NEET-PG 2013 - Microbiology Practice Questions

Q: Milk ring test is done to detect which organism present in milk?

Brucella. ***Brucella*** - The **milk ring test (MRT)** is a rapid serological test used for the detection of **Brucella antibodies** in milk samples, indicating an infection in the herd. - This test is crucial for screening dairy cattle and helps in the control and eradication of **brucellosis**, a zoonotic disease. *Bordetella* - **Bordetella** species are primarily associated with **respiratory infections** in humans and animals, such as whooping cough (B. pertussis). - They are not typically detected in milk using serological tests like the milk ring test. *Bartonella* - **Bartonella** species are known to cause diseases like **cat scratch disease** and **trench fever**, often transmitted by vectors. - They are not commonly associated with milk contamination or detected by the milk ring test. *Mycobacterium* - **Mycobacterium** species, particularly **M. bovis**, can cause tuberculosis in cattle and be transmitted through milk. - While important for milk safety, their detection usually involves different methods like **tuberculin skin tests**, **culture**, or **PCR**, not the milk ring test.

Q: Prions are best killed by

Autoclaving at 134°C (for 18 minutes). ***Autoclaving at 134°C (for 18 minutes)*** - **Prions** are highly resistant to conventional sterilization methods, and **autoclaving at 134°C for at least 18 minutes** is the **most effective method for sterilizing reusable medical instruments** contaminated with prions. - This high temperature and pressure protocol (WHO/CDC recommended) helps to denature the misfolded protein structure of prions, reducing their infectivity to safe levels. - **In the context of sterilization and disinfection**, this is the best practical method for surgical instruments that cannot be discarded. *Incineration at high temperatures* - **Incineration at 800-1000°C** achieves complete combustion and is **highly effective** at destroying prions. - However, incineration is used only for **single-use disposable items** and prion-contaminated waste, not for reusable surgical instruments. - In the clinical context of sterilization (implied by this topic), autoclaving is the preferred answer as it applies to reusable equipment. *Sodium hypochlorite solution* - **Sodium hypochlorite** (bleach) at **high concentrations** (20,000 ppm or 2% available chlorine) for extended contact times (1+ hours) can inactivate prions. - However, it is **corrosive to instruments**, damages tissue samples, and requires precise concentration and exposure conditions, making it less practical than autoclaving. *5% formalin solution* - Formalin is **not effective at inactivating prions**; it can actually **preserve and stabilize** prion infectivity. - Formalin cross-links proteins and preserves tissue morphology but does not reliably break down the highly stable **beta-sheet structures** characteristic of prions.

Q: Which is not a DNA virus?

Rhabdovirus. ***Rhabdovirus*** - Rhabdoviruses, such as the rabies virus, are characterized by their **single-stranded RNA genome** and distinctive bullet-shaped morphology. - They replicate in the cytoplasm of infected cells, using their **RNA-dependent RNA polymerase** to transcribe their genome. *Papovavirus* - Papovaviruses (now split into Papillomaviridae and Polyomaviridae) are **DNA viruses** known for causing warts and some cancers. - They possess a small, **double-stranded, circular DNA genome**. *Poxvirus* - Poxviruses are large, complex **DNA viruses** that replicate entirely within the cytoplasm of the host cell. - They have a **double-stranded DNA genome** and are notable for causing diseases like smallpox and molluscum contagiosum. *Parvovirus* - Parvoviruses are among the smallest viruses, characterized by their **single-stranded DNA genome**. - They require actively dividing host cells to replicate their **linear DNA**.

Q: Which of the following is a superantigen ?

TSST. ***TSST*** - **Toxic Shock Syndrome Toxin-1 (TSST-1)** is a classic example of a superantigen produced by *Staphylococcus aureus*. - Superantigens **bind directly to MHC class II molecules and T-cell receptors (TCRs)** outside of the antigen-binding groove, leading to non-specific activation of a large percentage of T cells and a massive release of cytokines. *Cholera toxin* - **Cholera toxin** is an exotoxin produced by *Vibrio cholerae* that causes massive fluid secretion in the intestine by **activating adenylate cyclase** in enterocytes. - It functions by **ADP-ribosylating the Gs alpha subunit**, leading to constitutive activation of cyclic AMP production, but it is not a superantigen. *Diphtheria toxin* - **Diphtheria toxin**, produced by *Corynebacterium diphtheriae*, inhibits protein synthesis in eukaryotic cells by **ADP-ribosylating elongation factor-2 (EF-2)**. - This action leads to cell death and the characteristic pseudomembrane formation in diphtheria, but it does not act as a superantigen. *Vero-cytoxin* - **Vero-cytoxin** (also known as Shiga toxin or Shiga-like toxin) is produced by *E. coli* O157:H7 and other Shiga toxin-producing *E. coli* (STEC). - It inhibits protein synthesis by **cleaving ribosomal RNA**, primarily causing damage to intestinal cells and renal endothelial cells, but it is not a superantigen.

