NEET-PG 2013 - Microbiology Practice Questions

Q: Maximum density of microfilariae in blood is reported to be between -

11 pm to 2 am. ***11 pm to 2 am*** - This period aligns with the **nocturnal periodicity** of *Wuchereria bancrofti* and *Brugia malayi* microfilariae, which are the most common causes of filariasis. - The microfilariae migrate to the **peripheral circulation** during these hours, making it the optimal time for blood smear collection for diagnosis. *9 pm to 11 pm* - While still within the active period for microfilarial migration, the **peak density** is generally observed slightly later. - Blood drawn during this time might show microfilariae, but in lower concentrations compared to the peak. *8 pm to 10 pm* - This timing is generally a little too early to consistently capture the **highest microfilarial load** in nocturnal periodic infections. - The microfilariae are still in the process of migrating from deeper tissues to the peripheral blood. *2 am to 5 am* - By this time, the microfilarial density in the peripheral blood of **nocturnal periodic species** usually starts to decline. - While some microfilariae may still be present, the count would likely be lower than during the earlier peak hours.

Q: An adolescent male developed vomiting and diarrhea 1 hour after having food from a restaurant. The most likely pathogen is?

Staphylococcus aureus. ***Staphylococcus aureus*** - The rapid onset of symptoms (within 1 hour) strongly suggests **pre-formed toxin ingestion**, which is characteristic of *Staphylococcus aureus* food poisoning. - While the typical incubation period is **1-6 hours** (average 2-4 hours), onset within 1 hour can occur with **high toxin loads** in contaminated food. - **Vomiting** is often the predominant symptom, occurring shortly after consuming contaminated food, which distinguishes it from other bacterial causes. *Clostridium perfringens* - Onset of symptoms caused by *Clostridium perfringens* is typically **8-16 hours** after ingestion, which is much longer than observed here. - It primarily causes **diarrhea and abdominal cramps** due to toxin production in the intestine, with minimal vomiting. *Vibrio parahaemolyticus* - Symptoms usually appear **4-96 hours** (average 12-24 hours) after consuming contaminated seafood, which is a longer incubation period than described. - It typically causes **watery diarrhea**, abdominal cramps, nausea, and occasional vomiting, but not within 1 hour. *Salmonella* - The incubation period for *Salmonella* infection is typically **6-72 hours** (average 12-36 hours), making it highly unlikely for symptoms to appear within 1 hour. - **Diarrhea, fever, and abdominal cramps** are common with *Salmonella*, but rapid-onset vomiting from pre-formed toxin is not its mechanism.

Q: Waterhouse-Friderichsen syndrome is seen in:

Neisseria meningitidis. ***Neisseria meningitidis*** - **Waterhouse-Friderichsen syndrome** is a severe complication of **meningococcal sepsis**, predominantly caused by *Neisseria meningitidis* [1]. - It is characterized by **adrenal gland hemorrhage**, leading to acute adrenal insufficiency, hemorrhagic skin rash, and shock [1]. *Pseudomonas* - While *Pseudomonas aeruginosa* can cause severe infections, including sepsis, it is **not typically associated** with Waterhouse-Friderichsen syndrome. - *Pseudomonas* infections often lead to **ecthyma gangrenosum** in immunocompromised patients, a different dermatological manifestation. *Yersinia* - *Yersinia* species can cause various infections, such as **yersiniosis** (gastroenteritis) and **plague** (*Yersinia pestis*). - These infections do not commonly present with the distinct features of **adrenal hemorrhage** and **fulminant sepsis** seen in Waterhouse-Friderichsen syndrome. *Pneumococci* - *Streptococcus pneumoniae* (**pneumococci**) is a common cause of **meningitis** and **sepsis**, especially in children and the elderly. - Although it can lead to severe bloodstream infections, it is **rarely specifically linked** to the adrenal hemorrhage syndrome known as Waterhouse-Friderichsen syndrome.

Q: Infective form of Hookworms?

