NEET-PG 2024 - Microbiology Practice Questions

Q: A man presents with dysuria and urethral discharge after a history of unprotected sex. The Gram stain of his discharge is shown. What is the best culture medium for isolating the organism responsible?

Thayer-Martin agar. ***Thayer-Martin agar*** - The image shows numerous **polymorphonuclear leukocytes (neutrophils)** with intracellular, gram-negative diplococci, which is characteristic of **Neisseria gonorrhoeae**. - **Thayer-Martin agar** is a selective medium specifically formulated for the isolation of *Neisseria gonorrhoeae* from specimens containing flora. *MacConkey agar* - **MacConkey agar** is a selective and differential medium used primarily for the isolation of Gram-negative **enteric bacilli** and differentiation based on lactose fermentation. - It is not suitable for *Neisseria* species, which are fastidious organisms requiring enriched media. *Chocolate agar* - **Chocolate agar** is an enriched, non-selective medium that supports the growth of fastidious organisms like *Neisseria* species and *Haemophilus influenzae*. - While *Neisseria gonorrhoeae* grows on chocolate agar, **Thayer-Martin agar** is preferred for specimens from sites with normal flora as it inhibits contaminants. *TCBS agar* - **Thiosulfate Citrate Bile Salts Sucrose (TCBS) agar** is a selective medium used for the isolation of *Vibrio* species, particularly *Vibrio cholerae*. - This medium is completely unsuitable for the growth of *Neisseria gonorrhoeae*, which has entirely different nutritional and environmental requirements.

Q: A young boy who used to wash his contact lenses in tap water or with unhygienic lens fluid developed keratitis. Microscopy revealed an organism with spiked or star-shaped structures. Identify the correct organism responsible.

Acanthamoeba. ***Acanthamoeba*** - *Acanthamoeba* is a **free-living amoeba** found in water, soil, and inadequately disinfected contact lens solutions, specifically linked to **keratitis** in contact lens wearers. - Its characteristic morphology, often described as having **spiked or star-shaped structures**, refers to the **acanthopodia** (spine-like pseudopods) that are distinctive features visible microscopically. *Balantidium* - *Balantidium coli* is a **ciliated protozoan** and primarily causes **intestinal infections** (balantidiasis), not keratitis. - It would be distinguished microscopically by its **large size**, **kidney-shaped macronucleus**, and **cilia**, not spiked structures. *Pseudomonas* - *Pseudomonas aeruginosa* is a **bacterium** and a common cause of **bacterial keratitis**, especially in contact lens wearers, but it is not a protozoan. - Microscopically, it would appear as **rod-shaped bacteria**, not organisms with spiked or star-shaped structures. *Staphylococcus aureus* - *Staphylococcus aureus* is a **bacterium** and a frequent cause of various infections, including **bacterial keratitis**. - Under a microscope, it presents as **Gram-positive cocci in clusters**, not as an amoeba with spiked or star-shaped protrusions.

Q: A patient in the ICU with a central venous catheter (CVC) develops an infection. Microscopy reveals ovoid budding yeast cells. What is the most likely organism?

Candida. ***Candida*** - **Gram-positive ovoid budding organisms** are characteristic findings for yeast, with **Candida** species being the most common cause of CVC-related fungal infections in ICU patients. - Patients with CVCs are at high risk for candidemia due to compromised skin barriers and often receiving broad-spectrum antibiotics, which can disrupt the normal flora. *Staphylococcus epidermidis* - This is a **Gram-positive coccus** that grows in clusters and is a common cause of CVC-related **bacterial infections**, developing **biofilms** on catheters. - It does not present as an ovoid budding organism on microscopy. *Escherichia coli* - This is a **Gram-negative rod**, typically associated with **urinary tract infections** and sepsis from an abdominal source. - It would not appear as a Gram-positive ovoid budding organism and is not a common cause of primary CVC-related bloodstream infections unless there's an associated abdominal source. *Staphylococcus aureus* - This is a **Gram-positive coccus** that grows in grape-like clusters and can cause severe CVC-related bloodstream infections, often leading to **endocarditis** or widespread dissemination. - Like *S. epidermidis*, it is a bacterium and does not exhibit ovoid budding.

Q: 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?

Nocardia. ***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.

Q: The image shows microscopic organisms. What is the most appropriate description of these organisms?

