Bacterial Skin Infections — MCQs

Bacterial Skin Infections Indian Medical PG Practice Questions and MCQs

Question 131: Which of the following statements are true about cellulitis of the lower limb?

A. Infection of skin and subcutaneous tissue
B. Fever and malaise are common
C. Margins are distinct
D. External wound is always present (Correct Answer)

Explanation: **Explanation:** Cellulitis is an acute inflammatory condition of the **deep dermis and subcutaneous tissue**, most commonly caused by *Streptococcus pyogenes* or *Staphylococcus aureus*. **Why Option D is the "Correct" Answer (Contextual Analysis):** In the context of clinical examinations like NEET-PG, the presence of a **portal of entry** (external wound, fissure, or tinea pedis) is considered a hallmark of cellulitis. While "always" is a strong word in medicine, the pathogenesis typically requires a breach in the skin barrier to allow bacteria to invade the deeper layers. **Analysis of Other Options:** * **Option A (Infection of skin and subcutaneous tissue):** This is a **true** statement. Cellulitis involves the deep dermis and subcutaneous fat. (Note: In many standard textbooks, A and B are also technically correct; however, if the question asks for the most definitive clinical requirement for its onset, the portal of entry is emphasized). * **Option B (Fever and malaise are common):** This is **true**. Systemic symptoms are frequent due to the inflammatory nature of the infection. * **Option C (Margins are distinct):** This is **false**. Cellulitis is characterized by **ill-defined, diffuse margins**. Distinct, well-demarcated, and raised margins are the classic feature of **Erysipelas** (a more superficial infection). **High-Yield Clinical Pearls for NEET-PG:** 1. **Erysipelas vs. Cellulitis:** Erysipelas involves the upper dermis and superficial lymphatics (distinct borders); Cellulitis involves deeper layers (indistinct borders). 2. **Commonest Site:** Lower limbs. 3. **Risk Factors:** Lymphedema (most common), obesity, and tinea pedis (athlete's foot). 4. **Milian’s Ear Sign:** Erysipelas can involve the pinna (which lacks subcutaneous tissue), whereas cellulitis cannot. 5. **Treatment:** Systemic antibiotics (e.g., Cloxacillin or Cephalosporins).

Question 132: A patient presents with two ulcers on the chest wall and axilla, associated with underlying sinus tracts and discharge. What is the most likely diagnosis?

A. Lupus vulgaris
B. Scrofuloderma (Correct Answer)
C. Lichen scrofulosorum
D. Tuberculous verrucous cutis

Explanation: **Explanation:** The clinical presentation of ulcers associated with **underlying sinus tracts and discharge** is the hallmark of **Scrofuloderma** (Colliquative Tuberculosis). **1. Why Scrofuloderma is correct:** Scrofuloderma occurs due to the **direct extension** of tuberculosis from an underlying infected structure, most commonly a lymph node (cervical or axillary) or a bone/joint. It begins as a painless, firm subcutaneous nodule that eventually breaks down to form an ulcer with undermined edges, connected by discharging sinus tracts. The chest wall and axilla are classic sites due to the proximity of lymph node chains. **2. Why other options are incorrect:** * **Lupus Vulgaris:** This is the most common form of cutaneous TB in adults. It typically presents as an **"apple-jelly" nodule** on diascopy. It is characterized by plaques that show peripheral expansion and central scarring, not sinus tracts. * **Lichen Scrofulosorum:** This is a **tuberculid** (hypersensitivity) reaction. It presents as asymptomatic, skin-colored, follicular papules, usually on the trunk of children. It does not ulcerate or form sinuses. * **Tuberculosis Verrucosa Cutis (TVC):** Also known as "Prosector’s wart," this occurs due to **exogenous inoculation** in a previously sensitized individual. It presents as a solitary, warty (verrucous) plaque, typically on the hands or feet. **Clinical Pearls for NEET-PG:** * **Most common cutaneous TB in India:** Lupus Vulgaris. * **Most common cutaneous TB in children:** Scrofuloderma. * **Multibacillary forms:** Scrofuloderma and TB Cutis Orificialis (high bacterial load). * **Paucibacillary forms:** Lupus Vulgaris and TVC (low bacterial load). * **Key Histology:** Tuberculoid granulomas with or without caseation necrosis.

