Duodenal aspirate is used in diagnosis of:
River blindness is caused by?
What is required for precipitation in comparison to agglutination?
Which of the following statements about the VDRL test is LEAST accurate?
A woman traveling from Bihar to Delhi is suspected to have Kala-azar. Suitable investigation is?
Which bacteria can be isolated using crystal violet blood agar?
Which of the following is an example of the transfer of drug resistance by conjugation?
Multiple drug resistance is transferred through -
Which medium is most commonly used for antibiotic sensitivity testing?
Which test is used to differentiate staphylococci from micrococci?
NEET-PG 2015 - Microbiology NEET-PG Practice Questions and MCQs
Question 21: Duodenal aspirate is used in diagnosis of:
- A. E histolytica
- B. Giardia lamblia (Correct Answer)
- C. Taenia solium
- D. Leishmania
Explanation: ***Giardia lamblia*** - **Duodenal aspiration** is a highly sensitive method for detecting **Giardia lamblia trophozoites** or cysts, especially in cases where stool examination is inconclusive. - This parasite primarily inhabits the **duodenum** and **upper jejunum**, making aspirate from this region an ideal diagnostic sample. *E histolytica* - **Entamoeba histolytica** (causes amoebiasis) is typically diagnosed by identifying **trophozoites** or **cysts** in **stool samples**, or through serology for invasive disease. - While it can affect the gastrointestinal tract, its primary site of colonization and pathology is the **colon**, not the duodenum. *Taenia solium* - **Taenia solium** (pork tapeworm) is diagnosed by identifying **proglottids** or **eggs** in **stool samples**. - It resides in the **small intestine**, but **duodenal aspirate** is not a standard diagnostic method for its detection. *Leishmania* - **Leishmania species** cause **leishmaniasis**, a disease diagnosed by detecting **amastigotes** in tissue biopsies (e.g., bone marrow, spleen, skin lesions) or through serological tests. - These parasites are intracellular and do not inhabit the **duodenal lumen**, making duodenal aspirate irrelevant for diagnosis.
Question 22: River blindness is caused by?
- A. Loa loa
- B. Ascaris
- C. B. malayi
- D. Onchocerca volvulus (Correct Answer)
Explanation: ***Onchocerca volvulus*** - **River blindness**, or **onchocerciasis**, is caused by the parasitic nematode *Onchocerca volvulus*. - This parasite is transmitted by the bite of infected **blackflies** (genus *Simulium*), which breed in fast-flowing rivers. *Loa loa* - *Loa loa* causes **Loiasis**, also known as African eye worm disease. - While it can manifest as an eye worm and cause itching and swelling, it does not typically lead to permanent blindness or the widespread skin lesions associated with river blindness. *Ascaris* - *Ascaris lumbricoides* causes **ascariasis**, an intestinal infection. - Symptoms are primarily gastrointestinal, such as abdominal pain, malnutrition, and, in severe cases, intestinal obstruction; it does not affect the eyes or cause blindness. *B. malayi* - *Brugia malayi* is one of the causes of **lymphatic filariasis**, also known as **elephantiasis**. - This disease primarily affects the lymphatic system, causing severe swelling in the limbs and genitals, but it does not cause blindness.
Question 23: What is required for precipitation in comparison to agglutination?
- A. Soluble antigen (Correct Answer)
- B. Increased temperature
- C. Specific cofactor
- D. Lower pH
Explanation: ***Soluble antigen*** - **Precipitation reactions** involve the interaction of antibodies with **soluble antigens** to form a detectable precipitate. - Unlike **agglutination**, which involves particulate antigens (e.g., cells), precipitation requires the antigen to be dissolved in a solution. *Increased temperature* - Most immunologic reactions, including precipitation and agglutination, are typically performed at **physiological temperatures** (e.g., 37°C) or room temperature. - An **increased temperature** is not a specific requirement that differentiates precipitation from agglutination. *Specific cofactor* - While some complex immunologic reactions might require **cofactors**, neither precipitation nor agglutination inherently requires a specific cofactor to occur. - The primary components are **antigen** and **antibody**. *Lower pH* - Both precipitation and agglutination reactions are sensitive to pH and typically occur within a **narrow pH range** close to neutral (e.g., pH 7.0-7.4). - A **lower pH** (acidic environment) could lead to antibody denaturation or non-specific aggregation, ultimately hindering the reaction rather than being a requirement.
Question 24: Which of the following statements about the VDRL test is LEAST accurate?
