Bacteriology Practice Questions

Q: Which organism commonly causes an 'appendicitis-like syndrome'?

Yersinia pseudotuberculosis. **Explanation:** The correct answer is **A. Yersinia pseudotuberculosis**. **Why it is correct:** *Yersinia pseudotuberculosis* (and occasionally *Yersinia enterocolitica*) is a Gram-negative coccobacillus that causes **Mesenteric Adenitis**. This condition involves inflammation of the mesenteric lymph nodes near the terminal ileum, which clinically mimics the symptoms of acute appendicitis (right lower quadrant pain, fever, and leukocytosis). This classic presentation is known as **"Pseudoappendicitis"** or an **"appendicitis-like syndrome."** The infection is typically zoonotic, transmitted via contaminated food or water. **Why the other options are incorrect:** * **B. Pasteurella multocida:** Primarily associated with cellulitis or soft tissue infections following **animal bites** (cats and dogs). It does not typically cause mesenteric lymphadenopathy. * **C. Bacillus cereus:** A common cause of food poisoning (emetic and diarrheal forms) associated with **reheated fried rice**. It causes gastroenteritis but not an appendicitis-like syndrome. * **D. Yersinia pestis:** The causative agent of **Plague** (Bubonic, Septicemic, and Pneumonic). While it causes severe lymphadenopathy (Buboes), these are usually inguinal or axillary, and the clinical course is far more fulminant and systemic. **High-Yield Clinical Pearls for NEET-PG:** * **Cold Enrichment:** *Yersinia* species are unique because they can grow at **4°C**, a property used for selective isolation in the lab. * **Safety Pin Appearance:** On Wayson or Giemsa stain, *Yersinia* shows characteristic **bipolar staining**. * **V and W Antigens:** These are plasmid-encoded virulence factors essential for the pathogenicity of *Yersinia* species. * **Differential Diagnosis:** Always consider *Yersinia* or *Campylobacter jejuni* in a pediatric patient presenting with "appendicitis" where the appendix appears normal during surgery.

Q: A 70-year-old nursing home patient refused the influenza vaccine and subsequently developed influenza. She died of acute pneumonia 1 week after contracting the "flu." What is the most common cause of acute post-influenzal pneumonia?

Staphylococcus aureus. ### Explanation **Correct Answer: C. Staphylococcus aureus** **Why it is correct:** Influenza virus infection damages the respiratory epithelium and impairs the mucociliary escalator, creating a fertile environment for secondary bacterial invasion. While *Streptococcus pneumoniae* is the most common cause of community-acquired pneumonia overall, **Staphylococcus aureus** is the classic and most feared cause of **post-influenzal pneumonia**. It typically presents as a "biphasic illness" where the patient initially improves from the flu but then develops a sudden, severe worsening of symptoms (high fever, productive cough, and respiratory distress). *S. aureus* pneumonia is often necrotizing and can lead to complications like lung abscesses or pneumatoceles. **Why the other options are incorrect:** * **A. Legionella:** This is associated with contaminated water sources (AC systems) and typically presents with GI symptoms (diarrhea) and hyponatremia. It is not specifically linked to post-viral secondary infections. * **B. Listeria:** This primarily causes meningitis or sepsis in neonates, the elderly, or immunocompromised individuals, usually via contaminated food. It is not a common cause of pneumonia. * **D. Klebsiella:** This is a common cause of pneumonia in chronic alcoholics or diabetics, characterized by "currant jelly sputum" and upper lobe involvement. It is not the primary pathogen associated with post-influenza sequelae. **High-Yield Clinical Pearls for NEET-PG:** * **Top 3 pathogens for post-viral pneumonia:** 1. *S. pneumoniae* (most frequent), 2. *S. aureus* (most characteristic/severe), 3. *H. influenzae*. * **Radiology:** *S. aureus* pneumonia often shows patchy infiltrates that can rapidly progress to cavitary lesions. * **MRSA:** In the modern clinical setting, community-acquired MRSA (CA-MRSA) is an increasing cause of fatal post-influenza pneumonia in previously healthy young adults.

Q: A man presented with diarrhea three days after consuming uncooked meat. Stool examination revealed comma-shaped organisms with red blood cells and white blood cells. What is the causative organism?

