INI-CET 2026 Practice Questions

Q: Which of the following statements are true about diphtheria toxin? A. It inhibits EF-2 B. It is an A-B type exotoxin C. It has particular affinity for myocardial and nervous tissue D. Toxin is produced only by strains carrying a plasmid Choose the correct answer:

A, B and C. ***A, B and C*** - Diphtheria toxin acts by **ADP-ribosylation of Elongation Factor-2 (EF-2)**, which halts protein synthesis and leads to cell death. - It is classified as an **A-B exotoxin**, where the 'B' subunit facilitates binding to host cell receptors and the 'A' subunit possesses the enzymatic activity; furthermore, it demonstrates organ-specific toxicity with a high affinity for **cardiac muscle** (causing myocarditis) and **nerve cells** (causing demyelination and polyneuritis). *A and C* - While this statement correctly identifies that the toxin inhibits EF-2 and affects heart/nerves, it is incomplete because it omits the important classification of the toxin structure as an **A-B exotoxin**. - A comprehensive answer must include the structural mechanism, which is a fundamental characteristic of *Corynebacterium diphtheriae* pathogenicity. *All are correct* - This option is incorrect because the toxin production is not determined by a plasmid, but rather by a **lysogenic bacteriophage (beta-phage)**. - The *tox* gene is integrated into the bacterial chromosome via this bacteriophage, which is required for the bacteria to produce exotoxin. *B and D* - This option incorrectly identifies the genetic source of toxin production; as noted, the toxin is encoded by a **lysogenic beta-phage**, not a plasmid. - While it correctly acknowledges the **A-B exotoxin** structure, it fails to include the mechanism of action (EF-2 inhibition) and the specific organ affinity, which are critical features.

Q: The virulence of Bacillus anthracis is mediated by two key plasmid-encoded factors. Which of the following is the correct biochemical composition?

pXO1 poly-D-glutamate capsule. ***pXO2–encoded poly-D-glutamate capsule and pXO1-encoded anthrax toxin*** - The virulence of *Bacillus anthracis* depends on two main plasmids: **pXO1**, which encodes the **three-part exotoxin** (lethal factor, edema factor, and protective antigen), and **pXO2**, which encodes the **poly-D-glutamate capsule**. - The **poly-D-glutamate capsule** is unique among bacteria because it is polypeptide-based rather than polysaccharide-based, which helps the organism evade **phagocytosis**. *pXO1 polysaccharide capsule* - The **capsule** of *Bacillus anthracis* is encoded by the **pXO2 plasmid**, not pXO1. - The capsule is biochemically composed of **poly-D-glutamic acid** (a polypeptide), not carbohydrates or polysaccharides. *pXO2 polysaccharide capsule* - While the **pXO2 plasmid** is correctly identified as the carrier for the capsule genes, the biochemical composition is incorrect. - The capsule is a **polypeptide** (poly-D-glutamate), providing protection against host immune surveillance. *pXO2 poly-D-glutamate capsule and pXO1 exotoxin* - Note: The option provided in the list (pXO2 poly-D-glutamate capsule) is biologically accurate in its description of the capsule, but the question asks for the complete biochemical composition implied by the plasmids listed. - This choice is an incorrect distracter based on the specific mapping of plasmid functions; **pXO1 carries toxins** (lethal factor, edema factor, and protective antigen) while **pXO2 carries the capsule** genes.

Q: A 38-year-old man with advanced HIV infection (CD4 count: 60 cells/mm³) presents with chronic watery diarrhea for 2 months, significant weight loss, intermittent fever, and fatigue. Colonoscopy is performed, and biopsy from the colonic mucosa demonstrates trophozoites with RBCs. What is the most likely causative organism?

