Gut Microbiome — MCQs
What is the physiological reflex responsible for post-meal defecation in children?
Anti-microbials are given with which type of diarrhea:
Cholera is caused by?
A cook prepares sandwiches for 10 people going for a picnic. Eight out of them develop severe gastroenteritis within 4-6 hours of consuming the sandwiches. It is likely that on investigation, the cook is found to be the carrier of -
Which of the following bacteria is microaerophilic?
All are true about culture media except:
Which of the following is an inflammatory bowel disease in children?
A young girl presents with abdominal pain and a recent change in bowel habit, with passage of mucus in stool. There is no associated blood in stool and symptoms are increased with stress. The most likely diagnosis is:
Fecal leucocytes are absent in all of the following, except:
Which of the following bacteria is classified as facultative anaerobe?
Gut Microbiome Indian Medical PG Practice Questions and MCQs
Question 1: What is the physiological reflex responsible for post-meal defecation in children?
- A. Gastro colic reflex (Correct Answer)
- B. Gastro gastric reflex
- C. Vasovagal reflex
- D. Colonoileal reflex
Explanation: ***Gastro colic reflex*** - This reflex is a **physiological response** to stomach distention by food, leading to increased motility in the **colon**. - It explains why bowel movements, especially in infants and young children, often occur shortly **after eating**. *Gastro gastric reflex* - This reflex primarily involves communication **between different parts of the stomach**, controlling gastric motility and emptying. - It does not directly induce colonic contractions or defecation after a meal. *Vasovagal reflex* - The vasovagal reflex is a systemic response involving the **vagus nerve** that can cause a drop in heart rate and blood pressure, leading to fainting. - While it can be triggered by various stimuli, it is not the mechanism responsible for post-meal defecation. *Colonoileal reflex* - This reflex occurs when the colon is distended, slowing the movement of chyme from the **ileum into the colon**. - Its primary function is to prevent overloading the colon, not to stimulate post-meal defecation.
Question 2: Anti-microbials are given with which type of diarrhea:
- A. Secretory diarrhea
- B. Rotavirus
- C. Osmotic diarrhea
- D. Traveller's diarrhea (Correct Answer)
Explanation: Andi-microbials are often recommended for **traveler's diarrhea**, especially if symptoms are severe or there is a likely bacterial origin [1]. Common pathogens **E. coli, Salmonella, Shigella**, and **Campylobacter** are effectively treated with antibiotics, reducing duration and severity [1]. *Secretory diarrhea* - This type of diarrhea results from increased active secretion of water and electrolytes, often due to **toxins** (e.g., cholera). - While antimicrobials may be used in specific bacterial infections causing secretory diarrhea, the primary treatment focuses on **rehydration**, as the issue isn't always directly bacterial [2]. *Rotavirus* - Rotavirus is a **viral infection**, and therefore, antimicrobials (antibiotics) are ineffective against it. - Treatment for rotavirus is primarily **supportive**, focusing on hydration and symptom management. *Osmotic diarrhea* - Osmotic diarrhea occurs when there is an excess of **osmotically active solutes** in the gut drawing water into the lumen (e.g., lactose intolerance, laxative abuse). - Antimicrobials are generally not indicated for osmotic diarrhea unless there is a co-occurring bacterial infection, as the underlying problem is not microbial.
Question 3: Cholera is caused by?
- A. Enterococcus
- B. E.coli
- C. Vibrio cholerae O1 (Correct Answer)
- D. Vibrio parahemolyticus
Explanation: ***Vibrio cholerae O1*** - **Cholera** is primarily caused by **toxigenic strains** of *Vibrio cholerae*, with serogroup **O1** being the most common and historically significant cause of epidemics and pandemics. - This bacterium produces **cholera toxin**, which leads to profuse watery diarrhea by acting on the intestinal epithelial cells. *Enterococcus* - **Enterococcus** species are common inhabitants of the human gastrointestinal tract and are often associated with **nosocomial infections**, such as urinary tract infections, endocarditis, and bacteremia. - They do not typically cause the severe, watery diarrhea characteristic of cholera. *Vibrio parahemolyticus* - *Vibrio parahemolyticus* is a common cause of **foodborne illness**, particularly associated with consuming **raw or undercooked seafood**. - It causes a form of gastroenteritis characterized by abdominal pain, watery diarrhea, nausea, vomiting, and fever, but it is distinct from cholera. *E.coli* - While various strains of **Escherichia coli (E. coli)** can cause diarrheal diseases (e.g., enterotoxigenic *E. coli* causing traveler's diarrhea, enterohemorrhagic *E. coli* causing bloody diarrhea), **E. coli** is not the causative agent of cholera. - The pathogenesis and specific toxins produced differ significantly from those of *Vibrio cholerae*.