Campylobacter jejuni. ### Explanation The correct answer is **Campylobacter jejuni**. This case highlights the classic presentation of inflammatory diarrhea caused by this organism. **1. Why Campylobacter jejuni is correct:** * **Morphology:** *C. jejuni* is characteristically described as a **comma-shaped** (or S-shaped/seagull-wing) Gram-negative rod. * **Clinical Presentation:** It is a leading cause of bacterial gastroenteritis worldwide, often transmitted via **undercooked poultry/meat** or unpasteurized milk. * **Stool Findings:** Unlike *Vibrio*, *Campylobacter* causes **inflammatory diarrhea**. The presence of **RBCs and WBCs** (fecal leukocytes) in the stool indicates mucosal invasion and inflammation, which is a hallmark of this pathogen. **2. Why other options are incorrect:** * **Vibrio cholerae:** While also comma-shaped, it causes **non-inflammatory, watery "rice-water" stools**. It does not invade the mucosa, so RBCs and WBCs are typically absent. * **Shigella:** Causes bacillary dysentery (RBCs/WBCs present), but the organism is a **straight rod**, not comma-shaped. * **Yersinia enterocolitica:** Can cause inflammatory diarrhea and pseudoappendicitis, but it is a **coccobacillus** and is more commonly associated with contaminated pork or cold storage (psychrophilic). **3. High-Yield Clinical Pearls for NEET-PG:** * **Culture:** Requires special media (e.g., **Skirrow’s medium**) and is **microaerophilic**, growing best at **42°C** (heat-tolerant). * **Motility:** Exhibits characteristic **"darting motility."** * **Complications:** Strongly associated with **Guillain-Barré Syndrome** (due to molecular mimicry with gangliosides) and Reactive Arthritis. * **Treatment:** Erythromycin or Azithromycin (though most cases are self-limiting).

Q: Swimming pool conjunctivitis is caused by which of the following microorganisms?

Chlamydia. **Explanation:** The correct answer is **Chlamydia**. Specifically, "Swimming pool conjunctivitis" refers to **Inclusion Conjunctivitis** caused by **Chlamydia trachomatis (Serotypes D-K)**. **Why Chlamydia is correct:** This condition occurs when the eyes are exposed to infected genital secretions, often in inadequately chlorinated swimming pools. It presents as an acute follicular conjunctivitis with mucopurulent discharge and preauricular lymphadenopathy. On cytology, it is characterized by the presence of **Halberstaedter-Prowazek (HP) inclusion bodies** (intracytoplasmic) near the nucleus of conjunctival epithelial cells. **Why the other options are incorrect:** * **Pseudomonas:** While *Pseudomonas aeruginosa* is a common cause of contact lens-associated keratitis and "swimmer’s ear" (otitis externa), it is not the classic cause of swimming pool conjunctivitis. * **Coxsackievirus:** This is a common cause of **Acute Hemorrhagic Conjunctivitis (AHC)**, often associated with Enterovirus 70. It presents with subconjunctival hemorrhages rather than the follicular pattern seen in Chlamydia. * **Mycoplasma:** These organisms are primarily associated with respiratory and urogenital infections (like atypical pneumonia or urethritis) but are not standard causes of infectious conjunctivitis. **High-Yield Clinical Pearls for NEET-PG:** * **Trachoma vs. Inclusion Conjunctivitis:** Trachoma is caused by Serotypes **A, B, Ba, and C** (leading cause of preventable blindness), while Inclusion Conjunctivitis is caused by **D-K**. * **Drug of Choice:** Oral **Azithromycin** (single dose) or Doxycycline. * **Adenovirus:** Note that Adenovirus (Types 3, 7) causes **Pharyngoconjunctival Fever**, which is also associated with swimming pools but typically presents with a triad of fever, pharyngitis, and conjunctivitis.

Q: Calymmatobacterium granulomatosis causes which of the following conditions?

