Bacteriology — MCQs

Bacteriology Indian Medical PG Practice Questions and MCQs

Question 2391: Primary complex of M bovis involves:

A. Tonsil and skin
B. Tonsil and intestine (Correct Answer)
C. Tonsil and lung
D. Skin and Intestine

Explanation: ***Tonsil and intestine*** - *Mycobacterium bovis* is primarily transmitted through **consumption of contaminated milk and dairy products**, making the **alimentary tract** the main route of infection - The primary complex (Ghon complex) involves the **initial site of infection plus regional lymph nodes** - In alimentary tuberculosis, the organisms enter through the **intestinal mucosa** (Peyer's patches) or **tonsillar tissue**, creating foci with associated mesenteric or cervical lymphadenopathy - Both tonsils and intestines are part of the **alimentary system**, representing the typical primary complex for M. bovis in humans *Tonsil and lung* - This incorrectly combines **two different routes of entry** (alimentary and respiratory) - A primary complex involves a **single portal of entry**, not multiple unrelated organ systems - While M. bovis can rarely cause pulmonary TB through inhalation, this would create a separate lung + hilar node complex, not a combined tonsil-lung complex *Tonsil and skin* - **Skin involvement** requires direct inoculation through cuts or abrasions and does not form a primary complex with tonsillar infection - These represent different portals of entry and would not occur together as a primary complex *Skin and Intestine* - **Skin infection** by M. bovis is rare and requires occupational exposure with direct inoculation (e.g., veterinarians, butchers) - This incorrectly pairs two different routes of infection that would not form a single primary complex

Question 2392: 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 2393: 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 2394: 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 2395: 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 2396: Anaplasma phagocytophilum mainly affects -

A. Neutrophils (white blood cells) (Correct Answer)
B. Red Blood Cells (RBCs)
C. Macrophages (immune cells)
D. Platelets (thrombocytes)

Explanation: ***Neutrophils (white blood cells)*** - *Anaplasma phagocytophilum* specifically infects and replicates within **neutrophils**, leading to the characteristic morulae observed inside these cells. - This infection causes **human granulocytic anaplasmosis (HGA)**, primarily affecting white blood cells. *Red Blood Cells (RBCs)* - While other tick-borne diseases like **babesiosis** infect RBCs, *Anaplasma phagocytophilum* does not target red blood cells. - RBCs are responsible for oxygen transport and lack the necessary cellular machinery for *Anaplasma* replication. *Macrophages (immune cells)* - Macrophages are significant immune cells but are not the primary target cell for *Anaplasma phagocytophilum*. - Infections that primarily target macrophages include some **bacterial** and **parasitic infections** like *Leishmania*. *Platelets (thrombocytes)* - Platelets are crucial for **blood clotting** and are not directly infected by *Anaplasma phagocytophilum*. - Although **thrombocytopenia** (low platelet count) is a common finding in anaplasmosis, it is an indirect effect of the infection, not due to direct platelet invasion.

Question 2397: Proteus isolated from a patient of UTI will show which biochemical reaction.

A. Production of phenylpyruvic acid from phenylalanine (Correct Answer)
B. Hydrolysis of esculin in bile
C. Sensitivity to colchicine
D. Sensitivity to bacitracin

Explanation: ***Production of phenylpyruvic acid from phenylalanine*** - *Proteus* species possess the enzyme **phenylalanine deaminase**, which deaminates phenylalanine to **phenylpyruvic acid**. - This reaction is a **key biochemical test** used to identify *Proteus*, *Providencia*, and *Morganella* species. *Hydrolysis of esculin in bile* - This reaction is characteristic of **Group D streptococci** and **enterococci**, not *Proteus* species. - The organism hydrolyzes **esculin** in the presence of bile, turning the agar black. *Sensitivity to colchicine* - **Colchicine** is an anti-inflammatory drug, not part of standard **biochemical identification tests** for bacteria. - This is not a recognized biochemical reaction used to identify *Proteus* or any bacterial species. *Sensitivity to bacitracin* - **Bacitracin sensitivity** is primarily used to differentiate **Group A streptococci** (e.g., *Streptococcus pyogenes*) from other beta-hemolytic streptococci. - It is an **antibiotic susceptibility test**, not a biochemical reaction characteristic of *Proteus* species.

Question 2398: Bacteria most commonly involved in bowel decomposition after death is?

