Bacterial Skin Infections — MCQs

Bacterial Skin Infections Indian Medical PG Practice Questions and MCQs

Question 101: Erysipeloid disease is also known as which of the following?

A. St. Anthony's fire
B. Fish handler's disease
C. Red man syndrome (Correct Answer)
D. Holy fire

Explanation: **Explanation:** **Erysipeloid**, caused by the Gram-positive rod ***Erysipelothrix rhusiopathiae***, is a zoonotic occupational disease. It is commonly referred to as **"Red man syndrome"** (not to be confused with the vancomycin-induced infusion reaction) because it presents as a characteristic well-demarcated, violaceous, or purplish-red plaque, typically on the hands. **Analysis of Options:** * **Option C (Correct):** Erysipeloid is historically termed "Red man syndrome of Rosenbach." It occurs in individuals handling contaminated animal products (meat, poultry, or fish) where the bacteria enter through skin abrasions. * **Option B (Incorrect):** While Erysipeloid is often called **"Fish-handler’s disease"** in clinical practice, in the context of this specific nomenclature question, "Red man syndrome" is the classic synonym used in dermatological texts for Erysipeloid. (Note: *Mycobacterium marinum* is also associated with fish handling but causes Fish tank granuloma). * **Option A & D (Incorrect):** **St. Anthony’s Fire** and **Holy Fire** are synonyms for **Erysipelas**, which is a superficial cutaneous infection caused by *Streptococcus pyogenes* (Group A Strep). Erysipelas is characterized by a bright red, edematous, warm plaque with a "raised border," distinct from the violaceous hue of Erysipeloid. **High-Yield Clinical Pearls for NEET-PG:** * **Causative Agent:** *Erysipelothrix rhusiopathiae* (Gram-positive, non-spore-forming, catalase-negative rod). * **Occupational Risk:** Butchers, fishermen, and veterinarians. * **Clinical Feature:** Painful, pruritic, violaceous lesion with central clearing; usually lacks systemic symptoms (unlike Erysipelas). * **Treatment of Choice:** **Penicillin** is the first-line treatment. Note that the organism is intrinsically **resistant to Vancomycin**.

Question 102: Which form of leprosy is considered the most unstable?

A. Borderline Borderline (BB) (Correct Answer)
B. Borderline Lepromatous (BL)
C. Borderline Tuberculoid (BT)
D. Tuberculoid Tuberculoid (TT)

Explanation: **Explanation:** The classification of leprosy follows the **Ridley-Jopling scale**, which is based on the host’s cell-mediated immunity (CMI). **Borderline Borderline (BB) leprosy** is considered the most unstable form because it represents a precarious midpoint on the immunological spectrum. Patients with BB leprosy do not stay in this stage for long; they almost always shift (downgrade) toward the lepromatous pole (BL/LL) if untreated, or shift (upgrade/reverse) toward the tuberculoid pole (BT) during a type 1 lepra reaction. **Analysis of Options:** * **Borderline Borderline (BB):** Correct. It is immunologically "on a knife-edge." It is characterized by "punched-out" or Swiss-cheese appearance lesions and is rarely seen in clinical practice because of its rapid transition to other forms. * **Borderline Tuberculoid (BT) & Borderline Lepromatous (BL):** While these are also "borderline" and can undergo reactions, they possess a more defined immunological stance than BB and are relatively more stable. * **Tuberculoid (TT) & Lepromatous (LL):** These are the **stable poles** of the spectrum. TT represents high CMI (localized disease), while LL represents low/absent CMI (generalized disease). They do not shift across the spectrum. **NEET-PG High-Yield Pearls:** * **Most common type in India:** Borderline Tuberculoid (BT). * **Stable poles:** TT and LL. * **Punched-out/Swiss-cheese lesions:** Pathognomonic for BB leprosy. * **Lepra Reactions:** Type 1 (Reversal) reactions are most common in borderline forms (BT, BB, BL), while Type 2 (ENL) is seen in BL and LL. * **Face sparing:** Typically seen in TT; the "immune-privileged" sites (axilla, groin, midline of back) are spared in LL.

