SARS is caused by novel variant of?
Smallest cestode among the following:
Most sensitive test for detecting microfilariae?
A patient presents with suspected diphtheria. What media will be used to diagnose this condition?
Which of the following is the most likely cause in a case of granuloma with positive AFB?
DNA transfer in bacteria by phage is:
What is the causative agent for malignant otitis externa?
Whipple's disease is caused by:
Sporulation occurs in which phase of bacterial growth curve:
Which antibody is seen in recent infection?
FMGE 2019 - Microbiology FMGE Practice Questions and MCQs
Question 11: SARS is caused by novel variant of?
- A. Coronavirus (Correct Answer)
- B. Toga virus
- C. Lyssa virus
- D. Pox virus
Explanation: ***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.
Question 12: Smallest cestode among the following:
- A. H. nana (Correct Answer)
- B. Schistosoma
- C. T. saginata
- D. T. solium
Explanation: ***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.
Question 13: Most sensitive test for detecting microfilariae?
- A. Membrane filtration technique (Correct Answer)
- B. Diethylcarbamazine (DEC) challenge test
- C. Fluorescence-based immunoassay
- D. Thick blood smear
Explanation: ***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.
Question 14: A patient presents with suspected diphtheria. What media will be used to diagnose this condition?
- A. Chocolate agar
- B. Cary-Blair
- C. Loffler's serum slope (Correct Answer)
- D. Lowenstein-Jensen
Explanation: ***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*.
Question 15: Which of the following is the most likely cause in a case of granuloma with positive AFB?
- A. Syphilis
- B. Cat scratch disease
- C. Leprosy
- D. Tuberculosis (Correct Answer)
Explanation: ***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.
Question 16: DNA transfer in bacteria by phage is:
- A. Transformation
- B. Conjugation
- C. Translation
- D. Transduction (Correct Answer)
Explanation: ***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.
Question 17: What is the causative agent for malignant otitis externa?
- A. Streptococcus
- B. Staphylococcus aureus
- C. Influenza
- D. Pseudomonas (Correct Answer)
Explanation: ***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.
Question 18: Whipple's disease is caused by:
- A. Virus
- B. Helminths
- C. Protozoa
- D. Bacteria (Correct Answer)
Explanation: **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.
Question 19: Sporulation occurs in which phase of bacterial growth curve:
- A. Decline phase
- B. Stationary phase (Correct Answer)
- C. Lag phase
- D. Log phase
Explanation: ***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.
Question 20: Which antibody is seen in recent infection?
- A. IgE
- B. IgM (Correct Answer)
- C. IgD
- D. IgG
Explanation: ***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.