Q.1 Which bacterium is most commonly responsible for impetigo?
Staphylococcus aureus
Streptococcus pyogenes
Pseudomonas aeruginosa
Escherichia coli
Explanation - Impetigo is primarily caused by Staphylococcus aureus, although Streptococcus pyogenes can also be involved, especially in non-bullous forms.
Correct answer is: Staphylococcus aureus
Q.2 Bullous impetigo is primarily characterized by:
Non-blistering crusts
Large fluid-filled blisters
Deep ulcerations
Erythematous plaques without blisters
Explanation - Bullous impetigo, caused by Staphylococcus aureus, presents with large, fragile, fluid-filled blisters due to epidermal toxin production.
Correct answer is: Large fluid-filled blisters
Q.3 Erysipelas most commonly affects which layer of the skin?
Epidermis
Dermis
Subcutaneous tissue
Muscle
Explanation - Erysipelas is an acute infection that affects the upper dermis and superficial lymphatics, leading to raised, well-demarcated erythematous plaques.
Correct answer is: Dermis
Q.4 Which of the following is the first-line treatment for mild localized impetigo?
Oral vancomycin
Topical mupirocin
Oral ciprofloxacin
Topical corticosteroids
Explanation - Topical mupirocin is effective for mild, localized impetigo, targeting Staphylococcus aureus and Streptococcus pyogenes.
Correct answer is: Topical mupirocin
Q.5 Necrotizing fasciitis is most commonly caused by:
Staphylococcus aureus
Streptococcus pyogenes
Clostridium tetani
Mycobacterium leprae
Explanation - Necrotizing fasciitis, a rapidly spreading infection of fascia and subcutaneous tissue, is most often caused by Streptococcus pyogenes.
Correct answer is: Streptococcus pyogenes
Q.6 Which of the following is a hallmark feature of cellulitis?
Well-demarcated, raised lesions
Rapidly spreading erythema with warmth and tenderness
Presence of vesicles and pustules
Hyperpigmented macules
Explanation - Cellulitis is a diffuse bacterial infection of the dermis and subcutaneous tissue, presenting with warmth, erythema, swelling, and tenderness.
Correct answer is: Rapidly spreading erythema with warmth and tenderness
Q.7 Which condition is characterized by honey-colored crusts?
Erysipelas
Impetigo
Cellulitis
Necrotizing fasciitis
Explanation - Impetigo often presents with golden-yellow crusts over erythematous lesions, particularly in children.
Correct answer is: Impetigo
Q.8 Staphylococcal scalded skin syndrome (SSSS) primarily affects which age group?
Newborns and young children
Teenagers
Adults
Elderly
Explanation - SSSS occurs mainly in infants and young children due to circulating exfoliative toxins from Staphylococcus aureus, causing widespread epidermal peeling.
Correct answer is: Newborns and young children
Q.9 Which diagnostic method is most useful to confirm bacterial skin infections?
Skin biopsy for histopathology
Bacterial culture and Gram stain
Patch testing
Wood's lamp examination
Explanation - Bacterial culture and Gram stain help identify the causative organism in skin infections, guiding appropriate antibiotic therapy.
Correct answer is: Bacterial culture and Gram stain
Q.10 Which of the following systemic antibiotics is preferred for severe cellulitis?
Amoxicillin-clavulanate
Topical clindamycin
Azithromycin
Oral terbinafine
Explanation - Amoxicillin-clavulanate provides broad-spectrum coverage against Staphylococcus aureus and Streptococcus species, suitable for severe cellulitis.
Correct answer is: Amoxicillin-clavulanate
Q.11 What differentiates erysipelas from cellulitis?
Erysipelas involves deeper dermis
Cellulitis has sharply demarcated borders
Erysipelas has raised, well-defined borders
Cellulitis is painless
Explanation - Erysipelas is a superficial dermal infection with sharply demarcated, raised erythematous plaques, unlike cellulitis, which is diffuse and less defined.
Correct answer is: Erysipelas has raised, well-defined borders
Q.12 Pustular lesions on the scalp in children are most likely caused by:
Folliculitis
Impetigo
Cellulitis
Erysipelas
Explanation - Folliculitis is an infection of hair follicles, often presenting with pustules and erythema, commonly caused by Staphylococcus aureus.