Question 103: Tuberculosis verrucosa cutis is a form of:

A. Tuberculid
B. Primary tuberculosis
C. Postprimary tuberculosis with good resistance (Correct Answer)
D. Postprimary tuberculosis with poor resistance

Explanation: **Explanation:** Cutaneous tuberculosis is classified based on the mode of infection (exogenous vs. endogenous) and the host's immune status. **Tuberculosis Verrucosa Cutis (TVC)**, also known as "Prosector’s wart," occurs due to **exogenous inoculation** of *Mycobacterium tuberculosis* into the skin of a person who has **previously been infected** and has developed **strong cell-mediated immunity (CMI)**. Because the host has high resistance, the lesion remains localized, and the bacterial load is low (paucibacillary). **Analysis of Options:** * **Option C (Correct):** TVC is a **postprimary** infection because it occurs in sensitized individuals. The "good resistance" (high CMI) prevents systemic spread and results in the characteristic hyperkeratotic, verrucous (wart-like) plaque. * **Option A:** **Tuberculids** (e.g., Erythema induratum, Papulonecrotic tuberculid) are hypersensitivity reactions to internal TB; the organism cannot be cultured from the skin lesions. * **Option B:** **Primary tuberculosis** (e.g., Tuberculous Chancre) occurs in a non-sensitized individual with no prior immunity. * **Option C:** **Postprimary with poor resistance** describes conditions like **Scrofuloderma** or **Lupus Vulgaris** (moderate-to-good) or **Miliary TB** (very poor), where the body cannot effectively contain the spread. **High-Yield Clinical Pearls for NEET-PG:** * **Most common type** of cutaneous TB in India: **Lupus Vulgaris** (overall) or **Scrofuloderma** (in children). * **TVC Clinical Presentation:** Warty plaque, usually on the hands, knees, or buttocks. * **Diagnosis:** Mantoux test is strongly positive; Histopathology shows pseudoepitheliomatous hyperplasia and granulomas. * **Key Distinction:** Unlike Lupus Vulgaris, TVC **does not** show "apple-jelly nodules" on diascopy.

Question 104: What is the most common type of leprosy?

A. Tuberculoid (TT)
B. Borderline Tuberculoid (BT) (Correct Answer)
C. Mid-Borderline (BB)
D. Lepromatous (LL)

Explanation: **Explanation:** In the Ridley-Jopling classification of Leprosy, the disease is viewed as a spectrum based on the host's cell-mediated immunity (CMI). **Why Borderline Tuberculoid (BT) is correct:** **Borderline Tuberculoid (BT)** is the most common clinical presentation of leprosy worldwide, particularly in India. It represents a state where the CMI is present but not strong enough to localize the infection completely (unlike TT). Patients typically present with a few asymmetrical, hypopigmented patches with satellite lesions and peripheral nerve involvement. Because the majority of patients fall into the "borderline" categories rather than the polar ends, BT emerges as the most frequent subtype encountered in clinical practice. **Analysis of Incorrect Options:** * **Tuberculoid (TT):** This is the stable polar form with high CMI. While common, it is less frequent than BT. It is characterized by a single, well-defined, anesthetic hairless patch. * **Mid-Borderline (BB):** This is the most unstable form of leprosy. It is clinically rare because patients rapidly shift (upgrade or downgrade) toward the BT or BL poles. * **Lepromatous (LL):** This is the stable polar form with minimal CMI and high bacterial load (multibacillary). While it has the most severe systemic involvement, its prevalence is lower than the BT subtype. **NEET-PG High-Yield Pearls:** * **Most common type in India:** Borderline Tuberculoid (BT). * **Most unstable type:** Mid-Borderline (BB). * **Type most prone to Type 1 Reaction:** BT and BL (Borderline spectrum). * **Type most prone to Type 2 Reaction (ENL):** BL and LL. * **Lepromin Test:** Strongly positive in TT, negative in LL. (Note: It is a prognostic test, not a diagnostic one).

Question 105: Type-II lepra reaction is found in which classification of leprosy?