Q: What are the changes in the variable region of immunoglobulins?

Idiotype. ***Idiotype*** - **Idiotype** refers to the unique set of antigenic determinants in the **variable region** of an antibody molecule, specifically within the **hypervariable regions (complementarity-determining regions, CDRs)**. - These unique determinants allow antibodies to recognize specific antigens and are generated by the specific **V(D)J gene rearrangements** in B cells. *Isotype* - **Isotype** refers to the constant region of an antibody, determining its class (e.g., **IgG, IgM, IgA, IgD, IgE**). - This region defines the antibody's effector functions and has nothing to do with the antigen-binding variability. *Allotype* - **Allotype** refers to minor genetic variations within the **constant region** of an antibody molecule within a species. - These variations are due to different alleles inherited from parents and are not associated with the variable region that binds to antigens. *Epitope* - An **epitope** is the specific part of an **antigen** that an antibody or T-cell receptor recognizes and binds to. - It is a feature of the antigen, not a change within the variable region of the immunoglobulin itself.

Q: Which of the following bacteria is not capsulated?

Proteus. ***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.

Q: What is the cause of rabies in wild animals?

Wild-type rabies virus. ***Wild-type rabies virus*** - Rabies in wild animals is caused by infection with the **wild-type rabies virus (Lyssavirus)**, which is maintained in specific wildlife reservoirs. - Rabies virus is a **neurotropic RNA virus** belonging to the family *Rhabdoviridae*. - This virus is transmitted through the saliva of an infected animal, typically via a **bite**. *Laboratory passage in rabbits* - **Laboratory passage in animals**, particularly rabbits, was a historical *method for attenuating the rabies virus* to develop vaccines (e.g., Pasteur's vaccine), not a cause of infection in wild animals. - Attenuated viruses are **less virulent** and do not represent the primary cause of naturally occurring rabies in wildlife. *Fatal encephalitis within 6 days* - This statement describes a **rapid progression of the disease**, which can occur, but it is a *consequence of infection*, not the cause itself. - The incubation period for rabies can vary significantly in animals, from days to months, depending on the **site of the bite** and **viral load**. *Negri bodies are not observed* - **Negri bodies** are *pathognomonic microscopic inclusions* found in the brain cells of animals infected with rabies. - Their *absence* would generally suggest that the animal does not have rabies, making this an incorrect statement about the disease's characteristics.

Q: Child having perianal pruritus with the following eggs is due to -

E. vermicularis. ***E. vermicularis*** - **Enterobius vermicularis**, or **pinworm**, is a common cause of **perianal pruritus** in children, particularly at night, due to the female worms migrating to the perianal region to lay eggs. - The characteristic eggs are **oval, flattened on one side**, and are typically identified via the **scotch tape test** around the anus. *Ascaris* - **Ascaris lumbricoides** causes **ascariasis**, which usually presents with **gastrointestinal symptoms** or **pulmonary symptoms** during larval migration, not typically perianal pruritus. - Their eggs are characteristically **mammillated** (roughened outer layer) and typically found in **feces**, not perianal region. *Ancylostoma duodenale* - **Ancylostoma duodenale** causes **hookworm infection**, leading to **iron deficiency anemia** due to blood loss in the intestines. - Hookworm eggs are characteristically **oval, thin-shelled**, and contain a developing **larva**, found in feces. *S. stercoralis* - **Strongyloides stercoralis** causes **strongyloidiasis**, which can present with skin manifestations (larva currens), gastrointestinal issues, or pulmonary symptoms. - It is unique because it causes **auto-infection** and primarily diagnostic stages are **rhabditiform larvae** in stool, not eggs, although eggs are rarely seen in stool.

