Bacteriology — MCQs
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All of the following pairs are true except:
Which of the following is NOT an investigation for syphilis?
A 50-year-old paddy farmer presented to the emergency room in shock. Attendants claim that he had sudden onset of fever with difficulty in breathing about 2 days ago and subsequently also developed hemoptysis. Sputum sample was collected, and Wayson staining was done. The organism isolated was indole positive, methyl red positive, and Voges-Proskauer positive, and fermented glucose, mannitol, and maltose. It also did not hydrolyze urea. Stalactite growth was seen in the ghee broth. What is the drug of choice for the above condition and which vector transmits the disease?
Which of the following properties is/are seen in the members of family Enterobacteriaceae?
Which of the following organisms shows a 'school of fish' appearance on microscopy?
What is true about Helicobacter pylori?
Which of the following factors is mainly responsible for virulence in Streptococcus?
What is the major antigenic determinant of H. influenzae?
What is true about Shigella dysenteriae Type I?
Whitemore bacillus is:
Bacteriology Indian Medical PG Practice Questions and MCQs
Question 971: All of the following pairs are true except:
- A. Kleb-Loeffler bacillus: Corynebacterium diphtheria
- B. Koch Week bacillus: Hemophilus influenzae (Correct Answer)
- C. Eaton's agent: Mycoplasma pneumoniae
- D. Battey bacillus: Mycobacterium intracellular
Explanation: ### Explanation The correct answer is **B** because **Koch-Weeks bacillus** is the eponym for ***Haemophilus aegyptius***, not *Haemophilus influenzae*. While both belong to the same genus, *H. aegyptius* is specifically associated with acute contagious conjunctivitis (pink eye) and Brazilian Purpuric Fever. **Analysis of Options:** * **A. Kleb-Loeffler bacillus (Corynebacterium diphtheriae):** This is a **true** pair. Named after Klebs (who first saw it) and Loeffler (who first cultured it). It is a Gram-positive, non-motile, club-shaped rod characterized by metachromatic (volutin) granules. * **C. Eaton’s agent (Mycoplasma pneumoniae):** This is a **true** pair. Named after Monroe Eaton, who isolated it in 1944. It is the smallest free-living organism and lacks a cell wall, making it naturally resistant to beta-lactams. * **D. Battey bacillus (Mycobacterium intracellulare):** This is a **true** pair. It is a Non-Tuberculous Mycobacteria (NTM) belonging to Runyon Group III (Non-photochromogens). It was named after the Battey State Hospital in Georgia where it was first studied. **NEET-PG High-Yield Pearls:** * **Koch’s Bacillus:** *Mycobacterium tuberculosis*. * **Hansen’s Bacillus:** *Mycobacterium leprae*. * **Friedlander’s Bacillus:** *Klebsiella pneumoniae*. * **Morax-Axenfeld Bacillus:** *Moraxella lacunata* (causes angular blepharoconjunctivitis). * **Pfeiffer’s Bacillus:** *Haemophilus influenzae*. * **Whitmore’s Bacillus:** *Burkholderia pseudomallei* (causes Melioidosis). * **Preisz-Nocard Bacillus:** *Corynebacterium pseudotuberculosis*.
Question 972: Which of the following is NOT an investigation for syphilis?
- A. VDRL
- B. FTA-ABS
- C. Weil-Felix (Correct Answer)
- D. TPI
Explanation: **Explanation:** The correct answer is **C. Weil-Felix**. This test is used for the diagnosis of **Rickettsial infections**, not syphilis. It is a heterophile agglutination test based on the cross-reactivity between antibodies produced in rickettsial diseases and antigens of certain strains of *Proteus* (*P. vulgaris* OX-19, OX-2, and *P. mirabilis* OX-K). **Analysis of Options:** * **VDRL (Venereal Disease Research Laboratory):** This is a **Non-Treponemal (Nonspecific)** screening test. It detects 'reagin' antibodies (IgM and IgG) against cardiolipin-cholesterol-lecithin antigen. It is highly sensitive but lacks specificity, often leading to Biological False Positives (BFP). * **FTA-ABS (Fluorescent Treponemal Antibody Absorption):** This is a **Treponemal (Specific)** test. It uses killed *T. pallidum* as the antigen. It is often the first test to become positive after infection and remains positive for life, making it the "gold standard" for confirming a diagnosis. * **TPI (Treponema Pallidum Immobilization):** This is the most specific treponemal test. It involves observing the loss of motility of live *T. pallidum* (Nichol’s strain) in the presence of patient serum and complement. Due to technical complexity, it is now largely replaced by FTA-ABS and TPHA. **High-Yield Clinical Pearls for NEET-PG:** 1. **Screening:** VDRL/RPR (Non-specific). 2. **Confirmation:** FTA-ABS/TPHA (Specific). 3. **Treatment Monitoring:** VDRL titers are used to monitor response to therapy (titers fall after treatment), whereas Treponemal tests remain positive for life. 4. **Neurosyphilis:** CSF-VDRL is the highly specific test for diagnosis. 5. **Congenital Syphilis:** FTA-ABS 19S IgM is the investigation of choice.