Filariform larva. ***Filariform larva*** - The **filariform larva (L3)** is the infective stage of hookworms, capable of penetrating intact skin. - Upon penetration, these larvae migrate through the bloodstream to the lungs, then up the bronchial tree to be swallowed, eventually maturing in the intestines. *Egg* - Hookworm **eggs** are passed in the feces of infected individuals and are not infective to humans directly. - They require favorable conditions (warm, moist soil) to embryonate and hatch into rhabditiform larvae. *Rhabditiform larva* - The **rhabditiform larva (L1)** is the first larval stage that hatches from the egg in the soil. - It is a non-infective, free-living stage that feeds on bacteria and molts twice to become the infective filariform larva. *Adult worm* - **Adult worms** reside in the small intestine of the host and are not the infective form. - They attach to the intestinal mucosa and feed on blood, causing the characteristic anemia associated with hookworm infection.

Q: Which staining method is specifically used for the detection of mycoplasma?

Dienes method. ***Dienes method*** - The **Dienes staining method** is a specialized procedure used specifically to identify **Mycoplasma colonies** grown on agar medium. - It works by staining the characteristic **fried-egg appearance** of Mycoplasma colonies. *Fontana method* - The Fontana method is a **silver impregnation stain** used primarily for the visualization of **spirochetes**, such as *Treponema pallidum*. - It is not suitable for detecting Mycoplasma due to their distinct cellular structure and size differences compared to spirochetes. *Lavaditi method* - The Lavaditi method is another type of **silver stain** developed for the detection of **spirochetes** in tissue sections. - Similar to the Fontana method, it is not appropriate for the identification of Mycoplasma. *No applicable method* - This statement is incorrect as the **Dienes method** is, in fact, specifically applicable and widely used for the detection and identification of Mycoplasma colonies. - There are established microbiological techniques for identifying Mycoplasma.

Q: Macrophage tropic strains of HIV use which co-receptor?

CCR5. ***CCR5*** - **Macrophage-tropic** HIV strains, also known as **R5 strains**, primarily use the **CCR5 co-receptor** to enter target cells. - These strains are typically involved in the **initial infection** and transmission of HIV. - CCR5-tropic viruses are usually the **predominant strains transmitted** during sexual transmission. *CXCR4* - **T-cell-tropic** HIV strains, or **X4 strains**, preferentially utilize the **CXCR4 co-receptor** for cell entry. - These strains are associated with a **more rapid decline in CD4+ T-cell counts** during later stages of HIV infection. - Emergence of X4 strains is linked to **disease progression**. *CCR3* - While a chemokine receptor, **CCR3** is not a primary co-receptor used by common HIV strains for entry into macrophages or T cells. - CCR3 is primarily involved in **eosinophil chemotaxis** and allergic responses. *CCR2* - **CCR2** is another chemokine receptor but is **not a major co-receptor** for HIV entry. - While some laboratory-adapted strains may show minor usage, it is not clinically significant for macrophage-tropic HIV strains.

Q: JSB stain is used for which parasite?

Filaria. ***Filaria*** - The **JSB stain (Jaswant Singh Battacharya stain)** is a rapid Romanowsky-type stain specifically developed for the diagnosis of **microfilariae** in blood films. - It allows for clear visualization of the sheaths and nuclei of microfilariae, which is crucial for species identification and diagnosis of **filariasis**. *Malaria* - **Giemsa stain** is the gold standard for identifying malaria parasites in thick and thin blood smears, not JSB stain. - Giemsa allows for detailed morphological differentiation of malaria species and stages within **red blood cells**. *Kala azar* - **Kala-azar (visceral leishmaniasis)** is diagnosed by detecting **Leishman bodies (amastigotes)** in bone marrow, splenic, or lymph node aspirates. - Stains like **Giemsa** or **Leishman stain** are traditionally used for visualizing these amastigotes. *Sleeping sickness* - **Sleeping sickness (African trypanosomiasis)** is diagnosed by identifying **trypomastigotes** in blood smears, lymph node aspirates, or cerebrospinal fluid. - **Giemsa stain** is commonly used for the microscopic examination of these specimens to detect the parasites.

Q: Which organism is responsible for producing Draughtsman (Concentric Rings) on culture?

