FMGE 2024 - Microbiology PYQs Practice Questions

Q: A patient presents with a history of watery diarrhea and vomiting. The pathogen exhibited darting motility. Which is the best selective media for the involved pathogen?

TCBS. ***Correct: TCBS*** - **Thiosulfate Citrate Bile Salts Sucrose (TCBS) agar** is the most widely used selective medium for isolating *Vibrio cholerae* and other *Vibrio* species from clinical and environmental samples - The clinical presentation of **watery diarrhea and vomiting** with **darting motility** is characteristic of *Vibrio cholerae* - *Vibrio cholerae* ferments **sucrose** in TCBS medium, producing **yellow colonies**, contrasting with the blue-green colonies of non-sucrose fermenters like *Vibrio parahaemolyticus* - The medium contains **bile salts** that inhibit most Gram-positive bacteria while allowing Vibrio species to grow *Incorrect: Nutrient media* - Nutrient media is a **general-purpose** medium that supports the growth of a wide variety of non-fastidious organisms, making it **non-selective** for *Vibrio* - It lacks the inhibitory agents (bile salts) and specific markers (sucrose) necessary for selective isolation and differentiation of *Vibrio* species *Incorrect: Cetrimide agar* - This medium is specifically selective for **Pseudomonas aeruginosa**, as cetrimide (a quaternary ammonium compound) inhibits the growth of most other bacteria - *Vibrio cholerae* would likely be inhibited or overgrown by other organisms on this medium, making it unsuitable for isolation *Incorrect: Potassium Tellurite Agar* - Potassium Tellurite Agar (McLeod's medium) is a selective medium primarily used for the isolation of **Corynebacterium diphtheriae** - The tellurite salt inhibits most other respiratory flora but does not specifically enhance or select for the growth of *Vibrio* species [Practice more Microbiology PYQs on OnCourse]

Q: Which of the following is the vector responsible for transmitting Orientia tsutsugamushi?

Mite. ***Mite***- *Orientia tsutsugamushi*, the causative agent of **scrub typhus**, is transmitted to humans by the bite of the **larval stage** (chiggers) of mites belonging to the Trombiculidae family, such as *Leptotrombidium deliense*. - Mites are crucial in the infectious cycle because they maintain the pathogen through **transovarial transmission**, acting as both the **vector** and the **reservoir**. *Tick* - Ticks are the vectors for other rickettsial diseases, most notably **Rocky Mountain spotted fever** (*Rickettsia rickettsii*) and tularaemia. - Tick-borne infections typically involve different reservoirs (e.g., small mammals, deer) and produce distinct clinical syndromes from scrub typhus. *Louse* - Lice (specifically the body louse) are the vectors for **epidemic typhus** (*Rickettsia prowazekii*) and trench fever. - Transmission of louse-borne pathogens involves scratching infectious feces into the skin, which is not the mechanism for *Orientia tsutsugamushi*. *Flea* - Fleas, particularly the oriental rat flea, transmit **murine typhus** (*Rickettsia typhi*) and **plague** (*Yersinia pestis*). - This type of vector is typically associated with peridomestic rodents, contrasting with the outdoor, vegetation-associated exposure risk characteristic of **scrub typhus**. [Practice more Microbiology PYQs on OnCourse]

Question 1

A patient presents with a history of watery diarrhea and vomiting. The pathogen exhibited darting motility. Which is the best selective media for the involved pathogen?

Accepted Answer

TCBS

Answer

Potassium Tellurite Agar

Answer

Cetrimide agar

Answer

Nutrient media

Question 2

Which of the following is the vector responsible for transmitting Orientia tsutsugamushi?

Accepted Answer

Mite

Answer

Flea

Answer

Tick

Answer

Louse

FMGE 2024 — Microbiology