FMGE 2018 — Microbiology

Q: Biological indicator for determining efficacy of autoclaving is

Bacillus stearothermophilus. ***Bacillus stearothermophilus*** - *Bacillus stearothermophilus* (now *Geobacillus stearothermophilus*) is a **thermoduric spore-forming bacterium** used as a biological indicator for **autoclave efficacy**. - Its spores are highly **resistant to heat**, making them ideal for challenging the sterilization process. *Pseudomonas aeruginosa* - *Pseudomonas aeruginosa* is a **Gram-negative bacterium** known for causing hospital-acquired infections, but it is **not used as a biological indicator** for autoclaving. - It is **less resistant to heat** and sterilization methods compared to bacterial spores. *Clostridium perfringens* - *Clostridium perfringens* is a **spore-forming anaerobic bacterium** associated with gas gangrene and food poisoning. - While it forms spores, its **heat resistance profile is different** from that of *Bacillus stearothermophilus*, and it is not the standard biological indicator for autoclaving. *Salmonella typhi* - *Salmonella typhi* is a **Gram-negative bacterium** that causes typhoid fever. - It is a **pathogen but not a spore-former**, and therefore, it is easily killed by autoclaving and not suitable as a biological indicator for monitoring sterilization effectiveness. [Practice more Microbiology PYQs on OnCourse]

Q: Classical complement is activated by:

Ag-Ab complex. ***Ag-Ab complex*** - The **classical complement pathway** is initiated by the binding of **C1q** to an antigen-antibody complex, specifically involving **IgM** or certain subclasses of **IgG**. - This binding triggers a cascade of events leading to the activation of the complement system, ultimately resulting in the **lysis of target cells**, **opsonization**, and **inflammation**. *C3 Convertase* - **C3 convertase** is an enzyme complex formed later in the complement cascade, responsible for cleaving C3 into C3a and C3b. - While essential for all complement pathways, it is a **downstream effector** and not the initial activator of the classical pathway. *C1* - **C1** is a complex protein that includes C1q, C1r, and C1s. While C1 plays a crucial role in the classical pathway, it is **activated by** the antigen-antibody complex, not an independent activator. - The activation sequence is: **Ag-Ab complex → C1q binding → C1 activation → cascade initiation**. Thus, the Ag-Ab complex is the primary trigger, and C1 is the responder. *IgA* - **IgA** primarily functions in mucosal immunity and is generally **not an activator** of the classical complement pathway. - Instead, IgA can activate the **alternative complement pathway** under specific circumstances, but not the classical pathway through direct binding to C1q. [Practice more Microbiology PYQs on OnCourse]

Q: In Plasmodium vivax malaria, relapse is caused by:

Hypnozoite. ***Hypnozoite*** - **Hypnozoites** are dormant forms of *Plasmodium vivax* and *P. ovale* that persist in the liver for months to years after initial infection. - These dormant hepatic stages can later reactivate, develop into merozoites, and cause a **relapse** of malaria symptoms even after successful treatment of the blood-stage infection. - Relapses are a defining feature of *P. vivax* malaria and require treatment with **primaquine** or **tafenoquine** for radical cure to eliminate hypnozoites. *Incorrect: Schizont* - **Schizonts** are stages where asexual reproduction occurs, either in liver cells (hepatic schizonts) or red blood cells (erythrocytic schizonts). - Erythrocytic schizonts cause acute malaria symptoms but do not cause delayed relapses as they are cleared by standard antimalarial treatments. - Hepatic schizonts complete their cycle within 1-2 weeks and do not remain dormant. *Incorrect: Sporozoite* - **Sporozoites** are the infective stage injected by the mosquito that travel to the liver to initiate infection. - They differentiate into either developing schizonts or dormant hypnozoites but do not directly cause relapses. - Sporozoites represent the initial infection, not the mechanism of relapse. *Incorrect: Gametocyte* - **Gametocytes** are the sexual stage found in human blood that are ingested by mosquitoes to continue the parasite lifecycle. - They are responsible for transmission to mosquitoes but do not cause human symptoms or relapses in the host. - Gametocytes do not remain dormant in the liver. [Practice more Microbiology PYQs on OnCourse]

