Bacteriology — MCQs

Bacteriology Indian Medical PG Practice Questions and MCQs

Question 1111: Bannwah's syndrome develops secondary to infection with which of the following organisms?

A. Borrelia burgdorferi
B. Treponema pallidum (Correct Answer)
C. Bacillus cereus
D. Actinomyces israelii

Explanation: **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.

Question 1112: Actinomycosis is sensitive to which of the following antibiotics?

A. Streptomycin
B. Nystatin
C. Penicillin (Correct Answer)
D. Iodoxuridine

Explanation: **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.

Question 1113: A 30-year-old farmer presents with high fever, painful inguinal lymphadenopathy, vomiting, and diarrhea with hypotension. Which stain will help in the diagnosis?

A. Wayson's stain (Correct Answer)
B. Neisser stain
C. Albes stain
D. McFadyean's stain

Explanation: ### Explanation **Diagnosis: Bubonic Plague (*Yersinia pestis*)** The clinical presentation of a farmer (occupational exposure to rodents/fleas) with high fever, painful inguinal lymphadenopathy (**Buboes**), and signs of septicemic shock (hypotension, GI symptoms) is classic for **Plague**, caused by *Yersinia pestis*. **1. Why Wayson’s Stain is Correct:** *Yersinia pestis* is a Gram-negative coccobacillus. When stained with **Wayson’s stain** (or Giemsa/Methylene blue), it exhibits a characteristic **"Safety-pin appearance"** due to **bipolar staining** (the ends of the bacilli stain more intensely than the center). This is a high-yield diagnostic feature for rapid identification from lymph node aspirates. **2. Analysis of Incorrect Options:** * **B. Neisser stain:** Used to demonstrate **metachromatic granules** (Volutin granules) in *Corynebacterium diphtheriae*. * **C. Albert’s stain:** The standard differential stain for *Corynebacterium diphtheriae* to visualize granules in a "Chinese letter" arrangement. * **D. McFadyean’s stain:** Used to demonstrate the **capsule** of *Bacillus anthracis*. It uses polychrome methylene blue, which stains the capsule pink against blue bacilli (M'Fadyean reaction). **3. Clinical Pearls for NEET-PG:** * **Vector:** Oriental rat flea (*Xenopsylla cheopis*). * **Reservoir:** Wild rodents (sylvatic plague) and urban rats (rattus rattus). * **Culture:** Shows a characteristic **"Stalactite growth"** in ghee broth and "Ghee-pot appearance." * **Virulence Factor:** Fraction 1 (F1) antigen (capsular) is highly specific. * **Drug of Choice:** Streptomycin (Gentamicin is a common alternative).

Question 1114: Which E. coli strain is known to cause hemolytic uremic syndrome?

A. Enteropathogenic
B. Enterotoxigenic
C. Enteroinvasive
D. Enterohemorrhagic (Correct Answer)

Explanation: **Explanation:** The correct answer is **Enterohemorrhagic *E. coli* (EHEC)**. The most common serotype associated with this condition is **O157:H7**. **1. Why EHEC is correct:** EHEC produces **Shiga-like toxins (Verotoxins)**, specifically Stx1 and Stx2. These toxins enter the bloodstream and bind to **Gb3 receptors**, which are highly expressed on renal glomerular endothelial cells. This leads to endothelial damage, microvascular thrombosis, and platelet consumption. The resulting clinical triad of **Hemolytic Uremic Syndrome (HUS)** includes: * Microangiopathic hemolytic anemia (Schistocytes on smear) * Thrombocytopenia * Acute Renal Failure **2. Why other options are incorrect:** * **Enteropathogenic (EPEC):** Primarily causes infantile diarrhea in developing countries. It acts via "attachment and effacement" (A/E) lesions but does not produce toxins that cause HUS. * **Enterotoxigenic (ETEC):** The leading cause of **Traveler’s diarrhea**. It produces Heat-labile (LT) and Heat-stable (ST) toxins, causing watery diarrhea without systemic complications. * **Enteroinvasive (EIEC):** Clinically similar to *Shigella* (dysentery), it invades the colonic mucosa causing inflammation and ulceration, but it typically does not cause HUS. **NEET-PG High-Yield Pearls:** * **Source:** Undercooked ground beef (hamburger meat) or unpasteurized apple cider. * **Diagnosis:** EHEC O157:H7 does **not** ferment **Sorbitol** (unlike other *E. coli*); it grows as colorless colonies on Sorbitol MacConkey (SMAC) agar. * **Treatment Warning:** Antibiotics are generally **avoided** in EHEC infections as they may increase toxin release and worsen the risk of HUS.