Question 973: A 50-year-old paddy farmer presented to the emergency room in shock. Attendants claim that he had sudden onset of fever with difficulty in breathing about 2 days ago and subsequently also developed hemoptysis. Sputum sample was collected, and Wayson staining was done. The organism isolated was indole positive, methyl red positive, and Voges-Proskauer positive, and fermented glucose, mannitol, and maltose. It also did not hydrolyze urea. Stalactite growth was seen in the ghee broth. What is the drug of choice for the above condition and which vector transmits the disease?
- A. Vector: 1 / Drug of choice: Streptomycin
- B. Vector: 3 / Drug of choice: Ampicillin
- C. Vector: 2 / Drug of choice: Gentamycin
- D. Vector: 3 / Drug of choice: Streptomycin (Correct Answer)
Explanation: ### Explanation The clinical presentation and laboratory findings point towards **Pneumonic Plague**, caused by ***Yersinia pestis***. **1. Why the Correct Answer is Right:** * **Clinical Clues:** A farmer presenting with rapid-onset fever, respiratory distress, and hemoptysis suggests Pneumonic Plague (the most severe form). * **Laboratory Clues:** * **Wayson Stain:** Shows characteristic **"Safety-pin appearance"** (bipolar staining). * **Culture:** **"Stalactite growth"** in ghee broth and "Ghee-pot appearance" are pathognomonic for *Y. pestis*. * **Biochemicals:** It is a non-motile, Gram-negative coccobacillus that is Indole (+), MR (+), and ferments glucose/mannitol. * **Vector:** The primary vector for *Yersinia pestis* is the **Rat Flea (*Xenopsylla cheopis*)**. * **Drug of Choice:** **Streptomycin** remains the traditional drug of choice for Plague (Gentamicin is an alternative). **2. Analysis of Incorrect Options:** * **Option A:** While Streptomycin is the drug of choice, Vector 1 (likely referring to a different vector like a tick or louse) is incorrect. * **Option B:** Ampicillin is not effective against *Y. pestis*; the organism is naturally resistant to many beta-lactams. * **Option C:** While Gentamicin is an effective alternative, Streptomycin is the classical "gold standard" answer for NEET-PG. Furthermore, the vector association must match the Rat Flea. **3. High-Yield Clinical Pearls for NEET-PG:** * **Safety-pin appearance:** Also seen in *Pasteurella multocida* and *Donovanosis (Klebsiella granulomatis)*, but the clinical context of "Stalactite growth" is unique to *Yersinia*. * **Temperature Sensitivity:** *Y. pestis* is motile at 25°C but **non-motile at 37°C** (though the plague bacillus itself is generally considered non-motile in most clinical contexts). * **Virulence Factors:** Fraction 1 (F1) antigen, V and W antigens, and Pesticin. * **Forms of Plague:** Bubonic (most common, involves lymph nodes/buboes), Septicemic, and Pneumonic (highly infectious via droplets).
Question 974: Which of the following properties is/are seen in the members of family Enterobacteriaceae?