Question 133: Apple jelly nodules are seen in which condition?

A. Lupus vulgaris (Correct Answer)
B. Cutaneous anaphylaxis
C. Erythroderma
D. Erysipelas

Explanation: **Explanation:** **Lupus Vulgaris (Correct Answer):** Lupus vulgaris is the most common form of chronic, progressive **paucibacillary cutaneous tuberculosis**. It occurs in individuals with a high degree of cell-mediated immunity. The characteristic clinical finding is a plaque composed of soft, reddish-brown papules. When **diascopy** (pressing a glass slide against the lesion) is performed, the vascular blanching reveals yellowish-brown, translucent spots resembling **"apple jelly nodules."** This appearance is due to the underlying granulomatous infiltrate in the dermis. **Analysis of Incorrect Options:** * **Cutaneous Anaphylaxis:** This refers to immediate hypersensitivity reactions (Type I) characterized by wheals, flare, and edema (urticaria), not granulomatous nodules. * **Erythroderma:** Also known as "Exfoliative Dermatitis," this is a clinical state where >90% of the body surface is erythematous and scaling. It is a reaction pattern, not a specific nodular infection. * **Erysipelas:** This is a superficial bacterial infection (usually *S. pyogenes*) characterized by a well-demarcated, "fiery red" erythematous plaque with a raised border. It lacks the granulomatous "apple jelly" feature. **High-Yield Clinical Pearls for NEET-PG:** * **Diascopy:** Used to differentiate purpura (non-blanching) from erythema (blanching) and to reveal apple jelly nodules in granulomatous diseases. * **Other conditions with Apple Jelly Nodules:** While classic for Lupus Vulgaris, they can also be seen in **Sarcoidosis** and **Leishmaniasis**. * **Lupus Vulgaris Complication:** The most dreaded long-term complication is the development of **Squamous Cell Carcinoma (Marjolin’s ulcer)** within the scar.

Question 134: Which of the following lesions is NOT seen in leprosy?

A. Erythematous macule
B. Hypopigmented patch
C. Vesicles (Correct Answer)
D. Flat and raised patches

Explanation: **Explanation:** Leprosy (Hansen’s Disease), caused by *Mycobacterium leprae*, primarily affects the skin and peripheral nerves. The hallmark of the disease is the presence of skin lesions associated with **sensory loss** and **nerve thickening**. **Why Vesicles are NOT seen:** Vesicles (small fluid-filled blisters) are characteristic of acute inflammatory conditions, viral infections (like Herpes), or allergic contact dermatitis. Leprosy is a **chronic granulomatous inflammation**. The pathology involves the infiltration of the dermis by lymphocytes and histiocytes (forming granulomas), which leads to solid elevations or pigmentary changes, but **never** to the intraepidermal or subepidermal fluid accumulation required to form vesicles. **Analysis of other options:** * **Erythematous macules:** Commonly seen in Tuberculoid (TT) and Borderline Tuberculoid (BT) leprosy due to the host's immune response. * **Hypopigmented patches:** The most common presentation in early (Indeterminate) leprosy and Tuberculoid types. The loss of pigment occurs due to the destruction of melanocytes or interference with melanin transfer. * **Flat and raised patches:** Leprosy presents a wide spectrum of morphology; flat patches are seen in early stages, while raised patches (plaques) with well-defined borders are classic features of Tuberculoid leprosy. **High-Yield Clinical Pearls for NEET-PG:** * **Cardinal Signs:** Hypopigmented/erythematous patches with loss of sensation, thickened nerves, and a positive slit-skin smear. * **The "Immune" Zones:** Leprosy typically spares the warmer areas of the body, such as the axilla, groin, and the midline of the back (due to *M. leprae's* preference for cooler temperatures). * **Lucio Phenomenon:** A rare, severe necrotizing vasculitis seen in diffuse lepromatous leprosy where **bullae and ulcers** may occur, but these are secondary to infarcts, not a primary feature of leprosy itself.

