Bacteriology Practice Questions

Q: Bannwah's syndrome develops secondary to infection with which of the following organisms?

Treponema pallidum. **Explanation:** **Bannwarth’s Syndrome** (also known as Garin-Bujadoux-Bannwarth syndrome) is a clinical triad characterized by lymphocytic pleocytosis in the CSF, cranial neuropathy (most commonly facial nerve palsy), and painful radiculoneuritis. While historically associated with various spirochetes, in modern clinical practice and NEET-PG examinations, it is classically recognized as the hallmark of **Early Disseminated Lyme Disease (Stage 2)**, caused by **Borrelia burgdorferi**. *Note: There appears to be a discrepancy in the provided key. In standard medical literature, Bannwarth’s Syndrome is the neuroborreliosis manifestation of Borrelia burgdorferi, not Treponema pallidum.* **Analysis of Options:** * **A. Borrelia burgdorferi (Correct):** This spirochete causes Lyme disease. Bannwarth’s syndrome represents the neurological involvement during the second stage of the infection, particularly common in European cases. * **B. Treponema pallidum:** Causes Syphilis. While it can cause Neurosyphilis (tabes dorsalis, general paresis), it is not the causative agent of Bannwarth’s syndrome. * **C. Bacillus cereus:** A gram-positive rod associated with food poisoning (emetic and diarrheal forms) and endophthalmitis. * **D. Actinomyces israelii:** An anaerobic bacterium causing "lumpy jaw" (cervicofacial actinomycosis) characterized by sulfur granules. **High-Yield Clinical Pearls for NEET-PG:** * **Lyme Disease Stages:** 1. *Early Localized:* Erythema chronicum migrans (bull’s eye rash). 2. *Early Disseminated:* Bannwarth’s Syndrome, AV block, multiple erythema migrans. 3. *Late:* Chronic arthritis, acrodermatitis chronica atrophicans. * **Vector:** *Ixodes* tick (also transmits Babesia and Anaplasma). * **Treatment:** Doxycycline is the drug of choice; Ceftriaxone is used for neurological or cardiac involvement.

Q: Actinomycosis is sensitive to which of the following antibiotics?

Penicillin. **Explanation:** **Actinomycosis** is a chronic, granulomatous infection caused by *Actinomyces* species (most commonly *A. israelii*). Despite their fungal-sounding name, these organisms are **Gram-positive, anaerobic, non-acid-fast branching bacteria**. 1. **Why Penicillin is Correct:** Because *Actinomyces* are true bacteria (possessing a peptidoglycan cell wall and lacking a nuclear membrane), they are highly susceptible to antibacterial agents. **High-dose Penicillin G** is the drug of choice. Treatment typically requires a prolonged course (weeks to months) due to the dense fibrotic nature of the lesions and the presence of "sulfur granules" which limit drug penetration. 2. **Why Other Options are Incorrect:** * **Streptomycin (A):** This is an aminoglycoside primarily used for aerobic Gram-negative bacteria and *M. tuberculosis*. It is ineffective against the anaerobic environment where *Actinomyces* thrives. * **Nystatin (B):** This is an antifungal medication. While *Actinomyces* was historically confused with fungi due to its branching morphology, it is a bacterium; therefore, antifungals have no effect. * **Iodoxuridine (D):** This is an antiviral agent used primarily for Herpes Simplex Keratitis. It has no role in treating bacterial infections. **High-Yield Clinical Pearls for NEET-PG:** * **Morphology:** Characterized by "Sulfur granules" (yellowish colonies of bacteria) in pus. * **Clinical Presentation:** Most common form is **Cervicofacial actinomycosis** ("Lumpy Jaw"), often following dental procedures or poor oral hygiene. * **Diagnosis:** Crushing a sulfur granule and performing a Gram stain reveals Gram-positive branching filaments. * **Alternative Treatment:** In patients allergic to penicillin, **Tetracyclines** or Erythromycin are the preferred alternatives.

Q: What is the ideal percentage of CO2 required for the growth of Brucella abortus?

