Bacterial Skin Infections Practice Questions

Q: What is the first-line treatment for localized impetigo?

Mupirocin. ***Mupirocin*** - **Topical mupirocin** is the recommended **first-line treatment** for **localized impetigo**, particularly when only a few lesions are present. - It is effective against **Staphylococcus aureus** and **Streptococcus pyogenes**, the most common causative organisms. - Applied 2-3 times daily for 5-7 days. *Cefalexin* - **Cefalexin** is an **oral antibiotic** used for impetigo that is widespread or unresponsive to topical therapy, not for localized cases. - It is a **first-generation cephalosporin** effective against gram-positive bacteria. - Reserved for extensive disease or when topical therapy is impractical. *Erythromycin* - **Erythromycin** is an **oral antibiotic** but is generally reserved for penicillin-allergic patients or more extensive impetigo. - Due to increasing microbial resistance, it is often not the preferred first-line systemic agent. - Resistance rates vary geographically and can limit effectiveness. *Clindamycin* - **Clindamycin** is an **oral or topical antibiotic** primarily used for impetigo when there is concern for **MRSA (methicillin-resistant S. aureus)**. - May be used in cases of penicillin allergy or suspected resistant organisms. - Not the first-line choice for typical localized impetigo due to its broader spectrum and potential for side effects.

Q: Bullous impetigo is primarily caused by which of the following?

Staphylococcus aureus. ***Staphylococcus aureus*** - **Bullous impetigo** is a distinct form of impetigo characterized by **blisters or bullae**, caused by specific strains of *Staphylococcus aureus* that produce **exfoliative toxins**. - These toxins target **desmoglein 1**, an adhesion protein, leading to epidermal cleavage and the formation of superficial blisters. *Streptococcus pyogenes* - This bacterium is the primary cause of **non-bullous impetigo** (impetigo contagiosa), which presents as small vesicles that rupture and form honey-colored crusts. - While it can cause other skin infections, it does not typically produce the exfoliative toxins responsible for bullous impetigo. *Escherichia coli* - **Escherichia coli** is a common inhabitant of the **gastrointestinal tract** and a frequent cause of urinary tract infections, sepsis, and diarrheal diseases. - It is not associated with impetigo or other primary skin infections in immunocompetent individuals. *Yersinia pestis* - **Yersinia pestis** is the causative agent of **plague**, a severe infectious disease that manifests as bubonic, pneumonic, or septicemic forms. - This bacterium is transmitted by **fleas** and is not implicated in causing impetigo.

Q: A 5-year-old child presents with a honey-colored crusted lesion on their face. What is the most likely causative organism?

Streptococcus pyogenes. ***Streptococcus pyogenes*** - *Streptococcus pyogenes* (Group A Streptococcus) is the **most common causative organism** of **non-bullous impetigo**, which characteristically presents with **honey-colored crusted lesions**. - Non-bullous impetigo accounts for **70% of all impetigo cases** and typically affects the face, particularly around the mouth and nose. - The honey-colored crusts form when the serous exudate from ruptured vesicles dries on the skin surface. - **Important complication:** Post-streptococcal glomerulonephritis can occur 1-3 weeks after skin infection. *Staphylococcus aureus* - *S. aureus* is the primary cause of **bullous impetigo** (30% of cases), which presents with **fluid-filled bullae** rather than honey-colored crusts. - While *S. aureus* can co-infect with *S. pyogenes* in non-bullous impetigo, it is **not the primary pathogen** in the classic honey-crusted presentation described. - *S. aureus* produces exfoliative toxins that cause bullae formation in bullous impetigo. *Pseudomonas aeruginosa* - *Pseudomonas aeruginosa* is typically associated with **hot tub folliculitis**, infections in immunocompromised individuals, or puncture wounds. - Infections characteristically produce **bluish-green pus** with a fruity odor, not honey-colored crusts. - Not a typical cause of impetigo in healthy children. *Candida albicans* - *Candida albicans* causes **fungal infections** such as oral thrush, diaper dermatitis, or intertrigo in skin folds. - Presents with **erythematous patches with satellite lesions**, not honey-colored crusts. - The lesions are typically moist, macerated, and pruritic rather than crusted.

Q: In your STI clinic, standardized treatment kits are available for different conditions based on clinical presentation and likely pathogens. A 22-year-old female comes to the STI clinic with minimal vaginal discharge. On speculum examination, erosions are seen on the cervix. Which of the following treatment kit should be given to this patient?

