Bacteriology — MCQs

Bacteriology Indian Medical PG Practice Questions and MCQs

Question 2191: Which of the following statements is TRUE about tetanus (Clostridium tetani)?

A. Trismus and neck stiffness are early signs
B. Gram -ve spore forming organism
C. Produces tetanolysin and tetanospasmin (Correct Answer)
D. Generalized tonic-clonic seizure occurs on hyperstimulation

Explanation: ***Produces tetanolysin and tetanospasmin*** - *Clostridium tetani* produces two exotoxins: **tetanospasmin** (a neurotoxin responsible for muscle spasms) and **tetanolysin** (a hemolysin whose role in pathogenesis is less clear but may contribute to tissue damage). - **Tetanospasmin** blocks the release of inhibitory neurotransmitters, leading to unopposed muscle excitation. *Trismus and neck stiffness are early sign* - While **trismus** (lockjaw) and **neck stiffness** are indeed characteristic early signs of tetanus, this statement is not the *most complete* or *fundamental* truth about the *mechanism* of the disease, which is toxin production. - Early symptoms also include difficulty swallowing and muscle spasms localized to the wound area before becoming generalized. *Gram -ve spore forming organism* - *Clostridium tetani* is a **Gram-positive**, not Gram-negative, bacterium. - It is an **anaerobic**, spore-forming rod, and its spores are highly resistant to heat and disinfectants. *Generalized tonic-clonic seizure occurs on hyperstimulation* - Tetanus causes **generalized tonic spasms** and **convulsions**, especially in response to sensory stimuli (hyperstimulation). - These are typically sustained, painful muscle contractions rather than classic generalized tonic-clonic seizures, though severe cases can resemble seizures.

Question 2192: Most common organism responsible for pseudomembranous colitis is:

A. Clostridium botulinum
B. Clostridium butyricum
C. Clostridium histolyticum
D. Clostridium difficile (Correct Answer)

Explanation: ***Clostridium difficile*** - **_Clostridium difficile_** is the most common causative organism for **pseudomembranous colitis**, an inflammation of the colon characterized by the formation of pseudomembranes. - This condition often develops after **antibiotic use** that disrupts the normal gut flora, allowing **_C. difficile_** to proliferate and produce toxins. *Clostridium botulinum* - **_Clostridium botulinum_** is responsible for **botulism**, a severe neuroparalytic illness caused by its potent toxins. - It does not cause pseudomembranous colitis, and its primary mode of action is through **neuromuscular blockade**, not intestinal inflammation. *Clostridium butyricum* - **_Clostridium butyricum_** is primarily known for producing **butyric acid** and is sometimes used as a probiotic. - It is not associated with causing pseudomembranous colitis or other significant human infections in healthy individuals. *Clostridium histolyticum* - **_Clostridium histolyticum_** is involved in **gas gangrene** and other soft tissue infections, producing powerful enzymes that break down tissues. - It is not implicated in the pathogenesis of pseudomembranous colitis.

Question 2193: The most frequent cause of scalded skin syndrome is?

A. Meningococci
B. Staphylococci (Correct Answer)
C. Pneumococci
D. Enterococci

Explanation: ***Staphylococci*** - **Staphylococcus aureus** produces an **exotoxin (exfoliatin)** that targets desmosomes, leading to epidermal cleavage and the characteristic blistering seen in **staphylococcal scalded skin syndrome (SSSS)**. - SSSS is primarily seen in **infants and young children** due to their immature renal clearance of the exfoliatin toxin and lack of protective antibodies. *Meningococci* - **Neisseria meningitidis** is known to cause **meningitis** and **meningococcemia**, which can present with a **purpuric rash** but not typically widespread blistering characteristic of scalded skin syndrome. - The skin manifestations of meningococcal disease are usually due to **vasculitis** and **coagulopathy**, not exotoxin-mediated epidermal separation. *Pneumococci* - **Streptococcus pneumoniae** is a common cause of **pneumonia**, **otitis media**, and **meningitis**. - It does not produce exotoxins that cause the characteristic skin peeling seen in scalded skin syndrome. *Enterococci* - **Enterococci** are opportunistic pathogens primarily associated with **urinary tract infections**, **bacteremia**, and **nosocomial infections**. - They are not known to produce toxins that cause epidermolysis or scalded skin syndrome.

