Bacteriology — MCQs
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Which of the following vectors is known to transmit a disease that can be identified by the presence of spirochetes under dark-field microscopy?
Which anaerobic organism is known to cause multiple abscesses with discharging sinuses and demonstrates sulfur granules in pus?
Which organism is the most common cause of acute bacterial prostatitis?
Which microorganism is the most common cause of pyogenic osteomyelitis?
A chronic alcoholic is presenting with clinical features of meningitis. Most likely organism to grow on CSF culture:
Granuloma inguinale is caused by:
Which of the following statements about anthrax toxin is false?
What is the causative agent of Rhinoscleroma?
Which of the following statements about Listeria is false?
In human infections, the morula form is seen in which of the following organisms?
Bacteriology Indian Medical PG Practice Questions and MCQs
Question 2371: Which of the following vectors is known to transmit a disease that can be identified by the presence of spirochetes under dark-field microscopy?
- A. Anopheles
- B. Ixodes scapularis ticks (Correct Answer)
- C. Louse
- D. Rat flea
Explanation: ***Ixodes scapularis ticks*** - *Ixodes scapularis* ticks are the primary vectors for **Lyme disease**, caused by the spirochete *Borrelia burgdorferi*. - **Spirochetes** can be identified in tissue samples or cultures using **dark-field microscopy** or silver staining techniques. - Direct visualization from patient samples is uncommon; diagnosis typically relies on serology and clinical presentation. *Louse* - Lice (e.g., *Pediculus humanus corporis*) transmit **relapsing fever** (*Borrelia recurrentis*) and epidemic typhus (*Rickettsia prowazekii*). - *Borrelia recurrentis* spirochetes are readily visible in **peripheral blood smears** using Wright or Giemsa stain during febrile episodes. - While this is also a spirochete disease, the question specifically refers to dark-field microscopy, which is classically associated with Lyme disease spirochete identification. *Anopheles* - The *Anopheles* mosquito is the vector for **malaria**, caused by *Plasmodium* parasites, not spirochetes. - Malaria is diagnosed by identifying ring forms, trophozoites, and schizonts within red blood cells on blood smears. *Rat flea* - The rat flea (*Xenopsylla cheopis*) is the primary vector for **bubonic plague** (*Yersinia pestis*) and murine typhus (*Rickettsia typhi*). - *Yersinia pestis* is a gram-negative coccobacillus, not a spirochete.
Question 2372: Which anaerobic organism is known to cause multiple abscesses with discharging sinuses and demonstrates sulfur granules in pus?
- A. Nocardia asteroides
- B. Salmonella enterica
- C. Francisella tularensis
- D. Actinomyces (Correct Answer)
Explanation: ***Actinomyces*** - *Actinomyces* species are classic causes of **actinomycosis**, characterized by chronic, suppurative infections with **multiple abscesses**, draining sinuses, and the presence of **sulfur granules** in pus. - They are **anaerobic or microaerophilic gram-positive bacteria** that are part of the normal flora of the mouth and gastrointestinal tract, causing infection when mucosal barriers are disrupted. *Nocardia asteroides* - *Nocardia asteroides* causes **nocardiosis**, which can also present with abscesses, but it is an **aerobic bacterium** and typically does not produce sulfur granules. - Nocardial infections often involve the lungs, skin, or central nervous system, particularly in **immunocompromised individuals**. *Salmonella enterica* - *Salmonella enterica* is a facultative anaerobic Gram-negative bacterium known for causing **gastroenteritis**, typhoid fever, and bacteremia. - It is not associated with the formation of multiple abscesses with draining sinuses or sulfur granules. *Francisella tularensis* - *Francisella tularensis* causes **tularemia**, a zoonotic disease characterized by ulceroglandular lesions, fever, and lymphadenopathy. - It does not typically cause multiple abscesses with draining sinuses or produce sulfur granules.
Question 2373: Which organism is the most common cause of acute bacterial prostatitis?
- A. Enterococcus
- B. Streptococcus viridans
- C. Peptostreptococcus
- D. E.coli (Correct Answer)
Explanation: ***E.coli*** - **E.coli** is the most common cause of **acute bacterial prostatitis**, accounting for a significant majority of cases. - It is a **gram-negative rod** commonly found in the gastrointestinal tract and can ascend into the urinary tract and prostate. *Enterococcus* - While **Enterococcus species** can cause urinary tract infections and, less commonly, prostatitis, they are a distant second to E.coli in frequency. - They are **gram-positive cocci** and are often associated with catheter-associated infections or healthcare-acquired infections. *Streptococcus viridans* - **Streptococcus viridans** group bacteria are typically commensals of the oral cavity and are more known for causing **endocarditis** or dental infections. - They are not a common cause of acute bacterial prostatitis. *Peptostreptococcus* - **Peptostreptococcus** is a genus of **anaerobic gram-positive cocci** commonly found in the normal flora of the mouth, gastrointestinal tract, and vagina. - They are typically involved in **polymicrobial anaerobic infections** but are not a primary or common cause of acute bacterial prostatitis.
