Dysbiosis and Disease — MCQs

10 questions

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

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?

True about Crohn's disease except

A person returns to Delhi from Bangladesh after 2 days and has diarrhea. Stool examination shows RBC's in stool. The likely organism causing is ?

Which of the following parasitic infections is characteristically associated with colitis?

Which of the following is the BEST method for diagnosis of C. difficile infection?

Following are true of Gram negative bacterial cell wall compared to Gram positive bacteria except:

Patient presenting with abdominal pain, diarrhea taking clindamycin for 5 days. Treated with metronidazole symptoms subsided. What is the causative agent -

Traveller's diarrhoea is caused by:

Q10

Which virus is NOT associated with human cancer?

Dysbiosis and Disease Indian Medical PG Practice Questions and MCQs

Question 1: 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

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.

Question 2: 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

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**.

Question 3: True about Crohn's disease except

A. Transmural
B. Recurrence is more common
C. Rectum is involved (Correct Answer)
D. Fissures are formed

Explanation: ***Rectum is involved*** - While Crohn's disease can affect any part of the gastrointestinal tract from mouth to anus, **rectal involvement is much less common** and often spares the rectum in typical cases, especially when compared to ulcerative colitis. [1] - The disease typically exhibits **skip lesions**, meaning there are healthy segments of the bowel between affected areas, and the rectum is frequently one of these spared regions. [1] *Transmural* - Crohn's disease is characterized by **transmural inflammation**, meaning the inflammation extends through all layers of the bowel wall, from the mucosa to the serosa. [1] - This transmural involvement can lead to complications such as **fistulas, strictures, and abscesses**. *Recurrence is more common* - **Recurrence after surgery is very common** in Crohn's disease, with many patients experiencing disease relapse within a few years post-operation. - This high recurrence rate often necessitates ongoing medical management and sometimes further surgical interventions. *Fissures are formed* - Due to the **transmural inflammation** and chronic nature of Crohn's disease, patients often develop **fissures**, which are deep cracks or excoriations, particularly in the perianal area. - These fissures can be quite painful and complicated by **fistula formation** or abscesses.

Question 4: A person returns to Delhi from Bangladesh after 2 days and has diarrhea. Stool examination shows RBC's in stool. The likely organism causing is ?

A. Enteropathogenic E. Coli
B. Salmonella typhi
C. Enterotoxigenic E. Coli
D. Shigella dysenteriae (Correct Answer)

Explanation: ***Shigella dysenteriae*** - This organism causes **bacillary dysentery**, characterized by fever, abdominal cramps, and frequent, small-volume stools containing **blood and mucus (RBCs)**, which fits the clinical picture of a traveler experiencing diarrhea with RBCs in stool. - The rapid onset (within 2 days of return) and the presence of **RBCs in stool** are highly suggestive of an invasive bacterial pathogen like *Shigella*. *Enteropathogenic E. Coli* - **EPEC** typically causes **watery diarrhea**, particularly in infants, by disrupting intestinal microvilli. - It does **not usually cause bloody stools** or significant red blood cells in the stool. *Salmonella typhi* - While *Salmonella typhi* causes **typhoid fever**, its initial presentation is typically with fever, headache, and constipation, followed by a **pea-soup diarrhea** in later stages, which is usually not bloody. - The rapid onset of bloody diarrhea within 2 days is less characteristic of typhoid fever, which has a longer incubation period. *Enterotoxigenic E. Coli* - **ETEC** is a common cause of **traveler's diarrhea**, but it produces toxins that lead to **watery, non-bloody diarrhea**. - The presence of **RBCs in the stool** makes ETEC an unlikely cause in this scenario.

Question 5: Which of the following parasitic infections is characteristically associated with colitis?