Bacillus anthracis. ***Bacillus anthracis*** - *Bacillus anthracis* is the organism responsible for producing the characteristic **"Draughtsman" or "Concentric Rings"** pattern on culture media - On blood agar, colonies show a **"Medusa head"** appearance with **concentric rings** and **comma-shaped projections** radiating outward from the center - This distinctive morphology results from chains of bacilli growing in parallel alignment, creating the characteristic pattern - The colonies are typically **non-hemolytic, grey-white, and have irregular edges** *H. ducreyi* - *Haemophilus ducreyi* causes **chancroid** and is difficult to culture - Colonies appear as **small, grey-yellow, translucent** with a **cohesive ("school of fish")** appearance when pushed across the agar - Does not produce concentric rings *B. pertussis* - *Bordetella pertussis* grows on **Bordet-Gengou agar** or **Regan-Lowe medium** - Colonies have a characteristic **"mercury droplet"** or **"bisected pearl"** appearance due to their smooth, shiny, convex morphology - This is completely different from the Draughtsman pattern *Pneumococci* - *Streptococcus pneumoniae* produces **alpha-hemolytic colonies** on blood agar - Colonies are **small, dome-shaped, mucoid** with a **central umbilication** (draughtsman or checker-piece appearance refers to the depression, not concentric rings) - The "draughtsman" term when applied to pneumococci refers to the flattened checker-piece shape, not the concentric ring pattern of *B. anthracis*

Q: Pneumococcal vaccine is prepared from ?

Capsular polysaccharide. ***Capsular polysaccharide*** - The **polysaccharide capsule** of *Streptococcus pneumoniae* is the primary virulence factor, protecting the bacteria from phagocytosis. - Vaccines, such as **PCV13** (pneumococcal conjugate vaccine) and **PPSV23** (pneumococcal polysaccharide vaccine), are designed targeting these capsular polysaccharides to elicit a protective immune response. *Cell surface antigen* - While bacteria possess various **cell surface antigens**, not all are immunogenic or provide protective immunity as effectively as the capsular polysaccharides for *S. pneumoniae*. - For pneumococcus, the **capsule** is the most critical surface component for vaccine development due to its role in virulence and serotype specificity. *From exotoxin* - *S. pneumoniae* primarily causes disease through its **polysaccharide capsule** and other bacterial components, not through the production of an **exotoxin** that would be targeted by a vaccine. - Vaccines developed from exotoxins (e.g., diphtheria or tetanus toxoids) target specific toxins, which is not the mechanism for pneumococcal vaccines. *From M protein* - **M protein** is a major virulence factor for *Streptococcus pyogenes* (Group A Strep), not *Streptococcus pneumoniae*. - Vaccines targeting M protein are associated with **Group A Streptococcus** infections, for protection against diseases like rheumatic fever.

Q: Which fungus is commonly known as golden yellow jelly fungus?

Tremella mesenterica. ***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 1

Maximum density of microfilariae in blood is reported to be between -

Accepted Answer

11 pm to 2 am

Answer

9 pm to 11 pm

Answer

8 pm to 10 pm

Answer

2 am to 5 am

Question 2

An adolescent male developed vomiting and diarrhea 1 hour after having food from a restaurant. The most likely pathogen is?

Accepted Answer

Staphylococcus aureus

Answer

Clostridium perfringens

Answer

Vibrio parahaemolyticus

Answer

Salmonella

Question 3

Waterhouse-Friderichsen syndrome is seen in:

Accepted Answer

Neisseria meningitidis

Answer

Yersinia

Answer

Pseudomonas

Answer

Pneumococci

Question 4

Infective form of Hookworms?

Accepted Answer

Filariform larva

Answer

Egg

Answer

Rhabditiform larva

Answer

Adult worm

Question 5

Which staining method is specifically used for the detection of mycoplasma?

Accepted Answer

Dienes method

Answer

Fontana method

Answer

Lavaditi method

Answer

No applicable method

Question 6

Macrophage tropic strains of HIV use which co-receptor?

Accepted Answer

CCR5

Answer

CXCR4

Answer

CCR3

Answer

CCR2

Question 7

JSB stain is used for which parasite?

Accepted Answer

Filaria

Answer

Kala azar

Answer

Sleeping sickness

Answer

Malaria

Question 8

Which organism is responsible for producing Draughtsman (Concentric Rings) on culture?

Accepted Answer

Bacillus anthracis

Answer

B. pertussis

Answer

H. ducreyi

Answer

Pneumococci

Question 9

Pneumococcal vaccine is prepared from ?

Accepted Answer

Capsular polysaccharide

Answer

Cell surface antigen

Answer

Exotoxin

Answer

M protein

Question 10

Which fungus is commonly known as golden yellow jelly fungus?

Accepted Answer

Tremella mesenterica

Answer

T. tonsurans

Answer

Epidermophyton floccosum

Answer

T. mentagrophytes

NEET-PG 2013 — Microbiology