NEET-PG 2024 Practice Questions

Q: What is the primary function of IL-8?

Chemotaxis. ***Chemotaxis*** - **IL-8** (also known as **CXCL8**) is a potent **chemokine** that primarily functions to recruit and activate **neutrophils** to sites of inflammation. - It guides these immune cells by forming a chemical gradient, allowing them to extravasate from blood vessels and migrate to the infected or injured tissue. *Lymphocyte proliferation* - Lymphocyte proliferation is primarily stimulated by **IL-2**, which acts as a growth factor for T cells. - While IL-8 contributes to the inflammatory environment, its direct role in inducing lymphocyte cell division is minor compared to its chemotactic function. *TH1 activation* - **TH1 cell activation** is mainly driven by **IL-12** and **IFN-γ**, which promote the differentiation and function of T helper 1 cells, crucial for fighting intracellular pathogens. - IL-8's role is unrelated to guiding TH1 cell differentiation. *Fever* - Fever is primarily induced by **pyrogenic cytokines** such as **IL-1**, **IL-6**, and **TNF-α**, which act on the hypothalamus to raise body temperature. - While IL-8 is part of the inflammatory response that can sometimes coincide with fever, it does not directly act as a pyrogen. *B cell activation* - **B cell activation** and differentiation are primarily regulated by interleukins such as **IL-4**, **IL-5**, **IL-6**, and **IL-21**, which promote antibody production and class switching. - IL-8 does not play a significant role in B cell function; its action is focused on innate immunity, particularly neutrophil recruitment.

Q: A patient from Bihar is admitted with splenomegaly and clinical features suggestive of leishmaniasis. What is the vector responsible for transmitting this disease?

Phlebotomus. ***Phlebotomus*** - **Phlebotomus** (sandfly), specifically ***Phlebotomus argentipes*** in India, is the principal vector for transmitting **Leishmania donovani** parasites causing **visceral leishmaniasis (kala-azar)**. - Bihar is a highly endemic region for kala-azar in India. - The sandfly transmits the parasite when it takes a blood meal from an infected host and then bites an uninfected individual. *Rat flea* - The **rat flea** (**Xenopsylla cheopis**) is the primary vector for diseases like **bubonic plague** and **murine typhus**, not leishmaniasis. - It transmits bacteria such as *Yersinia pestis* and *Rickettsia typhi*. *Black fly* - **Black flies** (**Simulium species**) are vectors for **onchocerciasis** (river blindness), caused by the parasitic worm *Onchocerca volvulus*. - They transmit the microfilariae when biting humans. *Chrysops fly* - The **Chrysops fly** (deer fly or mango fly) is the vector for **Loa loa filariasis** (African eye worm). - It transmits *Loa loa* eyeworm larvae when it bites humans.

Q: A patient living with HIV presents with foulsmelling stools. Microscopic examination of the stool reveals no cysts or ova, but a 200-micrometer larva is observed. What is the most likely pathogen?

Strongyloides stercoralis. ***Strongyloides stercoralis*** - The presence of **larvae** in the stool [2], particularly **rhabditiform larvae**, is characteristic of *Strongyloides stercoralis* infection, as this parasite has an **autoinfective cycle** involving larval stages in the human host [2]. - In HIV-positive patients, *Strongyloides* can cause **hyperinfection syndrome**, leading to severe gastrointestinal symptoms like foul-smelling stools, and increased larval shedding [2]. *Ascaris lumbricoides* - *Ascaris lumbricoides* is a large intestinal nematode, but it typically presents with **ova** (eggs) in the stool, not larvae, as the eggs hatch in the small intestine. - While it can cause gastrointestinal symptoms, the hallmark microscopic finding in stool samples is the presence of **mammillated or decorticated eggs**. *Ancylostoma duodenale* - *Ancylostoma duodenale* (hookworm) infections are identified by the presence of **eggs** in the stool [1], which are typically oval with a thin shell and contain a developing larva. - Hookworm larvae usually develop in **soil** and infect humans through skin penetration, rather than being commonly found in stool samples from intestinal infection [1]. *Schistosoma mansoni* - *Schistosoma mansoni* is a **blood fluke** that causes intestinal schistosomiasis, characterized by the presence of **spined eggs** in the stool. - The parasite's life cycle involves **freshwater snails** as intermediate hosts, and a **larval stage (cercariae)** that penetrates human skin, but larvae are not typically found in human stool.

Q: A patient was diagnosed with Escherichia coli O157:H7 infection. In this designation, what does the "H" stand for?

Flagella. **Flagella** - The "H" in bacterial designations like *Escherichia coli* O157:H7 refers to the **H antigen**, which is associated with bacterial **flagella**. - Flagellar antigens are important for serotyping bacteria, identifying different strains based on their unique flagellar protein compositions. *Lipopolysaccharide (LPS)* - The "O" in bacterial designations like *E. coli* O157 refers to the **O antigen**, which is part of the **lipopolysaccharide (LPS)** layer on the outer membrane of Gram-negative bacteria. - LPS is a major component of the bacterial outer membrane and acts as an **endotoxin**. *Capsule* - The "K" in some bacterial serotypes (e.g., *Klebsiella pneumoniae* K1) refers to the **K antigen**, which is associated with the **capsule**. - The capsule is a protective layer surrounding some bacteria that helps them evade phagocytosis. *Fimbriae* - **Fimbriae** (also known as pili) are short, hair-like appendages on the surface of some bacteria that aid in **adhesion** to host cells. - While fimbriae have their own antigenic properties, they are not typically designated by the "H" prefix in standard serotyping, which specifically refers to flagellar antigens.

