Bacteriology Practice Questions

Q: What is the primary site of action of tetanospasmin in the nervous system?

Presynaptic terminals of the spinal cord. ***Presynaptic terminals of the spinal cord*** - **Tetanospasmin** is transported via **retrograde axonal transport** to the central nervous system, specifically targeting the **presynaptic terminals** of inhibitory interneurons in the spinal cord. - It interferes with the release of **inhibitory neurotransmitters** like **GABA** and **glycine**, leading to uncontrolled muscle spasms. *Postsynaptic terminals of the spinal cord* - This is incorrect because tetanospasmin acts by preventing the release of inhibitory neurotransmitters from the **presynaptic terminal**, rather than directly affecting the postsynaptic receptor. - While the absence of inhibition is perceived at the postsynaptic terminal, the direct mechanism of action is presynaptic. *Neuromuscular junction* - This is incorrect because **tetanospasmin** does not primarily act at the neuromuscular junction; that is the site of action for toxins like **botulinum toxin**. - Tetanospasmin is transported to the central nervous system to exert its effects. *Muscle fibers* - This is incorrect as **tetanospasmin** does not act directly on muscle fibers. - Its action is on the **nervous system**, leading to altered neuronal signaling that indirectly affects muscle contraction.

Q: Early reactions of the lepromin test are read at:

48 hours. ***48 hours*** - The **early reaction** of the lepromin test, known as the **Fernandez reaction**, is read at **48-72 hours** after intradermal injection of lepromin antigen. - This represents a **delayed-type hypersensitivity (Type IV) reaction** mediated by T-cells, not humoral antibodies. - The reaction appears as an indurated papule or nodule at the injection site, with **48 hours** being the standard reading time. - It is **positive in tuberculoid leprosy** and reflects pre-existing cell-mediated immunity to *Mycobacterium leprae*. *24 hours* - At 24 hours, the reaction is typically **too early** to assess the Fernandez reaction adequately. - The peak induration of the delayed-type hypersensitivity reaction occurs at **48-72 hours**, not 24 hours. - Reading at 24 hours may miss or underestimate the early reaction. *36 hours* - While 36 hours falls within the developing phase, it is **not the standard reading time** for the Fernandez reaction. - The reaction continues to develop and is optimally assessed at **48 hours** or later. *72 hours* - 72 hours is also within the acceptable window for reading the **Fernandez reaction** (48-72 hours). - However, **48 hours** is more commonly cited as the standard reading time in most references. - The **late reaction (Mitsuda reaction)** is read much later at **3-4 weeks** and reflects stronger cell-mediated immunity, seen as granuloma formation.

Q: What is the most common cause of pedal botryomycosis?

Staphylococcus aureus. ***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)

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

Salmonella. ***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.

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

Gram positive bacillus. ***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.

Q: The incubation period of gonorrhoea is

2 to 15 days. The typical incubation period for **gonorrhoea** is **2-7 days in males** and up to **14 days in females**, aligning with **CDC guidelines** for *Neisseria gonorrhoeae* infection. Many cases remain **asymptomatic**, particularly in women, making this timeframe crucial for contact tracing and screening protocols. *Less than 24 hrs* - An incubation period of less than 24 hours is **medically implausible** for bacterial STIs, as it doesn't allow sufficient time for bacterial colonization and host immune response. - Such rapid onset is more characteristic of **toxin-mediated illnesses** or **hypersensitivity reactions**, not bacterial infections. *1 to 2 days* - While theoretically possible with **very high bacterial load** or in highly susceptible individuals, this represents the **absolute minimum** timeframe and is not typical. - The **majority of gonorrhoea cases** develop symptoms beyond this very short window, making it an inadequate representation of the standard incubation period. *12 to 25 days* - This timeframe is **too prolonged** for gonorrhoea and more characteristic of **chlamydia infections**, which have an incubation period of **7-21 days**. [1] - Gonorrhoea typically manifests much earlier due to the **aggressive nature** of *Neisseria gonorrhoeae* compared to other bacterial STIs.

Q: Botryomycosis is caused by:

Bacteria. ***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.

Q: 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?

Waxy envelope. ***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.

Q: Which bacteria has amphitrichous flagella?

Campylobacter jejuni. ***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 1

What is the primary site of action of tetanospasmin in the nervous system?

Accepted Answer

Presynaptic terminals of the spinal cord

Answer

Postsynaptic terminals of the spinal cord

Answer

Neuromuscular junction

Answer

Muscle fibers

Question 2

Early reactions of the lepromin test are read at:

Accepted Answer

48 hours

Answer

36 hours

Answer

72 hours

Answer

24 hours

Question 3

All the following statements regarding cervicofacial actinomycosis are true, except:

Accepted Answer

10-20% of actinomycosis cases occur in cervicofacial region.

Answer

The discharging pus contains visible 'sulphur granules'

Answer

There is usually history of trauma such as tooth extraction or a blow to the jaw

Answer

Cultures on blood agar often produce a typical 'molar tooth' morphology

Question 4

What is the most common cause of pedal botryomycosis?

Accepted Answer

Staphylococcus aureus

Answer

Streptomyces

Answer

All of these

Answer

Nocardia brasiliensis

Question 5

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

Accepted Answer

Salmonella

Answer

E. coli

Answer

Citrobacter

Answer

Klebsiella

Question 6

Which of the following statements about Helicobacter pylori is false?

Accepted Answer

Gram positive bacillus

Answer

Urease positive bacillus

Answer

Highly associated with duodenal ulcer

Answer

Resistant to acidic pH of stomach

Question 7

The incubation period of gonorrhoea is

Accepted Answer

2 to 15 days

Answer

Less than 24 hrs

Answer

1 to 2 days

Answer

12 to 25 days

Question 8

Botryomycosis is caused by:

Accepted Answer

Bacteria

Answer

Fungus

Answer

Virus

Answer

Protozoa

Question 9

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?

Accepted Answer

Waxy envelope

Answer

Streptokinase production

Answer

Toxic shock syndrome toxin production

Answer

Nutritional requirement for factors V and X

Question 10

Which bacteria has amphitrichous flagella?

Accepted Answer

Campylobacter jejuni

Answer

Aquaspirillum serpens

Answer

Spirillum minus

Answer

Listeria monocytogenes

Bacteriology — MCQs

Bacteriology — MCQs

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