Microbiome and Immune System Indian Medical PG Practice Questions and MCQs
Practice Indian Medical PG questions for Microbiome and Immune System. These multiple choice questions (MCQs) cover important concepts and help you prepare for your exams.
Microbiome and Immune System Indian Medical PG Question 1: Which of the following is not considered an antigen-presenting cell?
- A. Macrophages
- B. Langerhans cells
- C. Thymocytes (Correct Answer)
- D. B lymphocytes
Microbiome and Immune System Explanation: ***Thymocytes***
- Thymocytes are **developing T cells** found in the thymus and do not function as antigen-presenting cells (APCs) [1].
- Unlike APCs, thymocytes are primarily involved in the **maturation** and selection of T lymphocytes.
*Langerhans cells*
- Langerhans cells are a type of **dendritic cell** found in the skin and are effective antigen-presenting cells to T cells [1].
- They play a crucial role in **immune surveillance** and response to skin infections.
*Macrophages*
- Macrophages are well-known antigen-presenting cells that engulf pathogens and present antigens to T cells [1].
- They are also involved in **phagocytosis** and secrete various cytokines to modulate immune responses.
*M-cells*
- M-cells (microfold cells) are specialized epithelial cells that transport antigens from the intestinal lumen to underlying immune cells.
- Although not traditional APCs, they play a role in immune surveillance and stimulating **mucosal immunity**.
**References:**
[1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Diseases of the Immune System, pp. 200, 207-208.
Microbiome and Immune System Indian Medical PG Question 2: Which of the following is a type of inflammatory bowel disease primarily affecting the small intestine? a) Coeliac disease b) Tropical sprue c) Regional ileitis d) Cystic fibrosis e) Ulcerative colitis
- A. Ulcerative colitis
- B. Cystic fibrosis
- C. Tropical sprue
- D. Regional ileitis (Correct Answer)
- E. Coeliac disease
Microbiome and Immune System Explanation: ***Regional ileitis***
- **Regional ileitis** is another name for **Crohn's disease** when it primarily affects the **ileum**, which is part of the small intestine [1].
- Crohn's disease is a type of **inflammatory bowel disease (IBD)** [1] characterized by **transmural inflammation** that can affect any part of the gastrointestinal tract, but most commonly involves the small intestine.
*Ulcerative colitis*
- **Ulcerative colitis** is an **inflammatory bowel disease** that exclusively affects the **large intestine (colon and rectum)** [2].
- Unlike Crohn's disease, it involves continuous inflammation of the mucosa and submucosa, usually starting in the rectum and extending proximally [2].
*Cystic fibrosis*
- **Cystic fibrosis** is a **genetic disorder** that affects the lungs, pancreas, liver, and intestine, leading to the production of **thick, sticky mucus**.
- While it can cause malabsorption and intestinal issues due to pancreatic insufficiency, it is not primarily an inflammatory bowel disease in itself.
*Tropical sprue*
- **Tropical sprue** is a malabsorption syndrome thought to be caused by **environmental factors and microbial changes** in the small intestine, typically affecting individuals in tropical regions [3].
- It results in abnormal small intestinal architecture and nutrient malabsorption, but it is not classified as an inflammatory bowel disease like Crohn's or ulcerative colitis.
*Coeliac disease*
- **Coeliac disease** is an **immune-mediated condition** triggered by the ingestion of **gluten**, leading to damage of the small intestinal villi [3].
- While it affects the small intestine and involves an immune response, it is distinct from inflammatory bowel diseases which are characterized by chronic, relapsing inflammation of the GI tract.
Microbiome and Immune System Indian Medical PG Question 3: A clinically depressed farmer complains of extreme weakness, a daily rise and fall in fever, and night sweats. Small gram-negative rods are isolated from blood cultures after a 2-week incubation period. Which of the following organisms is the most likely etiologic agent?
- A. Campylobacter jejuni
- B. Francisella tularensis
- C. Brucella melitensis (Correct Answer)
- D. Salmonella enteritidis
Microbiome and Immune System Explanation: ***Brucella melitensis***
- This organism is known to cause **brucellosis**, which presents with **undulant fever** (daily rise and fall), night sweats, and fatigue, consistent with the patient's symptoms. The profession of a **farmer** puts him at higher risk due to exposure to infected livestock.