Q: Quellung reaction is seen with:

Pneumococcus. ***Pneumococcus*** - The Quellung reaction, also known as the **Neufeld reaction**, is a classic immunological test used to identify bacteria based on their **capsular polysaccharides**. - In the presence of specific antisera, the capsule of **_Streptococcus pneumoniae_** (Pneumococcus) swells visibly when viewed under a microscope, appearing larger and more refractile. - **Pneumococcus is the CLASSIC organism** associated with the Quellung reaction in clinical microbiology and is the standard answer in medical examinations. - While other encapsulated bacteria (_Haemophilus influenzae_, _Klebsiella pneumoniae_, _N. meningitidis_) can theoretically show capsular swelling, the test is primarily used for and associated with pneumococcal identification. *Gonococcus* - **_Neisseria gonorrhoeae_** (Gonococcus) is a Gram-negative diplococcus that causes sexually transmitted infections. - It does not possess a prominent polysaccharide capsule that exhibits the Quellung reaction in routine clinical practice. *Staphylococcus* - **_Staphylococcus_** species are Gram-positive cocci that form grape-like clusters. - While some staphylococci produce capsules or slime layers, these are not characterized using the Quellung reaction. *Streptococcus* - While _S. pneumoniae_ is technically a species of Streptococcus, in clinical terminology **"Pneumococcus" is the specific term** that denotes this particular organism. - When asked about the Quellung reaction, **"Pneumococcus" is the preferred and correct answer** rather than the broader genus term "Streptococcus." - The Quellung test is not routinely used for other Streptococcus species (like _S. pyogenes_, _S. agalactiae_) in standard clinical practice, making "Pneumococcus" the most accurate answer. [Practice more Microbiology PYQs on OnCourse]

Q: Otomycosis is most commonly caused by:

Aspergillus fumigatus. ***Aspergillus fumigatus*** - **Aspergillus species**, particularly *A. fumigatus* and *A. niger*, are the most frequent causes of **otomycosis**, accounting for 80-90% of cases. - They thrive in damp, warm environments, making the external auditory canal an ideal site for their growth, often presenting with a **black or grayish fungal debris**. *Mucor* - **Mucor** is a less common cause of otomycosis and is more often associated with **rhinocerebral mucormycosis** in immunocompromised individuals. - While it can cause opportunistic infections, its prevalence in otomycosis is significantly lower compared to Aspergillus. *Actinomycetes* - **Actinomycetes** are **filamentous bacteria**, not fungi, and are typically associated with **actinomycosis**, a chronic suppurative infection. - They are known to cause infections in the head and neck, but not typically otomycosis, which is a fungal infection of the ear. *Candida albicans* - **Candida albicans** is the second most common cause of otomycosis, but it is less prevalent than Aspergillus species. - Infections by Candida tend to be more common in individuals with a history of **antibiotic use** or in **immunocompromised patients**, and often present with a *creamy white discharge*. [Practice more Microbiology PYQs on OnCourse]

6 Previous Year Questions with Answers & Explanations

Questions

Biological indicator for determining efficacy of autoclaving is

Classical complement is activated by:

In Plasmodium vivax malaria, relapse is caused by:

Quellung reaction is seen with:

Otomycosis is most commonly caused by:

Which one of the following is a major component in activation of the complement alternative pathway?

