FMGE 2019 - Microbiology Practice Questions

Q: SARS is caused by novel variant of?

Coronavirus. ***Coronavirus*** - **Severe Acute Respiratory Syndrome (SARS)** is caused by a novel strain of **coronavirus**, specifically SARS-CoV. - Coronaviruses are a large family of viruses known to cause respiratory illnesses ranging from the common cold to more severe diseases. *Togavirus* - Togaviruses are a family of **RNA viruses** that include **Rubella virus** and **Alphaviruses** (e.g., Eastern equine encephalitis virus). - They are typically transmitted by **arthropod vectors** and do not cause SARS. *Lyssavirus* - Lyssaviruses belong to the family Rhabdoviridae and are the causative agents of **rabies**, a severe neurological disease. - They are transmitted through the bite of an infected animal and are not associated with SARS. *Poxvirus* - Poxviruses are a family of **DNA viruses** that include **Variola virus** (smallpox) and **Monkeypox virus**. - They are known for causing characteristic skin lesions and are not responsible for SARS.

Q: Smallest cestode among the following:

H. nana. ***H. nana*** - *Hymenolepis nana* (dwarf tapeworm) is the **smallest cestode** infecting humans, typically measuring only 15-40 mm in length. - Its small size and direct life cycle (often without an intermediate host) contribute to its ability to cause **autoinfection**. *Schistosoma* - *Schistosoma* species are **trematodes (flukes)**, not cestodes (tapeworms). - They are known for causing **schistosomiasis** and are distinct from tapeworms in morphology and life cycle. *T. saginata* - *Taenia saginata* (beef tapeworm) is one of the **largest human tapeworms**, often reaching lengths of 4-12 meters. - Its large size and characteristic **proglottids** (segments) are key identifying features. *T. Solium* - *Taenia solium* (pork tapeworm) is also a **large cestode**, measuring 2-7 meters in length. - It is clinically significant for causing **cysticercosis** if humans ingest its eggs.

Q: Most sensitive test for detecting microfilariae?

Membrane filtration technique. ***Membrane filtration technique*** - The **membrane filtration technique** is considered the most sensitive test for detecting **microfilariae** because it concentrates microfilariae from a larger volume of blood (typically 1 mL or more) onto a filter membrane, increasing detection rates, especially in low-parasite density infections. - This method physically traps the microfilariae, allowing for microscopic examination of the concentrated sample after staining, which enhances visualization. *Diethylcarbamazine (DEC) challenge test* - The **DEC challenge test** uses **diethylcarbamazine** to provoke the release of microfilariae into the peripheral blood, especially in cases of occult filariasis or when microfilaria numbers are low. - While it can be useful in certain diagnostic situations, it is **less sensitive** than membrane filtration for directly detecting circulating microfilariae and carries the risk of inducing severe adverse reactions due to rapid parasite killing. *Fluorescence-based immunoassay* - **Fluorescence-based immunoassays** detect **antigens** or **antibodies** related to filarial infection, providing evidence of exposure or active infection. - While valuable for diagnosis, especially in antibody detection for chronic or occult infections, they do not directly detect live microfilariae and thus are not the most sensitive method for *detecting microfilariae themselves*. *Thick blood smear* - A **thick blood smear** is a common and quick method for detecting microfilariae by examining a drop of blood for their presence. - However, it is **less sensitive** than the membrane filtration technique, particularly in persons with low microfilaremia, as it examines a much smaller volume of blood.

Q: A patient presents with suspected diphtheria. What media will be used to diagnose this condition?

Loffler's serum slope. ***Loffler's serum slope*** - **Löffler's serum slope** is a specific enrichment medium used for the isolation and identification of *Corynebacterium diphtheriae*, the causative agent of diphtheria. - It enhances the characteristic **metachromatic granules** (Babes-Ernst bodies) within the bacteria, aiding in microscopic identification. *Chocolate agar* - **Chocolate agar** is a non-selective enrichment medium often used for fastidious organisms like *Haemophilus influenzae* and *Neisseria* species. - While it supports the growth of many bacteria, it is not specifically optimized for the isolation or enhanced identification of *Corynebacterium diphtheriae*. *Cary-Blair* - **Cary-Blair transport medium** is designed to preserve enteric pathogens like *Salmonella* and *Shigella* in fecal samples during transport. - It is not a primary culture medium for *Corynebacterium diphtheriae* and would not be used for diagnosis of diphtheria. *Lowenstein-Jensen* - **Lowenstein-Jensen (LJ) medium** is a specialized egg-based medium primarily used for the isolation and culture of *Mycobacterium tuberculosis*. - It contains malachite green to inhibit the growth of other bacteria and is not suitable for the growth of *Corynebacterium diphtheriae*.