A. Borderline (BB)
B. Lepromatous (LL) (Correct Answer)
C. Borderline tuberculoid (BT)
D. Tuberculoid (TT)

Explanation: **Explanation:** Type-II Lepra Reaction, also known as **Erythema Nodosum Leprosum (ENL)**, is a Type-III hypersensitivity reaction (immune-complex mediated). It occurs exclusively in patients with a high bacillary load and low cell-mediated immunity (CMI). **Why Lepromatous (LL) is correct:** In the Ridley-Jopling classification, **Lepromatous (LL)** and **Borderline Lepromatous (BL)** leprosy are characterized by an abundance of *Mycobacterium leprae* (high Bacteriological Index). When treatment begins or during physiological stress, there is a massive release of antigens. These antigens combine with circulating antibodies to form immune complexes that deposit in tissues, leading to the systemic inflammatory features of ENL. **Why the other options are incorrect:** * **Tuberculoid (TT) and Borderline Tuberculoid (BT):** These poles have high CMI and very few bacilli (paucibacillary). Because there is an insufficient antigenic load to form significant immune complexes, Type-II reactions do not occur. Instead, these types are prone to **Type-I (Reversal) Reactions**, which are Type-IV hypersensitivity reactions. * **Borderline (BB):** While BB can occasionally transition toward the lepromatous pole, it is most classically associated with severe Type-I reactions due to its immunological instability. **High-Yield Clinical Pearls for NEET-PG:** * **Clinical Features:** Characterized by tender, evanescent, erythematous nodules, fever, lymphadenopathy, arthritis, and iridocyclitis. * **Drug of Choice:** **Thalidomide** is the gold standard for Type-II reactions. Steroids and Clofazimine are also used. * **Timing:** Unlike Type-I reactions (which often occur shortly after starting MDT), Type-II reactions can occur before, during, or even years after completing treatment. * **Key Lab Finding:** Neutrophilic leukocytosis and increased ESR/CRP.

Question 106: What is the drug of choice in Type I Lepra reaction with severe neuritis?

A. Systemic steroid (Correct Answer)
B. Clofazimine
C. Thalidomide
D. Chloroquine

Explanation: **Explanation:** **Type I Lepra Reaction (Reversal Reaction)** is a Delayed Type Hypersensitivity (Type IV) reaction occurring in borderline cases of leprosy. It is characterized by acute inflammation of existing skin lesions and, more critically, **acute neuritis** (nerve pain, tenderness, and loss of function). **Why Systemic Steroids are the Correct Choice:** The primary goal in managing Type I reactions, especially with **severe neuritis**, is to rapidly suppress cell-mediated inflammation to prevent permanent nerve damage and physical disability. **Systemic Corticosteroids (e.g., Prednisolone)** are the gold standard because they provide rapid anti-inflammatory and immunosuppressive action. The standard regimen usually starts at 40–60 mg/day, tapered over several months. **Analysis of Incorrect Options:** * **B. Clofazimine:** While it has anti-inflammatory properties and is used in Type II reactions (ENL) to help taper steroids, it is too slow-acting for the acute management of severe neuritis in Type I reactions. * **C. Thalidomide:** This is the **drug of choice for Type II Lepra Reaction (ENL)**. It is ineffective in Type I reactions because it does not address the Type IV hypersensitivity mechanism. * **D. Chloroquine:** This is a third-line agent occasionally used for mild Type II reactions (ENL) but has no role in managing Type I reactions or acute neuritis. **High-Yield Clinical Pearls for NEET-PG:** * **Type I Reaction:** Type IV Hypersensitivity; occurs in BT, BB, BL; key feature is **Neuritis**; DOC: **Steroids**. * **Type II Reaction (ENL):** Type III Hypersensitivity; occurs in BL, LL; key feature is **Erythema Nodosum** (tender nodules); DOC: **Thalidomide** (Steroids are also used, but Thalidomide is specific). * **Nerve Involvement:** If a patient on MDT develops new sensory/motor loss without skin changes, suspect "Silent Neuritis"—this also requires urgent systemic steroids.

Question 107: A skin smear is negative in which type of leprosy?