- A. They are catalase-positive
- B. They are oxidase-negative
- C. They ferment glucose
- D. All are true (Correct Answer)
Explanation: The family **Enterobacteriaceae** is a large group of Gram-negative bacilli that inhabit the intestinal tract of humans and animals. To identify these organisms in a laboratory setting, four "cardinal features" are used to define the family. ### **Explanation of Properties** 1. **Catalase-positive (Option A):** Most members of this family produce the enzyme catalase, which breaks down hydrogen peroxide into water and oxygen. (Exception: *Shigella dysenteriae* type 1). 2. **Oxidase-negative (Option B):** This is a crucial diagnostic feature. They lack cytochrome c oxidase. This property helps differentiate them from other Gram-negative rods like *Pseudomonas* and *Vibrio*, which are oxidase-positive. (Exception: *Plesiomonas*). 3. **Glucose Fermentation (Option C):** All members of Enterobacteriaceae are aerogenic or anaerogenic fermenters of glucose. They reduce nitrates to nitrites and are facultative anaerobes. Since all three statements are fundamental characteristics of the family, **Option D (All are true)** is the correct answer. ### **High-Yield Clinical Pearls for NEET-PG** * **Gram Stain:** They are all Gram-negative, non-sporing bacilli. * **Nitrate Reduction:** They reduce nitrates to nitrites (this is the basis of the "Dipstick Nitrite Test" used to diagnose UTI). * **Motility:** Most are motile by **peritrichous flagella**. Notable non-motile exceptions are *Klebsiella* and *Shigella*. * **Culture:** They grow well on MacConkey agar. Based on lactose fermentation, they are classified into: * **Lactose Fermenters (LF):** *Escherichia coli, Klebsiella*. * **Late Lactose Fermenters (LLF):** *Shigella sonnei*. * **Non-Lactose Fermenters (NLF):** *Salmonella, Shigella* (except *S. sonnei*), *Proteus, Yersinia*.
Question 975: Which of the following organisms shows a 'school of fish' appearance on microscopy?
- A. Hemophilus ducreyi (Correct Answer)
- B. Neisseria gonorrhoeae
- C. Chlamydia trachomatis
- D. Calymmatobacterium granulomatis
Explanation: ### Explanation **Correct Answer: A. Hemophilus ducreyi** *Hemophilus ducreyi* is the causative agent of **Chancroid** (soft chancre). On Gram staining of the scrapings from the ulcer base, the organism appears as small, Gram-negative coccobacilli. These bacteria tend to arrange themselves in parallel rows or chains, resembling a **'school of fish'** or a **'railway track'** appearance. This characteristic morphology is due to the way the organisms align along the strands of mucus or inflammatory exudate. **Analysis of Incorrect Options:** * **B. Neisseria gonorrhoeae:** This is a Gram-negative **diplococcus** typically found within polymorphonuclear leukocytes (intracellular). It is described as having a **'kidney-bean'** or 'coffee-bean' shape. * **C. Chlamydia trachomatis:** This is an obligate intracellular bacterium. On microscopy (Giemsa stain), it is identified by the presence of **Halberstaedter-Prowazek inclusion bodies** (intracytoplasmic inclusions) rather than a specific multicellular arrangement. * **D. Calymmatobacterium granulomatis (Klebsiella granulomatis):** The causative agent of Granuloma Inguinale (Donovanosis). It shows **Donovan bodies**, which are described as 'safety-pin' appearing organisms within large mononuclear cells (macrophages). **High-Yield Clinical Pearls for NEET-PG:** * **Chancroid (H. ducreyi):** Presents as **painful** genital ulcers with **painful** inguinal lymphadenopathy (Buboes). Remember: *"Ducreyi makes you cry"* (painful). * **Culture Media:** *H. ducreyi* is fastidious and requires **GC agar** or Mueller-Hinton agar supplemented with 1% IsoVitaleX and vancomycin. * **Differential Diagnosis:** Always differentiate from Syphilis (painless ulcer) and Herpes (vesicular lesions).
Question 976: What is true about Helicobacter pylori?
- A. Present in 85 to 90% of gastric ulcers.
- B. Present in 20 to 25% of duodenal ulcers.
- C. Transmitted from person to person via fecal-oral or orogastric routes. (Correct Answer)
- D. Commonly found in adults from developing countries.
Explanation: **Explanation:** *Helicobacter pylori* is a microaerophilic, Gram-negative spiral bacterium that colonizes the gastric mucosa. Understanding its epidemiology and clinical associations is crucial for NEET-PG. **1. Why Option C is Correct:** The primary reservoir for *H. pylori* is the human stomach. Transmission occurs predominantly through **person-to-person** contact. The two main routes are the **fecal-oral route** (ingestion of contaminated water or food) and the **oral-oral/orogastric route** (via dental plaque or vomitus). This explains why the infection often clusters within families. **2. Why the Other Options are Incorrect:** * **Options A & B:** These options reverse the clinical associations. *H. pylori* is present in approximately **70% of gastric ulcers** and nearly **90-95% of duodenal ulcers**. It is the most common cause of peptic ulcer disease worldwide. * **Option D:** While *H. pylori* is indeed common in developing countries, it is typically acquired during **early childhood**, not adulthood. In developing nations, the prevalence can reach 80% by age 20, whereas in developed nations, the acquisition rate is much lower. **Clinical Pearls for NEET-PG:** * **Virulence Factors:** **Urease** (neutralizes gastric acid by producing ammonia), **CagA** (associated with gastric cancer), and **VacA** (cytotoxin). * **Diagnosis:** **Urea Breath Test (UBT)** is the gold standard for non-invasive diagnosis and confirming eradication. Invasive gold standard is **Endoscopy with Biopsy** (Rapid Urease Test/CLO test). * **Oncogenesis:** It is classified as a Class I Carcinogen, linked to **Gastric Adenocarcinoma** and **MALToma**. * **Treatment:** Standard Triple Therapy includes a PPI + Amoxicillin + Clarithromycin for 10–14 days.