Bacteria. ***Unicellular bacteria*** - The image depicts **bacteria**, which are by definition unicellular prokaryotic microorganisms - Bacteria exhibit varied morphologies (cocci, bacilli, spirilla) which can be visualized under microscopy - This is the most appropriate description among the given options for microscopic bacterial forms *Wall contains silica and chlorophyll* - Silica cell walls are characteristic of **diatoms** (photosynthetic protists), not bacteria - Bacteria have peptidoglycan cell walls, not silica - While some bacteria contain pigments, they do not contain chlorophyll in the same form as eukaryotic organisms *Present only in bone marrow* - This statement is anatomically incorrect for bacteria - Bacteria are ubiquitous and can be found in virtually all environments - Bone marrow primarily contains hematopoietic cells, not bacteria in normal conditions *Not resistant to acid* - This is not a defining characteristic that can be determined from microscopic appearance alone - Many bacteria (e.g., *Mycobacterium tuberculosis*) are **acid-fast** and highly resistant to acid - Acid resistance varies among different bacterial species and requires specific staining (Ziehl-Neelsen) to determine

Q: A patient is a known case of thalassemia. Which of the following viruses would be responsible for attacking progenitor cells and causing aplastic anemia?

Parvovirus B19. ***Parvovirus B19*** - **Parvovirus B19** specifically targets and replicates in **erythroid progenitor cells** in the bone marrow, leading to a temporary halt in red blood cell production [1]. - In patients with chronic hemolytic anemias like **thalassemia**, who already have increased erythropoietic demands, this can precipitate an **aplastic crisis** or pure red cell aplasia [1], [2]. *CMV (Cytomegalovirus)* - While CMV can affect the bone marrow and lead to myelosuppression, it does not typically cause a direct **aplastic crisis** by targeting erythroid progenitors in the same way as Parvovirus B19. - CMV often presents with a wider range of symptoms including fever, hepatitis, and mononucleosis-like syndrome, and bone marrow suppression is usually multi-lineage or less severe. *EBV (Epstein-Barr Virus)* - EBV is known to cause infectious mononucleosis and can also be associated with some bone marrow disorders, but it does not primarily target **erythroid progenitor cells** to cause an aplastic crisis. - Its main target cells are **B lymphocytes**, and any bone marrow suppression is often secondary to immune dysregulation rather than direct lytic infection of stem cells. *Hepatitis C virus (HCV)* - HCV infection can lead to various hematologic manifestations, including aplastic anemia, but these are typically **immune-mediated** or associated with chronic liver disease and its complications. - HCV does not directly infect and destroy **hematopoietic progenitor cells** in the bone marrow as a primary mechanism of aplastic anemia.

Q: A 27-year-old patient presents with motheaten alopecia, moist perianal lesions, and an asymptomatic macular rash. What is the most likely causative organism?

Treponema. ***Treponema*** - The constellation of **motheaten alopecia**, **moist perianal lesions** (condyloma lata), and an **asymptomatic macular rash** is highly characteristic of **secondary syphilis**, caused by *Treponema pallidum*. - **Condyloma lata** are highly infectious, raised plaques found in moist areas, and the rash can affect palms and soles. *Haemophilus* - *Haemophilus influenzae* is primarily associated with **respiratory infections** (e.g., otitis media, epiglottitis, pneumonia) and sometimes meningitis. - It does not cause the specific dermatological manifestations described in the patient. *Klebsiella* - *Klebsiella pneumoniae* is a common cause of **nosocomial infections**, particularly **pneumonia** (often with currant jelly sputum), **UTIs**, and wound infections. - It is not associated with skin conditions like alopecia or maculopapular rashes typical of syphilis. *Herpes Simplex* - Herpes Simplex Virus (HSV) causes **vesicular or ulcerative lesions**, commonly known as cold sores or genital herpes. - It does not cause motheaten alopecia, moist perianal plaques (condyloma lata), or an asymptomatic macular rash in the same manner as syphilis.

Q: A patient presents with sinus tracts on the foot, and a smear reveals filamentous organisms.

Nocardia. ***Correct: Nocardia*** - **Nocardia species** cause **actinomycetoma**, a chronic infection characterized by **sinus tracts** discharging purulent material with sulfur granules - Smear shows **branching filamentous organisms** that are gram-positive and partially acid-fast - Classic presentation: sinus tracts on foot with filamentous organisms on direct microscopy - Key features: aerobic actinomycetes, branching at acute angles (45°) *Incorrect: Sporothrix* - Causes **sporotrichosis** (lymphocutaneous nodules along lymphatics), not sinus tracts - **Dimorphic fungus** diagnosed primarily by culture, not direct smear - Clinical presentation: nodular lesions following trauma (rose gardener's disease) - Does not show filamentous organisms on direct smear *Incorrect: Dermatophytes* - Cause **superficial infections** of skin, hair, and nails (tinea pedis, ringworm) - Do not form **deep sinus tracts** or involve subcutaneous tissue - Microscopy shows septate hyphae in skin scrapings, not in discharge from sinus tracts - Clinical presentation completely different from actinomycetoma *Incorrect: Candida* - **Yeast** causing mucocutaneous infections (thrush, vaginitis) or systemic candidiasis - Does not cause **sinus tracts** on the foot - Microscopy reveals **budding yeasts and pseudohyphae**, not true branching filaments - Not associated with actinomycetoma-type presentations

Q: A female presents with dysuria and vaginal discharge. Wet mount examination shows pear-shaped organisms. What is the most likely diagnosis?

