Bacteriology — MCQs

A 24-year-old woman is breastfeeding 3 weeks after giving birth to a normal term infant and notices fissures in the skin around her left nipple. Over the next 3 days, a 5-cm region near the nipple becomes erythematous and tender, with purulent exudate from a small abscess draining through a fissure. Which of the following organisms is most likely to be cultured from the exudate?

Bacteriology Indian Medical PG Practice Questions and MCQs

Question 2501: What is the most common cause of pedal botryomycosis?

A. Streptomyces
B. All of these
C. Nocardia brasiliensis
D. Staphylococcus aureus (Correct Answer)

Explanation: ***Correct: Staphylococcus aureus*** - **Botryomycosis** is a rare chronic **bacterial infection** (not fungal) that clinically mimics actinomycetoma, hence also called **"bacterial pseudomycetoma"** - **_Staphylococcus aureus_** is the **most common causative agent** (>40% of cases), especially in cutaneous/pedal forms - Presents with characteristic **granulomatous lesions** with sulfur granules containing bacterial colonies - Other bacterial causes include _Pseudomonas aeruginosa_, _E. coli_, and _Proteus_ *Incorrect: Streptomyces* - **_Streptomyces_** species cause **actinomycetoma** (true mycetoma), not botryomycosis - It's an aerobic actinomycete causing chronic granulomatous infection with sulfur granules - Classified as a distinct type of mycetoma, not a bacterial pseudomycetoma *Incorrect: Nocardia brasiliensis* - **_Nocardia brasiliensis_** is another significant cause of **actinomycetoma**, particularly in tropical regions - Belongs to the _Actinomycetales_ order (aerobic actinomycete) - Produces sulfur granules but is NOT a common pyogenic bacteria causing botryomycosis *Incorrect: All of these* - **Only _Staphylococcus aureus_** causes botryomycosis among the listed organisms - _Nocardia_ and _Streptomyces_ cause **actinomycetoma** (true mycetoma due to aerobic actinomycetes), which is clinically similar but etiologically distinct from botryomycosis - Botryomycosis = bacterial infection by pyogenic bacteria; Actinomycetoma = infection by filamentous bacteria (actinomycetes)

Question 2502: Which of the following statements about Helicobacter pylori is false?

A. Gram positive bacillus (Correct Answer)
B. Urease positive bacillus
C. Highly associated with duodenal ulcer
D. Resistant to acidic pH of stomach

Explanation: ***Gram positive bacillus*** - *Helicobacter pylori* is a **Gram-negative**, spiral-shaped bacterium, not Gram-positive. - Its Gram-negative cell wall structure is a key characteristic, distinguishing it from Gram-positive organisms. *Urease positive bacillus* - This statement is **true**; *H. pylori* produces large amounts of **urease**, an enzyme that hydrolyzes urea into ammonia and carbon dioxide. - The production of ammonia helps neutralize stomach acid, allowing *H. pylori* to survive in the acidic gastric environment. *Highly associated with duodenal ulcer* - This statement is **true**; *H. pylori* infection is a major cause of both **gastric and duodenal ulcers**. - It is present in over 90% of patients with duodenal ulcers and a significant proportion of those with gastric ulcers. *Resistant to acidic pH of stomach* - This statement is **true**; *H. pylori* has multiple mechanisms to survive in the harsh acidic environment of the stomach. - It produces **urease** to create an alkaline microenvironment and has **flagella** that allow it to burrow into the protective mucus layer.

Question 2503: Botryomycosis is caused by:

A. Bacteria (Correct Answer)
B. Fungus
C. Virus
D. Protozoa

Explanation: ***Bacteria*** - Despite its name, **botryomycosis** is a chronic deep **bacterial infection**, not fungal. - It's typically caused by **Staphylococcus aureus** or, less commonly, **Pseudomonas aeruginosa** [1]. *Fungus* - The "mycosis" in the name is misleading; it's **not a fungal infection**. - Fungal infections like **mycetoma** can cause similar granulomatous lesions but are caused by true fungi. *Virus* - **Viruses** are intracellular parasites that reproduce inside living cells and do not cause botryomycosis. - Viral infections typically present differently, often with **acute symptoms** and systemic involvement. *Protozoa* - **Protozoa** are single-celled eukaryotic organisms, responsible for diseases like malaria or giardiasis. - They do not cause botryomycosis, which is a bacterial granulomatous condition.

Question 2504: A patient with a cavitary lung lesion who coughs up sputum containing thin, acid-fast positive rods. Which of the following features would most likely be associated with these bacteria?

