NEET-PG 2022 — Microbiology
8 Previous Year Questions with Answers & Explanations
An HIV patient is admitted with malabsorption, fever, chronic diarrhea, and acid-fast positive organism. What is the likely causative agent?
Sheathed microfilariae with two nuclei at the tail tip is suggestive of?
A farmer presents you with a cauliflower-shaped mass on foot, which developed after a minor injury. Microscopy shows copper penny bodies. What is the most likely diagnosis?
All of the following statements are true regarding neutrophil extracellular trapping (NET) except for which of the following?
A female patient presents with complaints of thick white vaginal secretions. Which of the following can be used to identify the likely species of the causative agent?
A militant presents with rashes all over his body sparing the palms and soles. On examination, he was febrile and lice were noted. Which of the following is responsible for his condition?
A 45-year-old patient with a history of poorly controlled diabetes presents with sinus pain, nasal discharge, and facial swelling. A biopsy reveals broad, nonseptate hyphae branching at wide angles. What is the most likely causative agent?
A patient with HIV presents with extensive anogenital warts. Which HPV types are most commonly associated with malignant transformation in this setting?
NEET-PG 2022 - Microbiology NEET-PG Practice Questions and MCQs
Question 1: An HIV patient is admitted with malabsorption, fever, chronic diarrhea, and acid-fast positive organism. What is the likely causative agent?
- A. Giardia
- B. Microsporidia
- C. Isospora (Correct Answer)
- D. E. histolytica
Explanation: ***Isospora (Cystoisospora belli)*** - **Cystoisospora belli** (formerly *Isospora belli*) is a coccidian parasite common in HIV patients, causing **chronic watery diarrhea**, fever, and malabsorption, especially when the CD4 count is low. - The diagnosis is confirmed by identifying **acid-fast oocysts** in stool samples, which is the key distinguishing feature in this case. - The **acid-fast positive** property makes this the definitive answer among the given options. *Giardia* - **Giardia lamblia** causes malabsorption and chronic diarrhea but is typically characterized by **fatty, foul-smelling stools** and abdominal cramping. - While it can be diagnosed with stool examination, its cysts and trophozoites are **not acid-fast**, which excludes it based on the clinical description. *Microsporidia* - Microsporidia species like **Enterocytozoon bieneusi** can cause chronic diarrhea and malabsorption in HIV patients. - However, they are **intracellular obligate parasites** detected using specialized stains (modified trichrome or calcofluor white) rather than acid-fast staining, making them inconsistent with the **acid-fast positive** finding. *E. histolytica* - **Entamoeba histolytica** causes amebiasis, which can manifest as **amebic dysentery** with bloody stools or chronic non-bloody diarrhea. - Its trophozoites and cysts are **not acid-fast**, and the malabsorption syndrome is less prominent than with Cystoisospora, excluding it from consideration.
Question 2: Sheathed microfilariae with two nuclei at the tail tip is suggestive of?
- A. Onchocerca volvulus
- B. Brugia malayi (Correct Answer)
- C. Wuchereria bancrofti
- D. Loa loa
Explanation: ***Brugia malayi*** - Microfilariae of *Brugia malayi* are characterized by a **sheathed tail** with **two distinct nuclei** at the very tip of the tail. - This morphological feature, along with the presence of multiple discrete nuclei throughout the body, is key for its identification. *Wuchereria bancrofti* - While *Wuchereria bancrofti* also has a **sheathed tail**, its tail is typically **free of nuclei** or has terminal nuclei that are not distinct or paired. - The nuclei of *W. bancrofti* are more scattered and less clearly defined throughout the body compared to *Brugia*. *Onchocerca volvulus* - *Onchocerca volvulus* microfilariae are **unsheathed** and have a **tapered tail without nuclei**. - They are typically found in the skin, not the blood, and lack the characteristic two nuclei at the tail tip. *Loa loa* - *Loa loa* microfilariae are also **sheathed** but have a **tapered tail with nuclei extending to the tip**, not specifically two distinct nuclei at the tail. - Their nuclei are irregularly arranged within the tail, differentiating them from *Brugia malayi*.
Question 3: A farmer presents you with a cauliflower-shaped mass on foot, which developed after a minor injury. Microscopy shows copper penny bodies. What is the most likely diagnosis?
