Bacterial Skin Infections Practice Questions

Q: Leprosy affects all organs except which of the following?

Uterus. **Explanation:** Leprosy, caused by *Mycobacterium leprae*, is a chronic granulomatous disease that primarily targets cooler areas of the body. The fundamental principle governing its distribution is the **temperature sensitivity** of the organism; *M. leprae* thrives best at temperatures between **27°C and 30°C**. **Why Uterus is the Correct Answer:** The **Uterus** is located deep within the pelvic cavity, maintaining a core body temperature of approximately **37°C**. This high temperature is inhibitory to the growth and survival of *M. leprae*. Consequently, the uterus (along with the lungs, CNS, and pancreas) is classically considered "immune" or resistant to leprosy. **Analysis of Incorrect Options:** * **Eyes (A):** The anterior segment of the eye is cooler than the core body temperature. Leprosy frequently involves the eyes, leading to lagophthalmos, corneal ulcers, and iridocyclitis. * **Nerves (B):** Peripheral nerves are a primary target. The bacteria have a unique tropism for **Schwann cells**, leading to neuropathy and characteristic nerve thickening. * **Ovary (D):** While internal, the ovaries can occasionally be involved in lepromatous leprosy (LL) due to hematogenous spread, leading to oophoritis, though this is less common than testicular involvement. **NEET-PG High-Yield Pearls:** * **Organs Spared in Leprosy:** CNS (Brain and Spinal Cord), Lungs, Uterus, Pancreas, and the "Warm areas" of the skin (axilla, groin, midline of the back). * **Most Common Nerve Involved:** Ulnar nerve. * **Testicular Involvement:** Very common in LL; can lead to sterility and gynecomastia due to low scrotal temperature. * **Cardinal Signs:** Hypopigmented patches with sensory loss, thickened nerves, and positive skin smears for Acid-Fast Bacilli.

Q: A 23-year-old male presents with a painless penile ulcer and painless lymphadenopathy. What is the most likely diagnosis?

Syphilis. ### Explanation The clinical presentation of a **painless penile ulcer** (chancre) accompanied by **painless regional lymphadenopathy** is the classic hallmark of **Primary Syphilis**, caused by the spirochete *Treponema pallidum*. #### Why Syphilis is Correct: The primary chancre typically appears 3–4 weeks after exposure. It is characterized by a clean base, indurated (hard) edges, and a lack of exudate. Crucially, both the ulcer and the associated inguinal lymphadenopathy are **painless**, which distinguishes it from most other genital ulcerative diseases. #### Why Other Options are Incorrect: * **Chancroid (*Haemophilus ducreyi*):** Presents as a **painful**, soft ulcer with a ragged, undermined edge and a necrotic base. The associated lymphadenopathy (bubo) is also exquisitely painful. * **Donovanosis (Granuloma Inguinale):** Caused by *Klebsiella granulomatis*. It presents as beefy-red, painless, velvety ulcers. However, it is characterized by **pseudobuboes** (subcutaneous granulation) rather than true lymphadenopathy. * **Herpes (HSV-2):** Presents as multiple, small, **painful** vesicles that rupture to form shallow ulcers. It is often associated with systemic symptoms like fever and painful lymphadenopathy. #### NEET-PG High-Yield Pearls: * **Investigation of Choice:** Dark-field microscopy is the gold standard for primary syphilis (shows corkscrew motility). * **Hard Chancre:** Syphilis; **Soft Chancre:** Chancroid. * **Donovan Bodies:** Seen on tissue smears (Wrights/Giemsa stain) as "safety-pin" appearing organisms within macrophages (pathognomonic for Donovanosis). * **Rule of Thumb:** If the ulcer hurts, think Chancroid or Herpes; if it doesn't, think Syphilis or LGV (though LGV usually has painful nodes—the "Sign of the Groove").

Q: All of the following are modes of transmission of leprosy except?