A. Strongyloides
B. Clonorchis
C. Enterobius vermicularis
D. Trichuris trichiura (Correct Answer)

Explanation: ***Trichuris trichiura*** - Also known as **whipworm**, *Trichuris trichiura* primarily infects the **large intestine**, particularly the cecum and ascending colon. - Heavy infections can lead to **colitis**, characterized by bloody diarrhea, abdominal pain, and rectal prolapse in severe cases. *Strongyloides* - *Strongyloides stercoralis* infection (strongyloidiasis) primarily affects the **small intestine** and can cause symptoms like abdominal pain, diarrhea, and malabsorption. - While it can lead to gastrointestinal symptoms, it is not typically associated with prominent **colitis** as its primary manifestation. *Clonorchis* - *Clonorchis sinensis* (Chinese liver fluke) infects the **biliary ducts** of the liver, causing **cholangitis** and potentially cholangiocarcinoma. - It does not primarily cause **colitis** or involve the large intestine. *Enterobius vermicularis* - *Enterobius vermicularis* (pinworm) primarily resides in the **cecum and appendix**, causing perianal itching, especially at night. - While it can cause some localized irritation, it does not typically lead to **colitis** or significant inflammation of the large intestine.

Question 6: Which of the following is the BEST method for diagnosis of C. difficile infection?

A. Toxin gene detection by polymerase chain reaction (PCR) (Correct Answer)
B. Enzyme-linked immunosorbent assay (ELISA)
C. Culture
D. Glutamate dehydrogenase (GDH) antigen detection

Explanation: ***Toxin gene detection by polymerase chain reaction (PCR)*** - **Nucleic acid amplification tests (NAAT/PCR)** for toxin genes (tcdA and tcdB) have the **highest sensitivity and specificity** among single-test methods, making them the preferred standalone diagnostic test. - Provides **rapid results** (2-4 hours), allowing for timely diagnosis and management of **Clostridioides difficile infection** (CDI). - **Clinical note:** While NAAT is highly sensitive, guidelines recommend **two-step algorithms** (GDH or NAAT + toxin EIA) to distinguish colonization from active infection in certain clinical settings. *Enzyme-linked immunosorbent assay (ELISA)* - **ELISA** for toxins A and B has **moderate specificity** but **lower sensitivity** (70-85%) compared to NAAT, potentially missing cases with lower toxin levels. - While it detects actual toxin production, the sensitivity limitation makes it suboptimal as a standalone test. *Culture* - **Culture** can detect the presence of *C. difficile* organism but **does not confirm toxin production**, meaning colonization cannot be distinguished from active disease without additional testing. - It is **time-consuming** (2-5 days), which delays diagnosis and treatment. - Useful for **epidemiological studies and strain typing** but not for routine diagnosis. *Glutamate dehydrogenase (GDH) antigen detection* - **GDH detection** is highly sensitive (>95%) for the presence of *C. difficile* organism, but has **low specificity** as it detects both toxigenic and non-toxigenic strains. - Best used as a **screening test** in two-step algorithms; a **positive GDH test must be confirmed** with toxin detection (EIA or NAAT).

Question 7: Following are true of Gram negative bacterial cell wall compared to Gram positive bacteria except:

A. Thinner
B. Presence of lipopolysaccharide
C. Presence of outer membrane
D. Presence of Teichoic acid (Correct Answer)

Explanation: ***Presence of Teichoic acid*** - **Teichoic acid** is a unique component of the cell wall in **Gram-positive bacteria**, playing a role in cell wall structure and antigenicity. - Its presence is **not a characteristic of Gram-negative bacteria**, making this statement the exception. *Thinner* - The cell wall of **Gram-negative bacteria** is indeed **thinner** than that of Gram-positive bacteria. - This **thin peptidoglycan layer** (2-3 nm) is much less substantial compared to the thick peptidoglycan layer (20-80 nm) of Gram-positive bacteria. *Presence of lipopolysaccharide* - **Lipopolysaccharide (LPS)**, or endotoxin, is a characteristic component of the **outer membrane** of Gram-negative bacteria. - LPS contributes to the **pathogenicity** of Gram-negative bacteria and is absent in Gram-positive bacteria. *Presence of outer membrane* - **Gram-negative bacteria** have a unique **outer membrane** that lies external to the thin peptidoglycan layer. - This outer membrane contains LPS and porins, and is a distinguishing feature **absent in Gram-positive bacteria**, which have only a single cytoplasmic membrane.

