FMGE 2023 - Microbiology PYQs Practice Questions

Q: The culture media that is used to differentiate lactose fermenters and non-lactose fermenters is

Mac-Conkey agar. ***Mac-Conkey agar*** - MacConkey agar is a selective and differential medium containing **lactose** and a **pH indicator** (neutral red) to distinguish gram-negative bacteria based on their ability to ferment lactose. - **Lactose fermenters** (e.g., *E. coli*, *Klebsiella*) produce acid, causing the colonies and surrounding medium to turn pink/red, while **non-lactose fermenters** (e.g., *Salmonella*, *Shigella*) remain colorless or pale. *Bile salt agar* - Primarily used for the isolation and detection of **enteric pathogens** like *Salmonella* and *Shigella*. - It contains bile salts to suppress the growth of many non-enteric Gram-negative rods but is not the primary medium for differentiating lactose fermentation. *Thayer-Martin agar* - This is a **selective medium** used specifically for the isolation of *Neisseria gonorrhoeae* and *Neisseria meningitidis*. - It contains antimicrobial agents (**vancomycin**, **colistin**, **nystatin**, and **trimethoprim**) to inhibit the growth of normal flora, fungi, and other bacteria. *Sabouraud Dextrose Agar* - This is the standard medium used for the selective isolation and cultivation of **fungi** (yeasts and molds). - Its low pH (typically around 5.6) and high glucose concentration inhibit the growth of most bacteria, making it unsuitable for differentiating lactose fermentation among bacteria. [Practice more Microbiology PYQs on OnCourse]

Q: Which of the following is an acid-fast organism?

Mycobacterium avium. ***Mycobacterium avium*** - Mycobacteria are **classically acid-fast organisms** due to high mycolic acid content in their cell wall - They retain carbolfuchsin stain even after treatment with acid-alcohol (Ziehl-Neelsen or Kinyoun stain) - M. avium is an atypical mycobacterium commonly causing infections in immunocompromised patients (especially AIDS) *Streptococcus pneumoniae* - Gram-positive coccus, NOT acid-fast - Identified by Gram staining, not acid-fast staining *Escherichia coli* - Gram-negative bacillus, NOT acid-fast - Standard Gram staining is used for identification *Actinomyces* - Gram-positive, branching filamentous bacteria - May show partial acid-fastness in modified acid-fast staining, but NOT classically acid-fast like Mycobacterium - Actinomyces is NOT considered an acid-fast organism in standard microbiology [Practice more Microbiology PYQs on OnCourse]

Q: The stain used for identifying Cryptococcus is

India ink stain. ***India ink stain***- This stain is a **negative staining** method primarily used for rapid detection of the large **polysaccharide capsule** of *Cryptococcus neoformans*, especially in cerebrospinal fluid (CSF) samples. - The surrounding ink particles are excluded by the capsule, resulting in a characteristic **clear halo** around the yeast cell against a dark background.*Albert's stain*- Albert's stain is specialized for bacterial cytology, specifically used to demonstrate **metachromatic granules** (or volutin granules) in **Corynebacterium diphtheriae**.- It uses a mixture of **toluidine blue** and **malachite green** and is not applicable for fungal identification.*Silver staining*- **Grocott's methenamine silver (GMS) stain** is a histological silver stain used often in pathology to visualize fungal elements, staining the cell walls brown to black.- While effective for detecting *Cryptococcus* in **tissue biopsies**, it is not the standard rapid method for fluid samples like CSF.*Auramine-rhodamine stain*- This is a **fluorescent staining technique** used to identify **acid-fast bacilli (AFB)**, particularly species of **Mycobacterium**.- The stain binds to the **mycolic acid** in the cell wall, a component absent in fungal organisms like *Cryptococcus*. [Practice more Microbiology PYQs on OnCourse]

