FMGE 2025 - Microbiology PYQs Practice Questions

Q: Patient with HIV presenting with bouts of cough and fever. Which medium is appropriate for diagnosis?

Lowenstein-Jensen (LJ) medium. ***Lowenstein-Jensen (LJ) medium*** - This egg-based culture medium is the standard solid medium used globally for the isolation of **Mycobacterium tuberculosis**. - Given the patient's history of **HIV** and symptoms of cough and fever, **Pulmonary Tuberculosis (TB)** is the differential diagnosis most likely requiring this specialized medium. *Tinsdale media* - Tinsdale medium is specifically used for the primary isolation and identification of **Corynebacterium diphtheriae**. - The characteristic presentation of **diphtheria** (pseudomembrane, severe pharyngitis) differs significantly from the suspected chronic respiratory symptoms of TB. *MacConkey agar* - This is a selective and differential medium designed to isolate and differentiate **Gram-negative enteric bacilli** (e.g., *E. coli*, *Salmonella*). - It is completely inadequate for the isolation of the slow-growing, **acid-fast bacilli** characteristic of mycobacteria. *Loeffler serum slope (LSS)* - Loeffler serum slope is an enrichment medium primarily used to promote the growth and demonstration of characteristic morphology in **Corynebacterium diphtheriae**. - While sometimes used for initial inoculum, it is not the definitive medium required for the isolation of **Mycobacterium tuberculosis** due to its composition and intended purpose. [Practice more Microbiology PYQs on OnCourse]

Q: A firefighter was admitted with fever, cough, culture shown in the image reveals gram-negative, oxidase-positive bacilli. Colonies transilluminating while passing under UV light. Choose the correct agent.

Pseudomonas aeruginosa. ***Pseudomonas aeruginosa*** - This organism is a **gram-negative**, **oxidase-positive** bacillus, matching the description. The image shows growth with a characteristic green pigment (**pyocyanin** and **pyoverdin**). - The key identifier is the production of **pyoverdin**, a fluorescent siderophore, which causes the colonies to transilluminate under UV light. *Klebsiella* - *Klebsiella* is **oxidase-negative**, which rules it out based on the biochemical test results provided. - It typically produces large, **mucoid colonies** due to its prominent capsule and is a lactose fermenter, features not described here. *Staphylococcus aureus* - *Staphylococcus aureus* is a **gram-positive coccus**, not a gram-negative bacillus, making it incorrect based on the initial microscopy. - It is also **oxidase-negative** and characteristically forms opaque, often golden-yellow colonies, not greenish fluorescent ones. *Serratia* - *Serratia* is a gram-negative bacillus but is **oxidase-negative**, which is inconsistent with the findings. - Certain species like *Serratia marcescens* are known for producing a red pigment called **prodigiosin**, especially at room temperature, not a green fluorescent pigment. [Practice more Microbiology PYQs on OnCourse]

Q: A firefighter with fever and cough has a culture showing gram-negative, oxidase-positive bacilli with fluorescent colonies under UV light. Which of the following organisms is most likely causing the infection?

Pseudomonas aeruginosa. ***Pseudomonas aeruginosa***- This organism is a non-lactose fermenting, **Gram-negative bacillus** that is definitively **oxidase-positive**.- It characteristically produces the siderophore **pyoverdine**, which is fluorescent under UV light, confirming the most likely etiology.*Klebsiella*- *Klebsiella* species are **oxidase-negative** (**distinguishing factor**) and typically highly encapsulated, often causing consolidation in pneumonia.- They are also strong **lactose fermenters** and do not produce fluorescent pigments.*Staphylococcus aureus*- *S. aureus* is a **Gram-positive coccus** (stains purple) arranged in clusters, not a Gram-negative bacillus (stains pink).- It is non-motile, shows no fluorescence, and is identified by being coagulase and catalase positive.*Serratia*- *Serratia marcescens* is generally **oxidase-negative** (unlike the clinical finding) and belongs to the Enterobacteriaceae family.- Under room temperature, *Serratia* often produces a characteristic **red pigment** (**prodigiosin**), not a fluorescent pigment. [Practice more Microbiology PYQs on OnCourse]

Q: The toughness of bacterial cell walls is due to:

Peptidoglycan. ***Peptidoglycan***- This unique polymer forms a robust, mesh-like structural layer (the **murein layer**) that encases the bacteria, providing essential mechanical strength and rigidity to the cell wall. Its strong cross-links allow it to withstand extremely high internal **osmotic pressure**, preventing the cell from bursting (lysis). *Teichoic acid* - These are polymers found exclusively in **Gram-positive** bacteria, anchored either to the peptidoglycan or the plasma membrane (lipoteichoic acid). - They contribute to the cell wall's overall integrity, and act as antigens, but are not the primary element responsible for the physical **toughness**. *Lipopolysaccharides* - LPS molecules make up the outer leaflet of the **outer membrane** in **Gram-negative** bacteria. - They function primarily as an **endotoxin** (lipid A component) and an O-antigen, contributing to virulence and permeability, not the mechanical load-bearing structure. *Outer membrane* - This membrane is characteristic of **Gram-negative** bacteria and acts as a protective, selective barrier (excluding certain antibiotics and chemicals). - While providing protective resistance, the intrinsic mechanical **toughness** preventing osmotic lysis is conferred by the underlying **peptidoglycan** layer. [Practice more Microbiology PYQs on OnCourse]

Q: A group of students consumed fried rice in a restaurant. Six hours later, they start vomiting. What is the etiological agent?

