FMGE 2026 - Microbiology PYQs Practice Questions

Q: A patient presents with a painless ulcer over the leg with a characteristic black eschar at the center, as shown in the image. There is surrounding edema with minimal pain. Which of the following is the most likely causative organism?

Bacillus anthracis. ***Bacillus anthracis*** - Cutaneous anthrax typically presents as a **painless ulcerative lesion** with a pathognomonic **central black eschar** (necrotic scab). - The lesion is classically surrounded by **extensive edema** and an erythematous rim, with notably disproportionate lack of pain. *Staphylococcus aureus* - Commonly causes **furuncles**, **carbuncles**, or **cellulitis**, which are typically very painful and tender. - These infections typically result in **purulent discharge** and abscess formation rather than a dry, black necrotic eschar. *Clostridium perfringens* - Primarily associated with **gas gangrene**, which presents with crepitus, severe pain, and rapidly spreading tissue necrosis. - This condition is characterized by **foul-smelling exudate** and systemic toxicity, unlike the localized, relatively painless presentation of anthrax. *Rickettsia conorii* - Etiological agent of **Mediterranean Spotted Fever**, which typically presents with a **tache noire** (black spot) at the site of the tick bite, accompanied by fever and rash. - Unlike the isolated lesion of cutaneous anthrax, this is generally associated with a **triad of fever**, **rash**, and the **eschar**. [Practice more Microbiology PYQs on OnCourse]

Q: Which of the following mechanisms of genetic transfer is illustrated here?

Transduction. ***Transduction*** - Involves the transfer of bacterial DNA from one bacterium to another by a **bacteriophage** (bacterial virus) acting as a vector. - This can occur via **generalized transduction** (random segments of DNA packaged) or **specialized transduction** (specific genes near the phage integration site). *Transformation* - Involves the uptake of **naked or environmental DNA** by competent bacteria from the surrounding medium. - Does not require a vector or cell-to-cell contact and is historically demonstrated in **Streptococcus pneumoniae**. *Conjugation* - Requires **direct cell-to-cell contact** between bacteria, typically mediated by a **sex pilus** encoded by an **F-plasmid**. - Results in the unidirectional transfer of plasmid DNA or sometimes chromosomal DNA, often leading to rapid spread of **antibiotic resistance**. *Transposition* - Refers to the movement of **transposons** ('jumping genes') from one location to another within or between DNA molecules. - This is an **intracellular process** and does not act as a primary mechanism for horizontal gene transfer between distinct bacterial cells. [Practice more Microbiology PYQs on OnCourse]

Q: A patient presents with a painless genital ulcer followed by painful inguinal buboes (lymphadenopathy). Which strains of Chlamydia trachomatis are responsible for this condition?

L1–L3. ***L1–L3*** - These serovars of **Chlamydia trachomatis** are the causative agents of **lymphogranuloma venereum (LGV)**, a sexually transmitted infection. - The clinical presentation involves a transient, **painless genital ulcer** followed by the classic development of **painful inguinal lymphadenopathy** (buboes). *A, B, C* - These serovars are responsible for causing **trachoma**, a chronic keratoconjunctivitis that is the leading infectious cause of blindness worldwide. - They are typically transmitted via direct or indirect contact with eye, nose, or throat secretions rather than sexual contact. *D–K* - These strains cause common **sexually transmitted infections** including **urethritis**, **cervicitis**, and **pelvic inflammatory disease (PID)**. - They are the most frequent cause of bacterial sexually transmitted infections in developed countries but do not typically present with the pronounced **lymphadenopathy** seen in LGV. *B, C, D* - This grouping combines serovars associated with **trachoma** (B, C) and those causing **urogenital infections** (D), making it clinically incorrect. - There is no specific pathological entity associated with this collective group of **Chlamydia trachomatis** serovars. [Practice more Microbiology PYQs on OnCourse]

Q: Which of the following organisms is most likely responsible for this finding?

Candida albicans. ***Candida albicans*** - This organism is a common cause of **esophagitis** in immunocompromised patients, such as those with HIV or hematologic malignancies, often presenting with **white plaques (thrush)**. - Diagnosis is typically confirmed via endoscopy, which reveals **pseudomembranes** that can be scraped off, with biopsy showing **pseudohyphae** and **yeast cells**. *Aspergillus fumigatus* - Primarily causes **pulmonary disease**, such as **allergic bronchopulmonary aspergillosis (ABPA)** or **invasive aspergillosis** in neutropenic patients. - Histologically defined by **septate hyphae** with **acute-angle (45-degree) branching**. *Cryptococcus neoformans* - Primarily associated with **meningitis** in immunocompromised individuals, often presenting with subacute headache and altered mental status. - Typically identified by **india ink staining** of cerebrospinal fluid (CSF), showing **encapsulated yeast** with a **halo effect**. *Mucor species* - A highly aggressive fungal infection (mucormycosis) most commonly seen in patients with **diabetic ketoacidosis (DKA)**. - Characterized by **aseptate hyphae** with **wide-angle (90-degree) branching** and angioinvasion leading to tissue necrosis. [Practice more Microbiology PYQs on OnCourse]

Q: A patient develops acute flaccid paralysis after consuming improperly canned food the previous day. The illness is attributed to Clostridium botulinum toxin. What is the mode of transmission in this case?

