Bacteriology — MCQs
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Oil paint appearance on nutrient agar is seen in -
Proteus isolated from a patient of UTI will show which biochemical reaction.
Which of the following statements about Chromobacterium violaceum is false?
A chronic alcoholic is presenting with clinical features of meningitis. Most likely organism to grow on CSF culture:
Which of the following statements about Corynebacterium diphtheriae is true?
Granuloma inguinale is caused by:
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?
Anaplasma phagocytophilum mainly affects -
Bacteriology Indian Medical PG Practice Questions and MCQs
Question 2381: Oil paint appearance on nutrient agar is seen in -
- A. Staphylococcus aureus (Correct Answer)
- B. Streptococcus pyogenes
- C. Bordetella pertussis
- D. H. influenzae
Explanation: ***Staphylococcus aureus*** - *Staphylococcus aureus* forms characteristic **golden-yellow, smooth, opaque colonies** on nutrient agar with a **buttery or creamy consistency** - Some texts describe this appearance as **"oil paint-like"** due to the pigmented, smooth, and glistening surface that can resemble brushed paint - Colonies are typically **2-4 mm in diameter**, round, and show **golden pigmentation** (due to carotenoid pigments) - On **blood agar**, *S. aureus* shows **beta-hemolysis** with golden colonies *Streptococcus pyogenes* - *Streptococcus pyogenes* grows poorly on plain nutrient agar and requires **enriched media** like blood agar - On blood agar, it forms **small, translucent, grey-white colonies** surrounded by a wide zone of **beta-hemolysis** - Colonies are typically **pinpoint** in size and do not show pigmentation *Bordetella pertussis* - *Bordetella pertussis* is a **fastidious organism** that does **not grow on plain nutrient agar** - Requires specialized enriched media like **Bordet-Gengou agar** (with potato-glycerol-blood) or **Regan-Lowe agar** - On Bordet-Gengou agar, colonies appear as **small, smooth, pearl-like** or **"mercury droplet"** colonies after 3-7 days *H. influenzae* - *Haemophilus influenzae* is also fastidious and requires **X factor (hemin)** and **V factor (NAD)** for growth - Does **not grow on plain nutrient agar** - On **chocolate agar**, forms **small, smooth, translucent, greyish colonies** with a characteristic musty odor - Colonies are typically **1-2 mm** in diameter
Question 2382: 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 2383: Which of the following statements about Chromobacterium violaceum is false?
- A. Normal flora in human (Correct Answer)
- B. Gram negative
- C. Causes cellulitis
- D. Produces violet-colored pigment
Explanation: **This question asks for the FALSE statement about *Chromobacterium violaceum*.** ***Normal flora in human*** ✓ (FALSE STATEMENT - This is the correct answer) - *Chromobacterium violaceum* is **not considered normal flora** in humans. It is an environmental bacterium typically found in **soil and water** in tropical and subtropical regions. - Its presence in humans usually signifies a serious **opportunistic infection**, often resulting from exposure to contaminated environments. - Since this statement is FALSE, this is the correct answer. *Gram negative* (TRUE statement) - *Chromobacterium violaceum* is indeed a **Gram-negative bacterium**. This characteristic is crucial for its identification and determining appropriate antibiotic treatment. - Like other Gram-negative bacteria, it possesses an **outer membrane** containing lipopolysaccharide (LPS). *Causes cellulitis* (TRUE statement) - *Chromobacterium violaceum* can cause severe infections in humans, including **cellulitis**, often following skin breaches like cuts or abrasions. - The infections are frequently aggressive and can lead to systemic disease such as **sepsis and abscess formation**. *Produces violet-colored pigment* (TRUE statement) - *Chromobacterium violaceum* is notable for producing **violacein**, a distinctive **violet-colored pigment**. - This pigment production is a key identifying feature on culture media and is associated with some of its pathogenic properties.
Question 2384: 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 2385: Which of the following statements about Corynebacterium diphtheriae is true?
- A. All strains produce toxin
- B. Toxin production is dependent on iron concentration (Correct Answer)
- C. The toxin is heat stable
- D. It inhibits cAMP
Explanation: ***Toxin production is dependent on iron concentration*** - The production of **diphtheria toxin** by *Corynebacterium diphtheriae* is directly regulated by the iron concentration in the environment. - When **iron levels are low**, the diphtheria toxin repressor (DTxR) is inactivated, leading to increased toxin production. *All strains produce toxin* - Not all strains of *Corynebacterium diphtheriae* produce the diphtheria toxin; only those strains that are **lysogenized by a bacteriophage carrying the tox gene** are toxigenic. - Non-toxigenic strains can cause other infections but do not produce the classic diphtheria disease. *The toxin is heat stable* - The **diphtheria toxin** is a **heat-labile** protein, meaning its activity can be destroyed by heat. - Heating diphtheria toxin to 60°C for 30 minutes can inactivate its pathogenic effects. *It inhibits cAMP* - The diphtheria toxin does not inhibit **cAMP**; instead, it acts by **ADP-ribosylating and inactivating elongation factor-2 (EF-2)**, thereby inhibiting protein synthesis in eukaryotic cells. - Inhibition of EF-2 ultimately leads to cell death.
Question 2386: 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 2387: 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 2388: 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 2389: 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**.
Question 2390: 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.
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
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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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