- **Neuropsychiatric manifestations** including depression, fatigue, and malaise are well-recognized features of chronic brucellosis, explaining the patient's clinical depression.
- **_Brucella_ species** are characteristic for their slow growth, often requiring **extended incubation periods** (up to 2 weeks) in blood cultures, and appear as small gram-negative rods.
*Campylobacter jejuni*
- This bacterium is a common cause of **gastroenteritis**, leading to **diarrhea**, abdominal cramps, and fever. While it can cause bacteremia, it typically presents with more prominent gastrointestinal symptoms.
- _C. jejuni_ is a **curved or spiral-shaped** gram-negative rod, distinct from the small rods described, and does not typically cause an undulant fever pattern.
*Francisella tularensis*
- This agent causes **tularemia**, which can manifest with fever, chills, and fatigue, but often includes a characteristic **skin lesion (ulceroglandular)** and prominent lymphadenopathy.
- Although it is a small gram-negative rod, the specific **undulant fever pattern** and the farmer's exposure history are more indicative of brucellosis.
*Salmonella enteritidis*
- This bacterium commonly causes **food poisoning** with symptoms like diarrhea, fever, and vomiting. While it can lead to bacteremia, it is less likely to present with the prolonged, **undulant fever** seen in brucellosis.
- **_Salmonella_ species** are typically readily isolated from blood cultures within a few days, unlike the prolonged incubation needed for _Brucella_.
Microbiome and Immune System Indian Medical PG Question 4: The organism causing pseudomembranous colitis:
- A. Clostridium difficile (Correct Answer)
- B. Clostridium botulinum
- C. Clostridium tetani
- D. Clostridium perfringens
Microbiome and Immune System Explanation: ***Clostridium difficile***
- This bacterium is the primary cause of **pseudomembranous colitis**, an inflammation of the colon characterized by the formation of membranes on the mucosal surface.
- It produces **toxins A and B** which damage the intestinal lining, leading to severe diarrhea, abdominal pain, and fever.
*Clostridium botulinum*
- This organism is responsible for **botulism**, a severe form of food poisoning or wound infection.
- It produces a potent **neurotoxin** that causes flaccid paralysis by blocking acetylcholine release at neuromuscular junctions.
*Clostridium tetani*
- This bacterium causes **tetanus**, characterized by muscle spasms and rigidity.
- It produces the **tetanospasmin neurotoxin** which inhibits inhibitory neurotransmitters in the spinal cord.
*Clostridium perfringens*
- Primarily known for causing **gas gangrene** (myonecrosis) and certain types of food poisoning.
- It produces various **toxins**, including alpha-toxin, which contribute to tissue destruction and gas formation.
Microbiome and Immune System Indian Medical PG Question 5: Which of the following is not true about innate immunity
- A. Memory is seen (Correct Answer)
- B. It is relatively non specific
- C. It is first line of defence
- D. It is present prior to antigenic exposure
Microbiome and Immune System Explanation: ***Memory is seen***
- Innate immunity is characterized by a **lack of immunological memory**, meaning it does not \"remember\" previous encounters with pathogens to mount a stronger, faster response.
- This feature is a hallmark of **adaptive (acquired) immunity**, which develops memory cells after initial exposure.
*It is relatively non specific*
- Innate immune responses are **non-specific** and target broad categories of pathogens, rather than specific antigens.
- It recognizes conserved structures on pathogens, known as **Pathogen-Associated Molecular Patterns (PAMPs)**, shared by many different microbes.
*It is first line of defence*
- Innate immunity serves as the **body's immediate and primary defense** against invading pathogens.
- It provides rapid protection through physical barriers, cellular components, and soluble factors, often preventing infection before it takes hold.
*It is present prior to antigenic exposure*
- The components of innate immunity are **pre-existing and fully functional** before any exposure to pathogens or antigens.
- This readiness allows for an **instantaneous response** upon microbial invasion, without requiring prior sensitization.
