INI-CET 2026 - Microbiology PYQs Practice Questions

Q: The image shown depicts a piece of sterilization equipment. Which of the following statements regarding its sterilization properties is INCORRECT?

Prions are completely destroyed at 121°C for 15 minutes. ***Prions are completely destroyed at 121°C for 15 minutes*** - This statement is **incorrect** because **prions** are highly resistant to standard autoclaving protocols; they generally require more stringent methods such as **134°C** for 18 minutes in a pre-vacuum autoclave or specific chemical treatments like sodium hydroxide. - The standard cycle of **121°C for 15 minutes** is designed for vegetative bacteria, fungi, and viruses, but it is insufficient to denature the misfolded proteins associated with **prion diseases**. *It is a method of moist heat sterilization operating above 100°C* - The equipment shown is an **autoclave**, which utilizes **pressurized steam** to achieve temperatures significantly higher than the boiling point of water. - This elevated temperature effectively kills microorganisms through the **coagulation of cellular proteins** and enzymes, confirming the accuracy of this statement. *Bowie-Dick test positive* - While the test itself is designed to detect air leaks and ensure proper steam penetration for a successful cycle, saying [Practice more Microbiology PYQs on OnCourse]

Q: A 32-year-old woman with a history of splenectomy presents to the emergency department with sudden-onset high-grade fever, vomiting, hypotension, and rapidly progressive septic shock. Her symptoms began 2 weeks after a minor febrile illness. Which organism is the most likely causative agent of this life-threatening condition?

Streptococcus pneumoniae. ***Streptococcus pneumoniae*** - Patients with **asplenia** (post-splenectomy) are at significantly increased risk for overwhelming post-splenectomy infection (OPSI) due to defective clearance of **encapsulated organisms**. - *Streptococcus pneumoniae* is the most common cause of sepsis in asplenic patients, characterized by fulminant disease progression, high mortality rates, and rapid development of **septic shock**. *Escherichia coli* - While *Escherichia coli* is a common cause of sepsis (particularly urosepsis and intra-abdominal infections), it is not the classic pathogen associated with the unique susceptibility of the **asplenic patient**. - It lacks the specific capsular polysaccharide susceptibility profile that makes *S. pneumoniae* the primary concern in individuals without a functional **spleen**. *Staphylococcus aureus* - *Staphylococcus aureus* is a leading cause of skin and soft tissue infections, endocarditis, and osteomyelitis, but it is not typically characterized as an **encapsulated organism** that targets asplenic individuals. - The clinical presentation of rapid-onset septic shock following minor illness is more classic for the **fulminant course** of a pneumococcal infection in this specific patient demographic. *Pseudomonas aeruginosa* - *Pseudomonas aeruginosa* is an important cause of sepsis especially in **immunocompromised** or hospitalized patients, but it is not the most frequent pathogen associated with asplenia. - It generally presents in settings such as **ventilator-associated pneumonia**, burn wounds, or neutropenic fever, rather than the classic OPSI syndrome triggered by circulating **encapsulated bacteria**. [Practice more Microbiology PYQs on OnCourse]

Q: Which of the following reagents is used for the digestion and decontamination of a sputum sample collected for tuberculosis diagnosis?

NaOH with NALC. ***NaOH with NALC*** - **Sodium hydroxide (NaOH)** acts as a potent decontaminating agent that kills rapidly growing commensal flora present in the sputum, allowing for the selective growth of *Mycobacterium tuberculosis*. - **N-acetyl-L-cysteine (NALC)** serves as a mucolytic agent, digesting the sputum matrix and liquefying the sample so that the mycobacteria are released and can be concentrated via centrifugation. *HCl with NAC* - **Hydrochloric acid (HCl)** is not effectively used combined with NAC for primary sputum decontamination in standard **tuberculosis** culture protocols. - While acids can be used for decontamination, this specific combination is not the standard clinical reagent for *Mycobacterium tuberculosis* processing. *H2SO4 with NAC* - **Sulfuric acid (H2SO4)** is sometimes used in specific decontamination protocols (Petroff's method uses NaOH, but acid-based methods exist), but this is not the preferred or most common reagent pair known for this purpose. - Furthermore, **NAC** (N-acetylcysteine) is distinct from **NALC** (N-acetyl-L-cysteine), which is the standard, more effective mucolytic agent chosen for clinical lab processing. *HNO3 with NALC* - **Nitric acid (HNO3)** is a strong corrosive acid, not a standard reagent for the clinical decontamination of sputum samples for mycobacterial culture. - Using such a harsh chemical could risk killing the **mycobacteria** themselves, decreasing the sensitivity of the diagnostic test. [Practice more Microbiology PYQs on OnCourse]