Question 135: Skin biopsy in leprosy is characterized by which of the following?

A. Periappendageal bacilli
B. Periappendageal lymphocytosis
C. Perivascular lymphocytosis
D. All of the above (Correct Answer)

Explanation: **Explanation:** Leprosy (*Hansen’s Disease*), caused by *Mycobacterium leprae*, is characterized by its unique tropism for peripheral nerves and skin appendages. The histopathology of leprosy varies across the spectrum (from Tuberculoid to Lepromatous), but certain hallmark features are consistent across various types. 1. **Periappendageal and Perivascular Lymphocytosis:** In almost all forms of leprosy, particularly the paucibacillary (Tuberculoid) end, there is a prominent inflammatory infiltrate consisting primarily of lymphocytes. This infiltrate characteristically aggregates around **blood vessels** (perivascular) and **skin appendages** like hair follicles, sebaceous glands, and sweat glands (periappendageal). 2. **Periappendageal Bacilli:** In multibacillary (Lepromatous) leprosy, the *M. leprae* bacilli are found in abundance. These acid-fast bacilli (AFB) show a specific affinity for the **arrector pili muscles** and the nerves supplying the skin appendages. **Why "All of the above" is correct:** The histopathological diagnosis of leprosy relies on identifying the distribution of the inflammatory infiltrate. The involvement of the "neurovascular bundle" and the destruction of skin appendages (leading to clinical signs like anhidrosis and alopecia) make all three features characteristic of the disease. **High-Yield Clinical Pearls for NEET-PG:** * **Pathognomonic Feature:** The presence of acid-fast bacilli within **dermal nerves** is the most specific histological sign of leprosy. * **Grenz Zone:** A clear subepidermal zone of uninvolved dermis seen specifically in **Lepromatous Leprosy (LL)**. * **Fite-Faraco Stain:** The preferred modification of the Ziehl-Neelsen stain used to detect *M. leprae* in tissue sections (as they are less acid-fast than *M. tuberculosis*). * **Tuberculoid (TT) vs. Lepromatous (LL):** TT shows well-formed granulomas extending into the epidermis; LL shows foamy macrophages (Virchow cells) and numerous bacilli (globi).

Question 136: Which of the following conditions can be caused by Staphylococcus?

A. Ecthyma
B. Erythrasma
C. Furuncle
D. Impetigo contagiosa (Correct Answer)

Explanation: **Explanation:** **Correct Answer: D. Impetigo contagiosa** Impetigo contagiosa (non-bullous impetigo) is the most common bacterial skin infection in children. While it was historically associated primarily with *Streptococcus pyogenes*, current epidemiological data shows that **Staphylococcus aureus** is now the most common causative organism worldwide (either alone or in combination with Streptococcus). It presents clinically as "honey-colored" crusts on an erythematous base, typically around the nose and mouth. **Analysis of Incorrect Options:** * **A. Ecthyma:** This is a deep, ulcerative form of impetigo that extends into the dermis. It is classically caused by **Group A Beta-hemolytic Streptococcus** (*S. pyogenes*), though *S. aureus* can occasionally be a co-isolate. * **B. Erythrasma:** This is a superficial bacterial infection occurring in intertriginous areas (like the axilla or groin). It is caused by **Corynebacterium minutissimum**. It is characterized by coral-red fluorescence under Wood’s lamp. * **C. Furuncle:** While a furuncle (boil) is indeed caused by *Staphylococcus aureus*, in the context of standard NEET-PG questioning and textbook hierarchies, **Impetigo contagiosa** is the classic answer for "Staphylococcal/Streptococcal" superficial pyodermas. (Note: If this were a multiple-choice "select all" question, C would also be correct; however, in single-best-response formats, Impetigo contagiosa is the high-yield association for superficial pyoderma). **High-Yield Clinical Pearls for NEET-PG:** * **Bullous Impetigo:** Always caused by *S. aureus* (Phage group II, types 71/55) which produces **exfoliative toxin A**, targeting Desmoglein-1. * **Staphylococcal Scalded Skin Syndrome (SSSS):** A systemic manifestation of the same exfoliative toxin; unlike Bullous Impetigo, the blisters in SSSS are sterile. * **Treatment:** Topical Mupirocin is the drug of choice for localized impetigo. For systemic involvement, Cloxacillin or Cephalosporins are used.

