Microbiology
3 questionsName the parasite whose microfilariae have a sheath and no nuclei at the tail end.
A patient presents with a history of pastry intake causing food poisoning. What is the most likely causative agent?
A patient presented with 70% burns, and a sample was collected from the burn site. The image shows Gram-negative rods, and the suspected organism is an obligate aerobe. What is the most likely causative microbe?
NEET-PG 2021 - Microbiology NEET-PG Practice Questions and MCQs
Question 31: Name the parasite whose microfilariae have a sheath and no nuclei at the tail end.
- A. Brugia malayi
- B. Loa loa
- C. Onchocerca volvulus
- D. Wuchereria bancrofti (Correct Answer)
Explanation: **Wuchereria bancrofti** - **Wuchereria bancrofti** microfilariae are characterized by the presence of a **sheath** and a **clear tail end** that is devoid of nuclei. - This morphology is a key feature used in the microscopic differentiation of W. bancrofti from other filarial species. *Brugia malayi* - **Brugia malayi** microfilariae also have a **sheath**, but their tail end typically contains **two distinct nuclei** that are spaced apart. - They are generally shorter and have more kinky curves than W. bancrofti. *Loa loa* - **Loa loa** microfilariae possess a **sheath** but are distinguished by their **nuclei extending to the tip** of the tail, often in a more continuous pattern. - They are also known for their diurnal periodicity, which aids in diagnosis. *Onchocerca volvulus* - **Onchocerca volvulus** microfilariae are **unsheathed** and have nuclei that do **not extend to the tail tip**, leaving a distinct clear space. - They are typically found in the skin and subcutaneous tissue, rather than the blood.
Question 32: A patient presents with a history of pastry intake causing food poisoning. What is the most likely causative agent?
- A. Verotoxin-producing E. coli
- B. Bacillus cereus
- C. Staphylococcus aureus (Correct Answer)
- D. Enteroinvasive E. coli (EIEC)
Explanation: ***Staphylococcus aureus*** - *S. aureus* is a common cause of food poisoning linked to **creamy foods** like pastries, salads, and custards, as it produces **heat-stable enterotoxins** when allowed to proliferate. - The symptoms, typically rapid onset **nausea, vomiting**, and abdominal cramps, occur because of the **preformed toxins** in the food, not necessarily active infection. *Verotoxin-producing E. coli* - This strain, often **E. coli O157:H7**, is primarily associated with **undercooked beef** or contaminated produce, and typically causes **bloody diarrhea** and can lead to hemolytic uremic syndrome (HUS). - Its mechanism involves **verotoxins** directly damaging intestinal cells and blood vessels, which is different from the rapid, emetic-focused symptoms of *S. aureus* food poisoning. *Bacillus cereus* - *B. cereus* causes two main types of food poisoning: **emetic (vomiting)**, typically from **reheated rice**, and **diarrheal**, from meat products or vegetables. - While the emetic form can cause vomiting, it is most strongly associated with **rice dishes** and usually has a shorter incubation period than the diarrheal form, making *Staphylococcus aureus* a more classic cause for pastry-related outbreaks. *Enteroinvasive E. coli (EIEC)* - EIEC causes a disease similar to **shigellosis**, involving direct invasion of intestinal epithelial cells, leading to **bloody diarrhea** and fever. - It is typically spread through contaminated food and water and not specifically linked to pastry intake or characterized by the rapid onset emetic symptoms seen with preformed toxins.
Question 33: A patient presented with 70% burns, and a sample was collected from the burn site. The image shows Gram-negative rods, and the suspected organism is an obligate aerobe. What is the most likely causative microbe?
- A. Neisseria meningitidis (Meningococcus)
- B. Streptococcus pneumoniae (Pneumococcus)
- C. Pseudomonas aeruginosa (Correct Answer)
- D. Streptococcus pyogenes
Explanation: ***Pseudomonas aeruginosa*** - The image shows **Gram-negative rods**, and the patient has extensive **burns**, making *Pseudomonas aeruginosa* a highly likely causative agent due to its common association with burn wound infections. - *Pseudomonas aeruginosa* is an **obligate aerobe** and thrives in moist environments, making it a frequent colonizer of burn wounds, which are large, often moist surfaces. *Neisseria meningitidis (Meningococcus)* - *Neisseria meningitidis* is a **Gram-negative coccus**, typically appearing as diplococci, not rods, on Gram stain. - While it can cause severe infections, it is primarily associated with **meningitis** and **sepsis**, not typically burn wound infections. *Streptococcus pneumoniae (Pneumococcus)* - *Streptococcus pneumoniae* is a **Gram-positive coccus**, appearing as lancet-shaped diplococci or short chains, which contradicts the Gram-negative rod morphology seen in the image. - It is a common cause of **pneumonia** and **otitis media**, not primarily associated with burn wound infections. *Streptococcus pyogenes* - *Streptococcus pyogenes* is a **Gram-positive coccus** that grows in chains, which is inconsistent with the Gram-negative rod morphology. - Although it can cause skin infections like cellulitis and impetigo, it is not a typical cause of **burn wound infections** in the way *Pseudomonas aeruginosa* is.
