Bacteriology Practice Questions

Q: Urinary tract infection by a gram-positive organism in a young sexually active female is commonly due to which bacterium?

Staphylococcus saprophyticus. **Explanation:** The correct answer is **Staphylococcus saprophyticus**. **1. Why it is correct:** *Staphylococcus saprophyticus* is a coagulase-negative, gram-positive coccus that is a leading cause of uncomplicated Urinary Tract Infections (UTIs) specifically in **young, sexually active females** (often referred to as "Honeymoon Cystitis"). It possesses specific adhesins (like Uers) that allow it to adhere effectively to the uroepithelium. While *E. coli* is the overall most common cause of UTI, *S. saprophyticus* is the most common **gram-positive** cause in this specific demographic. **2. Why the other options are incorrect:** * **Bacillus subtilis (A):** This is a gram-positive spore-forming rod that is generally considered a non-pathogenic environmental contaminant and does not cause UTIs. * **Escherichia coli (B):** While *E. coli* is the #1 cause of UTIs globally, it is a **Gram-negative** rod. The question specifically asks for a **Gram-positive** organism. * **Streptococcus pyogenes (D):** Also known as Group A Streptococcus (GAS), it primarily causes pharyngitis and skin infections (impetigo, cellulitis). It is not a recognized cause of urinary tract infections. **3. High-Yield NEET-PG Pearls:** * **Novobiocin Resistance:** *S. saprophyticus* is characteristically resistant to Novobiocin, which differentiates it from *S. epidermidis* (which is sensitive). * **Catalase/Coagulase:** It is Catalase-positive but Coagulase-negative (CoNS). * **Urease:** It is Urease-positive, which can lead to an increase in urine pH. * **Demographic:** If a clinical vignette mentions a "young female" with UTI symptoms and a "Gram-positive coccus in clusters," always think of *S. saprophyticus*.

Q: Lymphangitis is caused by which bacterium?

Streptococcus. **Explanation:** **Lymphangitis** is the inflammation of the lymphatic channels, typically occurring as a result of an infection distal to the site. **Why Streptococcus is the correct answer:** The most common causative organism for acute lymphangitis is **Streptococcus pyogenes (Group A Beta-Hemolytic Streptococcus)**. These bacteria produce enzymes like hyaluronidase and streptokinase that break down connective tissue barriers, allowing the organism to spread rapidly into the lymphatic system. Clinically, this presents as painful, erythematous "red streaks" extending from the site of infection toward regional lymph nodes. **Analysis of Incorrect Options:** * **Staphylococcus:** While *Staphylococcus aureus* is a leading cause of localized skin infections (like abscesses or furuncles), it tends to remain localized due to the production of coagulase, which walls off the infection. It is a much less common cause of spreading lymphangitis compared to Streptococcus. * **Pneumococcus (*S. pneumoniae*):** This organism primarily causes respiratory tract infections (pneumonia, otitis media) and meningitis. It is not a typical pathogen associated with skin or lymphatic spread. * **Neisseria:** *N. meningitidis* and *N. gonorrhoeae* are associated with meningitis and sexually transmitted infections, respectively. They do not typically cause primary lymphangitis. **NEET-PG High-Yield Pearls:** * **Clinical Presentation:** Look for the classic "red streaks" on a limb moving proximally. * **Lymphadenitis vs. Lymphangitis:** Lymphadenitis refers to the inflammation of the lymph **nodes** themselves, whereas lymphangitis is the inflammation of the **vessels**. * **Other Causes:** In specific contexts, consider *Sporothrix schenckii* (nodular lymphangitis/Rose gardener’s disease) or *Pasteurella multocida* (following animal bites). * **Treatment:** Penicillin remains the drug of choice for Streptococcal lymphangitis.

Q: What is the most common causative organism for sepsis in newborns?

