NEET-PG 2012 Practice Questions

Q: Brutonian lines on gums are seen in poisoning with which of the following substances?

Lead. ***Lead*** - **Brutonian lines**, also known as **Burton's lines**, are a classic sign of chronic lead poisoning, appearing as a blue or blue-black line along the gum margin. - This discoloration is caused by the reaction of circulating lead with sulfur ions released by oral bacteria, forming lead sulfide deposits in the gingival tissue. *Mercury* - Mercury poisoning can cause **gingivitis**, **stomatitis**, and excessive salivation, but typically not the distinct Burton's lines. - A characteristic feature of chronic mercury poisoning is often **erected tremor** and **erethism** (changes in mood and irritability). *Arsenic* - Chronic arsenic poisoning can lead to **hyperkeratosis** and **hyperpigmentation** of the skin (rain drop pigmentation), as well as **peripheral neuropathy**. - It does not typically cause the specific gingival discoloration seen in lead poisoning. *Zinc* - Zinc intoxication is relatively rare and often results from excessive ingestion of zinc-containing supplements or industrial exposure. - Symptoms usually include **nausea, vomiting, diarrhea**, and sometimes **copper deficiency**, but not gum line discoloration.

Q: Which species of malaria is associated with nephrotic syndrome?

P. malariae. ***P. malariae*** - *P. malariae* infection is classically associated with **quartan fever** and can lead to **nephrotic syndrome**, particularly in children [1]. - The mechanism involves the deposition of immune complexes in the glomeruli, causing **membranoproliferative glomerulonephritis**. *P. vivax* - *P. vivax* is known for causing **benign tertian malaria** and frequently leads to **relapses** due to hypnozoites in the liver [1]. - While it can cause renal dysfunction, **nephrotic syndrome** is not a characteristic complication. *P. falciparum* - *P. falciparum* is responsible for the most severe form of malaria, often complicated by **cerebral malaria**, **acute renal failure**, and **blackwater fever** [1]. - Renal complications typically present as **acute tubular necrosis** rather than nephrotic syndrome. *P. ovale* - *P. ovale* causes **mild tertian malaria** similar to *P. vivax* and is also known for **relapses** due to hypnozoites [1]. - It is the least common form of malaria and is not typically associated with **nephrotic syndrome**.

Q: Which part of bacteria is most antigenic?

Lipopolysaccharide. ***Lipopolysaccharide (LPS)*** - The **O antigen** (polysaccharide component of LPS) in Gram-negative bacteria is one of the **most antigenic** bacterial components - Highly **immunogenic**, inducing strong antibody responses (both IgM and IgG) - Used as the basis for **serological typing** of Gram-negative bacteria (e.g., E. coli O157:H7) - The polysaccharide chains are structurally diverse with multiple epitopes, creating strain-specific immunity - While lipid A component has endotoxin activity, the polysaccharide portion is the primary antigenic determinant *Protein coat* - Bacterial **surface proteins** (flagella, pili, outer membrane proteins) are indeed antigenic - However, **polysaccharides** (including capsular polysaccharides and LPS) are classically considered more potent antigens - The term "protein coat" is also somewhat non-specific in bacteriology *Nucleic acid* - **Nucleic acids** (DNA, RNA) are generally **poor antigens** on their own - Not readily accessible to antibodies as they are intracellular - Can act as pathogen-associated molecular patterns (PAMPs) for innate immunity via TLRs, but are not major antibody targets *Lipids* - **Lipids** alone are generally **non-immunogenic** due to lack of structural complexity - Too small and lack sufficient epitopes to stimulate B cell responses effectively - May act as **haptens** requiring conjugation to carrier proteins

Q: Which of the following conditions is caused by Staphylococcus aureus?

Bullous impetigo. ***Bullous impetigo*** - Bullous impetigo is a superficial skin infection characterized by **blisters (bullae)**, and is specifically caused by **Staphylococcus aureus** producing exfoliative toxins. - The toxins produced by *S. aureus* cause intraepidermal cleavage, leading to the formation of the characteristic **flaccid bullae**. *Corynebacterium minutissimum infection* - *Corynebacterium minutissimum* causes **erythrasma**, a chronic superficial skin infection characterized by well-demarcated reddish-brown patches, often in intertriginous areas. - It does not cause bullous impetigo and is typically diagnosed by its coral-red fluorescence under a **Wood's lamp**. *Haemophilus ducreyi infection* - *Haemophilus ducreyi* is the causative agent of **chancroid**, a sexually transmitted infection characterized by painful genital ulcers with a necrotic base and often accompanied by swollen, tender regional lymph nodes. - It is not associated with skin blistering or bullous impetigo. *Propionibacterium acnes infection* - *Propionibacterium acnes* (now *Cutibacterium acnes*) is a bacterium commonly implicated in **acne vulgaris**, contributing to inflammation and comedone formation within hair follicles. - It causes inflammatory lesions like papules, pustules, nodules, and cysts, rather than bullous lesions.