Question 1115: What is the ideal percentage of CO2 required for the growth of Brucella abortus?

A. 2-5%
B. 5-10% (Correct Answer)
C. 15-20%
D. 25-30%

Explanation: **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.

Question 1116: Chlamydia causes all the following diseases except?

A. Non-gonococcal urethritis
B. Pneumonia
C. Trachoma
D. Parotitis (Correct Answer)

Explanation: **Explanation:** The correct answer is **Parotitis**. *Chlamydia* species are obligate intracellular bacteria that primarily infect columnar epithelial cells of the mucous membranes. They do not have a tropism for the salivary glands. Parotitis (inflammation of the parotid gland) is most commonly caused by viruses (e.g., **Mumps virus**) or bacteria like *Staphylococcus aureus*. **Analysis of Options:** * **Non-gonococcal urethritis (NGU):** *Chlamydia trachomatis* (Serotypes D-K) is the most common cause of NGU worldwide. It is a major cause of sexually transmitted infections (STIs) and can lead to complications like PID and infertility. * **Pneumonia:** *Chlamydia pneumoniae* causes atypical pneumonia in young adults. Additionally, *Chlamydia psittaci* causes Psittacosis (bird fancier's disease), and *C. trachomatis* can cause neonatal pneumonia (staccato cough) via vertical transmission. * **Trachoma:** Caused by *C. trachomatis* (Serotypes A, B, Ba, and C), this is a leading cause of preventable blindness globally, characterized by follicular conjunctivitis and scarring. **NEET-PG High-Yield Pearls:** * **Developmental Cycle:** *Chlamydia* exists in two forms: the **Elementary Body (EB)**, which is infectious and extracellular, and the **Reticulate Body (RB)**, which is the metabolically active, replicative intracellular form. * **Staining:** They are Gram-negative but poorly visualized; **Giemsa stain** is used to identify inclusion bodies (e.g., Halberstaedter-Prowazek bodies in Trachoma). * **Treatment of Choice:** Azithromycin (single dose) or Doxycycline (7 days). * **Lymphogranuloma Venereum (LGV):** Caused by serotypes L1, L2, and L3; presents with the "Groove sign."

Question 1117: Which of the following is not a toxin-mediated illness?

A. Toxic-Shock Syndrome
B. Food poisoning
C. Staphylococcal Scalded Skin Syndrome (SSSS)
D. Septic Shock (Correct Answer)

Explanation: **Explanation:** The core distinction in this question lies between **exotoxin-mediated diseases** and **host-mediated inflammatory responses.** **Why Septic Shock is the Correct Answer:** Unlike the other options, **Septic Shock** is not caused by a specific pre-formed or secreted bacterial toxin. Instead, it is a systemic inflammatory response triggered by the host's immune system. In Gram-negative sepsis, **Endotoxin (Lipopolysaccharide/LPS)**—a structural component of the cell wall—activates macrophages to release massive amounts of cytokines (TNF-α, IL-1, IL-6). This "cytokine storm" leads to peripheral vasodilation, capillary leak, and multi-organ failure. It is a host-driven pathology rather than a direct effect of a secreted toxin. **Analysis of Incorrect Options:** * **Toxic Shock Syndrome (TSS):** Caused by **TSST-1** (Staph. aureus) or Pyrogenic Exotoxin A (Strep. pyogenes). These act as **Superantigens**, non-specifically cross-linking MHC II and T-cell receptors, leading to massive T-cell activation. * **Food Poisoning:** Specifically *Staphylococcal* food poisoning is caused by the ingestion of **pre-formed Enterotoxins** (A-E) in contaminated food. The symptoms are a direct result of the toxin's action on the gut. * **SSSS (Ritter’s Disease):** Caused by **Exfoliative toxins (Epidermolytic toxins A & B)** produced by *Staphylococcus aureus*. These toxins proteolytically cleave **Desmoglein-1**, leading to the loss of cell-to-cell adhesion in the superficial epidermis. **High-Yield Clinical Pearls for NEET-PG:** * **Superantigens:** Remember TSST-1 and Enterotoxins. They bypass normal antigen processing. * **LPS (Endotoxin):** The toxic moiety is **Lipid A**. * **SSSS vs. TEN:** SSSS involves the superficial layer (subcorneal), while Toxic Epidermal Necrolysis (TEN) involves the dermo-epidermal junction (deeper) and is usually drug-induced.

Question 1118: Which of the following bacteria is NOT motile?