Pharmacology
7 questionsWhat is the mechanism of action of Methotrexate?
Which antitubercular drug reduces the efficacy of oral contraceptive pills (OCPs)?
A patient on digoxin therapy presents with atrial fibrillation and controlled ventricular rate. Upon evaluation, the patient's serum digoxin levels are elevated compared to previous values. Which of the following concomitant medications is most likely to have contributed to the enhanced digoxin toxicity?
A patient is taking metronidazole for anaerobic infection. Which of the following should be avoided during this period
Topiramate is used in
Which of the following drugs is used for the long term management of obesity
A 30-year-old male presents with a history of consuming an unknown substance. On examination, the patient has diaphoresis, headache, and features resembling acute coronary spasm. Which of the following clinical features is least likely to be present in this patient?
NEET-PG 2021 - Pharmacology NEET-PG Practice Questions and MCQs
Question 31: What is the mechanism of action of Methotrexate?
- A. Inhibition of Dihydrofolate reductase (Correct Answer)
- B. Inhibits pyrimidine synthesis
- C. Inhibits cell replication by acting on G phase of cell cycle
- D. Inhibits Thymidylate synthase
- E. Inhibits RNA polymerase
Explanation: ***Inhibition of Dihydrofolate reductase*** - **Methotrexate** is a **folate analog** that competitively inhibits **dihydrofolate reductase (DHFR)**, an enzyme essential for converting **dihydrofolate** to **tetrahydrofolate**. - This inhibition blocks the synthesis of **purines** and **pyrimidines**, thereby preventing DNA and RNA synthesis and ultimately inhibiting cell proliferation. *Inhibits pyrimidine synthesis* - While methotrexate ultimately inhibits pyrimidine synthesis by depleting tetrahydrofolate, its direct mechanism is not the inhibition of the pyrimidine synthesis pathway enzymes themselves. - Its primary action is upstream, by inhibiting DHFR. *Inhibits cell replication by acting on G phase of cell cycle* - Methotrexate primarily inhibits cells in the **S-phase** of the cell cycle, as it interferes with DNA synthesis. - It does not specifically target the G phase; rather, it affects cells that are actively attempting to replicate their DNA. *Inhibits Thymidylate synthase* - **Thymidylate synthase** is inhibited by drugs like **5-fluorouracil**, which directly blocks the conversion of **deoxyuridine monophosphate (dUMP)** to **deoxythymidine monophosphate (dTMP)**. - Methotrexate's effect on thymidylate synthesis is indirect, mediated by the depletion of the cofactor **N5,N10-methylene-tetrahydrofolate** due to DHFR inhibition. *Inhibits RNA polymerase* - **RNA polymerase** inhibition is the mechanism of drugs like **rifampin** (bacterial RNA polymerase) and **α-amanitin** (eukaryotic RNA polymerase). - Methotrexate does not directly inhibit RNA polymerase; its effects on RNA synthesis are secondary to depletion of nucleotide precursors through DHFR inhibition.
Question 32: Which antitubercular drug reduces the efficacy of oral contraceptive pills (OCPs)?
- A. Rifampicin (Correct Answer)
- B. Isoniazid
- C. Ethambutol
- D. Pyrazinamide
- E. Streptomycin
Explanation: ***Rifampicin*** - **Rifampicin** is a potent inducer of **cytochrome P450 enzymes**, particularly CYP3A4, which metabolize oral contraceptive pills (OCPs). - This increased metabolism leads to lower systemic levels of contraceptive hormones, reducing their efficacy and increasing the risk of **unintended pregnancy**. - Women on Rifampicin should use **additional barrier contraception** or alternative contraceptive methods. *Isoniazid* - **Isoniazid** is primarily metabolized by N-acetyltransferase and cytochrome P450, but it is not a significant enzyme inducer. - It does not typically interfere with the effectiveness of **oral contraceptive pills**. *Ethambutol* - **Ethambutol** is eliminated largely unchanged via renal excretion and is not a significant inducer or inhibitor of cytochrome P450 enzymes. - It does not interact with **oral contraceptive pills**. *Pyrazinamide* - **Pyrazinamide** is metabolized by the liver, but it does not significantly induce or inhibit the cytochrome P450 system involved in OCP metabolism. - It is not known to reduce the effectiveness of **oral contraceptive pills**. *Streptomycin* - **Streptomycin** is an aminoglycoside antibiotic that is not metabolized by the liver and does not affect cytochrome P450 enzymes. - It has no interaction with **oral contraceptive pills**.