Question 2194: Toxic shock syndrome is due to the following virulence factor:

A. M protein
B. Carbohydrate cell wall
C. Streptolysin O
D. Pyrogenic exotoxin (Correct Answer)

Explanation: ***Pyrogenic exotoxin*** - **Pyrogenic exotoxins**, specifically **Toxic Shock Syndrome Toxin-1 (TSST-1)** and other streptococcal pyrogenic exotoxins (SPEs), are **superantigens** responsible for the symptoms of **toxic shock syndrome**. - These superantigens bind directly to **MHC class II** and **T-cell receptors**, leading to a massive, non-specific release of **cytokines** that cause severe systemic inflammation and organ failure. *M protein* - **M protein** is a major virulence factor of **Streptococcus pyogenes**, contributing to its antiphagocytic properties and adherence. - While important for streptococcal infections, it is not the primary mediator of the **toxic shock syndrome** associated with *Staphylococcus aureus* or *Streptococcus pyogenes*. *Carbohydrate cell wall* - The **carbohydrate cell wall** is a structural component of bacteria, particularly Gram-positive bacteria, and can have some immunogenic properties. - However, it does not directly act as a specific virulence factor like a superantigen to cause the severe systemic symptoms characteristic of **toxic shock syndrome**. *Streptolysin O* - **Streptolysin O** is an **exotoxin produced by Streptococcus pyogenes** that causes **hemolysis** and is cardiotoxic and cytolytic. - While it contributes to tissue damage and can be involved in severe streptococcal infections, it is not the main superantigen responsible for the widespread systemic effects of **toxic shock syndrome**.

Question 2195: Which of the following statements about tetanus is true?

A. Anaerobic infection
B. Caused by C. Tetani (Correct Answer)
C. Cannot be prevented
D. Forms terminal spores

Explanation: ***Caused by C. Tetani*** - Tetanus is definitively caused by the bacterium **Clostridium tetani**, which is known for producing the potent neurotoxin **tetanospasmin**. - This neurotoxin is responsible for the characteristic **muscle spasms** and rigidity seen in tetanus. *Anaerobic infection* - While *Clostridium tetani* is an **anaerobic bacterium**, stating that tetanus is an "anaerobic infection" is a description of the causative agent, not the most definitive or unique statement about the disease itself. - The unique aspect of tetanus lies in the **neurotoxin production** by this specific anaerobe. *Cannot be prevented* - Tetanus is highly **preventable** through vaccination with the **tetanus toxoid**, which provides active immunity. - Public health efforts globally focus on widespread **immunization** to reduce the incidence of tetanus. *Forms terminal spores* - *Clostridium tetani* forms **spores**, but these are typically **subterminal** or terminal, depending on the strain, which is a characteristic of the bacterium, not the most defining statement about the disease process. - The spores are resilient and allow the bacterium to survive in harsh conditions until they find an **anaerobic environment** to germinate.

Question 2196: 45 yrs old Ramlal has intra-abdominal sepsis. The causative organism was found to be vancomycin, gentamicin and ampicillin resistant. It grows well in presence of 6.5% NaCl and arginine. Bile esculin hydrolysis is positive. Which of the following is the organism? -

A. Enterococcus fecalis (Correct Answer)
B. Streptococcus bovis
C. Streptococcus pneumoniae
D. Streptococcus agalactiae

Explanation: ***Enterococcus fecalis*** - *Enterococcus fecalis* is commonly associated with **intra-abdominal sepsis** and can exhibit resistance to **vancomycin, gentamicin, and ampicillin**. - Its ability to grow in **6.5% NaCl**, hydrolyze **bile esculin**, and utilize **arginine** are classic biochemical characteristics distinguishing it from streptococci. *Streptococcus bovis* - While *Streptococcus bovis* can hydrolyze **bile esculin**, it typically **does not grow in 6.5% NaCl** and is usually susceptible to **ampicillin**. - It is more commonly associated with **bacteremia in patients with colon cancer** or endocarditis, rather than multi-drug resistant intra-abdominal sepsis. *Streptococcus pneumoniae* - *Streptococcus pneumoniae* is known for causing pneumonia and meningitis but **does not grow in 6.5% NaCl** and has a **negative bile esculin test**. - It is also typically **penicillin-sensitive** (though resistance exists) and does not exhibit the multi-drug resistance profile described. *Streptococcus agalactiae* - *Streptococcus agalactiae* (Group B Strep) is known for causing neonatal sepsis and meningitis, but it **does not grow in 6.5% NaCl** and is **bile esculin negative**. - It is generally susceptible to **ampicillin** and does not fit the described multi-drug resistance pattern or biochemical profile.

Question 2197: Lues maligna is caused by?

A. Treponema (Correct Answer)
B. Borrelia
C. Leptospira
D. Brachyspira

Explanation: ***Treponema*** - **Lues maligna** is a severe, ulcerative form of **secondary syphilis**, which is caused by the bacterium **Treponema pallidum**. - This condition involves widespread necrotic skin lesions and systemic symptoms, occurring in individuals with an altered immune response to the spirochete. *Borrelia* - **Borrelia burgdorferi** is the causative agent of **Lyme disease**, characterized by erythema migrans, neurological symptoms, and arthritis. - Other Borrelia species cause relapsing fever, which is distinct from syphilis and lues maligna. *Leptospira* - **Leptospira interrogans** is responsible for **leptospirosis**, a zoonotic infection that can cause flu-like symptoms, liver and kidney damage, and jaundice (Weil's disease). - Its clinical presentation and transmission route are entirely different from syphilis. *Brachyspira* - **Brachyspira species** are primarily associated with intestinal infections in animals, particularly swine dysentery, and are not known to cause human systemic diseases like syphilis. - While some species can colonize the human gut, they do not cause infectious syphilis or its severe manifestations like lues maligna.