Question 977: Which of the following factors is mainly responsible for virulence in Streptococcus?
- A. Carbohydrate
- B. Streptokinase
- C. Streptodornase
- D. M protein (Correct Answer)
Explanation: **Explanation:** The primary virulence factor of *Streptococcus pyogenes* (Group A Streptococcus) is the **M protein**. It is a hair-like projection extending from the cell wall. **Why M protein is the correct answer:** The M protein is essential for streptococcal pathogenicity due to its **anti-phagocytic properties**. It acts by: 1. Inhibiting the alternative complement pathway by binding to Factor H, preventing opsonization by C3b. 2. Promoting adherence to host mucosal cells. 3. Being highly antigenic; however, there are over 100 serotypes, which allows for repeated infections. **Analysis of Incorrect Options:** * **A. Carbohydrate:** The Group-specific C-carbohydrate (Lancefield antigen) is used for the **classification** of Streptococci into groups (A-V), but it does not directly contribute to virulence. * **B. Streptokinase:** This is an enzyme that promotes the lysis of fibrin clots (fibrinolysis), facilitating the spread of the bacteria through tissues. While it is a virulence factor, it is not the *main* factor compared to the anti-phagocytic M protein. * **C. Streptodornase:** Also known as DNase, it liquefies thick pus by degrading DNA. Like streptokinase, it aids in the spread of infection but is secondary to the M protein's role in evading the immune system. **High-Yield Facts for NEET-PG:** * **Molecular Mimicry:** Antibodies against M protein cross-react with cardiac myosin, leading to **Acute Rheumatic Fever**. * **ASO Titre:** Used to diagnose post-streptococcal sequelae; however, it is typically low in skin infections (Impetigo) because skin lipids inhibit Streptolysin O. * **Hyaluronic acid capsule:** Another anti-phagocytic factor, but it is non-immunogenic because it mimics human connective tissue.
Question 978: What is the major antigenic determinant of H. influenzae?
- A. 'M' protein
- B. Capsular polysaccharide (Correct Answer)
- C. Catalase
- D. Coagulase
Explanation: **Explanation:** The major antigenic determinant and primary virulence factor of *Haemophilus influenzae* is its **capsular polysaccharide**. Based on the antigenic structure of this capsule, *H. influenzae* is classified into six serotypes (a through f). Among these, **serotype b (Hib)**—which contains a unique capsule made of **Polyribosyl Ribitol Phosphate (PRP)**—is clinically the most significant, historically causing over 95% of invasive diseases like meningitis and epiglottitis in children. The capsule is essential for pathogenicity as it allows the bacteria to resist phagocytosis and complement-mediated lysis. **Analysis of Incorrect Options:** * **'M' protein:** This is the major virulence factor and antigenic determinant of *Streptococcus pyogenes* (Group A Streptococcus), responsible for resisting phagocytosis. * **Catalase:** This is an enzyme used by many bacteria (like *Staphylococci*) to neutralize hydrogen peroxide; it is a biochemical marker, not a major antigenic determinant. * **Coagulase:** This is a characteristic enzyme produced by *Staphylococcus aureus* to convert fibrinogen to fibrin; it is used for laboratory identification but is not associated with *H. influenzae*. **High-Yield Clinical Pearls for NEET-PG:** * **Vaccine:** The Hib vaccine is a **conjugate vaccine** where the PRP capsule is conjugated to a protein carrier (like Tetanus toxoid) to induce a T-cell dependent immune response. * **Culture:** *H. influenzae* requires both **Factor X (Hemin)** and **Factor V (NAD)** for growth, typically provided by Chocolate Agar. * **Satellitism:** It grows around *Staphylococcus aureus* on blood agar because *S. aureus* provides the necessary Factor V. * **Non-typable H. influenzae (NTHi):** Strains lacking a capsule; these primarily cause mucosal infections like Otitis Media, Sinusitis, and exacerbations of COPD.