Question 2374: Which microorganism is the most common cause of pyogenic osteomyelitis?
- A. S. aureus (Correct Answer)
- B. Streptococcus spp.
- C. Corynebacterium spp.
- D. Neisseria gonorrhoeae (gonococcus)
Explanation: ***Staph aureus*** - **_Staphylococcus aureus_** is the most frequent cause of **pyogenic osteomyelitis** across all age groups and routes of infection. - Its ability to adhere to bone, form biofilms, and produce toxins contributes to its prevalence in bone infections. *Streptococcus spp.* - While various **_Streptococcus_** species can cause infections, they are less common causes of pyogenic osteomyelitis compared to **_Staphylococcus aureus_**. - **Group A _Streptococcus_** can cause severe invasive infections but rarely involves primary bone infection. *Corynebacterium spp.* - **_Corynebacterium_** species, particularly **_Corynebacterium striatum_**, are increasingly recognized as opportunistic pathogens, especially in immunocompromised individuals or those with foreign bodies. - However, they are not the most common cause of osteomyelitis in the general population. *Neisseria gonorrhoeae (gonococcus)* - **_Neisseria gonorrhoeae_** can cause **disseminated gonococcal infection (DGI)**, which may include joint involvement (**septic arthritis**). - While it can lead to bone pain and swelling, it primarily affects joints and is a less common cause of direct **pyogenic osteomyelitis** than **_S. aureus_**.
Question 2375: A chronic alcoholic is presenting with clinical features of meningitis. Most likely organism to grow on CSF culture:
- A. Streptococcus pneumoniae (Correct Answer)
- B. Neisseria meningitidis
- C. Escherichia coli
- D. Listeria monocytogenes
Explanation: ***Streptococcus pneumoniae*** - **Chronic alcoholism** is a significant risk factor for **pneumococcal infections**, including meningitis, due to impaired immune function. - **S. pneumoniae** is the most common cause of **bacterial meningitis** in adults, especially in those with underlying conditions like alcoholism. *Neisseria meningitidis* - While a common cause of meningitis, especially in **young adults** and crowded settings, it is not specifically associated with chronic alcoholism as a primary risk factor like *S. pneumoniae*. - **Meningococcal meningitis** often presents with a **petechial rash**, which is not mentioned in the clinical scenario. *Escherichia coli* - **E. coli meningitis** primarily affects **neonates** and **elderly** or immunocompromised individuals, usually associated with healthcare-acquired infections. - It is not a typical cause of community-acquired meningitis in an otherwise healthy adult alcoholic. *Listeria monocytogenes* - **Listeria monocytogenes** is a known cause of meningitis in **immunocompromised individuals**, **neonates**, and **elderly** people, often linked to contaminated food. - While chronic alcoholism does impair immunity, *S. pneumoniae* is a more frequently encountered pathogen in this specific population for meningitis.
Question 2376: Granuloma inguinale is caused by:
- A. Calymmatobacterium granulomatis (Correct Answer)
- B. Haemophilus ducreyi
- C. Chlamydia trachomatis
- D. Treponema pallidum
Explanation: ***Calymmatobacterium granulomatis*** - **Granuloma inguinale**, also known as **donovanosis**, is a sexually transmitted infection caused by **_Calymmatobacterium granulomatis_**. - This bacterium is notoriously difficult to culture, so diagnosis is typically made by identifying **Donovan bodies** (macrophages filled with bacteria) in tissue samples. *Haemophilus ducreyi* - **_Haemophilus ducreyi_** is the causative agent of **chancroid**, - Chancroid is characterized by **painful genital ulcers** with a ragged, undermined border, and often accompanied by **tender inguinal lymphadenopathy**. *Chlamydia trachomatis* - **_Chlamydia trachomatis_** is responsible for several conditions, including **chlamydia** (the most common bacterial STI), **lymphogranuloma venereum (LGV)**, and **trachoma**. - LGV presents with a transient, often unnoticed genital lesion followed by painful, suppurative lymphadenopathy, which is distinct from granuloma inguinale. *Treponema pallidum* - **_Treponema pallidum_** is the spirochete that causes **syphilis**, which progresses through several stages. - Primary syphilis manifests as a **painless chancre**, while secondary syphilis can involve a widespread rash, lymphadenopathy, and mucosal lesions.
Question 2377: Which of the following statements about anthrax toxin is false?