Question 4: A cook prepares sandwiches for 10 people going for a picnic. Eight out of them develop severe gastroenteritis within 4-6 hours of consuming the sandwiches. It is likely that on investigation, the cook is found to be the carrier of -
- A. Salmonella typhi
- B. Vibrio cholerae
- C. Entamoeba histolytica
- D. Staphylococcus aureus (Correct Answer)
Explanation: ***Staphylococcus aureus*** - The rapid onset of symptoms (4-6 hours) and the development of severe gastroenteritis in multiple individuals after consuming common food items (sandwiches) strongly suggest a **preformed toxin ingestion**. - **_Staphylococcus aureus_** is a common cause of food poisoning due to its ability to produce enterotoxins that are heat-stable and cause rapid onset of nausea, vomiting, and diarrhea. *Salmonella typhi* - **_Salmonella typhi_** causes typhoid fever, which typically has an incubation period of **1-3 weeks**, much longer than the 4-6 hours seen in this case. - The symptoms of typhoid fever are also more systemic, including high fever, headache, and abdominal pain, rather than acute gastroenteritis with rapid onset. *Vibrio cholerae* - **_Vibrio cholerae_** causes cholera, characterized by **profuse watery diarrhea** with a typical incubation period of **1-5 days**. - The rapid onset of symptoms in this scenario (4-6 hours) does not align with the incubation period of cholera. *Entamoeba histolytica* - **_Entamoeba histolytica_** causes amoebiasis, which has an incubation period ranging from **several days to weeks or even months**. - It typically presents with **bloody diarrhea** and abdominal pain, and its slow onset is inconsistent with the acute event described.
Question 5: Which of the following bacteria is microaerophilic?
- A. Campylobacter (Correct Answer)
- B. Pseudomonas
- C. Salmonella
- D. Vibrio cholerae
Explanation: ***Campylobacter*** - **Campylobacter jejuni** is a classic example of a microaerophilic bacterium, thriving in environments with **reduced oxygen (5-10% O2)** and **increased CO2 (5-10%)**. - This specific atmospheric requirement is crucial for its **growth** and **virulence**, often leading to gastroenteritis. *Vibrio cholerae* - **Vibrio cholerae** is a **facultative anaerobe**, meaning it can grow in both the presence and absence of oxygen. - It does not require low oxygen environments; optimal growth occurs **aerobically**. *Pseudomonas* - **Pseudomonas aeruginosa** is an **obligate aerobe**; it requires oxygen for respiration and growth. - It uses oxygen as the **final electron acceptor** in its electron transport chain. *Salmonella* - **Salmonella enterica** is a **facultative anaerobe**, capable of switching between aerobic and anaerobic respiration. - It can grow in the presence of oxygen, as well as in **anaerobic conditions** by fermenting sugars.
Question 6: All are true about culture media except:
- A. LJ medium is used for tubercle bacilli
- B. Loeffler's serum slope is used for Corynebacterium diphtheriae
- C. The best medium for anaerobes is chocolate agar (Correct Answer)
- D. Blood agar supports fastidious organisms
Explanation: ***The best medium for anaerobes is chocolate agar*** - **Chocolate agar** is an enriched medium used for the isolation of **fastidious organisms** like *Haemophilus influenzae* and *Neisseria* species, but it is not optimized for anaerobic growth. - Anaerobes require **anaerobic specific media** (e.g., thioglycollate broth, blood agar with reducing agents) and conditions (e.g., anaerobic jar) for optimal growth. *LJ medium is used for tubercle bacilli* - **Lowenstein-Jensen (LJ) medium** is a primary isolation medium specifically formulated for the growth of **mycobacteria**, including *Mycobacterium tuberculosis*. - It contains **malachite green**, which inhibits the growth of most other bacteria, and nutrients like **egg and asparagine** to support mycobacterial growth. *Loeffler's serum slope is used for Corynebacterium diphtheriae* - **Loeffler's serum slope** is an enrichment medium used to isolate and presumptively identify *Corynebacterium diphtheriae*. - It enhances the production of **metachromatic granules (Babes-Ernst granules)** by *C. diphtheriae*, which are visible upon staining. *Blood agar supports fastidious organisms* - **Blood agar** is an enriched medium containing 5% sheep blood, providing essential growth factors for many bacteria, including some **fastidious organisms**. - It is used to detect **hemolytic reactions**, which are important for differentiating various bacterial species.