5-10%. **Explanation:** *Brucella abortus* is a fastidious, Gram-negative coccobacillus that is **capnophilic**, meaning it requires an enriched carbon dioxide (CO2) atmosphere for primary isolation. **1. Why 5-10% is Correct:** Most strains of *Brucella abortus* (specifically Biotype 1) are strictly dependent on added CO2 for growth, especially during initial culture from clinical specimens. The ideal concentration is **5-10% CO2**. This environment mimics the metabolic conditions required for the organism to trigger its biosynthetic pathways. While *B. melitensis* and *B. suis* generally do not require supplemental CO2, *B. abortus* is the classic example of a capnophilic *Brucella* species. **2. Why Incorrect Options are Wrong:** * **2-5% (Option A):** This concentration is often insufficient to stimulate the growth of fastidious *B. abortus* strains, which require a more robust CO2 tension. * **15-20% and 25-30% (Options C & D):** These concentrations are excessively high. High levels of CO2 can lead to the acidification of the culture medium (forming carbonic acid), which inhibits the growth of *Brucella* species rather than promoting it. **3. NEET-PG High-Yield Pearls:** * **Culture Media:** Use **Castaneda’s medium** (a biphasic medium containing both solid and liquid phases) to reduce the risk of laboratory-acquired infections. * **Incubation:** Cultures should be incubated for at least **3-4 weeks** before being declared negative, although automated systems (like BACTEC) usually detect growth within 5-7 days. * **Clinical Presentation:** Look for **"Undulant Fever"** (Malta fever) and profuse sweating with a "mousy" odor. * **Diagnosis:** The **Standard Agglutination Test (SAT)** is the most common serological test; a titer of 1:160 or more is significant. Note that *Brucella* can show a **prozone phenomenon**, leading to false negatives at low dilutions.

Q: Which mycobacterium exclusively affects the skin?

Mycobacterium marinum. **Explanation:** **Mycobacterium marinum** is the correct answer because it is a photochromogenic atypical mycobacterium that grows optimally at **30–32°C**. This lower temperature requirement prevents it from causing systemic infections in the warmer internal organs of the human body (37°C), thus restricting its clinical manifestation **exclusively to the skin** and subcutaneous tissues. It typically causes "Fish Tank Granuloma" or "Swimming Pool Granuloma," often presenting as a sporotrichoid spread (linear nodules along lymphatics) following trauma in aquatic environments. **Analysis of Incorrect Options:** * **Mycobacterium fortuitum & Mycobacterium chelonae:** These are Rapidly Growing Mycobacteria (RGM). While they frequently cause skin and soft tissue infections (especially post-surgical or post-injection abscesses), they are also known to cause systemic diseases, including osteomyelitis, endocarditis, and disseminated infections in immunocompromised hosts. * **Mycobacterium xenopi:** This is a slow-growing mycobacterium primarily associated with **pulmonary infections**, often mimicking tuberculosis, especially in patients with pre-existing lung disease. It is not restricted to the skin. **High-Yield Clinical Pearls for NEET-PG:** * **Temperature Sensitivity:** *M. marinum* and *M. ulcerans* (which causes Buruli ulcer) both prefer cooler temperatures, explaining their predilection for the skin. * **Sporotrichoid Spread:** Differential diagnoses include *Sporothrix schenckii*, *M. marinum*, *Nocardia*, and *Leishmania*. * **Treatment:** *M. marinum* is typically treated with Clarithromycin, Rifampicin, or Ethambutol for 3–6 months. * **Culture:** It grows on Lowenstein-Jensen (L-J) medium but requires a lower incubation temperature (30°C) to thrive.

Q: Which of the following bacteria is NOT motile?

