NEET-PG 2012 - Microbiology PYQs Practice Questions

Q: Which of the following statements about Streptococcus is false?

Group A Streptococcus is catalase positive. ***Group A Streptococcus is catalase positive*** - This statement is false because all species of **Streptococcus**, including Group A Streptococcus (GAS), are **catalase-negative**. - The absence of the **catalase enzyme** is a key differentiating feature between streptococci and staphylococci, which are catalase-positive. *Group B causes neonatal meningitis* - **Group B Streptococcus (GBS)**, or *Streptococcus agalactiae*, is a well-known cause of **neonatal meningitis** and sepsis. - Infants can acquire GBS during passage through the birth canal from a colonized mother, leading to severe infections. *Group B lives in female genital tract* - GBS is a common commensal organism found in the **lower gastrointestinal** and **female genital tracts** of up to 30% of healthy women. - Its presence in the female genital tract poses a risk for transmission to neonates during childbirth. *Classification by Lancefield based on carbohydrate antigen* - The **Lancefield grouping system** classifies streptococci based on the presence of specific **carbohydrate antigens** in their cell walls. - This serological classification, developed by Rebecca Lancefield, divides streptococci into groups A, B, C, D, F, and G, which helps in identifying different species and their associated pathologies. [Practice more Microbiology PYQs on OnCourse]

Q: Which of the following statements is true regarding Wuchereria bancrofti?

Tail tip free from nuclei. ***Tail tip free from nuclei*** - The **microfilariae** of *Wuchereria bancrofti* are characterized by a **clean tail tip**, meaning there are no nuclei extending into the very end of the tail. - This feature is crucial for differentiating it from other microfilariae like *Brugia malayi*, which has two distinct nuclei in its tail tip. *Unsheathed* - *Wuchereria bancrofti* microfilariae are **sheathed**, meaning they retain an egg envelope as a loose covering. - An unsheathed microfilaria, like that of *Onchocerca volvulus*, lacks this outer covering. *Non-periodic* - *Wuchereria bancrofti* exhibits **nocturnal periodicity**, meaning its microfilariae are most abundant in the peripheral blood during the night. - Non-periodic microfilariae are found in the blood at any time of day, as seen with *Loa loa*. *None of the options* - This statement is incorrect because "Tail tip free from nuclei" is a true characteristic of *Wuchereria bancrofti* microfilariae. [Practice more Microbiology PYQs on OnCourse]

Q: From which strain of virus is the rabies vaccine prepared?

Fixed Virus. ***Fixed Virus*** - The rabies vaccine is prepared from **fixed virus strains**, which are **attenuated** forms of the rabies virus that have lost their pathogenicity for humans through serial passages in animals or cell cultures. - This attenuation allows the virus to induce an immune response without causing disease, making it safe and effective for vaccination. - Examples include **Pitman-Moore strain**, **Flury strain (HEP/LEP)**, and **SAD strain**. *Street virus* - The **street virus** is the term used for the **wild-type rabies virus** as it occurs naturally in infected animals and causes clinical rabies disease. - Due to its high pathogenicity and ability to cause lethal infection, the street virus is **not used** for vaccine production. *Wild virus* - **Wild virus** is another term referring to the naturally occurring, **virulent rabies virus** found in infected animals. - Like the street virus, it is too pathogenic to be used directly in vaccine preparation. *Pasteur virus* - While **Louis Pasteur** pioneered rabies vaccination, "Pasteur virus" is not a standard terminology for vaccine strains. - The term **"fixed virus"** specifically denotes laboratory-adapted, attenuated strains regardless of their origin. [Practice more Microbiology PYQs on OnCourse]

Q: What is the primary virulence factor of Neisseria gonorrhoeae?