A. Streptococcus pyogenes
B. Pseudomonas aeruginosa
C. Clostridium perfringens (Correct Answer)
D. Escherichia coli

Explanation: ***Clostridium perfringens*** - This bacterium is a ubiquitous **anaerobe** in the gut and is known for its rapid proliferation after death, producing gases that contribute to **bloating and decomposition**. - It is a primary cause of **gas gangrene** in living individuals, reflecting its tissue-destructive capabilities, which extend to post-mortem changes. - Produces large amounts of **hydrogen and CO2**, making it the most significant contributor to post-mortem gas formation and putrefaction. *Streptococcus pyogenes* - While a significant pathogen in life, causing conditions like **strep throat** and **necrotizing fasciitis**, it is not the primary agent of putrefaction. - Its role in post-mortem decomposition is generally less prominent compared to anaerobic gut flora. *Pseudomonas aeruginosa* - This bacterium is an opportunistic pathogen often associated with infections in immunocompromised individuals or in healthcare settings. - It is not typically identified as the most common or primary bacterium involved in the initial stages of post-mortem **bowel decomposition**, though it can be present in later stages. *Escherichia coli* - While *E. coli* is abundant in the bowel and participates in post-mortem decomposition, it is not the **most common** agent responsible for gas production and tissue decomposition. - *Clostridium perfringens* proliferates more rapidly and produces significantly more gas, making it the predominant bacterium in bowel putrefaction.

Question 2399: "Citron bodies" are boat- or leaf-shaped pleomorphic organisms found in exudates. This is a characteristic feature of which organism?

A. Cl. edematiens
B. Cl. septicum (Correct Answer)
C. Cl. tetani
D. Cl. welchii

Explanation: ***Cl. septicum*** - *Clostridium septicum* characteristically forms **"Citron bodies"** - boat-shaped or leaf-shaped pleomorphic organisms in exudates - These spindle-shaped, cigar-like forms are a **distinctive morphological feature** of this organism - Associated with **gas gangrene** and spontaneous myonecrosis, particularly in patients with underlying malignancy or neutropenia - The pleomorphic morphology distinguishes it from other clostridial species *Cl. welchii* - *Clostridium perfringens* (formerly *Cl. welchii*) appears as **large, rectangular, "boxcar-shaped" Gram-positive rods** - Does **not** form citron bodies or show the characteristic boat/leaf-shaped pleomorphism - Most common cause of gas gangrene but has different morphological appearance *Cl. edematiens* - *Clostridium oedematiens* (now *Clostridium novyi*) appears as **large, Gram-positive rods** with subterminal spores - Does not form citron bodies - Associated with gas gangrene but lacks the pleomorphic morphology described *Cl. tetani* - *Clostridium tetani* has characteristic **terminal spores** giving a "drumstick" or "tennis racket" appearance - Does not form citron bodies or pleomorphic shapes - Morphologically distinct with its terminal spore appearance

Question 2400: A patient presents with purulent urethral discharge and laboratory findings of gram-negative diplococci on modified Thayer-Martin media. What is the most likely diagnosis?

A. Treponema pallidum
B. Neisseria gonorrhoeae (Correct Answer)
C. Haemophilus ducreyi
D. Chlamydia trachomatis

Explanation: ***Neisseria gonorrhoeae*** - **Purulent urethral discharge** and identification of **gram-negative diplococci** on microscopy from a urethral swab are highly characteristic of *Neisseria gonorrhoeae* infection. - *N. gonorrhoeae* grows well on **modified Thayer-Martin media**, a selective medium specifically designed for *Neisseria* species. - This organism is the causative agent of **gonorrhea**, a common sexually transmitted infection. - The combination of clinical presentation (purulent discharge) and laboratory findings (gram-negative diplococci on Thayer-Martin media) makes this the definitive diagnosis. *Haemophilus ducreyi* - Causes **chancroid**, which presents with **painful genital ulcers** and **lymphadenopathy**, NOT purulent urethral discharge. - *H. ducreyi* is a gram-negative **bacillus** (rod-shaped), NOT diplococci. - It requires special media supplemented with X and V factors for growth, not primarily Thayer-Martin medium. *Treponema pallidum* - Causes **syphilis**, which typically presents with a **chancre** (painless ulcer) in primary stage and systemic symptoms in later stages. - Cannot be cultured on routine media and is identified by **darkfield microscopy** or serological tests. - Does not appear as gram-negative diplococci. *Chlamydia trachomatis* - Can cause urethritis with **mucopurulent or watery discharge**, but not typically purulent. - *Chlamydia* are **obligate intracellular bacteria** that cannot be visualized as gram-negative diplococci on gram stain. - Cannot be cultured on standard bacteriologic media like Thayer-Martin medium.

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

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Mycobacteria

Practice Questions

Spirochetes

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