Which fungus is commonly known as golden yellow jelly fungus?
Cytolytic activity of membrane attack complex is modulated by ?
Who discovered the bacterium Mycobacterium tuberculosis, which causes tuberculosis?
Who discovered the bacterium Treponema pallidum?
Which gene of Hepatitis B virus (HBV) is most commonly associated with mutations causing antiviral drug resistance?
Which of the following is not a sporicidal agent?
Which of the following agents is most effective in destroying bacterial spores?
All of the sterilization methods are properly matched except?
What is the commonly used percentage of glutaraldehyde for high-level disinfection in healthcare settings?
Which of the following is called Preisz-Nocard bacillus?
NEET-PG 2013 - Microbiology NEET-PG Practice Questions and MCQs
Question 21: Which fungus is commonly known as golden yellow jelly fungus?
- A. T. tonsurans
- B. Tremella mesenterica (Correct Answer)
- C. Epidermophyton floccosum
- D. T. mentagrophytes
Explanation: ***Tremella mesenterica*** - This fungus is commonly referred to as **golden yellow jelly fungus** or **witch's butter** due to its distinctive golden-yellow, gelatinous, and brain-like appearance. - It is a **jelly fungus** that typically grows on dead hardwood branches, especially after rain, and is known for its pliable, quivering texture. *T. tonsurans* - This refers to **Trichophyton tonsurans**, a dermatophytic fungus primarily known for causing **tinea capitis** (ringworm of the scalp). - Its common name relates to its effect on hair, causing breakage and a "black dot" appearance, rather than a golden yellow, jelly-like form. *Epidermophyton floccosum* - This is a dermatophytic fungus that specifically causes infections of the **skin and nails**, particularly **tinea pedis** (athlete's foot) and **tinea cruris** (jock itch). - It does not produce a fruiting body and is not described as a jelly-like fungus. *T. mentagrophytes* - This refers to **Trichophyton mentagrophytes**, another common dermatophyte responsible for various superficial fungal infections, including **tinea pedis**, **tinea corporis**, and **tinea unguium**. - Its clinical presentation is not that of a golden yellow jelly fungus.
Question 22: Cytolytic activity of membrane attack complex is modulated by ?
- A. Factor I
- B. Factor B
- C. Factor S (vitronectin) (Correct Answer)
- D. Factor H
Explanation: ***Correct Option: Factor S (vitronectin)*** - Vitronectin (S-protein) is a **plasma protein** that directly modulates the **cytolytic activity of the membrane attack complex (MAC)**. - It binds to the **C5b-7 complex** in the fluid phase, preventing its insertion into target cell membranes and thereby blocking the formation of the complete, functional MAC. - By inhibiting membrane insertion of C5b-7, vitronectin prevents the subsequent binding of **C8 and C9**, which are essential for the cytolytic pore formation. - This is a **direct modulation** of MAC's cytolytic activity at the MAC assembly stage. *Incorrect Option: Factor H* - Factor H is a regulatory protein that controls the **alternative pathway** of complement activation by promoting degradation of **C3b**. - By degrading C3b, Factor H prevents formation of **C5 convertase**, thereby reducing downstream MAC formation. - However, Factor H acts **early in the complement cascade** and does not directly modulate the cytolytic activity of already-formed MAC components. - Its effect is on **preventing MAC formation**, not on modulating MAC's cytolytic function itself. *Incorrect Option: Factor I* - Factor I is a **serine protease** that cleaves and inactivates C3b and C4b, requiring cofactors like Factor H or C4bp. - Like Factor H, it regulates complement activation **upstream** of MAC formation. - It does not directly interact with or modulate the cytolytic activity of the MAC. *Incorrect Option: Factor B* - Factor B is a component of the **alternative pathway C3 convertase** (C3bBb). - It **promotes complement activation** rather than modulating MAC's cytolytic activity. - Factor B functions early in the cascade and has no direct role in regulating MAC function.
Question 23: Who discovered the bacterium Mycobacterium tuberculosis, which causes tuberculosis?
- A. Jenner
- B. Louis Pasteur
- C. Robert Koch (Correct Answer)
- D. Lister
Explanation: ***Robert Koch*** - **Robert Koch** discovered the bacterium *Mycobacterium tuberculosis* in **1882**, identifying its role as the causative agent of tuberculosis. - His work was crucial in establishing the germ theory of disease and earned him the Nobel Prize in Physiology or Medicine in 1905. *Louis Pasteur* - **Louis Pasteur** was a pioneer in microbiology, known for his work on **pasteurization**, **vaccinations** (e.g., rabies and anthrax), and disproving spontaneous generation. - While he made significant contributions to understanding infectious diseases, he did not discover *Mycobacterium tuberculosis*. *Lister* - **Joseph Lister** was a British surgeon who revolutionized surgery by introducing **antiseptic techniques** using carbolic acid to prevent infections. - His contributions were fundamental to reducing mortality rates from surgical infections, but he did not discover the tuberculosis bacterium. *Jenner* - **Edward Jenner** is famous for developing the **smallpox vaccine**, which was a groundbreaking achievement in immunology and public health. - His work, though vital for preventing infectious diseases, predates and is unrelated to the discovery of *Mycobacterium tuberculosis*.