Entamoeba histolytica. ***Entamoeba histolytica*** - The presence of **trophozoites with ingested RBCs** (erythrophagocytosis) in a colonic biopsy is pathognomonic for **amoebiasis** caused by *Entamoeba histolytica*. - This organism can invade the colonic mucosa, leading to **flask-shaped ulcers**, bloody diarrhea, and systemic symptoms, even in immunocompromised patients. *Giardia lamblia* - Typically causes **malabsorption** and fatty, foul-smelling stools rather than bloody or mucus-filled diarrhea. - Biopsy or stool examination would reveal **pear-shaped trophozoites** with two nuclei, but it does not ingest RBCs. *Cryptococcus neoformans* - Primarily presents as a fungal pneumonia or **meningoencephalitis** in patients with advanced HIV/AIDS. - While it can be disseminated, it does not typically cause primary colonic mucosal disease characterized by trophozoites. *Cryptosporidium parvum* - A very common cause of **chronic secretory diarrhea** in severely immunocompromised patients (CD4 < 100). - Diagnosis is made via **acid-fast staining** of stool, showing small oocysts, not invasive trophozoites with erythrophagocytosis.

Q: Which of the following bacteria possesses two circular DNA molecules (i.e., two distinct chromosomes) in its genome?

Vibrio cholerae. ***Vibrio cholerae*** - This pathogen is unique among many bacteria because its genome is organized into **two distinct circular chromosomes** (Chromosome 1 and Chromosome 2). - This multipartite genome structure is essential for its environmental adaptation and **virulence regulation**. *Escherichia coli* - The genome of this organism typically consists of a **single circular chromosome**. - While it may contain **extrachromosomal plasmids**, it does not possess multiple main chromosomes. *Salmonella typhi* - This bacterium has a genome organized as a **single circular chromosome**. - It is known for its ability to survive within **macrophages**, but this is not related to a multi-chromosome genome structure. *Shigella dysenteriae* - Its genome is characterized by a **single circular DNA molecule**. - Pathogenicity is primarily driven by the **Shiga toxin** and the **virulence plasmid** (pINV), not by having multiple chromosomes.

Q: A diabetic patient presents with facial pain, black nasal eschar and eye pain following corticosteroid therapy. What is the etiological agent?

Rhizopus. ***Rhizopus*** - This species belongs to the order Mucorales, the primary causative agents of **rhinocerebral mucormycosis** in immunocompromised hosts, especially in patients with **diabetic ketoacidosis**. - The clinical presentation of **facial pain**, **black nasal eschar** (due to tissue necrosis/infarction), and **eye pain** (orbital involvement) is the classic hallmark of this invasive fungal infection. *Candida tropicalis* - Typically causes **candidemia** or disseminated candidiasis in immunocompromised patients, but it does not classically present with necrotic nasal eschars. - It is a yeast, whereas the cause of this patient's condition is an **angioinvasive mold**. *Aspergillus fumigatus* - While it can cause sinusitis in immunocompromised patients, it typically presents with **allergic fungal sinusitis** or invasive disease without the classic black eschar. - It is characterized by **septate hyphae** with acute angle branching, differing from the broad, non-septate hyphae of Mucorales. *Cryptococcus neoformans* - Usually presents as **meningoencephalitis** or pulmonary infection, particularly in patients with advanced HIV/AIDS. - It is an encapsulated yeast and does not cause the rapid, destructive tissue necrosis associated with **black eschar** formation in the sinuses.

Q: Which of the following vasculitis is NOT classified as a medium-vessel disease?

Microscopic polyangiitis (MPA). ***Microscopic polyangiitis (MPA)*** - This condition is classified as a **small-vessel vasculitis** because it primarily affects capillaries, venules, and arterioles. - It is strongly associated with **p-ANCA** and typically presents as a pauci-immune necrotizing vasculitis without granulomatous inflammation. *Polyarteritis nodosa (PAN)* - This is a classic example of a **medium-vessel vasculitis** characterized by necrotizing inflammation of medium-sized muscular arteries. - It typically spares the **pulmonary circulation** and is often associated with **Hepatitis B** infection. *Buerger's disease (Thromboangiitis obliterans)* - This is considered a **medium-vessel vasculitis** (or sometimes small-to-medium) that affects the arteries and veins of the extremities. - It is strongly associated with **tobacco use** and leads to segmental, thrombotic, occlusive inflammation. *Kawasaki disease* - This is a well-known **medium-vessel vasculitis** affecting children, classically causing mucocutaneous lymph node syndrome. - A major clinical concern with this disease is the development of **coronary artery aneurysms** due to its affinity for medium-sized vessels.