Question 8: Patient presenting with abdominal pain, diarrhea taking clindamycin for 5 days. Treated with metronidazole symptoms subsided. What is the causative agent -

A. Clostridium difficile (Correct Answer)
B. Clostridium welchii
C. Clostridium perfringens
D. Clostridium botulinum

Explanation: ***Clostridium difficile*** - **Clindamycin** is a common antibiotic associated with **Clostridium difficile** infection, which causes **antibiotic-associated diarrhea** and **colitis**. - The successful treatment with **metronidazole** further supports the diagnosis of *C. difficile* infection. *Clostridium welchii* (also known as *Clostridium perfringens*) - Primarily causes **gas gangrene** and **food poisoning**, with symptoms more acute and severe than described. - Not typically associated with antibiotic-induced diarrhea but rather **contaminated food** or **wound infections**. *Clostridium perfringens* - This bacterium is a common cause of **food poisoning** (type A) featuring **abdominal cramps** and **diarrhea**, and **gas gangrene** (type C) due to deep tissue infections. - While it can cause diarrhea, it's not the classic cause of **antibiotic-associated diarrhea** like *C. difficile*. *Clostridium botulinum* - Produces a **neurotoxin** that causes **flaccid paralysis**, not abdominal pain and diarrhea due to antibiotic use. - The infection is typically acquired through **improperly canned food** or **wound contamination**.

Question 9: Traveller's diarrhoea is caused by:

A. E. histolytica
B. E. coli (Correct Answer)
C. Giardia lamblia
D. Shigella

Explanation: ***E. coli*** - **Enterotoxigenic E. coli (ETEC)** is the most common cause of **traveler's diarrhea**, producing toxins that lead to watery stools. - The disease is typically acquired through ingestion of **contaminated food or water**, particularly in regions with poor sanitation. *E. histolytica* - This parasite causes **amoebiasis**, which can lead to **dysentery** (bloody diarrhea) or liver abscesses. - While it can cause diarrhea in travelers, it is not the most frequent pathogen associated with typical traveler's diarrhea. *Giardia lamblia* - **Giardiasis** typically results in **chronic, greasy, foul-smelling stools**, bloating, and malabsorption rather than acute watery diarrhea. - It's a common cause of **protracted diarrhea** in travelers but not the most frequent cause of acute onset. *Shigella* - This bacterium causes **shigellosis**, characterized by **dysentery (bloody, mucoid stools)**, fever, and abdominal cramps. - While a cause of bacterial diarrhea in travelers, it is less common than ETEC and presents with a more severe, invasive illness.

Question 10: Which virus is NOT associated with human cancer?

A. HPV
B. Measles virus (Correct Answer)
C. HHV-8
D. EBV

Explanation: ***Measles virus*** - The **measles virus** (rubeola) is primarily known for causing acute febrile illness with a characteristic rash and is not recognized as an **oncogenic virus** in humans. - While it can cause significant morbidity and mortality, particularly in unvaccinated populations, its mode of action does not involve **cellular transformation** or sustained **oncogene expression**. *HPV* - **Human Papillomavirus (HPV)**, particularly high-risk types like HPV-16 and HPV-18, is a well-established cause of **cervical cancer**, as well as other anogenital and oropharyngeal cancers. - HPV oncogenes, **E6** and **E7**, interfere with tumor suppressor proteins like p53 and Rb, promoting uncontrolled cell growth. *HHV-8* - **Human Herpesvirus 8 (HHV-8)**, also known as Kaposi's sarcoma-associated herpesvirus (KSHV), is the causative agent of **Kaposi's sarcoma**, a vascular tumor. - HHV-8 is also associated with primary effusion lymphoma and multicentric Castleman's disease due to its **latency-associated nuclear antigen (LANA)** and other viral oncogenes. *EBV* - **Epstein-Barr Virus (EBV)** is strongly linked to several human cancers, including **Burkitt's lymphoma**, **nasopharyngeal carcinoma**, and Hodgkin's lymphoma. - EBV transforms B lymphocytes through the expression of latency genes such as **LMP1** and **EBNA2**, which modulate cell growth and survival pathways.

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