Question 24: Who discovered the bacterium Treponema pallidum?
- A. Robert Koch
- B. Twort
- C. Ellerman
- D. Fritz Schaudinn and Erich Hoffmann (Correct Answer)
Explanation: ***Fritz Schaudinn and Erich Hoffmann*** - **Fritz Schaudinn** was a German zoologist, and **Erich Hoffmann** was a German dermatologist; they jointly discovered **Treponema pallidum** in **1905**. - Their discovery of the spirochete was a crucial step in understanding the etiology of **syphilis**. *Robert Koch* - **Robert Koch** is renowned for identifying the causative agents of **tuberculosis**, **cholera**, and **anthrax**. - He developed Koch's postulates, a fundamental set of criteria for establishing the causal relationship between a microbe and a disease. *Twort* - **Frederick Twort** was a British bacteriologist who is credited with the discovery of **bacteriophages** in **1915**. - His work involved examining transparent areas in bacterial cultures, leading to the identification of lytic viruses that infect bacteria. *Ellerman* - **Vilhelm Ellerman** was a Danish pathologist known for his work in **hematology** and **virology**. - Alongside **Olaf Bang**, he demonstrated that avian leukemia (erythroleukemia) could be transmitted by a filterable agent, indicating a viral etiology for some cancers.
Question 25: Which gene of Hepatitis B virus (HBV) is most commonly associated with mutations causing antiviral drug resistance?
- A. X gene
- B. S gene
- C. C gene
- D. P gene (Correct Answer)
Explanation: ***P gene*** - The **P gene** (polymerase gene) of HBV encodes the viral reverse transcriptase which is essential for viral replication. - Mutations in the P gene can lead to **antiviral drug resistance**, particularly to nucleos(t)ide analogues. *X gene* - The **X gene** encodes the X protein (HBx), a **transcriptional transactivator** involved in viral replication and pathogenesis. - While important for viral function, it is not the primary target for antiviral therapy, and mutations are less frequently associated with drug resistance. *S gene* - The **S gene** encodes the **surface antigens (HBsAg)**, which are crucial for viral entry and immune evasion. - Mutations in the S gene can lead to **vaccine escape mutants** or alter HBsAg detection, but not directly responsible for antiviral resistance. *C gene* - The **C gene** encodes the **core protein (HBcAg)** and the precore protein (HBeAg). - These proteins are involved in **viral particle assembly** and immune modulation, but mutations in this gene are not typically associated with resistance to antiviral drugs.
Question 26: Which of the following is not a sporicidal agent?
- A. Formaldehyde
- B. Glutaraldehyde
- C. Ethylene oxide
- D. Isopropyl alcohol (Correct Answer)
Explanation: ***Isopropyl alcohol*** - Isopropyl alcohol is an **antiseptic** and **disinfectant** that works by denaturing proteins and dissolving lipids, but it is not effective against bacterial spores. - Its efficacy against microbes is primarily for **vegetative bacteria**, fungi, and enveloped viruses. *Formaldehyde* - Formaldehyde is a potent **sporicide** that cross-links proteins and nucleic acids, making it effective for high-level disinfection and sterilization. - It is often used in solutions or as a gas for sterilizing heat-sensitive medical equipment. *Glutaraldehyde* - Glutaraldehyde is a **high-level disinfectant** and **sterilant** that works by alkylating protein and nucleic acid components, effectively killing spores. - It's commonly used for sterilizing endoscopic instruments and other heat-sensitive devices. *Ethylene oxide* - Ethylene oxide is a gaseous sterilant that **alkylates proteins** and nucleic acids, making it highly effective against all microorganisms, including spores, bacteria, and viruses. - It is frequently used for sterilizing heat-sensitive and moisture-sensitive medical devices.
Question 27: Which of the following agents is most effective in destroying bacterial spores?
