolytic and lack group-specific carbohydrates

Question 15

Streptococcus pneumoniae can evade phagocytosis by stimulating cells to engulf it but not digest it. Which molecule is responsible for this mechanism?

Accepted Answer

Phosphorylcholine

Question 16

Which disease caused by Streptococcus pneumoniae has a mortality rate approximately 20 times higher than other bacterial causes of the same condition?

Accepted Answer

Pneumococcal meningitis

Question 17

Which of the following Gram-positive pathogens is classified as a high G+C bacterium and is known for causing diphtheria?

Accepted Answer

Corynebacterium diphtheriae

Question 18

A patient presents with flaccid paralysis after consuming improperly canned food. Which toxin is responsible, and what is its mechanism of action?

Accepted Answer

Botulinum toxin; inhibits acetylcholine release at neuromuscular junctions

Question 19

Which of the following equations best represents the calculation of bacterial load in a food sample, given colony-forming units (CFU) and dilution factor?

Accepted Answer

$$	ext{Bacterial Load} = 	ext{CFU} 	imes 	ext{Dilution Factor}$$

Question 20

Which Gram-positive pathogen is an intracellular bacterium that can cross the placenta and cause meningitis in newborns, and what is a key preventive measure?

Accepted Answer

Listeria monocytogenes; at-risk individuals should avoid uncooked deli meats

Study Notes: Pathogenic Gram-Positive Bacteria (Chapter 19)

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