A. Indeterminate
B. Neuritic (Correct Answer)
C. Lepromatous
D. Borderline

Explanation: **Explanation:** The **Slit Skin Smear (SSS)** is a diagnostic tool used to detect Acid-Fast Bacilli (*Mycobacterium leprae*). The presence or absence of bacilli depends on the host’s cell-mediated immunity (CMI). **Why Neuritic Leprosy is the correct answer:** In **Pure Neuritic Leprosy**, the pathology is strictly confined to the peripheral nerves. Since there are no visible skin lesions (patches or nodules), a skin smear will naturally be negative for bacilli. Diagnosis in these cases usually requires a nerve biopsy or clinical evidence of nerve thickening and sensory loss. **Analysis of Incorrect Options:** * **Indeterminate Leprosy:** This is the earliest stage. While bacilli are very sparse and often difficult to find, the smear is not *categorically* negative by definition; however, it is usually paucibacillary. * **Lepromatous Leprosy (LL):** This represents the polar end with low CMI. It is **multibacillary**, meaning the skin smear is strongly positive with a high Bacteriological Index (BI) and presence of globi. * **Borderline Leprosy:** This spectrum (BT, BB, BL) shows varying degrees of positivity. While Borderline Tuberculoid (BT) is often smear-negative, the "Borderline" category as a whole includes types (like BL) that are smear-positive. **High-Yield Clinical Pearls for NEET-PG:** * **Bacteriological Index (BI):** Measures the density of bacilli (0 to 6+). * **Morphological Index (MI):** Measures the percentage of solid-staining (viable) bacilli; useful for monitoring treatment response. * **Sites for SSS:** Usually taken from 4–6 sites, including both earlobes and active lesions. * **Ridley-Jopling Classification:** Pure Neuritic leprosy is not formally part of this 5-group scale but is a recognized clinical entity in the Indian classification.

Question 108: Cutaneous lesions may be produced by the following mycobacteria, except?

A. M. intracellulare (Correct Answer)
B. M. Leprae
C. M. marinum
D. M. tuberculosis

Explanation: **Explanation:** The correct answer is **M. intracellulare**. While many mycobacteria are known to cause skin manifestations, *Mycobacterium intracellulare* (part of the *Mycobacterium avium* complex or MAC) primarily causes pulmonary disease, especially in immunocompromised patients or those with underlying lung pathology. It is rarely associated with primary cutaneous lesions. **Analysis of Options:** * **M. Leprae (Option B):** This is the causative agent of **Leprosy (Hansen’s Disease)**. It is a classic dermatological pathogen that presents with a spectrum of skin lesions ranging from hypopigmented patches (Tuberculoid) to diffuse nodules and infiltration (Lepromatous). * **M. marinum (Option C):** Known as the cause of **"Swimming Pool Granuloma"** or "Fish Tank Granuloma." It typically enters through abrasions and presents as a localized nodule or a series of nodules following a sporotrichoid distribution (along lymphatics). * **M. tuberculosis (Option D):** Cutaneous tuberculosis is well-documented. It presents in various forms depending on the host's immunity and mode of infection, such as **Lupus Vulgaris** (most common chronic form), **Scrofuloderma** (extension from underlying nodes), and **Warty Tuberculosis (Tuberculosis Verrucosa Cutis)**. **High-Yield Clinical Pearls for NEET-PG:** * **Most common cutaneous TB in India:** Lupus Vulgaris. * **Apple-jelly nodules:** Pathognomonic sign seen on diascopy in Lupus Vulgaris. * **Buruli Ulcer:** Caused by *M. ulcerans*. * **Sporotrichoid spread:** Besides *M. marinum*, it is also seen in Sporotrichosis, Nocardiosis, and Leishmaniasis. * **MAC (M. avium-intracellulare):** Most common systemic opportunistic bacterial infection in AIDS patients (CD4 <50), usually presenting with fever and weight loss rather than skin lesions.

Question 109: Bullous impetigo is caused by which bacterium?