Streptococcus agalactiae. **Explanation:** Neonatal sepsis is categorized into Early-Onset Sepsis (EOS, 72 hours). Globally, **Group B Streptococcus (GBS)**, also known as ***Streptococcus agalactiae***, remains the most common causative organism for neonatal sepsis, particularly EOS. It is typically transmitted vertically from the maternal birth canal during delivery. **Analysis of Options:** * **A. *Streptococcus agalactiae* (Correct):** It is the leading cause of EOS and neonatal meningitis worldwide. Maternal screening and intrapartum antibiotic prophylaxis (IAP) have reduced its incidence, but it remains the top pathogen in global literature. * **B. *Klebsiella pneumoniae*:** While *Klebsiella* and *E. coli* are the most common causes of neonatal sepsis in **India** and many developing countries (especially in NICU settings/LOS), *S. agalactiae* is the standard answer for the "most common" organism unless a specific geographical region or "Late-Onset" is specified. * **C. *Streptococcus pyogenes*:** Also known as Group A Strep; it is a rare cause of neonatal sepsis and more commonly associated with skin infections or pharyngitis in older children. * **D. *Haemophilus influenzae*:** While it can cause sepsis, it is much less common than GBS or Gram-negative bacilli in the neonatal period. **High-Yield Clinical Pearls for NEET-PG:** * **Most common cause of EOS (Global):** Group B Streptococcus (GBS). * **Most common cause of EOS/LOS (India):** *Klebsiella pneumoniae* (followed by *Staph. aureus* and *E. coli*). * **Most common cause of Meningitis in newborns:** GBS. * **Empiric Antibiotics:** Ampicillin + Gentamicin (covers GBS and Gram-negatives). * **Risk Factor:** Prematurity and Prolonged Rupture of Membranes (PROM >18 hours).

Q: Which form of actinomycosis is not seen?

Madura foot. **Explanation:** The correct answer is **Madura foot** because it is a clinical presentation of **Mycetoma**, not Actinomycosis. While both conditions can involve filamentous bacteria, they are distinct clinical entities. **1. Why Madura foot is the correct answer:** Madura foot (Eumycetoma or Actinomycetoma) is a chronic granulomatous infection of the subcutaneous tissue, typically involving the foot. It is caused by either fungi or aerobic actinomycetes (like *Nocardia* or *Actinomadura*). In contrast, **Actinomycosis** is caused by anaerobic, commensal bacteria (primarily *Actinomyces israelii*) that do not cause Madura foot. **2. Why other options are incorrect:** Actinomycosis is characterized by the endogenous spread of bacteria from mucosal surfaces to deeper tissues. The three most common clinical forms are: * **Cervicofacial (A):** The most common form (50-60%), often following dental procedures or poor oral hygiene ("Lumpy jaw"). * **Thoracic (B):** Caused by aspiration of oral secretions, leading to pulmonary lesions that can cross anatomical boundaries (ribs/chest wall). * **Abdominal (C):** Often follows appendicitis, bowel surgery, or the use of Intrauterine Devices (IUDs), typically presenting as an ileocecal mass. **Clinical Pearls for NEET-PG:** * **Pathogen:** *Actinomyces israelii* (Gram-positive, non-acid fast, anaerobic branching filaments). * **Hallmark:** Presence of **Sulfur granules** (yellowish clumps of organisms) in pus. * **Diagnosis:** "Ray Fungus" appearance on microscopy (though it is a bacterium, not a fungus). * **Treatment:** High-dose **Penicillin G** is the drug of choice (prolonged course).

Q: Safety pin appearance of bacteria is seen in which of the following?

Yersinia pestis. **Explanation:** The "safety pin" appearance refers to **bipolar staining**, where the ends of the rod-shaped bacteria stain more intensely than the center. This occurs because the organism exhibits a concentration of protoplasm at the poles. **1. Why Yersinia pestis is correct:** *Yersinia pestis*, the causative agent of Plague, is a Gram-negative coccobacillus. When stained with **Wayson, Giemsa, or Leishman stain**, it classically demonstrates bipolar staining, resembling a closed safety pin. This is a hallmark diagnostic feature in clinical specimens (like bubo aspirates). **2. Why the other options are incorrect:** * **Vibrio cholerae:** These are Gram-negative, comma-shaped (curved) rods. They are known for their "darting motility" on hanging drop preparations, not bipolar staining. * **Chlamydia:** These are obligate intracellular bacteria. They are visualized as "inclusion bodies" (e.g., Halberstaedter-Prowazek bodies) within host cells using Giemsa stain. * **Haemophilus influenzae:** These are pleomorphic Gram-negative coccobacilli. While they are small, they do not typically exhibit the distinct bipolar staining pattern of *Yersinia*. **3. NEET-PG High-Yield Pearls:** * **Other organisms showing Bipolar Staining:** Remember the mnemonic **"Y.B.P.C"** (You Better Pay Cash): *Yersinia pestis*, *Burkholderia pseudomallei* (Melioidosis), *Pasteurella multocida*, and *Calymmatobacterium granulomatis* (now *Klebsiella granulomatis* – causes Donovanosis/Granuloma Inguinale). * *Yersinia pestis* is also characterized by its **"Stalactite growth"** in ghee broth and **"Fried egg appearance"** on agar. * The vector for *Y. pestis* is the rat flea (*Xenopsylla cheopis*).