- A. VDRL is a treponemal-specific test with high specificity (Correct Answer)
- B. RPR is better than VDRL for monitoring drug therapy
- C. VDRL is a non-treponemal test and can give false positive results
- D. VDRL is a slide flocculation test for syphilis
Explanation: ***VDRL is a treponemal-specific test with high specificity*** - This statement is inaccurate because the **VDRL test** is a **non-treponemal** test, meaning it detects antibodies to cardiolipin, a lipid released from damaged host cells, rather than directly detecting antibodies to *Treponema pallidum*. - Non-treponemal tests like VDRL are known for their potential to produce **false-positive results** due to various conditions. *VDRL is a non-treponemal test and can give false positive results* - The **VDRL test** is indeed a **non-treponemal** test, detecting antibodies against cardiolipin, cholesterol, and lecithin. - Since it detects host-derived antibodies rather than specific *Treponema pallidum* antibodies, it is prone to **false-positive results** in conditions like autoimmune diseases, infections, and pregnancy. *RPR is better than VDRL for monitoring drug therapy* - Both **RPR (Rapid Plasma Reagin)** and VDRL are used to monitor response to therapy in syphilis, but **RPR is sometimes preferred** due to its ease of use (no need for a microscope), stability of reagents, and clearer macroscopic end-point. - The **titers of both VDRL and RPR typically decrease** after successful treatment, indicating a good response to therapy. *VDRL is a slide flocculation test for syphilis* - The **VDRL test** is a **flocculation test** where cardiolipin antigen mixed with a patient's serum (containing reagin antibodies) results in visible clumping or flocculation under a microscope. - It is used as a screening test for **syphilis**, caused by *Treponema pallidum*.
Question 25: A woman traveling from Bihar to Delhi is suspected to have Kala-azar. Suitable investigation is?
- A. P24 antigen
- B. Rk-39 test (Correct Answer)
- C. Combo RDT
- D. HRP-2 antigen
Explanation: ***Rk-39 test*** - The **Rk-39 test** is a rapid diagnostic test highly sensitive and specific for detecting antibodies against the **kinesin-related protein K39** of *Leishmania donovani*, the causative agent of **Kala-azar (visceral leishmaniasis)**. - It is particularly useful in **endemic regions** like Bihar for quick and accurate diagnosis, especially in patients with suspected Kala-azar presenting with fever, splenomegaly, and pancytopenia. *P24 antigen* - **P24 antigen** testing is primarily used for the diagnosis of **HIV infection**. - It detects the **core protein p24** of the HIV virus, which is not relevant for the diagnosis of Kala-azar. *Combo RDT* - A **Combo RDT** (Rapid Diagnostic Test), without further specification, typically refers to tests for **malaria**, which detect antigens like **HRP-2** and **aldolase**. - While RDTs are used for parasitic diseases, this general term does not specifically refer to a test for **Kala-azar**. *HRP-2 antigen* - **HRP-2 (Histidine-rich protein 2) antigen** is a specific marker for **Plasmodium falciparum**, used in the diagnosis of **malaria**. - It is not associated with the diagnosis of **Kala-azar**, which is caused by *Leishmania donovani*.
Question 26: Which bacteria can be isolated using crystal violet blood agar?
- A. Corynebacterium diphtheriae
- B. Staph aureus
- C. Meningococcus
- D. β-hemolytic streptococci (Correct Answer)
Explanation: ***β-hemolytic streptococci*** - **Crystal violet blood agar** is a selective medium that inhibits the growth of most Gram-positive bacteria, except for **beta-hemolytic streptococci**. - The crystal violet dye suppresses the growth of competing flora, allowing for better isolation and identification of these bacteria, which exhibit **complete hemolysis (beta-hemolysis)** on blood agar. *Corynebacterium diphtheriae* - This bacterium requires more specialized media, such as **Tinsdale agar** or **Loeffler's serum agar**, for optimal growth and identification due to specific nutritional requirements and colony morphology. - Crystal violet blood agar is not the primary medium used for its isolation. *Staph aureus* - **Staphylococcus aureus** is a common contaminant that is typically inhibited by the crystal violet in the medium. - It grows well on routine blood agar but is not selectively grown or isolated using crystal violet blood agar. *Meningococcus* - **Neisseria meningitidis** (Meningococcus) requires enriched media like **chocolate agar** or **Thayer-Martin agar** for successful isolation, as it is a fastidious organism. - Crystal violet blood agar is not suitable for its growth due to its inhibitory properties and lack of necessary nutrients.
Question 27: Which of the following is an example of the transfer of drug resistance by conjugation?
- A. Staphylococci to rifampicin
- B. Pneumococcus to penicillin G
- C. M tuberculosis to antitubercular drugs
- D. E coli to streptomycin (Correct Answer)
Explanation: **E coli to streptomycin** - The transfer of **streptomycin resistance** in *E. coli* is a classic example of **conjugation**, mediated by **transferable R-plasmids**. - **Conjugation** involves direct cell-to-cell contact and the transfer of genetic material via a **pilus**, allowing for efficient spread of resistance genes. *Staphylococci to rifampicin* - **Rifampicin resistance** in *Staphylococci* (e.g., MRSA) primarily results from **chromosomal mutations** in the *rpoB* gene, which alters the drug's binding site. - This type of resistance usually arises through **spontaneous mutation and selection**, rather than active transfer via conjugation. *Pneumococcus to penicillin G* - **Penicillin resistance** in *Pneumococcus* (e.g., **PEN-R *S. pneumoniae***) is often due to alterations in **penicillin-binding proteins (PBPs)**, acquired through **transformation**. - Transformation involves the uptake of **naked DNA** from the environment, not direct cell-to-cell contact as in conjugation. *M tuberculosis to antitubercular drugs* - **Drug resistance** in *Mycobacterium tuberculosis* to antitubercular drugs (such as isoniazid and rifampicin) is predominantly mediated by **chromosomal mutations**. - These mutations occur within genes encoding drug targets or drug-activating enzymes, leading to altered drug sensitivity.