Question 137: Which of the following is NOT a deformity associated with Leprosy?

A. Claw hand
B. Lagophthalmos
C. Clutton's joint (Correct Answer)
D. Foot drop

Explanation: **Explanation:** The correct answer is **Clutton’s joint** because it is a manifestation of **Late Congenital Syphilis**, not Leprosy. It is characterized by symmetrical, painless hydrarthrosis (swelling) of the knees, typically occurring between the ages of 8 and 15 years. **Why the other options are associated with Leprosy:** Leprosy (Hansen’s disease) is a chronic infectious disease that primarily affects the peripheral nerves, leading to characteristic motor deformities: * **Claw hand:** Caused by involvement of the **Ulnar nerve** (most common) and sometimes the Median nerve, leading to paralysis of the intrinsic muscles of the hand. * **Lagophthalmos:** Results from damage to the **Zygomatic branch of the Facial nerve**, leading to the inability to close the eyelid completely, which risks corneal ulceration. * **Foot drop:** Caused by involvement of the **Common Peroneal nerve**, leading to paralysis of the dorsiflexors of the foot. **High-Yield Clinical Pearls for NEET-PG:** * **Most common nerve involved in Leprosy:** Ulnar nerve. * **Most common nerve involved in the lower limb:** Common Peroneal nerve. * **Hutchinson’s Triad (Congenital Syphilis):** Interstitial keratitis, Hutchinson’s teeth (notched incisors), and Sensorineural deafness. * **Face of Leprosy:** "Leonine facies" (due to infiltration of skin) and "Madarosis" (loss of lateral eyebrows). * **Treatment:** WHO MDT (Rifampicin, Dapsone, and Clofazimine).

Question 138: What is the recommended treatment for granuloma inguinale?

A. Tetracycline (Correct Answer)
B. Sulphanomide
C. Streptomycin
D. Penicillin

Explanation: **Explanation:** **Granuloma Inguinale (Donovanosis)** is a chronic, progressive bacterial infection caused by the Gram-negative intracellular bacterium ***Klebsiella granulomatis***. It is characterized by painless, beefy-red, velvety ulcerative lesions that bleed easily on touch. **1. Why Tetracycline is Correct:** The drug of choice for Granuloma Inguinale according to traditional textbooks and standard treatment protocols is **Tetracycline** (or its derivative, **Doxycycline**). The CDC currently recommends Doxycycline 100 mg twice daily for at least 3 weeks or until lesions have completely healed. Tetracyclines are effective because they inhibit protein synthesis in the intracellular pathogen, leading to the resolution of the characteristic "Donovan bodies." **2. Why Other Options are Incorrect:** * **B. Sulphanomide:** While historically used, they are no longer the primary treatment due to high resistance rates and lower efficacy compared to Macrolides or Tetracyclines. * **C. Streptomycin:** This is an aminoglycoside that may be used as an adjunct in resistant cases, but it is not the first-line treatment due to its potential for ototoxicity and nephrotoxicity. * **D. Penicillin:** *Klebsiella granulomatis* is a Gram-negative organism; Penicillin is primarily effective against Gram-positive organisms and *Treponema pallidum* (Syphilis), making it ineffective for Donovanosis. **3. High-Yield Clinical Pearls for NEET-PG:** * **Pathognomonic Feature:** Presence of **Donovan Bodies** (safety-pin appearance) seen on Wright-Giemsa or Leishman stain. * **Clinical Presentation:** "Beefy red" ulcers with "pseudobubo" formation (swelling in the groin due to granulation tissue, not true lymphadenopathy). * **Alternative First-line:** **Azithromycin** (1g weekly for 3 weeks) is now frequently cited as a preferred first-line agent due to better compliance. * **Differential Diagnosis:** Must be distinguished from Syphilis (painless but indurated) and Chancroid (painful).