Klebsiella. **Explanation:** The motility of Enterobacteriaceae is a high-yield topic in microbiology. Bacterial motility is primarily determined by the presence of **flagella**. **1. Why Klebsiella is the correct answer:** *Klebsiella* species (notably *K. pneumoniae* and *K. oxytoca*) are characteristically **non-motile**. They lack flagella and are often surrounded by a thick polysaccharide capsule, which contributes to their mucoid appearance on culture media (like MacConkey agar). In the laboratory, they show a negative result on the Hanging Drop method and do not spread in semi-solid motility media. **2. Why the other options are incorrect:** * **E. coli:** Most strains are motile via **peritrichous flagella**. (Note: Some strains like EIEC may be non-motile, but as a genus, *E. coli* is considered motile). * **Salmonella:** Most species (e.g., *S. Typhi*) are motile with peritrichous flagella. The notable exceptions are *Salmonella* Gallinarum and *Salmonella* Pullorum. * **Proteus:** Highly motile bacteria known for their characteristic **"swarming motility"** on agar plates due to their vigorous peritrichous flagella. **3. Clinical Pearls & High-Yield Facts for NEET-PG:** * **Mnemonic for Non-Motile Organisms:** **"KYS"** – **K**lebsiella, **Y**ersinia (at 37°C), and **S**higella. * **Yersinia enterocolitica:** Unique because it is motile at 25°C but **non-motile at 37°C**. * **Vibrio cholerae:** Exhibits "darting motility." * **Listeria monocytogenes:** Exhibits "tumbling motility" at 25°C. * **Campylobacter:** Exhibits "corkscrew" or "darting" motility. * **Proteus:** Associated with "Dienes phenomenon" and urease production (leading to staghorn calculi).

Q: What type of diarrhea is caused by Vibrio cholerae?

Secretory. **Explanation:** **Vibrio cholerae** causes diarrhea through a potent enterotoxin known as **Cholera Toxin (Choleragen)**. This toxin works via an A-B subunit mechanism. The 'B' subunit binds to the GM1 ganglioside receptor on enterocytes, allowing the 'A' subunit to enter the cell. The 'A' subunit causes permanent activation of **adenylate cyclase**, leading to increased intracellular **cAMP** levels. This results in the hypersecretion of water and electrolytes (sodium, chloride, potassium, and bicarbonate) into the intestinal lumen, characteristic of **Secretory Diarrhea**. **Analysis of Options:** * **A. Osmotic:** This occurs when non-absorbable solutes (e.g., lactulose or malabsorption syndromes) remain in the gut and pull water in. In cholera, the secretion is active and toxin-mediated, not passive. * **C. Colloidal:** This is not a standard medical classification for diarrhea. * **D. Bloody:** Also known as dysentery, this is caused by invasive organisms (e.g., *Shigella*, *EIEC*, *Entamoeba histolytica*) that cause mucosal destruction. *V. cholerae* is non-invasive and does not cause blood in stools. **High-Yield Clinical Pearls for NEET-PG:** * **Stool Appearance:** Classically described as **"Rice-water stools"** (non-bilious, non-bloody, with a fishy odor). * **Culture Media:** TCBS (Thiosulfate Citrate Bile Salts Sucrose) agar is the selective medium where it forms **yellow colonies**. * **Enrichment Media:** Alkaline Peptone Water (APW) and Monsur’s media. * **Microscopy:** Shows characteristic **"Darting motility"** (inhibited by specific antisera in the Cholera Immobilization Test). * **Treatment:** The cornerstone is aggressive rehydration (ORS/IV fluids). Doxycycline is the drug of choice to reduce the duration of shedding.

Q: What is the most common microorganism found in pediatric subacute infective endocarditis?

Strep viridans. **Explanation:** Infective Endocarditis (IE) in children is categorized based on the clinical course and the virulence of the causative organism. **Why Strep viridans is correct:** * **Streptococcus viridans** (alpha-hemolytic streptococci) is the most common cause of **subacute** infective endocarditis in children, particularly those with underlying congenital heart disease (CHD) or rheumatic heart disease. * These organisms are low-virulence commensals of the oral cavity. They typically enter the bloodstream following dental procedures or minor oral trauma, leading to a gradual, indolent infection on previously damaged endocardium or prosthetic valves. **Analysis of Incorrect Options:** * **A. Staph aureus:** This is the most common cause of **acute** infective endocarditis. It is highly virulent, can affect healthy valves, and is the leading cause of IE in patients with central venous catheters or those undergoing cardiac surgery. * **C. E. coli:** Gram-negative bacilli like E. coli are rare causes of IE, occasionally seen in neonates or immunocompromised patients, but they are never the "most common" in the pediatric population. * **D. Pneumococci:** *Streptococcus pneumoniae* is an uncommon cause of IE in the post-antibiotic era. When it occurs, it usually presents as an acute, fulminant infection rather than a subacute one. **High-Yield Clinical Pearls for NEET-PG:** * **Most common underlying condition for pediatric IE:** Ventricular Septal Defect (VSD), followed by Tetralogy of Fallot (TOF). * **Culture-negative IE:** Most commonly due to prior antibiotic use or fastidious organisms like the **HACEK** group (*Haemophilus, Aggregatibacter, Cardiobacterium, Eikenella, Kingella*). * **Duke’s Criteria:** The gold standard for diagnosis (requires 2 major, 1 major + 3 minor, or 5 minor criteria). * **Prophylaxis:** Indicated for high-risk cardiac conditions only during dental procedures involving gingival manipulation.