Q: A 12-year-old presents with hypertension and hematuria. Serum C3 is raised. Renal biopsy shows subepithelial hump deposits on EM. What is the most likely diagnosis?

Post-streptococcal glomerulonephritis (PSGN). ***Post-streptococcal glomerulonephritis (PSGN)*** - The presentation of **hematuria** and **hypertension** in a child, combined with the classic **subepithelial humps** seen on electron microscopy, is pathognomonic for **PSGN**. - While typically associated with low C3, transient elevations can sometimes occur, or perhaps the prompt implies the classic finding of immune complex deposition; however, clinically, the **subepithelial humps** are the hallmark feature. *Goodpasture syndrome* - This condition involves **anti-glomerular basement membrane (anti-GBM) antibodies** targeting type IV collagen, typically presenting with **pulmonary hemorrhage** and **rapidly progressive glomerulonephritis**. - Renal biopsy classically shows **linear IgG deposition** on immunofluorescence rather than the **subepithelial humps** seen in PSGN. *Membranous glomerulonephritis* - This presents as **nephrotic syndrome** (not nephritic) and is characterized by **diffuse capillary wall thickening** and **subepithelial deposits** that form a 'spike and dome' pattern. - It is more common in adults and is frequently associated with conditions like **SLE**, **hepatitis B**, or **malignancy**. *Minimal change disease* - This is the most common cause of **nephrotic syndrome** in children, typically presenting with **edema** and severe proteinuria without hypertension or hematuria. - Renal biopsy shows normal light microscopy and **effacement of podocyte foot processes** on electron microscopy, with no deposits.

Q: A patient with long-standing chronic inflammatory disease develops systemic amyloidosis. Which amyloid protein subtype is characteristically deposited?

AA. ***AA amyloidosis*** - Occurs secondary to **chronic inflammatory conditions** (e.g., rheumatoid arthritis, osteomyelitis, inflammatory bowel disease) due to elevated levels of **serum amyloid A (SAA)** protein, an acute-phase reactant. - The SAA protein is synthesized by the liver and undergoes misfolding and deposition in tissues, typically affecting the **kidneys, spleen, and liver**. *ATTR amyloidosis* - This subtype is associated with **transthyretin (TTR)**, a protein produced in the liver that transports thyroxine and retinol binding protein. - It is predominantly linked to **familial amyloid polyneuropathy** or age-related systemic senile amyloidosis, rather than chronic inflammation. *Abeta2m amyloidosis* - Involves the deposition of **beta-2 microglobulin**, a component of the MHC class I molecule. - This subtype is characteristically seen in patients with **end-stage renal disease** who have undergone long-term **hemodialysis**, as the protein is not effectively filtered out. *AL amyloidosis* - Involves the deposition of **amyloid light chain** proteins derived from immunoglobulin light chains. - This is associated with **plasma cell dyscrasias**, such as **multiple myeloma**, rather than chronic inflammation.

Q: A patient presents with Hb 8 g/dL, MCV 62 fL, and low serum ferritin. Which type of anemia is most likely?

Iron deficiency anemia. ***Iron deficiency anemia*** - The combination of **microcytic anemia** (low MCV) and **low serum ferritin** is diagnostic for iron deficiency anemia, representing the body's depleted iron stores. - This is the most common cause of microcytic anemia, typically resulting from chronic blood loss, poor dietary intake, or malabsorption. *Sideroblastic anemia* - Characterized by inadequate utilization of iron for heme synthesis, usually leading to **high serum ferritin** and iron overload, rather than low, due to iron deposition in mitochondria. - Often shows **ringed sideroblasts** in the bone marrow, a classic feature that distinguishes it from iron deficiency. *Megaloblastic anemia* - Presents with **macrocytic anemia** (high MCV), not microcytic, due to impaired DNA synthesis (e.g., Vitamin B12 or folate deficiency). - The presence of **hypersegmented neutrophils** on a peripheral blood smear is a hallmark feature, which is not present in microcytic cases. *Aplastic anemia* - A **normocytic (or macrocytic)** anemia caused by bone marrow failure and pancytopenia, not typically microcytic. - Serum ferritin levels in aplastic anemia are usually **elevated** due to ineffective erythropoiesis and frequent blood transfusions.