Q: Which of the following statements about Mycoplasma is correct?

Mycoplasma pneumoniae can cause lung infections.. ***Mycoplasma pneumoniae can cause lung infections.*** - **_Mycoplasma pneumoniae_** is a well-known cause of **atypical pneumonia**, often referred to as "walking pneumonia." - It infects the respiratory tract, leading to symptoms like **cough**, **fever**, and **sore throat**. - It is one of the most common causes of community-acquired pneumonia, especially in young adults and children. *Penicillin is effective against Mycoplasma.* - **Penicillin** and other beta-lactam antibiotics target bacterial **cell wall synthesis**. - **_Mycoplasma_** species inherently **lack a cell wall**, rendering these antibiotics ineffective. - Treatment requires antibiotics that target other mechanisms like protein synthesis (macrolides, tetracyclines). *Mycoplasma has a thick cell wall.* - **_Mycoplasma_** species are unique among bacteria because they **completely lack a cell wall**, making them pleomorphic (variable in shape). - This absence of a cell wall is a key characteristic that distinguishes them from most other bacteria. - The lack of cell wall makes them resistant to beta-lactam antibiotics and allows them to pass through bacterial filters. *Mycoplasma can be easily cultured on standard blood agar.* - **_Mycoplasma_** species are extremely **fastidious organisms** that require **specialized culture media** such as PPLO (pleuropneumonia-like organism) agar enriched with serum and yeast extract. - They cannot grow on standard blood agar or routine bacterial culture media. - Colonies are very small ("fried egg" appearance) and may take **1-3 weeks** to grow, making culture challenging.

Q: Botulism is most commonly due to -

Home-canned vegetables. ***Home-canned vegetables*** - **Home-canned vegetables** are the **most common** source of botulism, particularly improperly processed low-acid vegetables like beans, corn, and asparagus - *Clostridium botulinum* spores survive inadequate heat treatment and germinate in the **anaerobic, low-acid environment** of improperly canned foods - The **lack of sufficient heat sterilization** (pressure canning at 121°C/250°F is required) allows spore survival and subsequent toxin production - Most foodborne botulism outbreaks are traced to **home-canned vegetables** rather than commercially processed foods *Meat* - While improperly preserved meats can cause botulism, they are **not the most common source** in epidemiological data - Commercial meat processing standards and refrigeration significantly reduce this risk - Meat-associated botulism is more common in certain cultural practices involving fermented or preserved meats *Egg* - **Eggs** are not associated with botulism as they do not provide the anaerobic environment necessary for *Clostridium botulinum* toxin production - Eggs are more commonly linked to **Salmonella infections** if improperly handled or undercooked *Milk* - **Milk** and dairy products are not typical sources of botulism - **Pasteurization** and refrigeration prevent conditions favorable for *C. botulinum* growth - Dairy products are more associated with **Listeria** or **Campylobacter** if contaminated

Q: What is a key distinguishing feature of meningococci compared to gonococci?

Ferment maltose. ***Ferment maltose*** - *Neisseria meningitidis* ferments both **glucose and maltose**, which is a key biochemical characteristic used for its identification. - *Neisseria gonorrhoeae* only ferments **glucose**, differentiating it from meningococci. *Are intracellular pathogens* - Both **meningococci** (*Neisseria meningitidis*) and **gonococci** (*Neisseria gonorrhoeae*) are facultative intracellular pathogens, meaning they can survive and replicate within host cells. - Therefore, this feature does not distinguish between the two. *Are catalase positive* - Both *Neisseria meningitidis* and *Neisseria gonorrhoeae* are **catalase-positive**, meaning they produce the enzyme catalase. - This characteristic is common to both and thus cannot be used to differentiate them. *Possess a capsule* - While *Neisseria meningitidis* possesses a **polysaccharide capsule**, which is a major virulence factor, *Neisseria gonorrhoeae* typically **lacks a capsule**. - However, the ability to ferment maltose is a more direct and commonly used biochemical distinguishing feature in laboratory settings.

Q: Which type of malaria is most commonly associated with renal failure?

Falciparum. ***Falciparum*** - **Plasmodium falciparum** is notorious for its ability to cause severe and complicated malaria, including **renal failure** due to its high parasitic biomass and tendency to block microvasculature [1]. - The parasite causes red blood cells to become **sticky**, leading to sequestration in capillaries of vital organs, including the kidneys, resulting in acute tubular necrosis [1]. *Vivax* - **Plasmodium vivax** typically causes milder forms of malaria, though it can occasionally lead to severe manifestations, **renal complications are rare** compared to P. falciparum [1]. - While it can cause some organ dysfunction, it generally does not cause the severe multi-organ involvement, particularly **acute renal failure**, that P. falciparum is known for [1]. *Malariae* - **Plasmodium malariae** is associated with a chronic form of malaria and is known to cause **nephrotic syndrome** (specifically malarial nephropathy) due to immune complex deposition, rather than acute renal failure [1]. - The renal pathology in P. malariae infection is typically a **glomerulonephritis** that develops after repeated infections, which is distinct from the acute renal failure seen with P. falciparum [1]. *Ovale* - **Plasmodium ovale** is the least common type of malaria and causes a benign form of the disease, similar to P. vivax [1]. - It rarely, if ever, causes severe complications like **renal failure** [1].