Vehicle-borne transmission. ***Vehicle-borne transmission*** - Ingestion of food contaminated with **pre-formed toxins**, such as those produced by *Clostridium botulinum* in improperly canned food, is classified as a classic example of **vehicle-borne transmission**. - A vehicle is an inanimate intermediate (like food, water, or blood) that carries an infectious agent or toxin from a reservoir or source to a susceptible host. *Direct transmission* - This involves immediate transfer of an infectious agent via **person-to-person contact** (e.g., touching, kissing, or sexual intercourse). - Botulism is not contagious; therefore, it cannot be transmitted from an infected person to a susceptible person through direct contact. *Indirect transmission* - This implies mechanisms like **airborne transmission** of droplet nuclei or transmission via **fomites** (inanimate objects like bedding or doorknobs). - While the canned food is inanimate, the specific categorization where food or water serves as the contaminated medium is strictly defined as vehicle-borne, which is a more specific subset of indirect transmission. *Vector-borne transmission* - This requires a living intermediary, typically an **arthropod** (e.g., mosquitoes, ticks, or fleas), to mechanically or biologically transfer a pathogen. - *Clostridium botulinum* is a soil-dwelling bacterium that produces toxins in anaerobic environments like cans; it does not rely on insect vectors for dissemination. [Practice more Microbiology PYQs on OnCourse]

Question 1

A patient presents with a painless ulcer over the leg with a characteristic black eschar at the center, as shown in the image. There is surrounding edema with minimal pain. Which of the following is the most likely causative organism?

Accepted Answer

Bacillus anthracis

Answer

Staphylococcus aureus

Answer

Clostridium perfringens

Answer

Rickettsia conorii

Question 2

Which of the following mechanisms of genetic transfer is illustrated here?

Accepted Answer

Transduction

Answer

Transformation

Answer

Conjugation

Answer

Transposition

Question 3

A patient presents with a painless genital ulcer followed by painful inguinal buboes (lymphadenopathy). Which strains of Chlamydia trachomatis are responsible for this condition?

Accepted Answer

L1–L3

Answer

A, B, C

Answer

D–K

Answer

B, C, D

Question 4

Which of the following organisms is most likely responsible for this finding?

Accepted Answer

Candida albicans

Answer

Aspergillus fumigatus

Answer

Cryptococcus neoformans

Answer

Mucor species

Question 5

A patient develops acute flaccid paralysis after consuming improperly canned food the previous day. The illness is attributed to Clostridium botulinum toxin. What is the mode of transmission in this case?

Accepted Answer

Vehicle-borne transmission

Answer

Direct transmission

Answer

Indirect transmission

Answer

Vector-borne transmission

Question 6

A patient presents with fever, sore throat, cervical lymphadenopathy, and laboratory findings show atypical lymphocytes on peripheral blood smear. Which of the following is the most likely causative organism?

Accepted Answer

Epstein–Barr virus

Answer

Cytomegalovirus

Answer

Human herpesvirus -6

Answer

Adenovirus

Question 7

Which of the following organisms is most likely represented?

Accepted Answer

Mycoplasma

Answer

Chlamydia

Answer

Legionella

Answer

Ureaplasma

Question 8

The Paul-Bunnell test is primarily used for the diagnosis of:

Accepted Answer

Epstein-Barr Virus (Infectious Mononucleosis)

Answer

Cytomegalovirus infection

Answer

Herpes Simplex Virus infection

Answer

Rubella

Question 9

A 20 year old female presented with abdominal pain and passage of motile segments in the stool. She claims to have barbecue pork at her friends house. No other complaints. What is the most likely causative agent?

Accepted Answer

Taenia solium

Answer

H. nana

Answer

E. vermicularis

Answer

T. saginata

Question 10

How does Epstein –Barr virus (EBV) cause Burkitt’s lymphoma?

Accepted Answer

Chromosomal translocation

Answer

Primer insertion

Answer

Receptor insertion

Answer

Viral integration into host genome

FMGE 2026 — Microbiology