- A. Sporotrichosis
- B. Blastomycosis
- C. Chromoblastomycosis (Correct Answer)
- D. Phaeohyphomycosis
Explanation: **Chromoblastomycosis** - The characteristic "cauliflower-shaped" lesion on the foot following a minor injury, especially in a farmer (indicating outdoor exposure), is highly suggestive of chromoblastomycosis. - The presence of **copper penny bodies** (also known as **sclerotic** or **muriform cells**) on microscopy is **pathognomonic** for chromoblastomycosis. *Blastomycosis* - Blastomycosis typically presents with **granulomatous lesions** that can ulcerate but are rarely described as cauliflower-shaped. - Microscopic examination would reveal **broad-based budding yeast cells**, not copper penny bodies. *Sporotrichosis* - Sporotrichosis usually presents as **subcutaneous nodules** that can ulcerate and spread lymphatically, forming a chain of lesions. - Microscopy shows **cigar-shaped budding yeasts** within macrophages or neutrophils, which are distinct from copper penny bodies. *Phaeohyphomycosis* - Phaeohyphomycosis encompasses a broad group of infections by dematiaceous fungi that produce **dark-walled hyphae** or yeast-like cells in tissue. - While it can cause subcutaneous nodules or cysts, the presence of distinct copper penny bodies points away from phaeohyphomycosis as the primary diagnosis.
Question 4: All of the following statements are true regarding neutrophil extracellular trapping (NET) except for which of the following?
- A. It is detected in blood during sepsis
- B. It is chromatin with antibacterial enzymes
- C. Mitochondrial DNA is seen (Correct Answer)
- D. It is produced in response to bacterial infection
Explanation: ***Mitochondrial DNA is seen*** - NETs (Neutrophil Extracellular Traps) are made primarily of **nuclear chromatin**, not mitochondrial DNA [2]. - The main purpose of NETs is to trap and kill pathogens, focusing on **nuclear genetic material** rather than mitochondrial components. *It is detected in blood during sepsis* - NETs can indeed be found in the **circulation during sepsis**, serving as a defense mechanism against infections. - Their presence in blood indicates an **active immune response**, particularly in severe systemic infections. *It is produced in response to bacterial infection* - NET formation is a known response to **bacterial infections**, as neutrophils deploy them to capture and neutralize pathogens. - This process helps in controlling infections, showcasing the importance of NETs in **innate immunity**. *It is chromatin with antibacterial enzymes* - NETs consist primarily of **decondensed chromatin**, embedded with **antimicrobial proteins** and enzymes to combat pathogens [1][2]. - This characteristic underscores their role in targeting and eliminating invading microorganisms effectively. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Inflammation and Repair, pp. 91-92. [2] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Inflammation and Repair, pp. 92-93.
Question 5: A female patient presents with complaints of thick white vaginal secretions. Which of the following can be used to identify the likely species of the causative agent?
- A. Brain heart infusion agar
- B. Sabouraud dextrose agar
- C. CHROMagar (Correct Answer)
- D. Birdseed agar
Explanation: ***CHROMagar*** - **CHROMagar Candida** is a differential and selective medium used for the isolation and presumptive identification of common yeast species, including *Candida albicans*, *Candida tropicalis*, and *Candida glabrata*, based on chromogenic reactions. - Different *Candida* species produce distinct colonies of varying colors on this medium, aiding in their **presumptive identification** directly from patient samples like vaginal secretions. *Birdseed agar* - This medium (also known as Staib's medium or Niger seed agar) is primarily used for the isolation and identification of **Cryptococcus neoformans**, which produces dark brown to black colonies due to its phenoloxidase activity. - While it's a fungal growth medium, it is not optimized for distinguishing common *Candida* species responsible for vaginal candidiasis. *Brain heart infusion agar* - **Brain heart infusion (BHI) agar** is a general-purpose, enriched non-selective medium used for the cultivation of a wide variety of fastidious bacteria, yeasts, and molds. - It does not contain differential components that would allow for the specific identification or differentiation of *Candida* species based on colony color or morphology. *Sabouraud dextrose agar* - **Sabouraud dextrose agar (SDA)** is a selective medium primarily used for the isolation and cultivation of pathogenic and nonpathogenic fungi, including yeasts and molds. - While *Candida* species will grow well on SDA, it does not provide differential characteristics (like distinct colony colors) to allow for the presumptive identification and differentiation of various *Candida* species.
Question 6: A militant presents with rashes all over his body sparing the palms and soles. On examination, he was febrile and lice were noted. Which of the following is responsible for his condition?
