Question 1

Which of the following best explains why the skin is generally an effective barrier to microbial invasion?

Accepted Answer

The outermost layer of the skin is made of dead, keratinized cells that are dry, salty, and acidic, making it inhospitable to most pathogens.

Question 2

A patient presents with a rapidly spreading rash on the palms and soles, fever, and muscle pain after a tick bite. Which pathogen is most likely responsible, and what is its key pathogenic mechanism?

Accepted Answer

Rickettsia rickettsii; invades endothelial cells and uses actin to move between cells, causing vascular damage.

Question 3

Which of the following statements about normal skin microbiota is CORRECT?

Accepted Answer

Normal skin microbiota can use sweat and sebum as nutrients, and their metabolic by-products can inhibit other microbes.

Question 4

A 15-year-old develops multiple red bumps and pus-filled lesions on the face. Which of the following best describes the pathogenesis of this condition?

Accepted Answer

Propionibacterium acnes multiplies in sebum, causing an inflammatory response and follicle wall rupture.

Question 5

Which of the following is a major virulence factor of Staphylococcus aureus that helps it evade the host immune system?

Accepted Answer

Production of protein A, which binds the Fc region of antibodies and inhibits phagocytosis.

Question 6

A hospital is experiencing an outbreak of boils and carbuncles among patients and staff. Which of the following is the most effective initial step to limit the spread of the causative agent?

Accepted Answer

Screening for and isolating carriers of Staphylococcus aureus, and enforcing strict hand hygiene.

Question 7

A newborn develops widespread blistering and peeling of the skin within 48 hours of redness. Which toxin is responsible, and what is the most likely causative organism?

Accepted Answer

Exfoliatin toxin produced by Staphylococcus aureus.

Question 8

Which of the following best explains why antibiotics are less effective in late-stage Lyme disease?

Accepted Answer

The spirochetes are not actively multiplying, making them less susceptible to antibiotics that target cell division.

Question 9

A child presents with a 'slapped cheek' rash and mild fever. Which virus is most likely responsible, and what is its preferred target in the body?

Accepted Answer

Parvovirus B-19; infects bone marrow cells.

Question 10

Which of the following is a distinguishing feature of rubeola (measles) compared to rubella (German measles)?

Accepted Answer

Rubeola is associated with Koplik spots in the mouth, while rubella is not.

Question 11

A patient develops a circular, expanding rash with central clearing after a tick bite, followed by neurological symptoms weeks later. Which organism is responsible, and what is its shape?

Accepted Answer

Borrelia burgdorferi; spirochete

Question 12

Which of the following best describes the pathogenesis of Rocky Mountain Spotted Fever?

Accepted Answer

The bacteria infect endothelial cells, causing vascular damage, clotting, and a characteristic rash.

Question 13

Which of the following is the most important preventive measure for both Rocky Mountain Spotted Fever and Lyme disease?

Accepted Answer

Avoiding tick exposure and promptly removing ticks.

Question 14

A child develops a superficial skin infection with yellowish crusts after a minor scrape. Which organism is most likely responsible, and what is a key virulence factor?

Accepted Answer

Streptococcus pyogenes; M protein

Question 15

Which of the following best explains why chickenpox can reappear as shingles later in life?

Accepted Answer

The virus establishes latency in sensory ganglia and reactivates when cell-mediated immunity declines.

Question 16

A patient with athlete's foot is found to have a fungal infection of the skin. Which enzyme is most likely produced by the causative organism, and what is its function?

Accepted Answer

Keratinase; degrades keratin to allow fungal invasion of the skin.

Question 17

Which of the following best describes the epidemiology of impetigo?

Accepted Answer

It is most common among poor children in hot, humid areas and spreads via person-to-person contact, insects, and fomites.

Question 18

Which of the following is a key reason why Staphylococcus aureus can cause recurrent infections in hospitals?

Accepted Answer

It is resistant to multiple antibiotics, including methicillin (MRSA) and sometimes vancomycin (VRSA).

Microbiology: Skin Structure, Microbiota, and Bacterial Skin Diseases (Chapter 22 Study Notes)

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