Q: The image shown here is used for the diagnosis of

Herpes simplex virus. ***Herpes simplex virus*** - The image is a transmission electron micrograph showing multiple enveloped virions with a characteristic dense central core and an icosahedral nucleocapsid, giving a "target" or "bull's-eye" appearance. - This morphology is a classic feature of the **Herpesviridae** family, which includes Herpes Simplex Virus (HSV), Varicella-Zoster Virus (VZV), and Cytomegalovirus (CMV). *Human immunodeficiency virus* - HIV is a **retrovirus**, and its mature virion has a distinct **cone-shaped** or **bar-shaped** core, which is morphologically different from the spherical, target-like core shown in the image. - The primary diagnostic methods for HIV are serological assays (e.g., **ELISA**) and nucleic acid tests (**PCR**), not electron microscopy. *Hepatitis B virus* - The complete infectious virion of HBV, known as the **Dane particle**, is a double-shelled spherical particle, which does not have the same internal structure as the virions in the image. - Serum from infected individuals also contains non-infectious spherical and filamentous particles of **HBsAg** which lack a nucleocapsid. *Human papillomavirus* - HPV is a **non-enveloped** DNA virus, whereas the virus in the micrograph is clearly surrounded by a lipid envelope. - It has a simple, small **icosahedral capsid** structure, lacking the complex, multi-layered appearance of a herpesvirus. [Practice more Microbiology PYQs on OnCourse]

Q: Which of the following immunoglobulins shows the highest concentration in serum?

IgG. ***IgG*** - **IgG** accounts for approximately **75-80%** of the total immunoglobulins in human serum, making it the highest in concentration.- Its high levels reflect its crucial roles in providing **long-term humoral immunity**, neutralizing toxins, and being the only class able to cross the **placenta** to confer passive immunity to the fetus.*IgM* - **IgM** is present at much lower concentrations (about 5-10%); it is primarily known for being the first antibody produced during a **primary immune response**. - Although it is the largest immunoglobulin (a pentamer) and effective at complement activation, its total serum concentration is substantially less than IgG.*IgA* - **IgA** constitutes about 10-15% of serum immunoglobulins, ranking second to IgG in concentration. - While abundant in serum, its primary functional significance lies in its dimeric form (**Secretory IgA**) found in mucosal secretions, protecting epithelial surfaces.*IgE* - **IgE** is the immunoglobulin present at the lowest serum concentration (trace amounts). - It is mainly bound to **mast cells** and **basophils** and is responsible for mediating immediate **Type I hypersensitivity** reactions (allergies). [Practice more Microbiology PYQs on OnCourse]

Question 1

The culture media that is used to differentiate lactose fermenters and non-lactose fermenters is

Accepted Answer

Mac-Conkey agar

Answer

Bile salt agar

Answer

Thayer-Martin agar

Answer

Sabouraud Dextrose Agar

Question 2

Which of the following is an acid-fast organism?

Accepted Answer

Mycobacterium avium

Answer

Streptococcus pneumoniae

Answer

Escherichia coli

Answer

Actinomyces

Question 3

The stain used for identifying Cryptococcus is

Accepted Answer

India ink stain

Answer

Albert's stain

Answer

Silver staining

Answer

Auramine-rhodamine stain

Question 4

The image shown here is used for the diagnosis of

Accepted Answer

Herpes simplex virus

Answer

Human immunodeficiency virus

Answer

Hepatitis B virus

Answer

Human papillomavirus

Question 5

Which of the following immunoglobulins shows the highest concentration in serum?

Accepted Answer

IgG

Answer

IgM

Answer

IgA

Answer

IgE

Question 6

Which of the following dimorphic fungi causes subcutaneous mycosis?

Accepted Answer

Sporothrix schenckii

Answer

Blastomyces dermatitidis

Answer

Penicilliosis marneffei

Answer

Histoplasma capsulatum

Question 7

Plasma sterilization is done by

Accepted Answer

Hydrogen peroxide

Answer

UV rays

Answer

Ethylene oxide

Answer

Gamma rays

Question 8

A cattle farmer presented with a lesion on the arm. Gram staining showed gram-positive rods with square ends with a central spore. Identify the organism.

Accepted Answer

Bacillus anthracis

Answer

Bacillus cereus

Answer

Pseudomonas aeruginosa

Answer

Brucella abortus

Question 9

Which of the following is least likely to cause mucormycosis?

Accepted Answer

Broad spectrum antibiotics

Answer

Neutropenia

Answer

Uncontrolled diabetes without DKA

Answer

Prolonged use of steroid

Question 10

Which among the following culture media is used in the identification of Salmonella?

Accepted Answer

Wilson and Blair medium

Answer

PLET medium

Answer

BCYE medium

Answer

Stuart's medium

FMGE 2023 — Microbiology