Q: A 25-year-old sexually active unmarried male presents with urethral discharge after unprotected sex with a sexual worker. A Gram stain was provided; what is the most likely causative organism?

Neisseria. ***Neisseria*** - **Neisseria gonorrhoeae** appears as **Gram-negative intracellular diplococci** within **polymorphonuclear neutrophils (PMNs)** on Gram stain, making it easily identifiable. - The clinical presentation of **urethral discharge** after unprotected sex with high-risk exposure strongly supports gonococcal urethritis. *Chlamydia* - **Chlamydia trachomatis** is an **obligate intracellular bacterium** that **cannot be visualized** on routine Gram stain. - Requires specialized testing like **nucleic acid amplification tests (NAATs)** or **direct fluorescent antibody (DFA)** for diagnosis. *Trichomonas* - **Trichomonas vaginalis** is a **protozoan parasite**, not a bacterium, so it **does not appear** on Gram stain. - Diagnosis requires **wet mount microscopy** showing motile trichomonads or **culture/molecular testing**. *Ureaplasma* - **Ureaplasma urealyticum** lacks a **cell wall**, making it **invisible** on Gram stain which relies on cell wall components. - Requires **specialized culture media** and **molecular methods** for identification and is less commonly associated with acute purulent urethritis.

Question 1

Which of the following statements regarding Salmonella infection is true?

Accepted Answer

Absence of Vi antibody indicates a poor prognosis.

Answer

Flagellar antigen forms chalky granular clumps.

Answer

Somatic antigen is a protein.

Answer

Serological classification is by Craige's scheme.

Question 2

Bannwah's syndrome develops secondary to infection with which of the following organisms?

Accepted Answer

Treponema pallidum

Answer

Borrelia burgdorferi

Answer

Bacillus cereus

Answer

Actinomyces israelii

Question 3

Actinomycosis is sensitive to which of the following antibiotics?

Accepted Answer

Penicillin

Answer

Streptomycin

Answer

Nystatin

Answer

Iodoxuridine

Question 4

What is the ideal percentage of CO2 required for the growth of Brucella abortus?

Accepted Answer

5-10%

Answer

2-5%

Answer

15-20%

Answer

25-30%

Question 5

Which mycobacterium exclusively affects the skin?

Accepted Answer

Mycobacterium marinum

Answer

Mycobacterium fortuitum

Answer

Myobacterium xenopi

Answer

Mycobacterium chelonei

Question 6

Which of the following bacteria is NOT motile?

Accepted Answer

Klebsiella

Answer

E. coli

Answer

Salmonella

Answer

Proteus

Question 7

What type of diarrhea is caused by Vibrio cholerae?

Accepted Answer

Secretory

Answer

Osmotic

Answer

Colloidal

Answer

Bloody

Question 8

What is the most common microorganism found in pediatric subacute infective endocarditis?

Accepted Answer

Strep viridans

Answer

Staph aureus

Answer

E. coli

Answer

Pneumococci

Question 9

A 25-year-old sexually active unmarried male presents with urethral discharge after unprotected sex with a sexual worker. A Gram stain was provided; what is the most likely causative organism?

Accepted Answer

Neisseria

Answer

Chlamydia

Answer

Trichomonas

Answer

Ureaplasma

Question 10

Which of the following statements about Corynebacterium diphtheriae is incorrect?

Accepted Answer

Toxin production is mediated by a lysogenic bacteriophage.

Answer

The primary mechanism of pathogenicity is toxin production.

Answer

The toxin is cytotoxic to myocardial and neuronal cells.

Answer

Diphtheria is more common in unvaccinated children.

Bacteriology — MCQs

Bacteriology — MCQs

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