- A. Ethanol
- B. Sodium hypochlorite
- C. Gamma radiation (Correct Answer)
- D. Chlorine
Explanation: ***Gamma radiation*** - **Gamma radiation** is the **most effective agent** for destroying **bacterial spores** among all the options listed - It achieves **complete sterilization** by causing irreversible DNA damage through ionization - Gamma radiation penetrates deeply and destroys all forms of microbial life, including the most resistant spores like *Bacillus* and *Clostridium* species - Used for **industrial sterilization** of medical equipment, pharmaceuticals, and heat-sensitive materials - Provides absolute reliability in spore destruction without the need for heat or prolonged contact time *Sodium hypochlorite* - **Sodium hypochlorite** does have **sporicidal activity** at high concentrations (5000-10000 ppm) with prolonged contact time - However, it requires **specific conditions** (high concentration, adequate contact time, organic matter removal) to be effective against spores - While useful as a chemical disinfectant, it is **less effective and less reliable** than gamma radiation for spore destruction - Commonly used for surface disinfection and water treatment *Chlorine* - **Chlorine gas** or aqueous chlorine solutions have limited sporicidal activity - Less effective than sodium hypochlorite at practical concentrations - More commonly used for water disinfection rather than spore destruction *Ethanol* - **Ethanol** is primarily **bactericidal** and **fungicidal** but **not sporicidal** - Cannot penetrate the resistant spore coat and cortex layers - Effective for vegetative bacteria but ineffective against bacterial spores
Question 28: All of the sterilization methods are properly matched except?
- A. Culture media - Autoclaving
- B. Glassware & syringes - Hot air oven
- C. Catgut suture - Radiation
- D. Bronchoscope - Autoclaving (Correct Answer)
Explanation: ***Bronchoscope - Autoclaving*** - **Autoclaving** uses high temperature and steam, which can damage the delicate heat-sensitive components and lenses of a bronchoscope. - **Bronchoscopes** are typically sterilized using **low-temperature sterilization methods** such as **ethylene oxide**, hydrogen peroxide plasma, or glutaraldehyde. *Catgut suture - Radiation* - **Radiation** (e.g., gamma irradiation) is a suitable and common method for sterilizing **heat-sensitive materials** like catgut sutures, ensuring sterility without compromising material integrity. - This method effectively destroys microorganisms by damaging their DNA. *Culture media - Autoclaving* - **Autoclaving** is the standard and most effective method for sterilizing **culture media**, which requires complete elimination of all microbial forms including spores. - The high heat and pressure achieved in an autoclave denature proteins and destroy microbial structures. *Glassware & syringes - Hot air oven* - A **hot air oven** is appropriate for sterilizing **heat-stable items** like glassware and metal syringes, as it provides dry heat that penetrates well and kills microorganisms by oxidation. - This method is particularly useful for items that can be damaged by moisture or steam.
Question 29: What is the commonly used percentage of glutaraldehyde for high-level disinfection in healthcare settings?
- A. 1%
- B. 2% (Correct Answer)
- C. 3%
- D. 4%
Explanation: ***2%*** - A **2% concentration of glutaraldehyde** is the most common and effective formulation used for **high-level disinfection** of heat-sensitive medical instruments. - This concentration achieves sporicidal activity after prolonged exposure and is effective against a broad spectrum of microorganisms including bacteria, viruses, and fungi. *1%* - A **1% concentration of glutaraldehyde** is generally considered too low for reliable **high-level disinfection** in healthcare settings. - While it may have some antimicrobial activity, it typically does not meet the necessary efficacy standards for disinfecting critical or semi-critical medical devices. *3%* - While a **3% concentration of glutaraldehyde** can be effective for disinfection, it is not the most commonly used, and the increased concentration can lead to **higher toxicity** and potential for skin and respiratory irritation for healthcare workers. - The slight increase in efficacy over 2% often does not outweigh the increased risks and cost associated with its use. *4%* - A **4% concentration of glutaraldehyde** is generally considered unnecessarily high for routine **high-level disinfection** and is not commonly used in clinical practice. - This higher concentration significantly increases the risk of **toxicity and occupational exposure issues**, with little additional benefit in terms of disinfection efficacy compared to 2%.
Question 30: Which of the following is called Preisz-Nocard bacillus?
- A. C. diphtheriae
- B. C. pseudotuberculosis (Correct Answer)
- C. M. tuberculosis
- D. Mycoplasma
Explanation: ***C. pseudotuberculosis*** - This bacterium is historically known as the **Preisz-Nocard bacillus**, named after its discoverers. - It is an important pathogen in animals, causing conditions like **caseous lymphadenitis** in sheep and goats. *C. diphtheriae* - This bacterium causes **diphtheria** and is known for producing a potent **exotoxin** that can lead to systemic complications. - It forms a characteristic **pseudomembrane** in the throat and is not associated with the Preisz-Nocard designation. *M. tuberculosis* - This is the causative agent of **tuberculosis** in humans, primarily affecting the lungs. - It is known for its **acid-fast staining** property and a complex pathogenesis involving granuloma formation. *Mycoplasma* - This genus includes bacteria that lack a **cell wall**, making them resistant to many common antibiotics. - They are known for causing various infections, including **atypical pneumonia** and genitourinary tract infections, but are not referred to as the Preisz-Nocard bacillus.