Question 28: Multiple drug resistance is transferred through -
- A. Transduction
- B. Transformation
- C. Conjugation (Correct Answer)
- D. Mutation
Explanation: ***Conjugation*** - Conjugation is a primary mechanism for the spread of **antibiotic resistance genes** among bacteria, including those responsible for multiple drug resistance. - It involves the direct transfer of **plasmids** (which often carry resistance genes) from one bacterial cell to another through a pilus. *Transduction* - Transduction is the process where bacteria acquire foreign DNA, including resistance genes, via a **bacteriophage (virus)**. - While it can transfer resistance, conjugation is a more common and clinically significant route for **multidrug resistance** spread. *Transformation* - Transformation involves the uptake of **naked DNA** from the environment by a bacterial cell. - While bacteria can acquire resistance genes this way, it is less efficient for widespread, rapid transfer of **multiple resistance traits** compared to conjugation. *Mutation* - Mutation refers to a change in the bacterial organism's own DNA, which can lead to the development of **drug resistance**. - However, mutation explains the *origin* of resistance in a single bacterium, not the *transfer* of resistance genes (especially multiple resistance) between different bacteria.
Question 29: Which medium is most commonly used for antibiotic sensitivity testing?
- A. CLED agar
- B. Mueller-Hinton agar (Correct Answer)
- C. Blood agar
- D. MacConkey agar
Explanation: ***Mueller-Hinton agar*** - It is specifically formulated to provide optimal conditions for bacterial growth and **diffusion of antibiotics**, ensuring accurate and reproducible results for sensitivity testing. - Its **low concentration of sulfonamide inhibitors (thymidine and thymine)** and proper calcium and magnesium levels are crucial for accurate results for particular antibiotics. - It is the **gold standard medium** recommended by CLSI (Clinical and Laboratory Standards Institute) for the Kirby-Bauer disk diffusion method. *Blood agar* - Blood agar is a **general-purpose enrichment medium** that supports the growth of a wide range of fastidious microorganisms and is used to detect hemolytic reactions. - While many bacteria grow on blood agar, its composition and opacity can **interfere with precise zone of inhibition measurements** in antibiotic susceptibility testing. *MacConkey agar* - MacConkey agar is a **selective and differential medium** used for the isolation of Gram-negative enteric bacteria and differentiation based on lactose fermentation. - Its selective agents (bile salts and crystal violet) and pH indicators would **interfere with the standardized conditions** required for accurate antibiotic sensitivity testing. *CLED agar* - **Cystine-Lactose-Electrolyte-Deficient (CLED) agar** is primarily used for the isolation and enumeration of urinary tract pathogens, as it prevents the swarming of *Proteus* species and differentiates lactose fermenters from non-fermenters. - It is **not optimized** for antibiotic diffusion or inhibition of bacterial growth in the same way Mueller-Hinton is.
Question 30: Which test is used to differentiate staphylococci from micrococci?
- A. Coagulase test
- B. Oxidation-Fermentation (O/F) test (Correct Answer)
- C. Novobiocin sensitivity
- D. Catalase test
Explanation: ***Oxidation-Fermentation (O/F) test*** - The **oxidation-fermentation (O/F) test** is used to determine whether an organism metabolizes carbohydrates strictly oxidatively, fermentatively, or both. - **Staphylococci** are facultative anaerobes that ferment glucose, while **micrococci** are strict aerobes that metabolize glucose oxidatively, making this test key for differentiation. *Catalase test* - The catalase test differentiates **catalase-positive** organisms (like both Staphylococci and Micrococci) from **catalase-negative** organisms (like Streptococci). - Since both Staphylococci and Micrococci are catalase-positive, this test cannot differentiate between them. *Coagulase test* - The coagulase test differentiates **Staphylococcus aureus** (coagulase-positive) from other **coagulase-negative Staphylococci (CoNS)**. - This test is specific for distinguishing within the Staphylococcus genus and does not apply to Micrococci. *Novobiocin sensitivity* - Novobiocin sensitivity is primarily used to differentiate **Staphylococcus saprophyticus** (resistant) from other **coagulase-negative Staphylococci** (sensitive). - It is not used to distinguish between the genera Staphylococci and Micrococci.