Transplacental spread. ### Explanation Leprosy, caused by *Mycobacterium leprae*, is a chronic infectious disease primarily affecting the skin and peripheral nerves. Understanding its transmission is crucial for NEET-PG, as it often involves distinguishing between proven routes and theoretical possibilities. **Why Transplacental Spread is the Correct Answer:** Congenital leprosy (transplacental transmission) is **not** a recognized mode of transmission. Studies have shown that even children born to mothers with highly infectious lepromatous leprosy are born free of the disease. The placenta acts as an effective barrier against *M. leprae*. Infection in infants usually occurs postnatally through close prolonged contact with the mother. **Analysis of Other Options:** * **Droplet Infection (Option D):** This is the **most common** and primary mode of transmission. Large numbers of bacilli are shed from the nasal mucosa of untreated multibacillary (MB) patients during sneezing or coughing. * **Breast Milk (Option A):** *M. leprae* has been identified in the breast milk of lactating mothers with lepromatous leprosy. While not the primary route, it is a documented potential mode of transmission. * **Insect Bites (Option B):** Mechanical transmission via arthropod vectors (like flies or mosquitoes) has been demonstrated in experimental settings, though its epidemiological significance in humans remains minor. **High-Yield Clinical Pearls for NEET-PG:** * **Incubation Period:** Average 3–5 years (longest among bacterial infections). * **Primary Site of Entry:** Respiratory tract (nasal mucosa) is the most common; skin-to-skin contact is secondary. * **Reservoirs:** Humans are the main reservoir, but **Nine-banded armadillos** are a known zoonotic source. * **Infectivity:** Leprosy is highly infectious but has low pathogenicity (most people have natural immunity).

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

External wound is always present. **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).

Q: A woman approaches a physician for contraceptive advice. On examination, there were two symmetrical ulcers on the vulva, which were well-defined with a firm base. Which of the following is the most likely cause?

Chancre. The clinical presentation of **symmetrical, well-defined ulcers with a firm base** on the vulva is a classic description of **Kissing Chancres**, which are the hallmark of **Primary Syphilis**. **1. Why "Chancre" is the correct answer:** A chancre is the primary lesion of syphilis, caused by *Treponema pallidum*. It is characteristically a single, painless, indurated (firm) ulcer with a clean base and well-defined margins [1]. In women, when these ulcers occur on opposing surfaces of the labia, they can develop as "kissing ulcers" due to autoinoculation, resulting in the symmetrical presentation described. **2. Why other options are incorrect:** * **Herpes (HSV-2):** Typically presents as multiple, shallow, extremely painful vesicles or erosions on an erythematous base [1]. They are not indurated (firm) and are rarely perfectly symmetrical "kissing" ulcers. * **Syphilis:** While a chancre is a manifestation of syphilis, in medical entrance exams, if both the clinical sign (Chancre) and the disease (Syphilis) are listed, the specific lesion name is often the preferred answer for "the most likely cause" of the physical finding. However, "Chancre" specifically describes the *ulcer* mentioned in the stem. * **Malignancy:** Vulvar squamous cell carcinoma usually presents as a chronic, irregular, fungating mass or a non-healing ulcer in older women, often associated with pruritus, rather than acute symmetrical ulcers. **Clinical Pearls for NEET-PG:** * **Hard Chancre (Syphilis):** Painless, indurated, clean base, heals spontaneously in 3–6 weeks. * **Soft Chancre (Chancroid/H. ducreyi):** Painful, non-indurated, ragged edges, necrotic/purulent base. * **Investigation of Choice:** Dark-ground microscopy (DGM) is the gold standard for primary syphilis; VDRL/RPR may be negative in the early stages. * **Treatment:** Injection Benzathine Penicillin G (2.4 million units IM) is the drug of choice.

Q: What is the drug of choice for the treatment of gonorrhoea in a pregnant patient who is allergic to beta-lactam antibiotics?