Question 33: A patient on digoxin therapy presents with atrial fibrillation and controlled ventricular rate. Upon evaluation, the patient's serum digoxin levels are elevated compared to previous values. Which of the following concomitant medications is most likely to have contributed to the enhanced digoxin toxicity?
- A. Triamterene
- B. KCL
- C. Atenolol
- D. Clarithromycin (Correct Answer)
- E. Amiodarone
Explanation: ***Clarithromycin*** - **Clarithromycin** is a **macrolide antibiotic** known to inhibit the cytochrome P450 3A4 (CYP3A4) enzyme system and **P-glycoprotein**. - This inhibition leads to decreased metabolism and **efflux of digoxin**, resulting in **increased serum digoxin levels** and enhanced toxicity. - Among the options, clarithromycin is the **most common cause** of elevated digoxin levels through P-gp inhibition. *Triamterene* - **Triamterene** is a **potassium-sparing diuretic** that can increase serum potassium. - **Hyperkalemia** generally *reduces* the binding of digoxin to Na+/K+-ATPase, thereby potentially *reducing* its toxic effects. - Does not significantly affect digoxin serum levels. *KCL* - **Potassium chloride (KCl)** is used to correct **hypokalemia**. - **Hypokalemia** can *potentiate* digoxin toxicity because low potassium increases digoxin binding to the Na+/K+-ATPase pump. - However, KCl supplementation *corrects* hypokalemia and would actually *reduce* toxicity risk, not increase serum digoxin levels. *Atenolol* - **Atenolol** is a **beta-blocker** primarily used to control heart rate and blood pressure. - While it can slow the heart rate like digoxin (additive pharmacodynamic effect), it does not significantly alter the **pharmacokinetics** or serum levels of digoxin. *Amiodarone* - **Amiodarone** is an **antiarrhythmic** that can inhibit P-glycoprotein and increase digoxin levels. - However, in this scenario, **clarithromycin** is more commonly associated with acute elevations in digoxin levels in clinical practice. - Amiodarone interactions are well-known and typically require dose adjustments at initiation.
Question 34: A patient is taking metronidazole for anaerobic infection. Which of the following should be avoided during this period
- A. Colchicine
- B. Alcohol (Correct Answer)
- C. Rifampicin
- D. Ciprofloxacin
- E. Warfarin
Explanation: ***Alcohol*** - Metronidazole inhibits **aldehyde dehydrogenase**, an enzyme responsible for metabolizing alcohol, leading to an accumulation of **acetaldehyde**. - This accumulation causes a **disulfiram-like reaction**, characterized by flushing, nausea, vomiting, headache, and palpitations, making alcohol avoidance crucial. *Colchicine* - Colchicine is used for gout and **familial Mediterranean fever**; there's no major contraindicated interaction with metronidazole. - While both can cause gastrointestinal side effects, combining them does not typically lead to a life-threatening interaction or necessitate avoidance. *Rifampicin* - Rifampicin is a potent **CYP450 enzyme inducer** and can decrease the effectiveness of many drugs, including metronidazole, by increasing its metabolism. - While an interaction exists, it typically involves reduced metronidazole efficacy rather than a strict contraindication requiring complete avoidance. *Ciprofloxacin* - Ciprofloxacin is a **quinolone antibiotic** and generally does not have a clinically significant, contraindicated interaction with metronidazole. - Both can individually cause **gastrointestinal side effects**, but their co-administration is not generally discouraged due to synergy in treatment or increased toxicity. *Warfarin* - Metronidazole can enhance the anticoagulant effect of warfarin by inhibiting its metabolism, potentially increasing **INR** and bleeding risk. - However, this interaction is **manageable with monitoring**; warfarin is not absolutely contraindicated and can be used with dose adjustments and frequent INR checks, unlike alcohol which must be completely avoided.