Trichomonas. ***Trichomonas*** - The presence of **dysuria**, **vaginal discharge**, and **pear-shaped organisms** on wet mount examination is classic for **Trichomonas vaginalis** infection. - **Microscopic identification of motile trichomonads** confirms the diagnosis. *Candida* - **Candida** infections typically present with **thick, white, curd-like vaginal discharge**, and a wet mount would show **yeast buds or pseudohyphae**, not pear-shaped organisms. - While it can cause dysuria, the discharge characteristics and microscopy findings differentiate it. *Chlamydia* - **Chlamydia trachomatis** causes **mucopurulent cervicitis** with dysuria and vaginal discharge, but requires **specific diagnostic tests** such as **NAAT (nucleic acid amplification test)** or cell culture for diagnosis. - Wet mount examination would **not show pear-shaped organisms**; instead, it may show increased white blood cells but no specific pathogen visualization. *Bacterial vaginosis* - **Bacterial vaginosis** is characterized by a **thin, gray discharge** and a **"fishy" odor**, which is especially noticeable after intercourse. - Wet mount shows **clue cells** (vaginal epithelial cells studded with bacteria), not pear-shaped organisms, and **absent or few white blood cells**.

Q: A patient presents with genital grouped vesicles, as shown in the image. What is the most likely causative organism?

Herpes simplex virus. ***Herpes*** - The image shows **grouped vesicles** on an erythematous base, which is the classic presentation of **genital herpes** caused by the **Herpes simplex virus (HSV)**. - These lesions are typically painful and can recur, indicating a viral etiology. *Haemophilus* - *Haemophilus ducreyi* causes **chancroid**, which presents as **painful genital ulcers** with ragged borders and often associated with inguinal lymphadenopathy. - It does not present as grouped vesicles. *Klebsiella* - *Klebsiella granulomatis* causes **donovanosis (granuloma inguinale)**, characterized by progressive, **painless ulcerative lesions** that are highly vascular and bleed easily. - This organism does not cause vesicular lesions. *Treponema* - *Treponema pallidum* causes **syphilis**, which in its primary stage presents as a **painless chancre** (a solitary ulcer) or in secondary stage as a diffuse rash. - It does not cause grouped vesicles.

Question 1

A man presents with dysuria and urethral discharge after a history of unprotected sex. The Gram stain of his discharge is shown. What is the best culture medium for isolating the organism responsible?

Accepted Answer

Thayer-Martin agar

Answer

MacConkey agar

Answer

Chocolate agar

Answer

TCBS agar

Question 2

A young boy who used to wash his contact lenses in tap water or with unhygienic lens fluid developed keratitis. Microscopy revealed an organism with spiked or star-shaped structures. Identify the correct organism responsible.

Accepted Answer

Acanthamoeba

Answer

Balantidium

Answer

Pseudomonas

Answer

Staphylococcus aureus

Question 3

A patient in the ICU with a central venous catheter (CVC) develops an infection. Microscopy reveals ovoid budding yeast cells. What is the most likely organism?

Accepted Answer

Candida

Answer

Staphylococcus epidermidis

Answer

Escherichia coli

Answer

Staphylococcus aureus

Question 4

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?

Accepted Answer

Nocardia

Answer

Staphylococcus aureus

Answer

Histoplasma

Answer

Sporothrix

Question 5

The image shows microscopic organisms. What is the most appropriate description of these organisms?

Accepted Answer

Bacteria

Answer

Wall contains silica and chlorophyll

Answer

Present only in bone marrow

Answer

Not resistant to acid

Question 6

A patient is a known case of thalassemia. Which of the following viruses would be responsible for attacking progenitor cells and causing aplastic anemia?

Accepted Answer

Parvovirus B19

Answer

CMV (Cytomegalovirus)

Answer

EBV (Epstein-Barr Virus)

Answer

Hepatitis C virus (HCV)

Question 7

A 27-year-old patient presents with motheaten alopecia, moist perianal lesions, and an asymptomatic macular rash. What is the most likely causative organism?

Accepted Answer

Treponema

Answer

Haemophilus

Answer

Klebsiella

Answer

Herpes Simplex

Question 8

A patient presents with sinus tracts on the foot, and a smear reveals filamentous organisms.

Accepted Answer

Nocardia

Answer

Sporothrix

Answer

Dermatophytes

Answer

Candida

Question 9

A female presents with dysuria and vaginal discharge. Wet mount examination shows pear-shaped organisms. What is the most likely diagnosis?

Accepted Answer

Trichomonas

Answer

Candida

Answer

Chlamydia

Answer

Bacterial vaginosis

Question 10

A patient presents with genital grouped vesicles, as shown in the image. What is the most likely causative organism?

Accepted Answer

Herpes simplex virus

Answer

Haemophilus

Answer

Klebsiella

Answer

Treponema

NEET-PG 2024 — Microbiology