Q: A patient presents with fever, headache, and neck stiffness suggestive of meningitis. CSF examination is performed, and Nigrosin stain reveals encapsulated budding yeast cells. Which of the following organisms is the most likely causative agent?

Cryptococcus neoformans. ***Cryptococcus neoformans*** - This organism is characterized as an **encapsulated budding yeast** that is classically identified in **cerebrospinal fluid (CSF)** using **India ink** or **Nigrosin stain**. - It is the most common cause of fungal meningitis, particularly in **immunocompromised patients** (e.g., those with AIDS), and the capsule appears as a clear halo against the dark background of the stain. *Aspergillus fumigatus* - This is a **mold** that typically presents as **septate hyphae** with acute-angle (45-degree) branching, not as budding yeast. - While it can invade the central nervous system, it usually causes **abscesses** or **vascular invasion** rather than the typical yeast-like presentation in CSF. *Pneumocystis jirovecii* - This organism is an **atypical fungus** that does not grow in culture and is typically identified in lung tissue or bronchoalveolar lavage fluid using **Methenamine silver stain**. - It classically causes **interstitial pneumonia** in immunocompromised hosts and does not typically infect the meninges as a budding yeast. *Histoplasma capsulatum* - This is a **dimorphic fungus** that exists as small, intracellular yeast forms within **macrophages** in host tissues. - It is typically identified via biopsy or antigen testing, not as an encapsulated yeast in the CSF, and usually presents with systemic symptoms like hepatosplenomegaly or pulmonary involvement. [Practice more Microbiology PYQs on OnCourse]

Question 1

The image shown depicts a piece of sterilization equipment. Which
of the following statements regarding its sterilization properties is
INCORRECT?

Accepted Answer

Prions are completely destroyed at 121°C for 15 minutes

Answer

It is a method of moist heat sterilization operating above 100°C

Answer

Bowie-Dick test positive

Answer

It is commonly used for sterilizing culture media

Question 2

A 32-year-old woman with a history of splenectomy presents to the emergency department with
sudden-onset high-grade fever, vomiting, hypotension, and rapidly progressive septic shock. Her
symptoms began 2 weeks after a minor febrile illness. Which organism is the most likely causative
agent of this life-threatening condition?

Accepted Answer

Streptococcus pneumoniae

Answer

Escherichia coli

Answer

Staphylococcus aureus

Answer

Pseudomonas aeruginosa

Question 3

Which of the following reagents is used for the digestion and decontamination of a sputum
sample collected for tuberculosis diagnosis?

Accepted Answer

NaOH with NALC

Answer

HCl with NAC

Answer

H2SO4 with NAC

Answer

HNO3 with NALC

Question 4

A patient presents with fever, headache, and neck stiffness suggestive of meningitis. CSF
examination is performed, and Nigrosin stain reveals encapsulated budding yeast cells. Which of
the following organisms is the most likely causative agent?

Accepted Answer

Cryptococcus neoformans

Answer

Aspergillus fumigatus

Answer

Pneumocystis jirovecii

Answer

Histoplasma capsulatum

Question 5

A female presents with high grade fever, diffuse erythematous rash and hypotension. She is
currently menstruating and using tampoons. The toxin responsible acts by?

Accepted Answer

Vbeta region of the T-cell receptor and MHC class II molecule

Answer

MHC class I molecule only

Answer

CD4 receptor only

Answer

B-cell receptor and IgG

Question 6

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 7

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 8

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 9

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 10

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

INI-CET 2026 — Microbiology