Question 35: Topiramate is used in
- A. 1st Line Treatment of ADHD
- B. Treatment of Acute Migraine
- C. Management of Seizures in Lennox-Gastaut Syndrome (Correct Answer)
- D. Treatment of Dementia
- E. Treatment of Bipolar Disorder
Explanation: ***Management of Seizures in Lennox-Gastaut Syndrome*** - Topiramate is an **antiepileptic drug** approved for the treatment of **partial-onset seizures**, tonic-clonic seizures, and seizures associated with **Lennox-Gastaut syndrome**. - Its multiple mechanisms of action, including blocking **voltage-gated sodium channels**, enhancing **GABAergic activity**, and antagonizing **AMPA/kainate glutamate receptors**, make it effective in managing complex seizure disorders. - This is a **primary FDA-approved indication** for topiramate. *1st Line Treatment of ADHD* - First-line treatments for ADHD typically involve **stimulants** like methylphenidate or amphetamines, or non-stimulants such as atomoxetine. - While topiramate can have cognitive side effects like "brain fog," it is **not considered a primary treatment** for ADHD. *Treatment of Acute Migraine* - Topiramate is used for **migraine prophylaxis (prevention)**, not for the acute treatment of a migraine attack. - Acute migraine treatments include triptans, NSAIDs, and CGRP inhibitors. - The key distinction is **prophylaxis vs. acute treatment**. *Treatment of Dementia* - There is **no evidence** that topiramate is effective in treating dementia or improving cognitive function in patients with dementia. - Current treatments for dementia often involve cholinesterase inhibitors or NMDA receptor antagonists. *Treatment of Bipolar Disorder* - While topiramate has been studied in bipolar disorder, it is **not FDA-approved** for this indication. - Standard mood stabilizers include lithium, valproate, carbamazepine, and atypical antipsychotics. - Topiramate lacks sufficient evidence for efficacy in bipolar disorder management.
Question 36: Which of the following drugs is used for the long term management of obesity
- A. Fenfluramine
- B. Sibutramine
- C. Liraglutide (Correct Answer)
- D. Metformin
- E. Orlistat
Explanation: ***Liraglutide*** - **Liraglutide** is a **GLP-1 receptor agonist** approved for **long-term weight management** in adults with obesity or overweight with comorbidities. - It works by **delaying gastric emptying**, increasing satiety, and reducing appetite, leading to sustained weight loss. *Fenfluramine* - **Fenfluramine** was an **anorectic drug** that was withdrawn from the market due to its association with **pulmonary hypertension** and **cardiac valvulopathy**. - It is **not used** for the long-term management of obesity due to severe cardiovascular side effects. *Sibutramine* - **Sibutramine** is a **serotonin-norepinephrine reuptake inhibitor** previously used for weight loss, but it was withdrawn due to increased risk of **cardiovascular events** such as heart attack and stroke. - It is **not recommended** for long-term obesity management due to its significant cardiovascular risks. *Orlistat* - **Orlistat** is a **pancreatic lipase inhibitor** that is approved for long-term obesity management but works by **reducing fat absorption** in the gastrointestinal tract. - While approved for long-term use, it is **less preferred** than GLP-1 agonists due to gastrointestinal side effects (steatorrhea, fecal incontinence) and lower efficacy in weight reduction compared to newer agents like liraglutide. *Metformin* - **Metformin** is primarily an **antidiabetic drug** used for type 2 diabetes and sometimes for polycystic ovary syndrome (PCOS). - While it may cause modest weight loss as a side effect, it is **not approved or indicated** as a primary drug for the long-term management of obesity in individuals without diabetes.
Question 37: A 30-year-old male presents with a history of consuming an unknown substance. On examination, the patient has diaphoresis, headache, and features resembling acute coronary spasm. Which of the following clinical features is least likely to be present in this patient?
- A. Hypertension
- B. Tachycardia
- C. Hyperthermia
- D. Bradycardia (Correct Answer)
- E. Mydriasis
Explanation: ***Bradycardia*** - The presented symptoms of diaphoresis, headache, and coronary spasm are consistent with **stimulant intoxication** (e.g., cocaine, amphetamines). - Stimulants typically cause **tachycardia** due to sympathetic overactivity, making bradycardia the least likely finding. *Hypertension* - **Stimulant intoxication** leads to increased sympathetic activity, causing **vasoconstriction** and elevated blood pressure. - This is a common and expected finding in cases presenting with coronary spasm due to substance abuse. *Tachycardia* - **Sympathetic overstimulation** from an unknown substance, particularly stimulants, directly increases heart rate. - This symptom closely aligns with the patient's presentation of diaphoresis and coronary spasm. *Hyperthermia* - Elevated body temperature is a frequent consequence of **stimulant overdose** due to increased metabolic activity and impaired thermoregulation. - **Diaphoresis** (sweating) can be a compensatory mechanism for hyperthermia or a direct effect of sympathetic activation. *Mydriasis* - **Pupillary dilation** is a characteristic finding in sympathomimetic toxidrome caused by stimulant drugs. - This occurs due to alpha-adrenergic stimulation of the radial muscle of the iris and is commonly seen with cocaine or amphetamine use.