NEET-PG 2013 - Microbiology Practice Questions

Q: Amoebic liver abscess can be diagnosed by demonstrating-

Trophozoites in the pus. ***Trophozoites in the pus*** - **Amoebic liver abscesses** are caused by the invasive **trophozoite stage** of *Entamoeba histolytica*. - Demonstrating **trophozoites** in the characteristic **'anchovy paste' pus** aspirated from the abscess cavity is diagnostic. *Cysts in the pus* - **Cysts** are the **infective stage** of *Entamoeba histolytica* and are typically found in the **feces**, not in an abscess. - Cysts are responsible for transmission and survival outside the host, but they do not cause invasive disease. *Cysts in the liver* - The disease in the liver is caused by **trophozoites**, which invade the intestinal wall and then spread to the liver. - **Cysts** are never found within the liver parenchyma or abscesses. *Trophozoites in the feces* - While **trophozoites** can be found in the feces during acute amoebic dysentery, their presence alone does not confirm a liver abscess. - Furthermore, **trophozoites** are fragile and often difficult to detect in stool samples, especially once the stool has cooled.

Q: Who discovered the bacterium Treponema pallidum?

Fritz Schaudinn and Erich Hoffmann. ***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.

Q: Who discovered the bacterium Mycobacterium tuberculosis, which causes tuberculosis?

Robert Koch. ***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*.

Q: Which of the following bacteria does not exhibit bipolar staining?

Haemophilus influenzae. ***Haemophilus influenzae*** - *Haemophilus influenzae* is a **pleomorphic coccobacillus** that typically stains uniformly and does not exhibit characteristic **bipolar staining**. - Its presence is often identified by Gram stain showing small, Gram-negative rods, but without the distinctive safety pin appearance. *Calymmatobacterium granulomatis* - *Calymmatobacterium granulomatis* (now *Klebsiella granulomatis*) is known to exhibit **bipolar staining**, often described as a **"safety pin" appearance**, especially in tissue smears from granuloma inguinale lesions. - This characteristic staining is due to the concentration of stain at the ends of the rod-shaped bacteria. *Yersinia pestis* - *Yersinia pestis*, the causative agent of plague, is classically described as having **bipolar staining**, giving it a distinctive **"safety pin" appearance** under a microscope. - This finding is a key diagnostic feature, particularly when observed in Gram-stained smears of clinical samples. *Francisella tularensis* - *Francisella tularensis* is a small, Gram-negative coccobacillus that is known to exhibit **bipolar staining**, though it may be less prominent than in *Yersinia pestis*. - This characteristic can assist in the microscopic identification of the bacterium, which causes tularemia.

Q: Which of the following bacteria is not capsulated?

Proteus. ***Proteus*** - *Proteus* species are **non-capsulated bacteria**; their primary virulence factor is urease production and motility via flagella. - While they can cause infections, the lack of a capsule means they do not evade phagocytosis in the same manner as the other listed options. *Pneumococcus* - **_Streptococcus pneumoniae_**, commonly known as pneumococcus, is a highly **capsulated bacterium**. - Its polysaccharide capsule is a major **virulence factor** that inhibits phagocytosis, contributing to its ability to cause pneumonia, meningitis, and other invasive diseases. *Klebsiella* - **_Klebsiella pneumoniae_** is a **heavily capsulated Gram-negative bacterium** with a prominent polysaccharide capsule. - The thick capsule gives colonies a **mucoid appearance** and serves as a major **virulence factor** that protects against phagocytosis, contributing to pneumonia, UTIs, and other infections. *Meningococcus* - **_Neisseria meningitidis_**, or meningococcus, is a **capsulated bacterium**. - Its **polysaccharide capsule** is vital for immune evasion and is the basis for serogrouping and vaccine development against meningococcal disease.

Q: Pseudomonas is which type of bacteria?