Question 1

A young female presents with fatigue, pallor, and symptoms suggestive of iron deficiency
anemia. A microscopic image of her stool examination is provided. Which of the following
statements is correct regarding the parasite identified?

Accepted Answer

Infection occurs by active penetration of infective larvae through the skin

Answer

Infection occurs by ingestion of cysts in contaminated food or water

Answer

The image represents eggs of Enterobius vermicularis

Answer

The parasite shown is Ascaris lumbricoides

Question 2

Which of the following statements are true about diphtheria toxin?
A. It inhibits EF-2
B. It is an A-B type exotoxin
C. It has particular affinity for myocardial and nervous tissue
D. Toxin is produced only by strains carrying a plasmid
Choose the correct answer:

Accepted Answer

A, B and C

Answer

A and C

Answer

All are correct

Answer

B and D

Question 3

The virulence of Bacillus anthracis is mediated by two key plasmid-encoded factors. Which of
the following is the correct biochemical composition?

Accepted Answer

pXO1 poly-D-glutamate capsule

Answer

pXO1 polysaccharide capsule

Answer

pXO2 polysaccharide capsule

Answer

pXO2 poly-D-glutamate capsule

Question 4

A 38-year-old man with advanced HIV infection (CD4 count: 60 cells/mm³) presents with
chronic watery diarrhea for 2 months, significant weight loss, intermittent fever, and fatigue.
Colonoscopy is performed, and biopsy from the colonic mucosa demonstrates trophozoites with
RBCs. What is the most likely causative organism?

Accepted Answer

Entamoeba histolytica

Answer

Giardia lamblia

Answer

Cryptococcus neoformans

Answer

Cryptosporidium parvum

Question 5

Which of the following bacteria possesses two circular DNA molecules (i.e., two distinct
chromosomes) in its genome?

Accepted Answer

Vibrio cholerae

Answer

Escherichia coli

Answer

Salmonella typhi

Answer

Shigella dysenteriae

Question 6

A diabetic patient presents with facial pain, black nasal eschar and eye pain following
corticosteroid therapy. What is the etiological agent?

Accepted Answer

Rhizopus

Answer

Candida tropicalis

Answer

Aspergillus fumigatus

Answer

Cryptococcus neoformans

Question 7

Which of the following vasculitis is NOT classified as a medium-vessel disease?

Accepted Answer

Microscopic polyangiitis (MPA)

Answer

Polyarteritis nodosa (PAN)

Answer

Buerger's disease (Thromboangiitis obliterans)

Answer

Kawasaki disease

Question 8

A 12-year-old presents with hypertension and hematuria. Serum C3 is raised. Renal biopsy
shows subepithelial hump deposits on EM. What is the most likely diagnosis?

Accepted Answer

Post-streptococcal glomerulonephritis (PSGN)

Answer

Goodpasture syndrome

Answer

Membranous glomerulonephritis

Answer

Minimal change disease

Question 9

A patient with long-standing chronic inflammatory disease develops systemic amyloidosis.
Which amyloid protein subtype is characteristically deposited?

Accepted Answer

AA

Answer

ATTR

Answer

Abeta2m

Answer

AL

Question 10

A patient presents with Hb 8 g/dL, MCV 62 fL, and low serum ferritin. Which type of anemia is
most likely?

Accepted Answer

Iron deficiency anemia

Answer

Sideroblastic anemia

Answer

Megaloblastic anemia

Answer

Aplastic anemia

INI-CET 2026

Microbiology

Pathology