- A. Increase cAMP
- B. Has three components
- C. Coded by plasmid
- D. Inhibits protein synthesis (Correct Answer)
Explanation: ***Inhibits protein synthesis*** - Anthrax toxin, specifically the **lethal factor (LF)**, is a **zinc-dependent metalloprotease** that cleaves and inactivates **mitogen-activated protein kinase kinase (MAPKKs)**, leading to cell death, not directly inhibiting protein synthesis. - The **edema factor (EF)** component of the toxin is an **adenylate cyclase** that increases **intracellular cyclic AMP (cAMP)**, which also does not directly inhibit protein synthesis. *Has three components* - Anthrax toxin is indeed composed of three distinct proteins: **protective antigen (PA)**, **edema factor (EF)**, and **lethal factor (LF)**. - PA is necessary for EF and LF to enter host cells, while EF causes edema and LF is responsible for cytotoxicity. *Increase cAMP* - The **edema factor (EF)** component of anthrax toxin is a **calmodulin-dependent adenylate cyclase**. - Once inside the cell, EF converts **ATP to cyclic AMP (cAMP)**, leading to increased intracellular cAMP levels, which disrupts water homeostasis and causes edema. *Coded by plasmid* - The genes encoding the anthrax toxin components (PA, EF, and LF) are located on a large plasmid known as **pXO1**. - This plasmid, along with another plasmid (pXO2) carrying genes for the capsule, is crucial for the full virulence of *Bacillus anthracis*.
Question 2378: What is the causative agent of Rhinoscleroma?
- A. Klebsiella rhinoscleromatis (Correct Answer)
- B. Staphylococcus aureus
- C. Pseudomonas aeruginosa
- D. Corynebacterium diphtheriae
Explanation: ***Klebsiella rhinoscleromatis*** - This bacterium is the **specific causative agent** of rhinoscleroma, a chronic progressive granulomatous disease affecting the upper respiratory tract. - It is a sub-species of *Klebsiella pneumoniae*. *Staphylococcus aureus* - *Staphylococcus aureus* is a common cause of various **skin infections**, **abscesses**, and systemic infections like **sepsis** and **endocarditis**. - It is not associated with rhinoscleroma. *Pseudomonas aeruginosa* - *Pseudomonas aeruginosa* is an **opportunistic pathogen** often associated with hospital-acquired infections, particularly in immunocompromised individuals. - It can cause **pneumonia**, urinary tract infections, and infections in burn patients, but not rhinoscleroma. *Corynebacterium diphtheriae* - *Corynebacterium diphtheriae* is the causative agent of **diphtheria**, characterized by the formation of a **pseudomembrane** in the throat and toxin-mediated systemic effects. - Its clinical presentation is distinct from rhinoscleroma.
Question 2379: Which of the following statements about Listeria is false?
- A. PALCAM agar is used for isolation
- B. Characteristic tumbling motility at 37°C (Correct Answer)
- C. Gram positive
- D. Umbrella shaped growth
Explanation: ***Characteristic tumbling motility at 37°C*** - *Listeria monocytogenes* exhibits **"tumbling motility" at 20-25°C**, but it is non-motile at 37°C. - This temperature-dependent motility is a key diagnostic feature, and the statement claiming motility at 37°C is incorrect. *Gram positive* - *Listeria monocytogenes* is indeed a **gram-positive bacillus**, a key characteristic aiding in its initial identification. - Its gram stain reaction distinguishes it from gram-negative bacteria, guiding appropriate treatment. *PALCAM agar is used for isolation* - **PALCAM (Polymyxin Acriflavin Lithium Chloride Ceftazidime Esculin Mannitol) agar** is a selective and differential medium specifically designed for the isolation and detection of *Listeria monocytogenes*. - It utilizes esculin hydrolysis and mannitol fermentation to differentiate *Listeria* species. *Umbrella shaped growth* - When cultured in a semi-solid medium, *Listeria monocytogenes* typically displays a characteristic **umbrella-shaped pattern of growth** at reduced temperatures (e.g., 20-25°C) due to its motility. - This macroscopic appearance is a classic identifier for *Listeria*.
Question 2380: In human infections, the morula form is seen in which of the following organisms?
- A. Chlamydiae
- B. Bartonella quintana
- C. Mycoplasma hominis
- D. Ehrlichia (Correct Answer)
Explanation: ***Correct: Ehrlichia*** - *Ehrlichia* species are **obligate intracellular bacteria** that replicate in host immune cells, forming distinctive microcolonies known as **morulae** (mulberry-like clusters). - The presence of morulae within the cytoplasm of **white blood cells** (monocytes or granulocytes) is the **key diagnostic feature** for ehrlichiosis. - The term "morula" comes from Latin for "mulberry," describing the characteristic clustered appearance visible on microscopy. *Incorrect: Chlamydiae* - *Chlamydiae* are obligate intracellular parasites with a unique developmental cycle involving elementary bodies (infectious form) and reticulate bodies (replicative form). - They form **intracytoplasmic inclusions** within vacuoles, but these are **not morulae**. *Incorrect: Bartonella quintana* - *Bartonella quintana* is a fastidious gram-negative bacillus associated with **trench fever** and bacillary angiomatosis. - Typically seen as individual or small clusters of bacteria, but **does not form morulae** within host cells. *Incorrect: Mycoplasma hominis* - *Mycoplasma hominis* is a small, **wall-less bacterium** that can cause genitourinary infections. - It is an extracellular pathogen or adheres to host cells but **does not invade or form intracytoplasmic morulae**.
Practice by Chapter
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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