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: Which PCR technique is best suited for identifying a syndrome with multiple causative agents?

Multiplex PCR. ***Multiplex PCR*** - **Multiplex PCR** allows for the simultaneous amplification of **multiple DNA targets** in a single reaction, making it ideal for identifying syndromes with numerous potential causative agents. - This method uses **multiple primer pairs** in one reaction tube, each designed to amplify a specific target sequence, thus efficiently detecting various pathogens or genetic markers. *RT-PCR* - **Reverse Transcription PCR (RT-PCR)** is used to detect **RNA targets** by first converting RNA into cDNA, which is then amplified. - While useful for RNA viruses or gene expression studies, it is not primarily designed for simultaneous detection of multiple diverse causative agents in the same way as multiplex PCR. *Nested PCR* - **Nested PCR** uses two sets of primers in sequential reactions to **increase sensitivity and specificity** by reducing non-specific binding. - This technique is generally employed to detect very low copies of a specific target or to overcome issues with non-specific amplification, rather than for identifying multiple different agents concurrently. *Conventional PCR* - **Conventional PCR** amplifies a **single specific DNA target** using one pair of primers per reaction. [1] - It requires separate reactions for each potential causative agent, making it inefficient and labor-intensive when testing for a syndrome with multiple etiologies. **References:** [1] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. (Basic Pathology) introduces the student to key general principles of pathology, both as a medical science and as a clinical activity with a vital role in patient care. Part 2 (Disease Mechanisms) provides fundamental knowledge about the cellular and molecular processes involved in diseases, providing the rationale for their treatment. Part 3 (Systematic Pathology) deals in detail with specific diseases, with emphasis on the clinically important aspects., pp. 56-57.

Q: A 2 year old child came with watery diarrhea. Electron Microscopy (EM) Image is shown here. Choose the correct pathogen.

Rota virus. ***Rota virus*** - The electron micrograph shows **double-layered viral particles** with a distinct wheel-like appearance, characteristic of **Rotavirus**, a major cause of severe watery diarrhea in young children. - Rotavirus is the most common cause of **severe dehydrating diarrhea** in infants and young children worldwide. *Norwalk virus* - Norwalk virus (now commonly referred to as **Norovirus**) particles are typically **smaller** and have an **amorphous** or indistinct surface morphology compared to the clearly structured Rotavirus. - Norovirus causes acute gastroenteritis but its electron microscopic appearance is less distinct and lacks the double-shelled structure seen here. *Adenovirus* - Adenoviruses are **larger, non-enveloped DNA viruses** with a distinct **icosahedral capsid** structure, often appearing hexagonal or pentagonal with prominent 'spikes' at the vertices. - While adenoviruses can cause gastroenteritis, their EM appearance is easily distinguishable from the image provided. *Astrovirus* - Astroviruses are **small, non-enveloped RNA viruses** that appear as **smooth-surfaced, star-shaped particles** on electron microscopy (hence the name "astro"). - They cause gastroenteritis in young children but lack the characteristic double-layered wheel-like structure of rotavirus. *ECHO virus* - ECHO viruses (Enteric Cytopathic Human Orphan viruses) are **picornaviruses**, which are very **small, non-enveloped RNA viruses** with an icosahedral shape. - Their EM image would show much smaller, less complex particles without the characteristic double-layered structure of rotavirus.

Question 1

What is the primary function of IL-8?

Accepted Answer

Chemotaxis

Answer

Lymphocyte proliferation

Answer

TH1 activation

Answer

Fever

Answer

B cell activation

Question 2

A patient from Bihar is admitted with splenomegaly and clinical features suggestive of leishmaniasis. What is the vector responsible for transmitting this disease?

Accepted Answer

Phlebotomus

Answer

Rat flea

Answer

Black fly

Answer

Chrysops fly

Question 3

A patient living with HIV presents with foulsmelling stools. Microscopic examination of the stool reveals no cysts or ova, but a 200-micrometer larva is observed. What is the most likely pathogen?

Accepted Answer

Strongyloides stercoralis

Answer

Ascaris lumbricoides

Answer

Ancylostoma duodenale

Answer

Schistosoma mansoni

Question 4

A patient was diagnosed with Escherichia coli O157:H7 infection. In this designation, what does the "H" stand for?

Accepted Answer

Flagella

Answer

Lipopolysaccharide (LPS)

Answer

Capsule

Answer

Fimbriae

Question 5

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 6

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 7

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 8

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 9

Which PCR technique is best suited for identifying a syndrome with multiple causative agents?

Accepted Answer

Multiplex PCR

Answer

RT-PCR

Answer

Nested PCR

Answer

Conventional PCR

Question 10

A 2 year old child came with watery diarrhea. Electron Microscopy (EM) Image is shown here. Choose the correct pathogen.

Accepted Answer

Rota virus

Answer

Norwalk virus

Answer

Adenovirus

Answer

ECHO virus

Answer

Astrovirus

NEET-PG 2024

Biochemistry

Community Medicine

Internal Medicine

Microbiology

Pathology

Pediatrics