Aerobic. ***Aerobic*** - **Pseudomonas aeruginosa** is a classic example of an **aerobic bacterium**, meaning it requires oxygen for growth and metabolism. - Its ability to thrive in aerobic environments contributes to its prevalence in hospital settings and its capacity to cause a wide range of infections. *Anaerobic* - Anaerobic bacteria grow in the absence of oxygen and often die in its presence. **Pseudomonas** does not exhibit this characteristic. - Examples of anaerobic bacteria include *Clostridium* species. *Microaerophilic* - Microaerophilic bacteria require oxygen but only in low concentrations (5-10%), higher concentrations are inhibitory. - **Pseudomonas** grows optimally in atmospheric oxygen levels, not restricted to low concentrations. *Obligate anaerobe* - Obligate anaerobes are severely inhibited or killed by oxygen. - This is the opposite of **Pseudomonas**, which strictly requires oxygen for survival.

Q: Which of the following is not a sporicidal agent?

Isopropyl alcohol. ***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.

Q: Which of the following agents is most effective in destroying bacterial spores?

Gamma radiation. ***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

Q: Cytolytic activity of membrane attack complex is modulated by ?

Factor S (vitronectin). ***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.

Q: Which of the following is a superantigen ?

TSST. ***TSST*** - **Toxic Shock Syndrome Toxin-1 (TSST-1)** is a classic example of a superantigen produced by *Staphylococcus aureus*. - Superantigens **bind directly to MHC class II molecules and T-cell receptors (TCRs)** outside of the antigen-binding groove, leading to non-specific activation of a large percentage of T cells and a massive release of cytokines. *Cholera toxin* - **Cholera toxin** is an exotoxin produced by *Vibrio cholerae* that causes massive fluid secretion in the intestine by **activating adenylate cyclase** in enterocytes. - It functions by **ADP-ribosylating the Gs alpha subunit**, leading to constitutive activation of cyclic AMP production, but it is not a superantigen. *Diphtheria toxin* - **Diphtheria toxin**, produced by *Corynebacterium diphtheriae*, inhibits protein synthesis in eukaryotic cells by **ADP-ribosylating elongation factor-2 (EF-2)**. - This action leads to cell death and the characteristic pseudomembrane formation in diphtheria, but it does not act as a superantigen. *Vero-cytoxin* - **Vero-cytoxin** (also known as Shiga toxin or Shiga-like toxin) is produced by *E. coli* O157:H7 and other Shiga toxin-producing *E. coli* (STEC). - It inhibits protein synthesis by **cleaving ribosomal RNA**, primarily causing damage to intestinal cells and renal endothelial cells, but it is not a superantigen.

Question 1

Amoebic liver abscess can be diagnosed by demonstrating-

Accepted Answer

Trophozoites in the pus

Answer

Trophozoites in the feces

Answer

Cysts in the pus

Answer

Cysts in the liver

Question 2

Who discovered the bacterium Treponema pallidum?

Accepted Answer

Fritz Schaudinn and Erich Hoffmann

Answer

Robert Koch

Answer

Twort

Answer

Ellerman

Question 3

Who discovered the bacterium Mycobacterium tuberculosis, which causes tuberculosis?

Accepted Answer

Robert Koch

Answer

Jenner

Answer

Louis Pasteur

Answer

Lister

Question 4

Which of the following bacteria does not exhibit bipolar staining?

Accepted Answer

Haemophilus influenzae

Answer

Yersinia pestis

Answer

Calymmatobacterium granulomatis

Answer

Francisella tularensis

Question 5

Which of the following bacteria is not capsulated?

Accepted Answer

Proteus

Answer

Pneumococcus

Answer

Klebsiella

Answer

Meningococcus

Question 6

Pseudomonas is which type of bacteria?

Accepted Answer

Aerobic

Answer

Anaerobic

Answer

Microaerophilic

Answer

Obligate anaerobe

Question 7

Which of the following is not a sporicidal agent?

Accepted Answer

Isopropyl alcohol

Answer

Formaldehyde

Answer

Glutaraldehyde

Answer

Ethylene oxide

Question 8

Which of the following agents is most effective in destroying bacterial spores?

Accepted Answer

Gamma radiation

Answer

Ethanol

Answer

Sodium hypochlorite

Answer

Chlorine

Question 9

Cytolytic activity of membrane attack complex is modulated by ?

Accepted Answer

Factor S (vitronectin)

Answer

Factor I

Answer

Factor B

Answer

Factor H

Question 10

Which of the following is a superantigen ?

Accepted Answer

TSST

Answer

Cholera toxin

Answer

Diphtheria toxin

Answer

Vero-cytoxin

NEET-PG 2013 — Microbiology