Correct answer is: Folliculitis
Q.13 Which toxin is responsible for the epidermal peeling in staphylococcal scalded skin syndrome?
Exfoliative toxin
Enterotoxin
Tetanospasmin
LPS endotoxin
Explanation - Exfoliative toxins A and B produced by Staphylococcus aureus cleave desmoglein-1, leading to widespread superficial epidermal detachment in SSSS.
Correct answer is: Exfoliative toxin
Q.14 Which is the most common site for erysipelas?
Lower legs
Face
Back
Palms
Explanation - Erysipelas commonly affects the lower extremities, especially the legs, though facial involvement can also occur.
Correct answer is: Lower legs
Q.15 Which of the following is a risk factor for developing cellulitis?
Diabetes mellitus
Asthma
Hypothyroidism
Migraine
Explanation - Diabetes mellitus predisposes to cellulitis due to impaired immunity and poor wound healing.
Correct answer is: Diabetes mellitus
Q.16 Mupirocin is effective because it:
Inhibits bacterial protein synthesis
Disrupts cell wall synthesis
Blocks DNA replication
Acts as an anti-inflammatory
Explanation - Mupirocin inhibits bacterial isoleucyl-tRNA synthetase, preventing protein synthesis, effective against Staphylococcus aureus and Streptococcus pyogenes.
Correct answer is: Inhibits bacterial protein synthesis
Q.17 Which of the following is the most severe form of staphylococcal skin infection?
Impetigo
Folliculitis
Staphylococcal scalded skin syndrome
Erysipelas
Explanation - SSSS is a severe staphylococcal infection leading to widespread epidermal peeling, fluid loss, and systemic symptoms.
Correct answer is: Staphylococcal scalded skin syndrome
Q.18 Hot tub folliculitis is most commonly caused by:
Pseudomonas aeruginosa
Streptococcus pyogenes
Staphylococcus aureus
Clostridium perfringens
Explanation - Hot tub folliculitis is caused by Pseudomonas aeruginosa, which thrives in poorly chlorinated water.
Correct answer is: Pseudomonas aeruginosa
Q.19 Which bacterial skin infection is known for rapid progression and systemic toxicity?
Cellulitis
Necrotizing fasciitis
Impetigo
Folliculitis
Explanation - Necrotizing fasciitis spreads rapidly along fascial planes and is often associated with severe systemic toxicity and high mortality.
Correct answer is: Necrotizing fasciitis
Q.20 Which of the following is a common complication of untreated impetigo?
Post-streptococcal glomerulonephritis
Lupus erythematosus
Psoriasis
Melanoma
Explanation - Non-bullous impetigo caused by Streptococcus pyogenes can lead to post-streptococcal glomerulonephritis as a rare complication.
Correct answer is: Post-streptococcal glomerulonephritis
Q.21 Which clinical feature is more typical of bullous impetigo compared to non-bullous impetigo?
Smaller pustules
Larger superficial blisters
Scaly patches
Hyperpigmented macules
Explanation - Bullous impetigo presents with large, fragile blisters due to Staphylococcus aureus exfoliative toxins, unlike the crusted small lesions of non-bullous impetigo.
Correct answer is: Larger superficial blisters
Q.22 Which factor predisposes individuals to staphylococcal skin infections?
Poor hygiene
High-fiber diet
Vitamin C supplementation
Low sunlight exposure
Explanation - Poor hygiene, skin trauma, and immunosuppression increase susceptibility to staphylococcal skin infections.
Correct answer is: Poor hygiene
Q.23 Which topical antibiotic is preferred for limited staphylococcal folliculitis?
Mupirocin
Gentamicin
Neomycin
Clindamycin lotion
Explanation - Topical mupirocin is effective for localized staphylococcal folliculitis due to its bactericidal activity against S. aureus.
Correct answer is: Mupirocin
Q.24 Which systemic sign may indicate progression of cellulitis to a more serious infection?
Fever and tachycardia
Mild itching
Localized dryness
Hyperpigmentation
Explanation - Systemic signs such as fever, tachycardia, and hypotension suggest severe infection and possible sepsis in cellulitis.
Correct answer is: Fever and tachycardia