A. Waxy envelope (Correct Answer)
B. Streptokinase production
C. Toxic shock syndrome toxin production
D. Nutritional requirement for factors V and X

Explanation: ***Waxy envelope*** - The presence of a **waxy envelope**, primarily due to high mycolic acid content in the cell wall, is a hallmark of **Mycobacterium tuberculosis**, which causes the described cavitary lung lesion and acid-fast rods. - This waxy layer contributes to the bacterium's **acid-fastness** and resistance to many antibiotics and host defenses. *Nutritional requirement for factors V and X (related to Haemophilus influenzae)* - This describes the growth requirements for **Haemophilus influenzae**, a common cause of respiratory infections but not typically associated with cavitary lung lesions or acid-fast rods. - *Haemophilus influenzae* is a **Gram-negative coccobacillus** and does not exhibit acid-fast staining properties. *Streptokinase (produced by Streptococci)* - **Streptokinase** is an enzyme produced by certain **Streptococcus species** that helps dissolve blood clots. - *Streptococci* are Gram-positive cocci and do not cause cavitary lung lesions with acid-fast rods; they are more commonly associated with pharyngitis, skin infections, and pneumonia (e.g., *Streptococcus pneumoniae*). *Toxic shock syndrome toxin (produced by Staphylococcus aureus)* - **Toxic shock syndrome toxin-1 (TSST-1)** is a superantigen produced by some strains of **Staphylococcus aureus**, leading to toxic shock syndrome. - *Staphylococcus aureus* is a **Gram-positive coccus** that can cause pneumonia and abscesses, but it does not produce acid-fast rods or typically form cavitary lung lesions with the specific characteristics mentioned.

Question 2505: Which bacteria has amphitrichous flagella?

A. Campylobacter jejuni (Correct Answer)
B. Aquaspirillum serpens
C. Spirillum minus
D. Listeria monocytogenes

Explanation: ***Campylobacter jejuni*** - *Campylobacter jejuni* typically exhibits **amphitrichous flagella**, meaning it possesses **single flagellum at both ends** of the bacterial cell. - This arrangement contributes to its characteristic **corkscrew-like motility**, which is important for its pathogenicity and ability to penetrate host mucus. *Spirillum minus* - *Spirillum minus* is known for its **tufts of lophotrichous flagella** at both ends, not a single flagellum at each end. - This bacterium is spiral-shaped and causes rat-bite fever, but its flagellar arrangement is distinct from amphitrichous. *Listeria monocytogenes* - *Listeria monocytogenes* is **peritrichous**, meaning it has flagella distributed all over its cell surface. - While motile, its flagellar arrangement is not amphitrichous; it uses these flagella for movement in the extracellular environment and **actin polymerization** for intracellular movement. *Aquaspirillum serpens* - *Aquaspirillum serpens* is characterized by **polar tufts of lophotrichous flagella**, similar to *Spirillum minus*, and not a single flagellum at each pole. - It is a Gram-negative aquaspirillum, and its flagellar arrangement provides efficient motility in aquatic environments.

Question 2506: Which of the following is a non-lactose-fermenting bacterium?

A. E. coli
B. Citrobacter
C. Salmonella (Correct Answer)
D. Klebsiella

Explanation: ***Salmonella*** - *Salmonella* is a classic example of a **non-lactose-fermenting** bacterium, which differentiates it from many other enteric gram-negative rods on differential media like MacConkey agar. - On MacConkey agar, *Salmonella* colonies typically appear **pale** or **colorless**, lacking the pink-red color indicative of lactose fermentation. *E. coli* - *E. coli* is a **lactose-fermenting** bacterium, producing acid and gas from lactose. - On MacConkey agar, *E. coli* colonies appear **pink to red** due to acid production from lactose fermentation. *Klebsiella* - *Klebsiella* species are also **lactose-fermenting** bacteria, known for their mucoid colonies. - On MacConkey agar, *Klebsiella* colonies are typically **pink** and often very **mucoid**. *Citrobacter* - *Citrobacter* species are generally **lactose-fermenting** bacteria, similar to *E. coli* and *Klebsiella*. - They produce **pink colonies** on MacConkey agar due to acid production from lactose.

Question 2507: Virulence determinant implicated in the pathogenesis of scarlet fever is -

A. M protein (immune evasion factor)
B. Pyrogenic exotoxin (toxin produced by bacteria) (Correct Answer)
C. Hyaluronidase (enzyme aiding tissue invasion)
D. Streptokinase (enzyme aiding bacterial spread)

Explanation: ***Pyrogenic exotoxin (toxin produced by bacteria)*** - Scarlet fever is caused by strains of **_Streptococcus pyogenes_** (Group A Streptococcus, GAS) that produce **streptococcal pyrogenic exotoxins (SPEs)**, also known as erythrogenic toxins. - These toxins act as superantigens, leading to the characteristic **scarlet rash** and other systemic symptoms of scarlet fever. *Hyaluronidase (enzyme aiding tissue invasion)* - **Hyaluronidase** is an enzyme produced by _S. pyogenes_ that degrades hyaluronic acid, a component of connective tissue, facilitating bacterial spread. - While it contributes to the invasiveness of GAS infections, it is **not directly responsible for the characteristic symptoms of scarlet fever**. *M protein (immune evasion factor)* - The **M protein** is a major virulence factor of _S. pyogenes_ that helps the bacteria resist phagocytosis and adhere to host cells. - It plays a critical role in the pathogenesis of various GAS infections but is **not the direct cause of the scarlet rash or systemic toxicity of scarlet fever**. *Streptokinase (enzyme aiding bacterial spread)* - **Streptokinase** is an enzyme produced by _S. pyogenes_ that activates plasminogen, leading to the dissolution of fibrin clots and aiding bacterial spread through tissues. - While important for bacterial dissemination, it is **not the specific virulence factor responsible for the clinical features of scarlet fever**.