Granuloma inguinale (Donovanosis). **Explanation:** **Granuloma inguinale**, also known as **Donovanosis**, is a chronic bacterial sexually transmitted infection caused by ***Klebsiella granulomatis*** (formerly known as *Calymmatobacterium granulomatosis*). It is characterized by painless, beefy-red, velvety ulcerative lesions that are highly vascular and bleed easily on touch. A hallmark of this condition is the absence of true inguinal lymphadenopathy; instead, patients develop "pseudobuboes" due to subcutaneous granulation tissue. **Analysis of Options:** * **Option A: Lymphogranuloma venereum (LGV):** This is caused by *Chlamydia trachomatis* (serotypes L1, L2, and L3). It typically presents with a transient primary lesion followed by painful inguinal lymphadenopathy (the "Groove sign"). * **Option C: Syphilis:** This is caused by the spirochete *Treponema pallidum*. Primary syphilis presents as a "Hard Chancre"—a single, painless, indurated ulcer with clean base and associated painless regional lymphadenopathy. * **Option D:** Incorrect, as Option B is the established causative agent. **High-Yield Clinical Pearls for NEET-PG:** * **Microscopy:** Diagnosis is confirmed by identifying **Donovan bodies** (safety-pin appearance) within large mononuclear cells (macrophages) on a Wright-Giemsa stain. * **Clinical Feature:** "Beefy red" ulcers that are non-tender. * **Treatment of Choice:** Azithromycin (1g orally once a week or 500mg daily) for at least 3 weeks or until lesions heal. * **Nomenclature Note:** Remember the name change from *Calymmatobacterium* to *Klebsiella granulomatis* based on phylogenetic similarity.

Question 1

Which of the following statements is true regarding Streptococcus pneumoniae?

Accepted Answer

The vaccine is made from capsular polysaccharide.

Answer

The vaccine is routinely given to Indian children.

Answer

It is catalase and oxidase positive.

Answer

It is bile insoluble and optochin sensitive.

Question 2

Which organism commonly causes an 'appendicitis-like syndrome'?

Accepted Answer

Yersinia pseudotuberculosis

Answer

Pasteurella multocida

Answer

Bacillus cereus

Answer

Yersinia pestis

Question 3

Mycoplasmas differ from chlamydiae in that they are

Accepted Answer

Able to grow on artificial cell-free media

Answer

Susceptible to penicillin

Answer

Able to cause urinary tract infection

Answer

Able to stain well with Gram's stain

Question 4

A man from Mexico presents with a clinical finding that, upon biopsy, reveals the presence of gram-negative bacilli. What is the most likely causative agent?

Accepted Answer

Klebsiella rhinoscleromatis

Answer

Mycobacterium leprae

Answer

Acinetobacter baumannii

Answer

Treponema pallidum

Question 5

A 70-year-old nursing home patient refused the influenza vaccine and subsequently developed influenza. She died of acute pneumonia 1 week after contracting the "flu." What is the most common cause of acute post-influenzal pneumonia?

Accepted Answer

Staphylococcus aureus

Answer

Legionella

Answer

Listeria

Answer

Klebsiella

Question 6

A man presented with diarrhea three days after consuming uncooked meat. Stool examination revealed comma-shaped organisms with red blood cells and white blood cells. What is the causative organism?

Accepted Answer

Campylobacter jejuni

Answer

Vibrio cholerae

Answer

Shigella

Answer

Yersinia enterocolitica

Question 7

Swimming pool conjunctivitis is caused by which of the following microorganisms?

Accepted Answer

Chlamydia

Answer

Pseudomonas

Answer

Coxsackievirus

Answer

Mycoplasma

Question 8

What does a positive tuberculin skin test indicate?

Accepted Answer

The patient has been infected with Mycobacterium tuberculosis.

Answer

The patient has an immunodeficiency.

Answer

The patient has developed resistance to tuberculin protein.

Answer

The patient is currently suffering from active tuberculosis disease.

Question 9

Which of the following is a characteristic feature on culture of Streptococcus pneumoniae organism?

Accepted Answer

Alpha-hemolytic colonies inhibited by optochin on blood agar and lysed by bile

Answer

Beta-hemolytic colonies that are bacitracin-resistant on blood agar

Answer

Beta-hemolytic colonies that are inhibited by bacitracin on blood agar

Answer

Catalase-negative organisms that hydrolyze esculin in 40% bile and 6.5% NaCl

Question 10

Calymmatobacterium granulomatosis causes which of the following conditions?

Accepted Answer

Granuloma inguinale (Donovanosis)

Answer

Lymphogranuloma venereum

Answer

Syphilis

Answer

None of the above

Bacteriology — MCQs

Bacteriology — MCQs

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