Question 979: What is true about Shigella dysenteriae Type I?
- A. Can lead to hemolytic uremic syndrome (Correct Answer)
- B. It is the commonest cause of dysentery
- C. Produces exotoxin which causes invasive gastroenteritis
- D. Lactose fermentation is present
Explanation: **Explanation:** **Shigella dysenteriae Type I** (also known as Shiga bacillus) is the most virulent species of the Shigella genus. 1. **Why Option A is Correct:** *S. dysenteriae* Type I produces the potent **Shiga Toxin (Stx)**. This toxin enters the bloodstream and targets the glomerular endothelial cells in the kidney. It causes microangiopathic hemolytic anemia, thrombocytopenia, and acute renal failure—collectively known as **Hemolytic Uremic Syndrome (HUS)**. This is a classic high-yield association for competitive exams. 2. **Why Other Options are Incorrect:** * **Option B:** While *S. dysenteriae* causes the most severe disease, **Shigella sonnei** is the most common cause of bacillary dysentery in developed countries, and **Shigella flexneri** is the most common in developing countries like India. * **Option C:** Shigella is primarily an **invasive** pathogen. While the Shiga toxin contributes to severity, the "invasive" nature of the gastroenteritis is due to the bacteria's ability to invade the colonic mucosa via M cells, not solely due to the exotoxin. * **Option D:** All Shigella species are **Non-Lactose Fermenters (NLF)**, appearing as pale/colorless colonies on MacConkey agar. (Note: *S. sonnei* is a late lactose fermenter). **High-Yield Clinical Pearls for NEET-PG:** * **Infective Dose:** Shigella has a very low ID50 (only 10–100 organisms), making it highly communicable. * **Motility:** It is **non-motile** (distinguishes it from Salmonella). * **Catalase Test:** *S. dysenteriae* Type I is **Catalase negative**, while all other Shigella species are Catalase positive. * **Drug of Choice:** Ceftriaxone or Azithromycin (due to increasing resistance to Fluoroquinolones).
Question 980: Whitemore bacillus is:
- A. Haemophilus influenza
- B. Burkholderia mallei
- C. Burkholderia pseudomallei (Correct Answer)
- D. Burkholderia cepaciae
Explanation: **Explanation:** **Burkholderia pseudomallei** is the correct answer. It is a Gram-negative, aerobic, motile bacillus and the causative agent of **Melioidosis**. It was historically termed *Whitemore’s bacillus* after Alfred Whitmore, who first described the disease in morphine addicts in Rangoon. **Analysis of Options:** * **Burkholderia pseudomallei (Correct):** Known as Whitemore’s bacillus. It is found in soil and surface water. On culture, it often shows a characteristic "wrinkled" appearance and a "safety-pin" (bipolar) staining pattern. * **Burkholderia mallei:** This is the causative agent of **Glanders**, a disease primarily affecting horses. Unlike *B. pseudomallei*, it is non-motile. * **Haemophilus influenzae:** Historically known as *Pfeiffer’s bacillus*. It is a pleomorphic Gram-negative coccobacillus requiring Factors X and V for growth. * **Burkholderia cepacia:** An opportunistic pathogen often associated with nosocomial infections and cystic fibrosis; it is not referred to as Whitemore’s bacillus. **High-Yield Clinical Pearls for NEET-PG:** * **Melioidosis Presentation:** Can range from localized abscesses to fatal septicemia. It is often called the **"Remarkable Mimicker"** because it can present similarly to Tuberculosis (pulmonary nodules/cavitation). * **Staining:** Shows **Bipolar staining** (Waysen’s stain or Methylene blue), giving it a "safety-pin" appearance. * **Culture:** Grows on Ashdown’s medium (selective), producing characteristic wrinkled, honey-colored colonies. * **Drug of Choice:** Initial intensive therapy usually requires **Ceftazidime** or Meropenem, followed by long-term maintenance with Cotrimoxazole.
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Staphylococci
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Streptococci and Enterococci
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Neisseria and Moraxella
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Corynebacterium and Listeria
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Bacillus and Clostridium
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Enterobacteriaceae
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Vibrio, Aeromonas, and Plesiomonas
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Pseudomonas and Related Bacteria
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Haemophilus and HACEK Group
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Bordetella and Brucella
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Mycobacteria
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Spirochetes
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