Question 7: Which of the following is an inflammatory bowel disease in children?
- A. Tropical sprue
- B. Cystic fibrosis
- C. Coeliac disease
- D. Regional ileitis (Correct Answer)
Explanation: ***Regional ileitis*** - Regional ileitis is another name for **Crohn's disease**, which is a type of **inflammatory bowel disease (IBD)** that can affect any part of the gastrointestinal tract, including the ileum, in children and adults. - IBD in children presents with chronic inflammation of the digestive tract, leading to symptoms such as **abdominal pain**, **diarrhea**, and **weight loss**. *Tropical sprue* - Tropical sprue is a **malabsorption syndrome** characterized by abnormalities in the small intestine, but it is caused by environmental factors and infections, not considered an inflammatory bowel disease. - It is typically seen in individuals living in or visiting tropical regions and is not classified as IBD. *Cystic fibrosis* - Cystic fibrosis is a **genetic disorder** that primarily affects the lungs and digestive system by producing thick, sticky mucus. - While it causes digestive issues due to **pancreatic insufficiency**, it is not an inflammatory bowel disease. *Coeliac disease* - Coeliac disease is an **autoimmune condition** triggered by the ingestion of gluten, leading to damage in the small intestine. - It is distinct from IBD as its pathology is primarily immune-mediated in response to gluten and does not involve chronic, idiopathic inflammation characteristic of IBD.
Question 8: A young girl presents with abdominal pain and a recent change in bowel habit, with passage of mucus in stool. There is no associated blood in stool and symptoms are increased with stress. The most likely diagnosis is:
- A. Amebiasis
- B. Irritable bowel syndrome (Correct Answer)
- C. Crohn's disease
- D. Ulcerative Colitis
Explanation: ***Irritable bowel syndrome*** - **Irritable bowel syndrome (IBS)** typically presents with **abdominal pain**, altered bowel habits (constipation, diarrhea, or mixed), and **mucus in stool** without blood [1]. - The symptoms are often exacerbated by **stress** and there is no evidence of structural or biochemical abnormalities [1]. *Amebiasis* - **Amebiasis** is an infection caused by *Entamoeba histolytica*, usually leading to **bloody diarrhea** (dysentery), abdominal pain, and fever. - The absence of blood in the stool and the presence of stress-related symptom exacerbation make amebiasis less likely. *Crohn's disease* - **Crohn's disease** is a type of inflammatory bowel disease characterized by **transmural inflammation** that can affect any part of the gastrointestinal tract. - Symptoms often include **abdominal pain**, diarrhea (which can be bloody), weight loss, and fatigue, and it does not typically show a direct correlation with stress as the primary exacerbating factor. *Ulcerative Colitis* - **Ulcerative colitis (UC)** is an inflammatory bowel disease characterized by **continuous inflammation** of the colon, typically starting in the rectum. - Key symptoms include recurrent **bloody diarrhea**, abdominal pain, and tenesmus, which are not described in this case, particularly the absence of blood.
Question 9: Fecal leucocytes are absent in all of the following, except:
- A. Cryptosporidiosis
- B. Clostridium perfringes infection
- C. Giardiasis
- D. Campylobacter infection (Correct Answer)
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.
Question 10: Which of the following bacteria is classified as facultative anaerobe?
- A. Bacteroides
- B. Pseudomonas
- C. Escherichia (Correct Answer)
- D. Clostridium
Explanation: ***Escherichia*** - *Escherichia coli* (E. coli) is a classic example of a **facultative anaerobe**, meaning it can grow in the presence or absence of oxygen. - It uses **aerobic respiration** when oxygen is available and switches to **fermentation** or **anaerobic respiration** in an anaerobic environment. *Bacteroides* - *Bacteroides* species are **obligate anaerobes**, meaning they can only survive and grow in the **complete absence of oxygen**. - They are a major component of the normal human gut flora and are sensitive to oxygen exposure. *Pseudomonas* - *Pseudomonas* species, such as *Pseudomonas aeruginosa*, are **obligate aerobes**, requiring **oxygen for growth and metabolism**. - They possess enzymes like cytochrome oxidase and catalase, which are essential for aerobic respiration. *Clostridium* - *Clostridium* species, like *Clostridium tetani* and *Clostridium perfringens*, are **obligate anaerobes**. - They lack the enzymes (e.g., superoxide dismutase, catalase) necessary to detoxify reactive oxygen species, making oxygen lethal to them.
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