A. Staphylococcus aureus (Correct Answer)
B. Pseudomonas
C. Haemophilus influenzae
D. Clostridium perfringens

Explanation: **Explanation:** **Bullous Impetigo** is a localized form of impetigo caused exclusively by **Staphylococcus aureus** (specifically Phage Group II, types 71 and 55). The underlying medical concept involves the production of **Exfoliative Toxins (ETA and ETB)** by the bacteria. These toxins act as "molecular scissors" that target and cleave **Desmoglein-1**, a cell-adhesion molecule in the desmosomes of the upper epidermis (stratum granulosum). This leads to acantholysis (loss of cell-to-cell adhesion), resulting in the formation of thin-walled, flaccid bullae that rupture easily. **Analysis of Incorrect Options:** * **B. Pseudomonas:** Typically associated with "Hot tub folliculitis" or Ecthyma gangrenosum in immunocompromised patients; it does not produce exfoliative toxins. * **C. Haemophilus influenzae:** More commonly associated with pediatric cellulitis (often with a violaceous/blue hue) or epiglottitis. * **D. Clostridium perfringens:** The primary causative agent of Gas Gangrene (clostridial myonecrosis), characterized by crepitus and profound systemic toxicity. **High-Yield Clinical Pearls for NEET-PG:** * **Non-bullous Impetigo:** The most common form; caused by *S. aureus* (most common) or *Streptococcus pyogenes*. It presents with characteristic **"honey-colored crusts."** * **Staphylococcal Scalded Skin Syndrome (SSSS):** A systemic manifestation of the same exfoliative toxins. Unlike bullous impetigo, the site of infection is distant, and the **Nikolsky sign is positive**. * **Histopathology:** Shows a subcorneal blister containing neutrophils and acantholytic cells. * **Treatment:** Topical Mupirocin is the first-line treatment for localized lesions. Systemic antibiotics (e.g., Cloxacillin or Cephalexin) are required for extensive cases.

Question 110: Green nail syndrome is caused by which bacterium?

A. Pseudomonas aeruginosa (Correct Answer)
B. Pleisomonas
C. Aeromonas
D. Burkholderia

Explanation: **Explanation:** **Green Nail Syndrome (Chloronychia)** is a clinical condition characterized by a distinct greenish discoloration of the nail plate. 1. **Why Pseudomonas aeruginosa is correct:** The characteristic green color is caused by the production of water-soluble pigments, primarily **pyocyanin** and **pyoverdin**, by the bacterium *Pseudomonas aeruginosa*. This organism thrives in moist environments. The infection typically occurs in nails already affected by onycholysis (separation of the nail from the bed) or chronic paronychia, where moisture becomes trapped, creating a niche for the bacteria to colonize. 2. **Why the other options are incorrect:** * **Pleisomonas & Aeromonas:** These are Gram-negative bacilli often associated with water-borne gastroenteritis or wound infections following exposure to fresh water, but they do not produce the pigments necessary to cause green nail syndrome. * **Burkholderia:** While *Burkholderia cepacia* can cause skin infections in specific settings (like "foot rot" in soldiers), it is not the causative agent of classic chloronychia. **High-Yield Clinical Pearls for NEET-PG:** * **Triad of Risk:** Onycholysis, chronic immersion in water (e.g., homemakers, bartenders), and exposure to detergents. * **Clinical Feature:** The green pigment does not involve the nail bed; it is deposited on the underside of the nail plate. * **Diagnosis:** Usually clinical; can be confirmed by culture or by the "white paper test" (pigment turns the paper green). * **Treatment:** Keeping the nail dry, topical antibiotics (e.g., Polymyxin B or Ciprofloxacin drops), or dilute acetic acid (vinegar) soaks to lower the pH.

Practice by Chapter

Impetigo

Practice Questions

Folliculitis, Furuncles, and Carbuncles

Practice Questions

Ecthyma

Practice Questions

Erysipelas and Cellulitis

Practice Questions

Staphylococcal Scalded Skin Syndrome

Practice Questions

Necrotizing Fasciitis

Practice Questions

Cutaneous Tuberculosis

Practice Questions

Leprosy

Practice Questions

Lyme Disease

Practice Questions

Syphilis

Practice Questions

Antibiotic Resistance in Dermatology

Practice Questions

Prophylaxis and Management

Practice Questions

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