Q: Which of the following is the most likely cause in a case of granuloma with positive AFB?

Tuberculosis. ***Tuberculosis*** - **Mycobacterium tuberculosis** is the classic cause of **granulomatous inflammation** with **positive AFB** staining in histopathology. - TB is the most common mycobacterial infection worldwide, and **AFB staining** is routinely positive in tissue specimens, making it the standard association for granuloma + AFB. *Leprosy* - While **Mycobacterium leprae** is acid-fast, **AFB positivity** is variable and often requires special techniques for demonstration. - Leprosy is much less common globally, and AFB demonstration in routine histopathology is less reliable compared to tuberculosis. *Syphilis* - Syphilis is caused by **Treponema pallidum**, a **spirochete** that is not acid-fast. - Although syphilis can cause granulomatous inflammation (**gummas**), **AFB staining** would be negative. *Cat scratch disease* - Cat scratch disease is caused by **Bartonella henselae**, a **Gram-negative bacterium**. - While it causes **granulomatous lymphadenitis**, **Bartonella** is not acid-fast, so **AFB** would be negative.

Q: DNA transfer in bacteria by phage is:

Transduction. ***Transduction*** - **Transduction** is the process by which foreign DNA is introduced into a cell by a virus or viral vector, specifically a **bacteriophage** in bacteria. - During transduction, the phage infects a bacterial cell, and its genetic material becomes incorporated into the host cell's DNA, or it may package bacterial DNA into new phage particles, which then infect other bacteria. *Transformation* - **Transformation** is the process where bacteria take up **naked DNA** from their environment. - This process does not involve a bacteriophage or any other viral vector. *Conjugation* - **Conjugation** is a process of genetic transfer between bacterial cells involving direct cell-to-cell contact through a **pilus**. - It typically involves the transfer of plasmids or other genetic elements, not mediated by a bacteriophage. *Translation* - **Translation** is the process by which messenger RNA (mRNA) is decoded to produce a specific **amino acid sequence** (protein). - This is a fundamental step in gene expression and does not involve the transfer of DNA between bacteria via a phage.

Q: What is the causative agent for malignant otitis externa?

Pseudomonas. ***Pseudomonas*** - **Malignant otitis externa** is a severe, rapidly progressive infection of the external auditory canal and skull base, primarily caused by **Pseudomonas aeruginosa**. - This opportunistic bacterium thrives in moist environments and commonly affects immunocompromised individuals, such as diabetics or the elderly. *Streptococcus* - While various *Streptococcus* species can cause common ear infections (e.g., **otitis media**), they are not the primary causative agent for malignant otitis externa. - Infections by *Streptococcus* typically present differently and affect other parts of the ear or body more commonly. *Staphylococcus aureus* - **Staphylococcus aureus** is a common cause of skin infections, including localized forms of otitis externa (e.g., furuncles), but it is rarely implicated in the aggressive, invasive form known as malignant otitis externa. - When *Staphylococcus aureus* is involved, it often presents differently and is less likely to cause skull base osteomyelitis. *Influenza* - **Influenza** is a viral infection primarily affecting the **respiratory system** and is not a bacterial pathogen responsible for otitis externa, malignant or otherwise. - Viral infections like influenza can predispose individuals to secondary bacterial infections, but they are not directly causative of this condition.