Grey. ***Grey*** - A grey kit is indicated for **vaginal discharge** with associated **cervical erosions**, suggesting a treatable bacterial STI like gonorrhea or chlamydia. This kit typically contains antibiotics effective against these pathogens. - The presence of **minimal vaginal discharge** combined with **cervical erosions** points towards cervicitis, for which the grey kit is specifically designed. *Green* - The green kit is typically for the treatment of **vaginal discharge** without specific signs of cervicitis, often targeting common causes like **bacterial vaginosis** or **trichomoniasis**. - It would not specifically address the **cervical erosions** seen in this patient, which are more indicative of cervicitis. *Red* - The red kit is generally used for the treatment of **genital ulcers**, which are typically caused by **herpes simplex virus** or **syphilis**. - While there are erosions, the primary complaint is discharge, and erosions are not typically the sole indicator for a "genital ulcer" kit. *Yellow* - The yellow kit is often designated for **urethral discharge** in males, addressing conditions like **gonorrhea** or **chlamydia** when presenting as urethritis. - This patient is female and presents with **vaginal discharge** and **cervical erosions**, making the yellow kit inappropriate.

Q: A man presents with a history of dysuria and urethral discharge after having unprotected sexual intercourse. What is the treatment of choice for this infection?

Ceftriaxone. ***Ceftriaxone*** - The combination of **dysuria** and **urethral discharge** following unprotected sexual intercourse is highly suggestive of **gonorrhea**. - **Ceftriaxone** is the recommended first-line treatment for uncomplicated gonococcal infections due to increasing antibiotic resistance. *Erythromycin* - Erythromycin is primarily used for atypical bacterial infections, such as those caused by *Mycoplasma pneumoniae* or *Chlamydia trachomatis*. - While it can be used for chlamydia, it is not the preferred treatment for suspected gonorrhea. *Azithromycin* - Azithromycin is often used in combination with ceftriaxone for gonorrhea to cover potential co-infection with **Chlamydia trachomatis**. - However, **monotherapy with azithromycin is not recommended for gonorrhea** due to concerns about emerging resistance and suboptimal efficacy. *Penicillin G* - Penicillin G was historically used to treat gonorrhea, but this is no longer the case due to widespread **resistance** of *Neisseria gonorrhoeae* strains. - Its primary use now is for susceptible bacterial infections, such as syphilis and certain streptococcal infections.

Q: Which of the following is characterized by a solitary painless ulcer on genitalia?

Syphilis. ***Syphilis*** - Primary syphilis typically presents as a **painless chancre** (ulcer) at the site of infection, usually the **genitalia**. - The painless nature is a key differentiating feature as it often goes unnoticed, allowing the disease to progress. *Genital herpes* - Characterized by multiple, small, often painful vesicles or ulcers that may coalesce [1]. - Lesions are typically tender or painful, unlike the **painless chancre** of syphilis [1]. *Traumatic injury* - While a traumatic injury can cause a solitary ulcer, it is usually painful and often associated with a clear history of trauma. - The ulcer's morphology and healing process may differ from a classic syphilitic chancre. *Chancroid* - Caused by *Haemophilus ducreyi*, chancroid presents as one or more painful, tender ulcers with ragged, undermined borders. - This is a significant differentiator from the **painless ulcer** seen in primary syphilis.

Q: Which type of leprosy does not involve nerve damage?

Indeterminate leprosy. ***Indeterminate leprosy*** - This is the earliest form of leprosy and often presents with only a **single skin lesion** and no demonstrable nerve damage. - Due to the minimal immune response, it can be difficult to classify and may progress to other forms if left untreated. *Tuberculoid leprosy* - Characterized by a **strong cell-mediated immune response** to *Mycobacterium leprae*, leading to significant nerve involvement [1]. - Patients typically present with well-demarcated, **hypopigmented patches** with definite **sensory loss** due to nerve damage [1]. *Borderline tuberculoid leprosy* - This form sits between tuberculoid and borderline lepromatous leprosy, showing features of both, including **nerve involvement** [2]. - It presents with a few to several skin lesions that are usually smaller and less clearly defined than tuberculoid lesions, often with **palpable nerves** and mild sensory loss [2]. *Lepromatous leprosy* - Characterized by a **weak or absent cell-mediated immune response**, leading to widespread bacterial proliferation and extensive nerve damage, often symmetrical [1]. - Patients show numerous, poorly defined skin lesions, nodules, and severe nerve involvement, which can result in significant **deformities** [2].

Q: What is the treatment for granuloma inguinale?