Q: What is the main causative organism of Gas gangrene?

Clostridium perfringens. **Explanation:** **Clostridium perfringens** (formerly *C. welchii*) is the primary causative agent of gas gangrene (clostridial myonecrosis), accounting for approximately 80–90% of clinical cases. It is a Gram-positive, anaerobic, spore-forming bacillus. The pathogenesis is driven by the production of potent exotoxins, most notably **Alpha-toxin (Lecithinase)**, which degrades cell membranes, leading to massive tissue necrosis, hemolysis, and toxemia. The characteristic "gas" in the tissues is produced by the fermentation of muscle carbohydrates by the bacteria. **Analysis of Incorrect Options:** * **A. Bacillus anthracis:** Causes Anthrax. While it can cause skin lesions (Malignant Pustule), it is an aerobic organism and does not cause myonecrosis or gas production. * **B. Clostridium tetani:** Causes Tetanus. It produces **Tetanospasmin**, which acts on the CNS to cause spastic paralysis (lockjaw). It does not cause invasive tissue destruction. * **C. Clostridium difficile:** Primarily causes antibiotic-associated diarrhea and **Pseudomembranous colitis**. It is not associated with wound infections or gangrene. **High-Yield Clinical Pearls for NEET-PG:** * **Nagler’s Reaction:** A specific biochemical test for *C. perfringens* that detects Lecithinase activity on egg yolk agar. * **Morphology:** It is described as "box-car shaped" bacilli and is notably **non-motile** (unlike most other Clostridia). * **Culture:** On blood agar, it shows a characteristic **target hemolysis** (double zone of hemolysis). * **Stormy Fermentation:** Rapid acid and gas production in litmus milk is a diagnostic feature.

Q: Which of the following is an exception among lactose non-fermenting bacteria?

Shigella sonnei. **Explanation:** The classification of Enterobacteriaceae is often based on their ability to ferment lactose on MacConkey agar. While the genus *Shigella* is classically categorized as **Lactose Non-Fermenters (LNF)**, producing pale/colorless colonies, **Shigella sonnei** is a notable exception. **1. Why Option A is Correct:** *Shigella sonnei* is a **Late Lactose Fermenter (LLF)**. Unlike most Shigella species, it possesses the genes to ferment lactose, but it does so slowly. On MacConkey agar, it initially appears as a non-fermenter (pale colonies) at 24 hours, but upon extended incubation (48–72 hours), it produces pink colonies. This is due to the presence of the enzyme $\beta$-galactosidase but a relative deficiency in lactose permease. **2. Why Options B, C, and D are Incorrect:** * **Shigella dysenteriae (Group A):** A true lactose non-fermenter. It is the most virulent species, producing the Shiga toxin. * **Shigella flexneri (Group B):** A true lactose non-fermenter and the most common cause of bacillary dysentery in developing countries. * **Shigella boydii (Group C):** A true lactose non-fermenter, primarily restricted to the Indian subcontinent. **High-Yield Clinical Pearls for NEET-PG:** * **Classification:** Shigella is grouped based on somatic 'O' antigens: A (*S. dysenteriae*), B (*S. flexneri*), C (*S. boydii*), and D (*S. sonnei*). * **Epidemiology:** *S. sonnei* is the most common cause of shigellosis in **developed countries**. * **Biochemical Key:** *S. sonnei* is also **Indole negative** and **Ornithine decarboxylase positive**, distinguishing it from other Shigella species. * **Other Late Lactose Fermenters:** Remember the mnemonic **"Vibrio SSS"** (*Vibrio cholerae*, *Shigella sonnei*, *Serratia*, and *Salmonella Paratyphi B*).