FMGE 2018 - Microbiology FMGE Practice Questions and MCQs

Question 1: Biological indicator for determining efficacy of autoclaving is

A. Bacillus stearothermophilus (Correct Answer)
B. Pseudomonas aeruginosa
C. Clostridium perfringens
D. Salmonella typhi

Explanation: ***Bacillus stearothermophilus*** - *Bacillus stearothermophilus* (now *Geobacillus stearothermophilus*) is a **thermoduric spore-forming bacterium** used as a biological indicator for **autoclave efficacy**. - Its spores are highly **resistant to heat**, making them ideal for challenging the sterilization process. *Pseudomonas aeruginosa* - *Pseudomonas aeruginosa* is a **Gram-negative bacterium** known for causing hospital-acquired infections, but it is **not used as a biological indicator** for autoclaving. - It is **less resistant to heat** and sterilization methods compared to bacterial spores. *Clostridium perfringens* - *Clostridium perfringens* is a **spore-forming anaerobic bacterium** associated with gas gangrene and food poisoning. - While it forms spores, its **heat resistance profile is different** from that of *Bacillus stearothermophilus*, and it is not the standard biological indicator for autoclaving. *Salmonella typhi* - *Salmonella typhi* is a **Gram-negative bacterium** that causes typhoid fever. - It is a **pathogen but not a spore-former**, and therefore, it is easily killed by autoclaving and not suitable as a biological indicator for monitoring sterilization effectiveness.

Question 2: Classical complement is activated by:

A. C3 Convertase
B. C1
C. Ag-Ab complex (Correct Answer)
D. IgA

Explanation: ***Ag-Ab complex*** - The **classical complement pathway** is initiated by the binding of **C1q** to an antigen-antibody complex, specifically involving **IgM** or certain subclasses of **IgG**. - This binding triggers a cascade of events leading to the activation of the complement system, ultimately resulting in the **lysis of target cells**, **opsonization**, and **inflammation**. *C3 Convertase* - **C3 convertase** is an enzyme complex formed later in the complement cascade, responsible for cleaving C3 into C3a and C3b. - While essential for all complement pathways, it is a **downstream effector** and not the initial activator of the classical pathway. *C1* - **C1** is a complex protein that includes C1q, C1r, and C1s. While C1 plays a crucial role in the classical pathway, it is **activated by** the antigen-antibody complex, not an independent activator. - The activation sequence is: **Ag-Ab complex → C1q binding → C1 activation → cascade initiation**. Thus, the Ag-Ab complex is the primary trigger, and C1 is the responder. *IgA* - **IgA** primarily functions in mucosal immunity and is generally **not an activator** of the classical complement pathway. - Instead, IgA can activate the **alternative complement pathway** under specific circumstances, but not the classical pathway through direct binding to C1q.

Question 3: In Plasmodium vivax malaria, relapse is caused by:

A. Hypnozoite (Correct Answer)
B. Schizont
C. Sporozoite
D. Gametocyte

Explanation: ***Hypnozoite*** - **Hypnozoites** are dormant forms of *Plasmodium vivax* and *P. ovale* that persist in the liver for months to years after initial infection. - These dormant hepatic stages can later reactivate, develop into merozoites, and cause a **relapse** of malaria symptoms even after successful treatment of the blood-stage infection. - Relapses are a defining feature of *P. vivax* malaria and require treatment with **primaquine** or **tafenoquine** for radical cure to eliminate hypnozoites. *Incorrect: Schizont* - **Schizonts** are stages where asexual reproduction occurs, either in liver cells (hepatic schizonts) or red blood cells (erythrocytic schizonts). - Erythrocytic schizonts cause acute malaria symptoms but do not cause delayed relapses as they are cleared by standard antimalarial treatments. - Hepatic schizonts complete their cycle within 1-2 weeks and do not remain dormant. *Incorrect: Sporozoite* - **Sporozoites** are the infective stage injected by the mosquito that travel to the liver to initiate infection. - They differentiate into either developing schizonts or dormant hypnozoites but do not directly cause relapses. - Sporozoites represent the initial infection, not the mechanism of relapse. *Incorrect: Gametocyte* - **Gametocytes** are the sexual stage found in human blood that are ingested by mosquitoes to continue the parasite lifecycle. - They are responsible for transmission to mosquitoes but do not cause human symptoms or relapses in the host. - Gametocytes do not remain dormant in the liver.