Q: Regarding fungal cell wall, all are true except:

Azoles act on them. ***Azoles act on them*** - **Azole antifungals** primarily target the **ergosterol synthesis** pathway, specifically inhibiting the **lanosterol 14-alpha-demethylase** enzyme, which is located in the fungal cell membrane, not the cell wall. - While the cell wall is crucial for fungal viability, agents targeting it (e.g., **echinocandins**) are distinct from azoles. *Contains chitin* - The fungal cell wall is indeed a complex structure composed of various carbohydrates, with **chitin** being a major structural polysaccharide that provides rigidity. - Chitin is a **beta-(1,4)-linked polymer of N-acetylglucosamine** and is a unique component distinguishing fungal cells from animal cells. *Prevent osmotic damage* - The rigid fungal cell wall provides structural support and protects the cell from **environmental stresses**, particularly **osmotic lysis** in hypotonic environments. - It maintains the cell's integrity against internal **turgor pressure**, which is essential for fungal growth and survival. *Does not contain peptidoglycan* - Fungal cell walls are distinct from bacterial cell walls in their composition; they **do not contain peptidoglycan**. - **Peptidoglycan** is a characteristic component of bacterial cell walls, which is targeted by antibiotics like penicillins.

Q: Binding of gp120 causes:

Facilitation of co-receptor binding. ***Facilitation of co-receptor*** - **gp120** binding to the **CD4 receptor** on target cells induces a conformational change in gp120, which then exposes or creates a binding site for a **chemokine co-receptor** (CCR5 or CXCR4). - This interaction is crucial for the subsequent steps of viral entry, as it allows the virus to make further contact with the cell surface. *Infection of target cell* - While binding of gp120 is the *first step* in infection, it does not directly cause the infection itself. - Infection occurs after a series of events including co-receptor binding, membrane fusion, and reverse transcription. *Fusing of virus and target cell* - **Fusion** of the viral and cellular membranes is primarily mediated by **gp41**, which is part of the gp160 envelope glycoprotein complex alongside gp120. - This fusion event *follows* the binding of gp120 to CD4 and the co-receptor, as gp120 binding initiates the conformational changes that expose and activate gp41. *None of the options* - One of the provided options accurately describes a direct consequence of gp120 binding, making this option incorrect.

Question 1

Brutonian lines on gums are seen in poisoning with which of the following substances?

Accepted Answer

Lead

Answer

Mercury

Answer

Zinc

Answer

Arsenic

Question 2

Which species of malaria is associated with nephrotic syndrome?

Accepted Answer

P. malariae

Answer

P. vivax

Answer

P. falciparum

Answer

P. ovale

Question 3

Which part of bacteria is most antigenic?

Accepted Answer

Lipopolysaccharide

Answer

Lipids

Answer

Nucleic acid

Answer

Protein coat

Question 4

Which of the following conditions is caused by Staphylococcus aureus?

Accepted Answer

Bullous impetigo

Answer

Corynebacterium minutissimum infection

Answer

Haemophilus ducreyi infection

Answer

Propionibacterium acnes infection

Question 5

Which of the following statements about Mycoplasma is correct?

Accepted Answer

Mycoplasma pneumoniae can cause lung infections.

Answer

Penicillin is effective against Mycoplasma.

Answer

Mycoplasma has a thick cell wall.

Answer

Mycoplasma can be easily cultured on standard blood agar.

Question 6

Botulism is most commonly due to -

Accepted Answer

Home-canned vegetables

Answer

Egg

Answer

Milk

Answer

Meat

Question 7

What is a key distinguishing feature of meningococci compared to gonococci?

Accepted Answer

Ferment maltose

Answer

Are intracellular pathogens

Answer

Are catalase positive

Answer

Possess a capsule

Question 8

Which type of malaria is most commonly associated with renal failure?

Accepted Answer

Falciparum

Answer

Vivax

Answer

Malariae

Answer

Ovale

Question 9

Regarding fungal cell wall, all are true except:

Accepted Answer

Azoles act on them

Answer

Contains chitin

Answer

Prevent osmotic damage

Answer

Does not contain peptidoglycan

Question 10

Binding of gp120 causes:

Accepted Answer

Facilitation of co-receptor binding

Answer

Infection of target cell

Answer

Fusing of virus and target cell

Answer

None of the options

NEET-PG 2012

Dental

Internal Medicine

Microbiology