Microbiome and Immune System Indian Medical PG Question 6: Following acute pharyngitis, a patient was on broad spectrum antibiotics. One week later he developed watery diarrhoea with a foul odour and abdominal cramps. Antibiotic induced colitis is confirmed. What is the most common cause of antibiotic induced colitis?
- A. Esch. coli
- B. Clostridium difficile (Correct Answer)
- C. Campylobacter jejuni
- D. Salmonella
Microbiome and Immune System Explanation: ***Clostridium difficile***
- **Clostridium difficile** infection is the most common cause of **antibiotic-induced colitis** [1], leading to symptoms like **watery diarrhea, foul odor**, and **abdominal cramps** [1].
- Antibiotics disrupt the normal gut flora, allowing **C. difficile** to overgrow and produce toxins that damage the colon [1].
*Esch. coli*
- While some strains of *E. coli* can cause **diarrhea** (e.g., ETEC, EHEC), it is not the primary cause of antibiotic-induced colitis [2].
- **Esch. coli** diarrhea is typically acquired through contaminated food or water, not antibiotic use [2].
*Campylobacter jejuni*
- *Campylobacter jejuni* typically causes **gastroenteritis** with **bloody diarrhea** and **fever**, often from consuming contaminated poultry.
- It is not directly associated with **antibiotic-induced colitis** as the primary causative agent.
*Salmonella*
- **Salmonella** infections usually result from contaminated food and present with **fever, abdominal cramps**, and **diarrhea** (which can be bloody).
- It is not the most common pathogen responsible for **antibiotic-induced colitis**.
Microbiome and Immune System Indian Medical PG Question 7: Fecal leucocytes are absent in all of the following, except:
- A. Cryptosporidiosis
- B. Clostridium perfringes infection
- C. Giardiasis
- D. Campylobacter infection (Correct Answer)
Microbiome and Immune System Explanation: ***Campylobacter infection***
- This infection causes **inflammatory diarrhea**, leading to the presence of **fecal leucocytes** as a response to intestinal tissue invasion.
- The inflammatory process results in disruption of the intestinal mucosa, attracting **neutrophils** and other inflammatory cells to the stool.
*Giardiasis*
- **Giardia lamblia** infection typically causes **non-inflammatory diarrhea** by interfering with nutrient absorption in the small intestine.
- Due to the non-invasive nature of the pathogen, **fecal leucocytes** are generally **absent** in the stool.
*Cryptosporidiosis*
- **Cryptosporidium parvum** primarily causes **non-inflammatory watery diarrhea** by adhering to and damaging the microvilli of the intestinal epithelium.
- While it can cause flattening of the villi, it does not typically lead to significant tissue invasion or the presence of **fecal leucocytes**.
*Clostridium perfringens infection*
- This bacterium causes **food poisoning** mainly through the production of **toxins** that affect the intestinal lining.
- The diarrhea is typically **non-inflammatory**, and **fecal leucocytes** are usually **absent** because there is no significant host immune cell invasion.
Microbiome and Immune System Indian Medical PG Question 8: A farmer presents with a subcutaneous wound on his foot with discharge. Microscopy of a white granule from the wound shows Gram-positive filamentous rods. What is the most likely organism?
- A. Staphylococcus aureus
- B. Histoplasma
- C. Nocardia (Correct Answer)
- D. Sporothrix
Microbiome and Immune System Explanation: ***Nocardia***
- The presence of **white granules** in the discharge, along with **Gram-positive, filamentous rods**, is highly characteristic of *Nocardia* infection, often forming **sulfur granules** (though not always yellow).
- *Nocardia* is a common soil bacterium, making it a likely pathogen in a **farmer with a subcutaneous wound** related to environmental exposure.
*Staphylococcus aureus*
- While *Staphylococcus aureus* can cause skin infections and abscesses, it presents as **Gram-positive cocci in clusters**, not filamentous rods.
- It does not typically form **granules** in the discharge in the same manner as *Nocardia*.
*Histoplasma*
- *Histoplasma* is a **dimorphic fungus** that causes systemic infections, often acquired by inhaling spores.
- It would appear as **yeast forms** in tissue or cultures, not Gram-positive filamentous rods, and is not typically associated with subcutaneous wounds forming granules.