Question 4: Quellung reaction is seen with:

A. Pneumococcus (Correct Answer)
B. Gonococcus
C. Staphylococcus
D. Streptococcus

Explanation: ***Pneumococcus*** - The Quellung reaction, also known as the **Neufeld reaction**, is a classic immunological test used to identify bacteria based on their **capsular polysaccharides**. - In the presence of specific antisera, the capsule of **_Streptococcus pneumoniae_** (Pneumococcus) swells visibly when viewed under a microscope, appearing larger and more refractile. - **Pneumococcus is the CLASSIC organism** associated with the Quellung reaction in clinical microbiology and is the standard answer in medical examinations. - While other encapsulated bacteria (_Haemophilus influenzae_, _Klebsiella pneumoniae_, _N. meningitidis_) can theoretically show capsular swelling, the test is primarily used for and associated with pneumococcal identification. *Gonococcus* - **_Neisseria gonorrhoeae_** (Gonococcus) is a Gram-negative diplococcus that causes sexually transmitted infections. - It does not possess a prominent polysaccharide capsule that exhibits the Quellung reaction in routine clinical practice. *Staphylococcus* - **_Staphylococcus_** species are Gram-positive cocci that form grape-like clusters. - While some staphylococci produce capsules or slime layers, these are not characterized using the Quellung reaction. *Streptococcus* - While _S. pneumoniae_ is technically a species of Streptococcus, in clinical terminology **"Pneumococcus" is the specific term** that denotes this particular organism. - When asked about the Quellung reaction, **"Pneumococcus" is the preferred and correct answer** rather than the broader genus term "Streptococcus." - The Quellung test is not routinely used for other Streptococcus species (like _S. pyogenes_, _S. agalactiae_) in standard clinical practice, making "Pneumococcus" the most accurate answer.

Question 5: Otomycosis is most commonly caused by:

A. Mucor
B. Actinomycetes
C. Candida albicans
D. Aspergillus fumigatus (Correct Answer)

Explanation: ***Aspergillus fumigatus*** - **Aspergillus species**, particularly *A. fumigatus* and *A. niger*, are the most frequent causes of **otomycosis**, accounting for 80-90% of cases. - They thrive in damp, warm environments, making the external auditory canal an ideal site for their growth, often presenting with a **black or grayish fungal debris**. *Mucor* - **Mucor** is a less common cause of otomycosis and is more often associated with **rhinocerebral mucormycosis** in immunocompromised individuals. - While it can cause opportunistic infections, its prevalence in otomycosis is significantly lower compared to Aspergillus. *Actinomycetes* - **Actinomycetes** are **filamentous bacteria**, not fungi, and are typically associated with **actinomycosis**, a chronic suppurative infection. - They are known to cause infections in the head and neck, but not typically otomycosis, which is a fungal infection of the ear. *Candida albicans* - **Candida albicans** is the second most common cause of otomycosis, but it is less prevalent than Aspergillus species. - Infections by Candida tend to be more common in individuals with a history of **antibiotic use** or in **immunocompromised patients**, and often present with a *creamy white discharge*.

Question 6: Which one of the following is a major component in activation of the complement alternative pathway?

A. C2
B. C3 (Correct Answer)
C. C4
D. C1

Explanation: ***C3*** - **C3** is a central component in all complement pathways. In the alternative pathway, spontaneous hydrolysis of **C3** leads to C3(H2O), initiating the formation of the **C3 convertase**. - This **C3 convertase** (C3bBb) further cleaves more **C3** into C3a and C3b, amplifying the pathway and leading to downstream complement activation. *C2* - **C2** is a crucial component of the **classical** and **lectin pathways**, where it is cleaved by C1s or MASP-2, respectively, to form C2b and C2a. - **C2a** then combines with C4b to form the **C3 convertase** (C4b2a) of these pathways; it does not play a direct role in initiating the alternative pathway. *C4* - **C4** is primarily involved in the **classical** and **lectin pathways**, where it is cleaved by C1s or MASP-2 to form C4a and C4b. - **C4b** binds to pathogens or immune complexes and then associates with C2a to form the **C3 convertase** (C4b2a), which is not part of the alternative pathway initiation. *C1* - **C1** is the initiating complex of the **classical complement pathway** and is composed of C1q, C1r, and C1s. - It recognizes and binds to antibody-antigen complexes or pathogen surfaces, but it has no direct role in the **alternative pathway activation**.