Spectinomycin. **Explanation:** The management of Gonorrhoea in pregnancy requires drugs that are both effective against *Neisseria gonorrhoeae* and safe for the fetus (Category B). **1. Why Spectinomycin is correct:** While the standard first-line treatment for uncomplicated gonorrhoea is a single dose of Ceftriaxone (a beta-lactam), it is contraindicated in patients with documented **beta-lactam allergies**. In such scenarios, especially during **pregnancy**, **Spectinomycin (2g IM single dose)** is the drug of choice. It is an aminocyclitol antibiotic that inhibits protein synthesis. It is highly effective against *N. gonorrhoeae* and is considered safe for use in all trimesters of pregnancy. **2. Why other options are incorrect:** * **Piperacillin:** This is a penicillin derivative (beta-lactam) [1]. It would trigger an allergic reaction in this patient and is not the standard treatment for gonorrhoea. * **Ceftriaxone:** Although it is the overall drug of choice for gonorrhoea, it is a third-generation cephalosporin. Due to the risk of cross-reactivity in patients with beta-lactam/penicillin allergies, it is avoided here [1]. * **Ciprofloxacin:** Fluoroquinolones are generally avoided in pregnancy due to potential risks to fetal cartilage development. Furthermore, there is widespread global resistance of *N. gonorrhoeae* to ciprofloxacin. **Clinical Pearls for NEET-PG:** * **Dual Therapy:** Always remember to treat for co-existing **Chlamydia** infection (usually with Azithromycin) unless ruled out. * **Spectinomycin Limitation:** It is ineffective against pharyngeal gonorrhoea; it is primarily used for urogenital and anorectal infections. * **Alternative:** If Spectinomycin is unavailable, a high dose of **Azithromycin (2g orally)** can be used, though it is associated with significant GI distress.

Q: 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?

Scrofuloderma. **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 1

Leprosy affects all organs except which of the following?

Accepted Answer

Uterus

Answer

Eyes

Answer

Nerves

Answer

Ovary

Question 2

Which of the following organisms is implicated in the causation of botryomycosis?

Accepted Answer

Staphylococcus aureus

Answer

Staphylococcus albus

Answer

Pseudomonas aeruginosa

Answer

Streptococcus pneumoniae

Question 3

A 23-year-old male presents with a painless penile ulcer and painless lymphadenopathy. What is the most likely diagnosis?

Accepted Answer

Syphilis

Answer

Chancroid

Answer

Donovanosis

Answer

Herpes

Question 4

All of the following are modes of transmission of leprosy except?

Accepted Answer

Transplacental spread

Answer

Breast milk

Answer

Insect bite

Answer

Droplet infection

Question 5

A 15-year-old boy presented with multiple hypoaesthetic macules with sloping edges, seen on the face, trunk, and arms. Histopathologic examination of a lesion shows numerous bacilli and granulomatous infiltration. What is your diagnosis?

Accepted Answer

Borderline leprosy

Answer

Tuberculoid leprosy

Answer

Lepromatous leprosy

Answer

Indeterminate leprosy

Question 6

What is the most clinically significant skin eruption associated with Mycoplasma pneumoniae infection?

Accepted Answer

Erythema multiforme major

Answer

Bullous eruptions

Answer

Toxic epidermal necrolysis

Answer

Pyostomatitis vegetans

Question 7

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

Accepted Answer

External wound is always present

Answer

Infection of skin and subcutaneous tissue

Answer

Fever and malaise are common

Answer

Margins are distinct

Question 8

A woman approaches a physician for contraceptive advice. On examination, there were two symmetrical ulcers on the vulva, which were well-defined with a firm base. Which of the following is the most likely cause?

Accepted Answer

Chancre

Answer

Herpes

Answer

Syphilis

Answer

Malignancy

Question 9

What is the drug of choice for the treatment of gonorrhoea in a pregnant patient who is allergic to beta-lactam antibiotics?

Accepted Answer

Spectinomycin

Answer

Piperacillin

Answer

Ceftriaxone

Answer

Ciprofloxacin

Question 10

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?

Accepted Answer

Scrofuloderma

Answer

Lupus vulgaris

Answer

Lichen scrofulosorum

Answer

Tuberculous verrucous cutis

Bacterial Skin Infections — MCQs

Bacterial Skin Infections — MCQs

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