- A. Rickettsia typhi
- B. Rickettsia prowazekii (Correct Answer)
- C. Rickettsia akari
- D. Rickettsia conorii
Explanation: ***Rickettsia prowazekii*** - This bacterium is the causative agent of **epidemic typhus**, which is transmitted by the **body louse** (Pediculus humanus corporis), consistent with the presence of lice. - The characteristic rash of epidemic typhus **spares the palms and soles** and often begins on the trunk, spreading centrifugally. *Rickettsia typhi* - This organism causes **murine typhus**, which is transmitted by **fleas**, particularly those found on rodents. - While it can cause a rash that typically spares the palms and soles, the transmission vector and typical setting (exposure to rodents) do not fit the clinical scenario as well as **body lice**. *Rickettsia akari* - This bacterium causes **rickettsialpox**, transmitted by **mites**. - The rash of rickettsialpox is typically papulovesicular, and a characteristic **eschar** (or black scab) is usually present at the site of the mite bite, which is not mentioned in the case. *Rickettsia conorii* - This organism causes **Mediterranean spotted fever** (also known as Boutonneuse fever), transmitted by **ticks**. - A distinguishing feature of this infection is the presence of a **tache noire** (eschar) at the site of the tick bite, which is absent in the patient's presentation.
Question 7: A 45-year-old patient with a history of poorly controlled diabetes presents with sinus pain, nasal discharge, and facial swelling. A biopsy reveals broad, nonseptate hyphae branching at wide angles. What is the most likely causative agent?
- A. Aspergillus fumigatus
- B. Rhizopus spp. (Correct Answer)
- C. Candida albicans
- D. Cryptococcus neoformans
Explanation: ***Rhizopus spp.*** - The patient's presentation with **sinus pain**, **nasal discharge**, **facial swelling**, and a history of **poorly controlled diabetes** is classic for **mucormycosis** (also known as zygomycosis). - **Biopsy findings** of **broad, nonseptate hyphae branching at wide/irregular angles** are pathognomonic for mucormycosis, most commonly caused by *Rhizopus* species. - Diabetes mellitus, particularly when poorly controlled with **ketoacidosis**, is a major risk factor for rhinocerebral mucormycosis. *Aspergillus fumigatus* - This fungus typically causes infections with **septate hyphae** that **branch at acute angles** (45 degrees), which is morphologically distinct from mucormycosis. - While *Aspergillus* can cause invasive sinusitis in immunocompromised patients, the specific hyphal morphology (nonseptate, wide-angle branching) points away from it. *Candida albicans* - *Candida albicans* is a yeast that typically appears as **oval budding cells** and **pseudohyphae** on microscopy, not broad, nonseptate hyphae. - While it can cause opportunistic infections in diabetic and immunocompromised patients, its microscopic appearance is entirely inconsistent with the biopsy findings. *Cryptococcus neoformans* - *Cryptococcus neoformans* is an **encapsulated yeast** that is typically identified by its **spherical or oval budding cells** with a characteristic **polysaccharide capsule** visible with India ink stain. - It primarily causes **meningitis** and pulmonary infections in immunocompromised hosts, and its morphology (yeast, not hyphae) is entirely different from the described findings.
Question 8: A patient with HIV presents with extensive anogenital warts. Which HPV types are most commonly associated with malignant transformation in this setting?
- A. Types 42 and 43
- B. Types 31 and 33
- C. Types 16 and 18 (Correct Answer)
- D. Types 6 and 11
Explanation: ***Types 16 and 18*** - **HPV types 16 and 18** are considered **high-risk** and are responsible for the majority of HPV-related cancers, including cervical, anal, and oropharyngeal cancers. - In HIV-positive individuals, the risk of malignant transformation from HPV infection is significantly increased due to **immunocompromise**. *Types 42 and 43* - **HPV types 42 and 43** are classified as **low-risk** HPV types. - They are primarily associated with **benign anogenital warts** and rarely cause malignant transformation. *Types 31 and 33* - **HPV types 31 and 33** are also considered **high-risk** types and can cause malignant transformation. - However, **types 16 and 18** are more frequently associated with HPV-related cancers than types 31 and 33. *Types 6 and 11* - **HPV types 6 and 11** are **low-risk** types and are the primary cause of **genital warts (condyloma acuminata)**. - While they can cause extensive warts, they have a very low potential for malignant transformation.