A. Klebsiella (Correct Answer)
B. E. coli
C. Salmonella
D. Proteus

Explanation: **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).

Question 1119: Babes Ernest granules are seen in which of the following?

A. Clostridium botulinum
B. Diphtheria (Correct Answer)
C. Anthrax
D. Clostridium welchii

Explanation: **Explanation:** **Babes-Ernest granules** (also known as metachromatic granules or volutin granules) are characteristic intracellular inclusions found in **Corynebacterium diphtheriae**. These granules represent stored polymerized inorganic polyphosphates that serve as energy reserves. They appear as distinct dark-purple or reddish spots when stained with special stains like **Albert’s, Neisser’s, or Ponder’s stain**, contrasting against the green or blue cytoplasm. This "metachromatic" property refers to the granules' ability to change the color of the dye (e.g., blue dye appearing reddish-purple). **Analysis of Options:** * **B. Diphtheria (Correct):** *C. diphtheriae* typically shows these granules at the poles of the bacilli, giving them a "beaded" appearance. This, combined with their "Chinese letter" or cuneiform arrangement, is a classic diagnostic feature. * **A. Clostridium botulinum:** These are gram-positive, anaerobic, spore-forming bacilli. They are identified by their subterminal spores, not metachromatic granules. * **C. Anthrax:** *Bacillus anthracis* is characterized by its large size, square ends (bamboo-stick appearance), and a prominent polypeptide capsule. * **D. Clostridium welchii (C. perfringens):** Known for being a capsulated, non-motile anaerobe that causes gas gangrene. It is identified by "box-car" shaped bacilli and a positive Nagler’s reaction. **High-Yield Clinical Pearls for NEET-PG:** * **Stains for Granules:** Remember the mnemonic **"P-A-N"** (Ponder’s, Albert’s, Neisser’s). * **Culture Media:** The gold standard for *C. diphtheriae* is **Löffler's Serum Slope** (rapid growth) and **Potassium Tellurite Agar** (black colonies). * **Arrangement:** The "Chinese letter" pattern is due to incomplete separation during binary fission (snapping division). * **Toxin:** The diphtheria toxin acts by inhibiting **EF-2** (Elongation Factor 2), halting protein synthesis.

Question 1120: Which of the following statements about Vibrio parahaemolyticus is FALSE?

A. It can tolerate a maximum of 1% salt.
B. It can tolerate a maximum of 3% salt.
C. It can tolerate a maximum of 7% salt.
D. It can tolerate a maximum of 10% salt. (Correct Answer)

Explanation: **Explanation:** *Vibrio parahaemolyticus* is a **halophilic** (salt-loving) bacterium, meaning it requires sodium chloride for growth. This characteristic distinguishes it from *Vibrio cholerae*, which can grow in the absence of salt. **Why Option D is the Correct (False) Statement:** While *Vibrio parahaemolyticus* thrives in saline environments, its salt tolerance has a specific upper limit. It grows optimally at **3% NaCl** and can tolerate concentrations up to **7-8%**. However, it **cannot tolerate or grow in 10% salt**. Therefore, the statement that it can tolerate a maximum of 10% salt is incorrect. **Analysis of Other Options:** * **Option A & B:** These are incorrect because the organism not only tolerates but **requires** these concentrations for optimal growth. It is a common cause of seafood-associated gastroenteritis because it thrives in the 1-3% salinity of coastal waters. * **Option C:** This is incorrect because 7% is near the upper limit of its tolerance range. It can still survive and grow at this concentration, though less optimally than at 3%. **High-Yield Clinical Pearls for NEET-PG:** * **Kanagawa Phenomenon:** Pathogenic strains produce a thermostable direct hemolysin (TDH) that causes Beta-hemolysis on **Wagatsuma agar**. * **Clinical Presentation:** It is the leading cause of "Seafood Poisoning" (ingestion of raw/undercooked fish or shellfish), presenting as watery diarrhea. * **Culture:** On **TCBS (Thiosulfate Citrate Bile Salts Sucrose) agar**, it produces **Green colonies** (non-sucrose fermenter), unlike *V. cholerae* which produces yellow colonies. * **Salt Tolerance Summary:** * *V. cholerae:* 0–3% (Non-halophilic) * *V. parahaemolyticus:* 1–7% (Halophilic) * *V. alginolyticus:* 1–10% (Highly halophilic)

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Staphylococci

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Streptococci and Enterococci

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Vibrio, Aeromonas, and Plesiomonas

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Mycobacteria

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Spirochetes

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