Microbiology
10 questionsWho discovered the bacterium Treponema pallidum?
Who discovered the bacterium Mycobacterium tuberculosis, which causes tuberculosis?
Which of the following bacteria does not exhibit bipolar staining?
Which of the following bacteria is not capsulated?
Pseudomonas is which type of bacteria?
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?
Glass vessels and syringes are best sterilised by -
NEET-PG 2013 - Microbiology NEET-PG Practice Questions and MCQs
Question 631: 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 632: 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 633: Which of the following bacteria does not exhibit bipolar staining?
- A. Haemophilus influenzae (Correct Answer)
- B. Yersinia pestis
- C. Calymmatobacterium granulomatis
- D. Francisella tularensis
Explanation: ***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.
Question 634: Which of the following bacteria is not capsulated?
- A. Pneumococcus
- B. Klebsiella
- C. Meningococcus
- D. Proteus (Correct Answer)
Explanation: ***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.
Question 635: Pseudomonas is which type of bacteria?
- A. Anaerobic
- B. Aerobic (Correct Answer)
- C. Microaerophilic
- D. Obligate anaerobe
Explanation: ***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.
Question 636: 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 637: 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 638: 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 639: 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 640: Glass vessels and syringes are best sterilised by -
- A. Dry heat sterilization in a hot air oven (Correct Answer)
- B. Steam sterilization in an autoclave
- C. Ethylene oxide sterilization
- D. Radiation sterilization
Explanation: **Dry heat sterilization in a hot air oven** - **Dry heat sterilization** (160-180°C for 1-2 hours) is the **traditional and preferred method** for **glassware and glass syringes**. - **Hot air ovens** achieve sterilization by oxidative destruction and protein denaturation, leaving items completely **dry** and free from moisture. - **Advantages**: No corrosion, no rusting, items remain dry, ideal for **powders, oils, and glassware** that can withstand high temperatures. - **Note**: This question refers to **glass syringes** (historically used, now largely replaced by disposable plastic syringes which are pre-sterilized by radiation). *Steam sterilization in an autoclave* - **Autoclaving** uses **moist heat** (121°C at 15 psi for 15 minutes) and is highly effective for most medical instruments. - **Disadvantage for glassware**: Rapid temperature changes and steam exposure can cause **thermal shock, cracking, or etching** of delicate glassware. - Items emerge **wet** and require drying, which is undesirable for certain laboratory applications. - **Modern context**: Standard method for surgical instruments and heat-stable plastics. *Ethylene oxide sterilization* - **Ethylene oxide (ETO)** is a **low-temperature chemical sterilization** method (50-60°C) for heat-sensitive items. - Used for plastics, rubber, electronics, and endoscopes that cannot tolerate heat. - Requires **long exposure** (12-24 hours) and **aeration period** (up to 7 days) to remove toxic residues. - **Not preferred** for routine glassware sterilization when heat methods are suitable. *Radiation sterilization* - **Gamma radiation or electron beam** sterilization is used for **pre-packaged disposable medical devices**, pharmaceuticals, and plastic syringes. - Highly effective but **expensive** and requires specialized facilities. - Not practical for **routine laboratory glassware** sterilization in clinical or research settings.