Persons with heterozygous sickle cell trait are protected from infection by:
Which of the following agents is most effective in destroying bacterial spores?
Who discovered the bacterium Treponema pallidum?
All of the sterilization methods are properly matched except?
Which of the following is not a sporicidal agent?
Amoebic liver abscess can be diagnosed by demonstrating-
The outer covering of diatoms is made of?
Pseudomonas is which type of bacteria?
Which anticoagulant is used when blood is sent for blood culture?
Which of the following bacteria is not capsulated?
NEET-PG 2013 - Microbiology NEET-PG Practice Questions and MCQs
Question 11: Persons with heterozygous sickle cell trait are protected from infection by:
- A. Pneumococcus
- B. P. falciparum (Correct Answer)
- C. P. vivax
- D. Salmonella
Explanation: ***P. falciparum*** - Individuals with heterozygous sickle cell trait have a **protective effect** against severe malaria caused by *P. falciparum* due to altered red blood cell morphology [1][2]. - The sickle hemoglobin (HbAS) provides a **selective advantage**, reducing the severity of malaria infections and the parasitic load [2][3]. *P. vivax* - Sickle cell trait does not confer significant protection against *P. vivax*, which primarily infects non-sickled red blood cells [2]. - The infection still occurs in individuals with the trait because it specifically affects the reticulocyte count, which is less impacted by sickling. *Salmonella* - While sickle cell disease is linked with increased susceptibility to **Salmonella infections**, the sickle cell trait itself does not provide protection against it [2]. - The trait does not influence immunity or susceptibility to bacterial pathogens like *Salmonella*. *Pneumococcus* - Individuals with sickle cell trait still have a normal risk of **invasive pneumococcal disease**, similar to those without the trait [2]. - Protection against *Pneumococcus* primarily relates to vaccination status and not to hemoglobinopathies. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Infectious Diseases, pp. 398-400. [2] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. Common Clinical Problems From Blood And Bone Marrow Disease, pp. 598-599. [3] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. (Basic Pathology) introduces the student to key general principles of pathology, both as a medical science and as a clinical activity with a vital role in patient care. Part 2 (Disease Mechanisms) provides fundamental knowledge about the cellular and molecular processes involved in diseases, providing the rationale for their treatment. Part 3 (Systematic Pathology) deals in detail with specific diseases, with emphasis on the clinically important aspects., pp. 50-51.
Question 12: 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 13: 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 14: 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 15: 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 16: Amoebic liver abscess can be diagnosed by demonstrating-
- A. Trophozoites in the pus (Correct Answer)
- B. Trophozoites in the feces
- C. Cysts in the pus
- D. Cysts in the liver
Explanation: ***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.
Question 17: The outer covering of diatoms is made of?
- A. Magnesium
- B. Silica (Correct Answer)
- C. Hydrocarbons
- D. None of the options
Explanation: ***Correct: Silica*** - The cell walls of diatoms are primarily composed of **hydrated amorphous silica (SiO2·nH2O)**. - This rigid, intricate outer covering is known as a **frustule**, which provides structural support and protection. - Diatoms are uniquely characterized by their intricate silica cell walls, making them easily identifiable under microscopy. *Incorrect: Magnesium* - **Magnesium (Mg)** is an important metal and a component of chlorophyll, essential for photosynthesis. - While diatoms do contain magnesium for metabolic processes, it is not the primary structural component of their outer covering. *Incorrect: Hydrocarbons* - **Hydrocarbons** are organic compounds consisting entirely of hydrogen and carbon, commonly found in fossil fuels. - Diatom cell walls are inorganic (mineral-based), not organic hydrocarbon structures. *Incorrect: None of the options* - This option is incorrect because **silica** is listed among the options and is the correct answer. - Diatom frustules are definitively composed of silica.
Question 18: 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 19: Which anticoagulant is used when blood is sent for blood culture?
- A. Sodium citrate
- B. EDTA
- C. Oxalate
- D. SPS (Correct Answer)
Explanation: ***SPS*** - **SPS (Sodium Polyanethol Sulfonate)** is the preferred anticoagulant for blood cultures because it inhibits phagocytosis and complement activation, allowing microorganisms to survive and grow. - It also neutralizes the bactericidal effect of aminoglycoside antibiotics, which might be present in the patient's blood. *Sodium citrate* - **Sodium citrate** works by binding to calcium ions, preventing blood coagulation, and is typically used for coagulation studies. - It is not suitable for blood cultures as it does not have the anti-phagocytic or antibiotic-neutralizing properties of SPS. *EDTA* - **EDTA (Ethylenediaminetetraacetic acid)** is a strong chelator of calcium and is primarily used for hematology tests like complete blood counts (CBC) as it preserves cell morphology. - It can be toxic to some bacteria and would inhibit microbial growth, making it unsuitable for blood cultures. *Oxalate* - Various **oxalates** (e.g., potassium oxalate) also act as anticoagulants by precipitating calcium, and are commonly found in tubes for glucose testing when combined with a glycolytic inhibitor. - Oxalates are generally unsuitable for blood cultures because they can inhibit the growth of certain microorganisms.
Question 20: 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.