Question 2198: The organism causing pseudomembranous colitis:

A. Clostridium difficile (Correct Answer)
B. Clostridium botulinum
C. Clostridium tetani
D. Clostridium perfringens

Explanation: ***Clostridium difficile*** - This bacterium is the primary cause of **pseudomembranous colitis**, an inflammation of the colon characterized by the formation of membranes on the mucosal surface. - It produces **toxins A and B** which damage the intestinal lining, leading to severe diarrhea, abdominal pain, and fever. *Clostridium botulinum* - This organism is responsible for **botulism**, a severe form of food poisoning or wound infection. - It produces a potent **neurotoxin** that causes flaccid paralysis by blocking acetylcholine release at neuromuscular junctions. *Clostridium tetani* - This bacterium causes **tetanus**, characterized by muscle spasms and rigidity. - It produces the **tetanospasmin neurotoxin** which inhibits inhibitory neurotransmitters in the spinal cord. *Clostridium perfringens* - Primarily known for causing **gas gangrene** (myonecrosis) and certain types of food poisoning. - It produces various **toxins**, including alpha-toxin, which contribute to tissue destruction and gas formation.

Question 2199: Noguchi's medium is used for?

A. Corynebacterium
B. Brucella
C. Borrelia (Correct Answer)
D. Bordetella

Explanation: ***Borrelia*** - While Hideyo Noguchi worked with various spirochetes, **Noguchi's medium** is **not** the standard medium for Borrelia species. - **Borrelia burgdorferi** (Lyme disease) is cultured in **Barbour-Stoenner-Kelly (BSK) medium** or modified Kelly-Pettenkofer medium. - **Borrelia recurrentis** (relapsing fever) may be cultured in enriched media but Noguchi's medium is not the primary choice. - **Note:** Historically, Noguchi's medium (serum with paraffin overlay) was developed for **Leptospira** culture, not Borrelia. *Corynebacterium* - **Corynebacterium diphtheriae** is cultured on **Loeffler's serum slope** or **tellurite agar (Tinsdale agar)** for characteristic colony morphology and differentiation. - Noguchi's medium is not used for Corynebacterium species. *Brucella* - **Brucella species** require enriched media such as **Brucella agar** or blood agar with 5-10% CO2. - Noguchi's medium is not used for Brucella isolation. *Bordetella* - **Bordetella pertussis** is cultured on **Bordet-Gengou agar** or **Regan-Lowe medium** containing charcoal and blood. - Noguchi's medium is not appropriate for Bordetella species. **Important Note:** The classical **Noguchi's medium** in microbiology textbooks is primarily associated with **Leptospira** (not among the options). This question may require review of the correct answer or option set.

Question 2200: Negative staining is used to demonstrate

A. Bacterial fimbriae
B. Bacterial spore
C. Bacterial flagella
D. Bacterial capsule (Correct Answer)

Explanation: ***Bacterial capsule*** - **Negative staining** uses acidic dyes (e.g., **India ink**, **Nigrosin**) that stain the background but not the bacterial cell or its capsule, making the **capsule appear as a clear halo** around the bacterial cell. - This technique is particularly useful for visualizing capsules because they are **polysaccharide-rich** and do not readily take up basic dyes used in positive staining. *Bacterial fimbriae* - Fimbriae are **hair-like appendages** that are much thinner and smaller than capsules, making them difficult to visualize with negative staining alone. - They are often seen using **electron microscopy** or specialized staining techniques due to their fine structure. *Bacterial spore* - **Bacterial spores** are highly resistant structures within the bacterial cell and are typically visualized using a **spore stain** (e.g., **Schaeffer-Fulton method**) where the spore is stained green and the vegetative cell red. - Negative staining would primarily show the outline of the spore or potentially the entire cell, but not highlight the internal spore structure specifically. *Bacterial flagella* - Flagella are **whip-like appendages** responsible for motility and require a **flagella stain** technique (e.g., Leifson's method) that coats the flagella to increase their thickness and visibility under a light microscope. - Negative staining does not provide the necessary contrast or thickening to easily observe flagella.

Practice by Chapter

Staphylococci

Practice Questions

Streptococci and Enterococci

Practice Questions

Neisseria and Moraxella

Practice Questions

Corynebacterium and Listeria

Practice Questions

Bacillus and Clostridium

Practice Questions

Enterobacteriaceae

Practice Questions

Vibrio, Aeromonas, and Plesiomonas

Practice Questions

Pseudomonas and Related Bacteria

Practice Questions

Haemophilus and HACEK Group

Practice Questions

Bordetella and Brucella

Practice Questions

Mycobacteria

Practice Questions

Spirochetes

Practice Questions

Want unlimited practice?

Get full access to all questions, explanations, and performance tracking.

Start For Free