Q: Whipple's disease is caused by:

Bacteria. **Bacteria** - Whipple's disease is caused by the bacterium **_Tropheryma whipplei_**, a rod-shaped, gram-positive actinobacterium. - This bacterium causes a chronic, systemic infection affecting various organ systems, most commonly the gastrointestinal tract. *Virus* - Viruses are intracellular parasites that reproduce inside living cells, and they are not the causative agent of Whipple's disease. - While viral infections can cause gastrointestinal symptoms, they do not lead to the distinct histopathological findings of Whipple's disease, such as **PAS-positive macrophages**. *Helminths* - Helminths are parasitic worms (e.g., tapeworms, roundworms) that can cause intestinal and systemic infections. - These organisms are multicellular eukaryotes and are distinct from the bacterial etiology of Whipple's disease. *Protozoa* - Protozoa are single-celled eukaryotic organisms that can cause a range of infections, often gastrointestinal (e.g., Giardia, Entamoeba). - While parasitic infections can cause malabsorption, the specific **PAS-positive macrophage infiltrates** seen in Whipple's disease are characteristic of bacterial infection, not protozoan.

Q: Sporulation occurs in which phase of bacterial growth curve:

Stationary phase. ***Stationary phase*** - When **nutrients become limited** and waste products accumulate, bacteria enter the stationary phase, triggering **sporulation** in spore-forming species as a survival mechanism. - In this phase, the rate of **bacterial growth equals the rate of bacterial death**, leading to a plateau in population size. *Decline phase* - The decline phase is characterized by a **net decrease in viable cells** due to continued depletion of nutrients and high accumulation of toxic waste products. - While cells are certainly stressed, sporulation typically occurs *before* this phase, as a preventative measure to survive impending harsh conditions. *Lag phase* - During the lag phase, bacteria are **adapting to new environmental conditions** and synthesizing necessary enzymes and components. - There is no increase in cell number during this phase, and they are preparing for growth, not entering a survival state like sporulation. *Log phase* - The log phase (or exponential phase) is characterized by **rapid binary fission** and exponential increase in bacterial numbers due to optimal growth conditions and abundant nutrients. - Cells are actively dividing; sporulation, which halts active division to form a dormant spore, would be counterproductive at this stage.

Q: Which antibody is seen in recent infection?

IgM. ***IgM*** - **IgM** is the first antibody produced during a **primary immune response** to a new infection. - Its presence indicates a **recent or ongoing acute infection**. *IgE* - **IgE** is primarily associated with **allergic reactions** and defense against parasites. - It is not typically an indicator of a recent bacterial or viral infection. *IgD* - **IgD** is mostly found on the surface of **B cells** and plays a role in B cell activation. - Its function in circulating blood is not well understood, and it is not used to diagnose recent infection. *IgG* - **IgG** is the most abundant antibody in serum and represents a **secondary, more delayed immune response**. - Its presence indicates **past exposure or chronic infection**, as it provides long-term immunity.

Question 1

SARS is caused by novel variant of?

Accepted Answer

Coronavirus

Answer

Toga virus

Answer

Lyssa virus

Answer

Pox virus

Question 2

Smallest cestode among the following:

Accepted Answer

H. nana

Answer

Schistosoma

Answer

T. saginata

Answer

T. solium

Question 3

Most sensitive test for detecting microfilariae?

Accepted Answer

Membrane filtration technique

Answer

Diethylcarbamazine (DEC) challenge test

Answer

Fluorescence-based immunoassay

Answer

Thick blood smear

Question 4

A patient presents with suspected diphtheria. What media will be used to diagnose this condition?

Accepted Answer

Loffler's serum slope

Answer

Chocolate agar

Answer

Cary-Blair

Answer

Lowenstein-Jensen

Question 5

Which of the following is the most likely cause in a case of granuloma with positive AFB?

Accepted Answer

Tuberculosis

Answer

Syphilis

Answer

Cat scratch disease

Answer

Leprosy

Question 6

DNA transfer in bacteria by phage is:

Accepted Answer

Transduction

Answer

Transformation

Answer

Conjugation

Answer

Translation

Question 7

What is the causative agent for malignant otitis externa?

Accepted Answer

Pseudomonas

Answer

Streptococcus

Answer

Staphylococcus aureus

Answer

Influenza

Question 8

Whipple's disease is caused by:

Accepted Answer

Bacteria

Answer

Virus

Answer

Helminths

Answer

Protozoa

Question 9

Sporulation occurs in which phase of bacterial growth curve:

Accepted Answer

Stationary phase

Answer

Decline phase

Answer

Lag phase

Answer

Log phase

Question 10

Which antibody is seen in recent infection?

Accepted Answer

IgM

Answer

IgE

Answer

IgD

Answer

IgG

FMGE 2019 — Microbiology