*Sporothrix*
- *Sporothrix schenckii* causes **sporotrichosis**, characterized by a **subcutaneous nodule** that progresses along lymphatic channels.
- It is a **dimorphic fungus** (yeast in tissue, mold in culture) and would not appear as Gram-positive filamentous rods on microscopy.
Microbiome and Immune System Indian Medical PG Question 9: A 36 years male presented with complaint of productive cough and fever for last 2 months. He has undergone kidney transplantation 2 years back. His sputum examination revealed a gram positive filamentous bacteria that showed acid fastness with modified Ziehl-Neelsen staining (1% H2SO4). The most likely etiological agent is ?
- A. Blastomyces dermatitidis
- B. Actinomyces israelii
- C. Nocardia asteroides (Correct Answer)
- D. Cryptosporidium parvum
Microbiome and Immune System Explanation: ***Nocardia asteroides***
- This patient, being an **immunocompromised kidney transplant recipient**, is highly susceptible to **opportunistic infections**. *Nocardia* species are **gram-positive, filamentous, branched bacteria** that are **weakly acid-fast** (positive with modified Ziehl-Neelsen staining, typically 1% H2SO4), commonly causing **pulmonary infections** with productive cough and fever.
- Pulmonary nocardiosis can mimic tuberculosis or other fungal infections, and the acid-fast staining characteristic helps differentiate it from non-acid-fast filamentous bacteria like *Actinomyces*.
*Blastomyces dermatitidis*
- This is a **dimorphic fungus** that causes **blastomycosis**, an endemic infection in certain geographic regions, which is usually diagnosed by visualization of broad-based budding yeasts or culture.
- It would not appear as a **gram-positive filamentous bacterium** with acid-fast properties in sputum.
*Actinomyces israelii*
- *Actinomyces israelii* is a **gram-positive, filamentous bacterium** that causes **actinomycosis**, often characterized by chronic abscesses, sinus tracts, and "sulfur granules."
- Unlike *Nocardia*, *Actinomyces* species are **not acid-fast**, which rules it out given the staining results.
*Cryptosporidium parvum*
- This is a **protozoan parasite** that causes **cryptosporidiosis**, primarily manifesting as **gastroenteritis** (diarrhea), especially in immunocompromised individuals.
- It would not present as a **filamentous bacterial form in sputum**, nor would it be diagnosed by Gram stain and acid-fast modified Ziehl-Neelsen staining in this context.
Microbiome and Immune System Indian Medical PG Question 10: Diagnosis of C. difficile infection is made by which of the following methods?
- A. Stool microscopy for pseudomembranes
- B. Culture
- C. Toxin gene detection by polymerase chain reaction (PCR) (Correct Answer)
- D. Enzyme-linked immunosorbent assay (ELISA)
Microbiome and Immune System Explanation: ***Toxin gene detection by polymerase chain reaction (PCR)***
- **PCR for toxin genes (tcdA and tcdB)** is the most sensitive and specific method for diagnosing **Clostridioides difficile infection (CDI)**, directly detecting the genetic material responsible for the pathology.
- This method is superior because it identifies the presence of toxigenic C. difficile, which is crucial for determining clinical significance and guiding treatment.
*Stool microscopy for pseudomembranes*
- While **pseudomembranes** are a hallmark of severe CDI, their detection requires **endoscopy** and is not a direct diagnostic test for the pathogen itself.
- Furthermore, their absence does not rule out CDI, as pseudomembranes may not form in all cases, especially milder ones.
*Culture*
- **Culture for C. difficile** can identify the presence of the organism, but it does not differentiate between toxigenic and non-toxigenic strains.
- Many individuals can be **colonized with non-toxigenic C. difficile** without having an active infection, leading to false positives if culture alone is used for diagnosis.
*Enzyme - linked immunosorbent assay (ELISA)*
- ELISA tests primarily detect **C. difficile toxins A and B** or **glutamate dehydrogenase (GDH)** antigen in stool.
- While rapid, ELISA for toxins A/B has **lower sensitivity** than PCR, potentially missing cases, and GDH detection alone only indicates the presence of C. difficile (toxigenic or non-toxigenic), requiring further toxin testing for confirmation.
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