Q: The fungus with septate hyphae and dichotomous branching is?

Aspergillus. ***Aspergillus*** - *Aspergillus* species are characterized by their **septate hyphae** and **acute-angle branching** (branching at approximately 45-degree angles), which are key distinguishing features in histopathology. - This branching pattern is sometimes referred to as "dichotomous branching" in medical literature, though true dichotomous branching is more characteristic of certain tissue forms. - This fungal morphology is often seen in infections such as **invasive aspergillosis** in immunocompromised patients. *Penicillium* - *Penicillium* also has **septate hyphae**, but its branching pattern is typically *not acute-angled or dichotomous*. - It is more commonly known for its **brush-like** conidiophores (penicillus) in culture rather than distinctive tissue branching patterns. *Mucor* - *Mucor* is a type of **zygomycete** (now classified under Mucorales) and is characterized by **aseptate or sparsely septate hyphae** with **irregular, right-angle branching**. - This is a key histological feature distinguishing it from *Aspergillus* in cases of **mucormycosis**. *Rhizopus* - Similar to *Mucor*, *Rhizopus* is also a zygomycete with **aseptate or sparsely septate hyphae** and **irregular, wide-angle branching**. - It is often identified in culture by the presence of **rhizoids** (root-like structures) and sporangiophores.

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

Body cavity is present in trematodes. ***Body cavity is present in trematodes*** - Trematodes are **flatworms** (Platyhelminthes), which are **acoelomate**, meaning they lack a true body cavity or coelom. - Their internal organs are embedded in a **parenchymal tissue** rather than being suspended within a fluid-filled cavity. *Alimentary canal is complete in Nematodes* - **Nematodes** (roundworms) possess a **complete alimentary canal**, with a distinct mouth, intestine, and anus. - This allows for **unidirectional flow of food** and waste through their digestive system. *Nematodes have separate sexes* - **Nematodes** are generally **dioecious**, meaning they have separate male and female individuals. - This sexual dimorphism is a characteristic feature for most species within this phylum. *Alimentary canal is Present but incomplete* - The statement refers to the digestive system of **Platyhelminthes** (flatworms) like trematodes and cestodes, where the alimentary canal is present but **incomplete** (lacking an anus). - This means they have a **single opening** that serves as both mouth and anus for digestion.

Question 1

Milk ring test is done to detect which organism present in milk?

Accepted Answer

Brucella

Answer

Mycobacterium

Answer

Bordetella

Answer

Bartonella

Question 2

Prions are best killed by

Accepted Answer

Autoclaving at 134°C (for 18 minutes)

Answer

Incineration at high temperatures

Answer

5% formalin solution

Answer

Sodium hypochlorite solution

Question 3

Which is not a DNA virus?

Accepted Answer

Rhabdovirus

Answer

Poxvirus

Answer

Papovavirus

Answer

Parvovirus

Question 4

Which of the following is a superantigen ?

Accepted Answer

TSST

Answer

Cholera toxin

Answer

Diphtheria toxin

Answer

Vero-cytoxin

Question 5

What are the changes in the variable region of immunoglobulins?

Accepted Answer

Idiotype

Answer

Isotype

Answer

Epitope

Answer

Allotype

Question 6

Which of the following bacteria is not capsulated?

Accepted Answer

Proteus

Answer

Pneumococcus

Answer

Klebsiella

Answer

Meningococcus

Question 7

What is the cause of rabies in wild animals?

Accepted Answer

Wild-type rabies virus

Answer

Laboratory passage in rabbits

Answer

Fatal encephalitis within 6 days

Answer

Negri bodies are not observed

Question 8

Child having perianal pruritus with the following eggs is due to -

Accepted Answer

E. vermicularis

Answer

Ascaris

Answer

Ancylostoma duodenale

Answer

S. stercoralis

Question 9

The fungus with septate hyphae and dichotomous branching is?

Accepted Answer

Aspergillus

Answer

Penicillium

Answer

Mucor

Answer

Rhizopus

Question 10

Which of the following statements about Helminths is false?

Accepted Answer

Body cavity is present in trematodes

Answer

Alimentary canal is complete in Nematodes

Answer

Nematodes have separate sexes

Answer

Alimentary canal is present but incomplete in trematodes

NEET-PG 2013 — Microbiology