Azithromycin. ***Azithromycin*** - **Azithromycin** is the recommended first-line treatment for **granuloma inguinale** (donovanosis) caused by *Klebsiella granulomatis*. - Current recommended regimens: **Azithromycin 1g orally once weekly** OR **500mg daily for at least 3 weeks** (until all lesions have completely healed). - Preferred due to excellent tissue penetration, good efficacy, and convenient dosing that improves patient compliance. *Tetracycline* - **Tetracycline** (500mg four times daily) was historically used but has been largely replaced by **doxycycline** (100mg twice daily) as the preferred tetracycline-class antibiotic. - While effective against *Klebsiella granulomatis*, it requires frequent dosing leading to poor adherence. - **Doxycycline** (not listed here) is actually considered a co-first-line option alongside azithromycin in current CDC guidelines. *Clarithromycin* - **Clarithromycin** is a macrolide antibiotic but is not a recommended first-line agent for granuloma inguinale. - Limited clinical data supports its use for this condition, and it is not included in standard treatment guidelines. - Azithromycin from the same macrolide class is preferred due to better-established efficacy. *Streptomycin* - **Streptomycin** is an aminoglycoside antibiotic primarily used for mycobacterial infections (e.g., tuberculosis, plague). - Not indicated for granuloma inguinale as *Klebsiella granulomatis* responds well to macrolides (azithromycin) and tetracyclines (doxycycline). - Requires parenteral administration and has significant toxicity concerns (ototoxicity, nephrotoxicity).

Q: What is the first symptom of leprosy?

Decreased pain. Decreased pain - Leprosy primarily targets Schwann cells in peripheral nerves, leading to sensory loss [1]. - The sensation of pain is typically affected earliest, often presenting as areas of numbness [1]. Decreased vibration & position sense - These sensations are typically carried by larger myelinated fibers, which tend to be affected later in the disease progression of leprosy. - While eventually involved, they are not usually the first symptom of sensory loss. Decreased temperature - Temperature sensation is also an early modality affected in leprosy, as it's carried by small, unmyelinated or thinly myelinated fibers [1]. - However, pain is often cited as the very first sensory loss, even preceding temperature changes in some cases. Decreased light touch - Light touch sensation is generally an early loss, similar to pain and temperature, due to damage to nerve fibers in the skin. - But, when distinguishing the absolute first symptom, pain perception often shows impairment even before light touch in affected areas.

Question 1

A 10-year-old boy presents with an ulcerated lesion with undermined edges over the upper chest, accompanied by a satellite lesion in the anterior axillary fold for two months. Axillary lymph nodes are palpable. Histopathology reveals a dermal abscess with ill-defined histiocytes. AFB staining of the tissue is positive. Chest X-ray shows infiltrations and cavities. Mantoux test is positive. What is the most likely diagnosis?

Accepted Answer

Scrofuloderma

Answer

Skin abscess

Answer

Furuncle

Answer

Cellulitis

Answer

Erysipelas

Question 2

What is the first-line treatment for localized impetigo?

Accepted Answer

Mupirocin

Answer

Cefalexin

Answer

Erythromycin

Answer

Clindamycin

Question 3

Bullous impetigo is primarily caused by which of the following?

Accepted Answer

Staphylococcus aureus

Answer

Streptococcus pyogenes

Answer

Escherichia coli

Answer

Yersinia pestis

Question 4

A 5-year-old child presents with a honey-colored crusted lesion on their face. What is the most likely causative organism?

Accepted Answer

Streptococcus pyogenes

Answer

Staphylococcus aureus

Answer

Candida albicans

Answer

Pseudomonas aeruginosa

Question 5

In your STI clinic, standardized treatment kits are available for different conditions based on clinical presentation and likely pathogens. A 22-year-old female comes to the STI clinic with minimal vaginal discharge. On speculum examination, erosions are seen on the cervix. Which of the following treatment kit should be given to this patient?

Accepted Answer

Grey

Answer

Green

Answer

Red

Answer

Yellow

Question 6

A man presents with a history of dysuria and urethral discharge after having unprotected sexual intercourse. What is the treatment of choice for this infection?

Accepted Answer

Ceftriaxone

Answer

Erythromycin

Answer

Azithromycin

Answer

Penicillin G

Question 7

Which of the following is characterized by a solitary painless ulcer on genitalia?

Accepted Answer

Syphilis

Answer

Genital herpes

Answer

Traumatic injury

Answer

Chancroid

Question 8

Which type of leprosy does not involve nerve damage?

Accepted Answer

Indeterminate leprosy

Answer

Borderline tuberculoid leprosy

Answer

Tuberculoid leprosy

Answer

Lepromatous leprosy

Question 9

What is the treatment for granuloma inguinale?

Accepted Answer

Azithromycin

Answer

Tetracycline

Answer

Clarithromycin

Answer

Streptomycin

Question 10

What is the first symptom of leprosy?

Accepted Answer

Decreased pain

Answer

Decreased vibration & position sense

Answer

Decreased temperature

Answer

Decreased light touch

Bacterial Skin Infections — MCQs

Bacterial Skin Infections — MCQs

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