Q: What is true about Legionella pneumonia?

Treated with penicillin. **Explanation:** *Note: There appears to be a discrepancy in the provided key. **Legionella is naturally resistant to Penicillin** because it produces beta-lactamases and is an intracellular pathogen. The standard treatment is Macrolides (Azithromycin) or Fluoroquinolones (Levofloxacin). However, if we must analyze the options based on the provided key:* **1. Why "Treated with Penicillin" is marked correct (Academic Context):** In some older examinations, this option was used to test the knowledge of Legionella’s susceptibility. However, clinically, Legionella is **not** treated with penicillin. If this is the intended answer in a specific question bank, it may be a "distractor" or an error in the source material. In modern NEET-PG standards, the correct treatment is **Macrolides**. **2. Analysis of Incorrect Options:** * **A. Occurs in epidemics:** While outbreaks occur (linked to cooling towers or AC systems), it is more commonly seen as **sporadic** cases of community-acquired or nosocomial pneumonia. * **C. Diagnosed from sputum:** Legionella is difficult to see on a Gram stain (it stains poorly) and is fastidious. Sputum culture has low sensitivity. The gold standard for rapid diagnosis is the **Urinary Antigen Test** (detects Serogroup 1). * **D. More common in children:** Legionella primarily affects **older adults**, smokers, and the immunocompromised. It is rare in children. **High-Yield Clinical Pearls for NEET-PG:** * **Culture Media:** Requires **BCYE (Buffered Charcoal Yeast Extract)** agar supplemented with L-cysteine and iron. * **Clinical Feature:** Often presents with **hyponatremia**, high fever, and gastrointestinal symptoms (diarrhea). * **Transmission:** Inhalation of aerosols from contaminated water sources (ACs, showers); **no person-to-person spread.** * **Drug of Choice:** Azithromycin or Levofloxacin.

Question 1

Urinary tract infection by a gram-positive organism in a young sexually active female is commonly due to which bacterium?

Accepted Answer

Staphylococcus saprophyticus

Answer

Bacillus subtilis

Answer

Escherichia coli

Answer

Streptococcus pyogenes

Question 2

Lymphangitis is caused by which bacterium?

Accepted Answer

Streptococcus

Answer

Staphylococcus

Answer

Pneumococcus

Answer

Neisseria

Question 3

What is the most common cause of liver abscess in chronic granulomatous disease?

Accepted Answer

Staphylococcus aureus

Answer

Klebsiella

Answer

Peptostreptococcus

Answer

E.coli

Question 4

What is the most common causative organism for sepsis in newborns?

Accepted Answer

Streptococcus agalactiae

Answer

Klebsiella pneumoniae

Answer

Streptococcus pyogenes

Answer

Haemophilus influenzae

Question 5

Which form of actinomycosis is not seen?

Accepted Answer

Madura foot

Answer

Cervicofacial

Answer

Thoracic

Answer

Abdominal

Question 6

Safety pin appearance of bacteria is seen in which of the following?

Accepted Answer

Yersinia pestis

Answer

Vibrio cholerae

Answer

Chlamydia

Answer

Haemophilus influenzae

Question 7

What is the main causative organism of Gas gangrene?

Accepted Answer

Clostridium perfringens

Answer

Bacillus anthrax

Answer

Clostridium tetani

Answer

Clostridium difficile

Question 8

Which of the following statements regarding Clostridium perfringens is incorrect?

Accepted Answer

Gas gangrene producing strains of Clostridium perfringens produce heat resistant spores.

Answer

It is the commonest cause of gas gangrene.

Answer

It is normally present in human faeces.

Answer

The principal toxin of Clostridium perfringens is the alpha toxin.

Question 9

Which of the following is an exception among lactose non-fermenting bacteria?

Accepted Answer

Shigella sonnei

Answer

Shigella dysenteriae

Answer

Shigella flexneri

Answer

Shigella boydii

Question 10

What is true about Legionella pneumonia?

Accepted Answer

Treated with penicillin

Answer

Occurs in epidemics

Answer

Diagnosed from sputum

Answer

More common in children

Bacteriology — MCQs

Bacteriology — MCQs

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