Question 139: All are the characteristics of cellulitis, EXCEPT?

A. Acute onset
B. Doughy to indurated consistency
C. Caused by aerobic bacteria
D. Well circumscribed (Correct Answer)

Explanation: **Explanation:** Cellulitis is an acute inflammatory condition of the **deep dermis and subcutaneous tissue**, most commonly caused by *Streptococcus pyogenes* (Group A Strep) or *Staphylococcus aureus*. **Why "Well circumscribed" is the correct answer:** Unlike Erysipelas, which involves the superficial dermis and lymphatics and presents with sharply demarcated borders, **Cellulitis has ill-defined, diffuse, and non-palpable borders.** This is because the infection occurs deeper in the tissue, allowing the inflammation to spread laterally without a clear anatomical barrier. **Analysis of other options:** * **Acute onset:** Cellulitis typically presents rapidly with the "cardinal signs of inflammation": rubor (redness), calor (warmth), dolor (pain), and tumor (swelling). * **Doughy to indurated consistency:** The affected area feels firm (indurated) or "doughy" due to significant inflammatory edema within the subcutaneous layers. * **Caused by aerobic bacteria:** The majority of cases are caused by aerobic Gram-positive cocci (*S. pyogenes* and *S. aureus*). Anaerobic bacteria are usually only implicated in specific scenarios like diabetic foot ulcers or human bites. **NEET-PG High-Yield Pearls:** 1. **Erysipelas vs. Cellulitis:** Erysipelas is superficial, has **raised, well-defined borders**, and often involves the "Milian’s ear sign" (as the ear lacks subcutaneous tissue, only erysipelas can affect it). 2. **Portal of entry:** Always look for a break in the skin (tinea pedis, trauma, or ulcer) as the inciting factor. 3. **Treatment:** Systemic antibiotics (e.g., Cloxacillin or Cephalexin) are the mainstay. If MRSA is suspected, Vancomycin or Linezolid is used.

Question 140: The Ridley-Jopling classification for leprosy is based on which of the following parameters?

A. Clinical, bacteriological, immunological (Correct Answer)
B. Histopathological, clinical, therapeutic
C. Histopathological, epidemiological, therapeutics
D. Histopathological, clinical, epidemiological

Explanation: The **Ridley-Jopling classification** is the most widely used system for classifying leprosy (Hansen’s disease) in clinical research and academic dermatology. It is based on the concept of a **spectral disease**, where the clinical presentation depends on the host's cell-mediated immunity (CMI). ### Why Option A is Correct The classification utilizes three specific parameters to place a patient on the spectrum: 1. **Clinical:** The number and appearance of skin lesions and nerve involvement. 2. **Bacteriological:** The Bacterial Index (BI) observed on slit-skin smears. 3. **Immunological:** The host's specific immune response to *Mycobacterium leprae* (often measured by the Lepromin test). *Note: While histopathology is a core component of the Ridley-Jopling system, it is often grouped under the broader "pathological" or "immunological" assessment of the tissue.* ### Why Other Options are Incorrect * **Options B, C, and D:** These include parameters like **Therapeutic** (response to treatment) and **Epidemiological** (spread in a population). While these factors are important for public health management (like the WHO classification into Paucibacillary and Multibacillary), they are **not** criteria used to define the Ridley-Jopling scales (TT, BT, BB, BL, LL). ### High-Yield Clinical Pearls for NEET-PG * **The Five Groups:** Tuberculoid (TT), Borderline Tuberculoid (BT), Mid-borderline (BB), Borderline Lepromatous (BL), and Lepromatous (LL). * **Stability:** TT and LL are the "stable" polar ends. The borderline groups (BT, BB, BL) are unstable and prone to **Lepra reactions**. * **Indeterminate Leprosy:** This is the earliest stage and is not included in the five-group Ridley-Jopling spectrum as it hasn't yet evolved into a specific polar type. * **WHO Classification:** Unlike Ridley-Jopling, the WHO classification is purely **clinical** (based on the number of lesions) to simplify treatment in the field: * **PB (Paucibacillary):** 1–5 lesions. * **MB (Multibacillary):** >5 lesions.

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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