Pili (fimbriae). ***Pili (fimbriae)*** - **Pili are the PRIMARY virulence factor** of *Neisseria gonorrhoeae*, essential for **initial attachment and colonization** of urogenital mucosa - Enable bacteria to **adhere to non-ciliated epithelial cells**, resisting mechanical clearance by urination and secretions - Undergo **antigenic variation** to evade host immune responses - Without pili, *N. gonorrhoeae* cannot establish infection *Endotoxin (lipooligosaccharide)* - *N. gonorrhoeae* possesses **LOS (lipooligosaccharide)** which causes inflammation and tissue damage - While important for pathogenesis, it is a **secondary virulence factor** - LOS contributes to symptoms but cannot cause infection without prior colonization via pili *Exotoxin* - *N. gonorrhoeae* does **not produce significant exotoxins** - Pathogenicity is mediated through **adherence factors (pili), LOS, and surface proteins** rather than secreted protein toxins - This is not a mechanism of gonococcal virulence *All of the above are incorrect* - This statement is false as **pili (fimbriae)** are definitively the primary virulence factor for *N. gonorrhoeae* [Practice more Microbiology PYQs on OnCourse]

Q: Which of the following is the most potent stimulator of Naive T-cells?

Mature dendritic cells. ***Mature dendritic cells*** - **Mature dendritic cells** are the most potent professional antigen-presenting cells (APCs) for activating **naive T cells** due to their efficient antigen processing, presentation abilities, and high expression of costimulatory molecules (e.g., CD80, CD86) and MHC-peptide complexes. - Activated by pathogens or inflammatory signals, they migrate to secondary lymphoid organs where they initiate primary immune responses by presenting antigens to and activating naive T cells. *Follicular dendritic cells* - **Follicular dendritic cells** primarily present intact antigens to **B cells** in germinal centers of secondary lymphoid organs, playing a crucial role in B cell maturation, selection, and antibody production. - They lack MHC class II molecules and thus cannot directly present antigens to naive T cells. *Macrophages* - While **macrophages** are professional APCs, they are generally less efficient than mature dendritic cells at activating **naive T cells**, especially in the initiation of primary immune responses. - They are more involved in presenting antigens to already activated T cells and clearing pathogens, often acting as secondary APCs. *B-cell* - **B cells** can act as APCs, but they are generally less efficient than **dendritic cells** in activating **naive T cells**, especially for the primary immune response. - Their primary role in antigen presentation is to present processed antigens to **helper T cells** to receive costimulation for their own activation and differentiation into plasma cells, often after being activated themselves. [Practice more Microbiology PYQs on OnCourse]

Question 1

Which of the following statements about Streptococcus is false?

Accepted Answer

Group A Streptococcus is catalase positive

Answer

Group B causes neonatal meningitis

Answer

Group B lives in female genital tract

Answer

Classification by Lancefield based on carbohydrate antigen

Question 2

Which of the following statements is true regarding Wuchereria bancrofti?

Accepted Answer

Tail tip free from nuclei

Answer

Unsheathed

Answer

Non-periodic

Answer

None of the options

Question 3

From which strain of virus is the rabies vaccine prepared?

Accepted Answer

Fixed Virus

Answer

Street virus

Answer

Wild virus

Answer

Pasteur virus

Question 4

What is the primary virulence factor of Neisseria gonorrhoeae?

Accepted Answer

Pili (fimbriae)

Answer

All of the above are incorrect

Answer

Endotoxin (lipooligosaccharide)

Answer

Exotoxin

Question 5

Which of the following is the most potent stimulator of Naive T-cells?

Accepted Answer

Mature dendritic cells

Answer

Macrophages

Answer

B-cell

Answer

Follicular dendritic cells

Question 6

What is the most common bacterial cause of multiple sinus tracts resulting from an infection of the great toe?

Accepted Answer

Actinomyces

Answer

Tuberculosis

Answer

Pseudomonas aeruginosa

Answer

Staphylococcus aureus

Question 7

Rhabditiform larvae are seen in which of the following?

Accepted Answer

Strongyloides stercoralis

Answer

Taenia solium

Answer

Diphyllobothrium latum

Answer

Trichinella spiralis

Question 8

Which of the following statements about trematodes is true?

Accepted Answer

Two hosts required

Answer

Segmented

Answer

Anus present

Answer

Body cavity present

Question 9

Who discovered the malarial parasite?

Accepted Answer

Charles Louis Alphonse Laveran

Answer

Ronald Ross

Answer

Paul Muller

Answer

Pampania

Question 10

Aseptate hyphae is not seen in which of the following fungi?

Accepted Answer

Aspergillus

Answer

Rhizopus

Answer

Mucor

Answer

Penicillium

NEET-PG 2012 — Microbiology