Question 2508: Which of the following statements about Campylobacter jejuni is correct?

A. Gram-positive coccus
B. Most often occurs several days after consumption of undercooked chicken. (Correct Answer)
C. Symptoms may initially mimic appendicitis
D. Macrolides should be used in all cases

Explanation: ***Most often occurs several days after consumption of undercooked chicken.*** - *Campylobacter jejuni* infections are typically acquired through the consumption of **contaminated food or water**, with **undercooked poultry** being a common source. - The **incubation period** for *Campylobacter* gastroenteritis is usually **2 to 5 days**, explaining the delay between consumption and symptom onset. - This is the most characteristic epidemiological feature of *Campylobacter* infection. *Gram-positive coccus* - *Campylobacter jejuni* is a **Gram-negative, curved (seagull-shaped) rod**, not a Gram-positive coccus. - Its characteristic **spiral or S-shaped morphology** and staining properties are key for laboratory identification. - It is microaerophilic and grows best at 42°C. *Symptoms may initially mimic appendicitis* - While *Campylobacter* infections can cause **abdominal pain** and sometimes **right lower quadrant tenderness** (particularly in children), this is not the most characteristic or common presentation. - The hallmark feature is **acute diarrhea** (often bloody), which helps differentiate it from appendicitis. - When mimicking appendicitis does occur, it's typically due to mesenteric adenitis rather than the primary infection pattern. *Macrolides should be used in all cases* - Most *Campylobacter* infections are **self-limiting** and do not require antibiotic treatment. - **Macrolides** (e.g., azithromycin, erythromycin) are reserved for **severe cases**, immunocompromised patients, or those with prolonged symptoms. - Routine antibiotic use is not recommended for uncomplicated cases and may contribute to antimicrobial resistance.

Question 2509: What is the causative agent of Yaws?

A. Treponema endemicum
B. Treponema pallidum
C. Treponema carateum
D. Treponema pertenue (Correct Answer)

Explanation: ***Treponema pertenue*** - This spirochete is the **causative agent** of **Yaws**, a chronic disfiguring infectious disease primarily affecting the skin, bones, and joints. - Yaws is typically transmitted through **direct skin-to-skin contact** with infectious lesions in tropical and subtropical regions. *Treponema carateum* - This bacterium is responsible for **Pinta**, another non-venereal treponemal infection. - Pinta primarily causes **skin lesions** characterized by dyschromic patches, but does not involve bone or joint destruction as is seen in Yaws. *Treponema pallidum* - This species has several subspecies, with *Treponema pallidum subspecies pallidum* being the cause of **venereal syphilis**. - While *T. pallidum* is a treponemal infection, its clinical presentation and mode of transmission are distinct from Yaws. *Treponema endemicum* - This subspecies of *Treponema pallidum* is the causative agent of **Bejel** (also known as endemic syphilis). - Like Yaws, Bejel is a non-venereal treponemal infection, but it primarily affects mucosal surfaces and bones, with different clinical characteristics than Yaws.

Question 2510: A 24-year-old woman is breastfeeding 3 weeks after giving birth to a normal term infant and notices fissures in the skin around her left nipple. Over the next 3 days, a 5-cm region near the nipple becomes erythematous and tender, with purulent exudate from a small abscess draining through a fissure. Which of the following organisms is most likely to be cultured from the exudate?

A. Candida albicans
B. Lactobacillus acidophilus
C. Listeria monocytogenes
D. Staphylococcus aureus (Correct Answer)

Explanation: ***Staphylococcus aureus*** - This presentation of **mastitis with abscess formation** is overwhelmingly caused by **_Staphylococcus aureus_**, especially in breastfeeding women. - The organism gains entry through **nipple fissures**, leading to erythema, tenderness, and purulent exudate characteristic of a bacterial infection. *Candida albicans* - While it can cause **nipple soreness** and **thrush** in infants, it typically presents as burning pain and shiny skin, not usually with a localized abscess and purulent exudate. - *Candida* infections are more common with **antibiotic use** or in women with compromised immune systems. *Lactobacillus acidophilus* - This is a common **probiotic organism** found in the gut and vagina, known for its beneficial role. - It does not cause purulent infections or mastitis in this context. *Listeria monocytogenes* - This bacterium is primarily known for causing **foodborne illness** and can lead to severe infections like meningitis or sepsis, particularly in pregnant women and neonates. - It is not a common cause of superficial abscesses or mastitis in breastfeeding women.

Practice by Chapter

Staphylococci

Practice Questions

Streptococci and Enterococci

Practice Questions

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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