INI-CET 2021 - Microbiology PYQs Practice Questions

Q: A 32 year old laborer working at a construction site presented with fever and hemoptysis. The sputum sample collected for examination showed the following. The smear will be stained by which of the following sequences?

Carbol fuchsin - acid - alcohol- methylene blue. ***Carbol fuchsin - acid - alcohol- methylene blue*** - The image displays thin, red, rod-shaped bacteria against a blue background, characteristic of **acid-fast bacilli** stained using the **Ziehl-Neelsen (ZN) method**. This staining sequence identifies *Mycobacterium tuberculosis*. - The ZN stain involves **carbol fuchsin** as the primary stain, followed by **acid-alcohol** as a decolorizer, and then **methylene blue** as a counterstain. *Methylene blue- malachite green-acetic acid - water* - This sequence is not a standard microbiological staining procedure for identifying common pathogens or acid-fast bacteria. - It does not contain the necessary components to achieve **acid-fast staining**, which is crucial for identifying mycobacteria. *Gentian violet - iodine - alcohol saffranin* - This sequence describes the reagents used in a **Gram stain**, which differentiates bacteria based on their cell wall composition. - Gram staining would show either purple (Gram-positive) or pink (Gram-negative) bacteria, not the red acid-fast bacilli seen in the image. *Methanol - methylene blue-acid - water* - While methylene blue is a counterstain in ZN, this sequence is incomplete and incorrect for standard acid-fast staining or other common bacterial stains. - It lacks **carbol fuchsin** as the primary stain, which is essential for acid-fast bacteria to retain the stain after destaining. [Practice more Microbiology PYQs on OnCourse]

Q: Identify the organism from the life cycle shown in the image given below

Cryptosporidium. ***Cryptosporidium*** - This life cycle demonstrates **oocysts** being shed in feces and sporulating in the environment, which is characteristic of *Cryptosporidium*. - The infection of **intestinal cells** and the development of **trophozoites**, **schizonts**, and **gametes** within the same host also align with the *Cryptosporidium* life cycle. - *Cryptosporidium* oocysts are **immediately infective** upon shedding and contain **four sporozoites** without sporocysts. *Cystoisospora* - While *Cystoisospora* also produces **oocysts**, their oocysts contain **two sporocysts**, each with four sporozoites, whereas *Cryptosporidium* oocysts are immediately infective and contain **four sporozoites** upon shedding. - *Cystoisospora* typically involves a **monoxenous** life cycle (one host), but the distinct oocyst structure differentiates it from *Cryptosporidium*. *Plasmodium knowlesi* - *Plasmodium knowlesi* is a parasite responsible for **malaria** and its life cycle involves an **insect vector** (mosquito) and a **vertebrate host** (human or monkey). - The diagram shows a fecal-oral transmission route with **oocysts** and tissue cysts, which is not consistent with the **blood-borne transmission** and liver/blood stage development of *Plasmodium*. *Toxoplasma gondii* - *Toxoplasma gondii* has a complex life cycle with **definitive host** (cats) and **intermediate hosts** (humans, animals), producing **oocysts** in cat feces. - However, *Toxoplasma* oocysts contain **two sporocysts** with **four sporozoites each**, and the parasite forms **tissue cysts** in intermediate hosts, which differs from the *Cryptosporidium* life cycle shown with direct intestinal infection and immediate oocyst infectivity. [Practice more Microbiology PYQs on OnCourse]

Q: Which pathogen causes attachment - effacement lesion in the intestinal mucosa as shown in the image?

Enteropathogenic Escherichia coli. ***Enteropathogenic Escherichia coli*** - **Enteropathogenic E. coli (EPEC)** is characterized by its ability to cause **"attachment and effacement" (A/E) lesions** on intestinal epithelial cells, as depicted in the image. This involves the effacement of microvilli and pedestal formation. - EPEC utilizes the **Type III secretion system** to inject effector proteins into the host cell, leading to actin rearrangement and the characteristic A/E lesion. *Enterotoxigenic Escherichia coli* - **Enterotoxigenic E. coli (ETEC)** causes diarrhea by producing **heat-labile (LT) and/or heat-stable (ST) toxins**, which stimulate fluid and electrolyte secretion. - ETEC primarily mediates its effects through toxins that cause increased cAMP/cGMP, leading to secretory diarrhea without significant host cell damage. *Diffusely adherent Escherichia coli* - **Diffusely adherent E. coli (DAEC)** is known to adhere to the entire surface of epithelial cells in a diffuse pattern. - While it can cause diarrhea, its mechanism involves a different adhesion pattern and does not typically result in the dramatic attachment/effacement changes seen with EPEC. *Enteroinvasive Escherichia coli* - **Enteroinvasive E. coli (EIEC)** invades and destroys the epithelial cells of the colon, leading to symptoms similar to **shigellosis**, including dysentery (bloody, mucoid stools). - Its pathogenic mechanism involves intracellular replication and direct destruction of host cells, not the localized attachment and effacement seen in the image. [Practice more Microbiology PYQs on OnCourse]

Question 1

A patient presented with meningitis, and the CSF sample shows Gram-negative diplococci on Gram staining and microscopy. Which of the following features/tests will be characteristic of the organism?

Accepted Answer

Oxidase positive, catalase positive, ferments glucose and maltose

Answer

Catalase negative, optochin sensitive, alpha-hemolytic

Answer

Oxidase negative, catalase positive, coagulase positive

Answer

Catalase positive, urease positive, does not ferment glucose

Question 2

A 32 year old laborer working at a construction site presented with fever and hemoptysis. The sputum sample collected for examination showed the following. The smear will be stained by which of the following sequences?

Accepted Answer

Carbol fuchsin - acid - alcohol- methylene blue

Answer

Methylene blue- malachite green-acetic acid - water

Answer

Gentian violet - iodine - alcohol saffranin

Answer

Methanol - methylene blue-acid - water

Question 3

Identify the organism from the life cycle shown in the image given below

Accepted Answer

Cryptosporidium

Answer

Cystoisospora

Answer

Plasmodium knowlesi

Answer

Toxoplasma gondii

Question 4

Which pathogen causes attachment - effacement lesion in the intestinal mucosa as shown in the image?

Accepted Answer

Enteropathogenic Escherichia coli

Answer

Enterotoxigenic Escherichia coli

Answer

Diffusely adherent Escherichia coli

Answer

Enteroinvasive Escherichia coli

INI-CET 2021 — Microbiology