Bacillus cereus. ***Bacillus cereus***- The short incubation period (1 to 6 hours) and the primary symptom being **vomiting** are highly characteristic of the **emetic-type** food poisoning caused by *B. cereus*. - The emetic form is typically associated with contaminated **cooked rice** (like fried rice) that has been improperly stored, allowing the bacteria to proliferate and produce the heat-stable toxin, **cereulide**. *Clostridium botulinum* - This bacterium causes **botulism**, a severe neuroparalytic syndrome (e.g., descending flaccid paralysis, diplopia), not typically an acute emetic gastroenteritis. - The incubation period for botulism is usually longer (12 to 36 hours), and it is most often linked to improperly canned or vacuum-packed foods. *Escherichia coli* - Diarrheagenic *E. coli* strains typically require a longer incubation period (usually 1 or more days) and cause symptoms dominated by **diarrhea** (either watery or bloody), with vomiting being a less prominent feature. - Common infectious sources are often fecally contaminated water or uncooked produce, rather than cooked and cooled rice. *Shigella dysentriae* - *S. dysentriae* causes **bacillary dysentery**, characterized by a longer incubation period (1 to 7 days) and symptoms including fever, severe abdominal cramping, and **bloody, mucoid stools** (dysentery). - While systemic symptoms might occur, the rapid onset of vomiting alone is not characteristic of Shigellosis. [Practice more Microbiology PYQs on OnCourse]

Question 1

Patient with HIV presenting with bouts of cough and fever. Which medium is appropriate for diagnosis?

Accepted Answer

Lowenstein-Jensen (LJ) medium

Answer

MacConkey agar

Answer

Loeffler serum slope (LSS)

Answer

Tinsdale media

Question 2

A firefighter was admitted with fever, cough, culture shown in the image reveals gram-negative, oxidase-positive bacilli. Colonies transilluminating while passing under UV light. Choose the correct agent.

Accepted Answer

Pseudomonas aeruginosa

Answer

Staphylococcus aureus

Answer

Serratia

Answer

Klebsiella

Question 3

A firefighter with fever and cough has a culture showing gram-negative, oxidase-positive bacilli with fluorescent colonies under UV light. Which of the following organisms is most likely causing the infection?

Accepted Answer

Pseudomonas aeruginosa

Answer

Staphylococcus aureus

Answer

Serratia

Answer

Klebsiella

Question 4

The toughness of bacterial cell walls is due to:

Accepted Answer

Peptidoglycan

Answer

Teichoic acid

Answer

Lipopolysaccharides

Answer

Outer membrane

Question 5

A group of students consumed fried rice in a restaurant. Six hours later, they start vomiting. What is the etiological agent?

Accepted Answer

Bacillus cereus

Answer

Clostridium botulinum

Answer

Shigella dysentriae

Answer

Escherichia coli

Question 6

A 70-year-old man with a prosthetic valve was admitted with a murmur and blood culture positive for Gram-positive cocci. Choose the most common agent causing prosthetic valve infective endocarditis.

Accepted Answer

Staphylococcus epidermidis

Answer

Staphylococcus aureus

Answer

Streptococcus viridans

Answer

Enterococci

Question 7

A patient’s laboratory results were positive for malarial antigen, and the Widal test findings were as follows: O ag >1:300, H ag >1:20, A >1:20, B >1:20. What is the most likely diagnosis?

Accepted Answer

Recent infection by Salmonella spp

Answer

Past infection

Answer

Patient has taken TAB vaccine

Answer

Convalescence

Question 8

A patient's sample is positive for infectious Hepatitis B. Choose the correct serological marker combination for this condition.

Accepted Answer

HBsAg + HBeAg

Answer

HBcAg

Answer

HBeAg

Answer

HBs + Anti Hbe

Question 9

Which of the following is the culture medium used for tuberculosis?

Accepted Answer

LJ medium

Answer

Chocolate agar

Answer

MacConkey medium

Answer

Blood agar

Question 10

What is the most common causative organism of prosthetic heart valve endocarditis?

Accepted Answer

S. epidermidis

Answer

S. aureus

Answer

S. viridans

Answer

Enterococcus

FMGE 2025 — Microbiology