NEET-PG 2012 - Microbiology Practice Questions

Q: Which complement proteins are formed in the liver?

C2, C4. ***C2, C4*** - While **all complement proteins (C1-C9) are primarily synthesized in the liver**, this question (NEET PG 2012) expects this as the answer based on the context of **classical pathway activation**. - **C2** and **C4** are essential components of the **C3 convertase (C4b2a)** in both the classical and lectin pathways. - These proteins work together in the early activation steps of complement-mediated immunity. - **Clinical relevance:** Deficiencies in C2 or C4 lead to increased susceptibility to **autoimmune diseases** (especially SLE) and **recurrent infections**. *C3, C6* - **C3** is the most abundant complement protein and central to all three pathways (classical, alternative, lectin). - **C6** is part of the membrane attack complex (MAC: C5b-C6-C7-C8-C9). - Both are indeed synthesized in the liver, but this was not the expected answer for this examination question. *C5, C8* - Both **C5** and **C8** are synthesized in the liver and are crucial components of the **membrane attack complex (MAC)**. - C5 is cleaved into C5a (potent anaphylatoxin) and C5b (initiates MAC formation). - C8 binds to the C5b-C7 complex and recruits C9 for membrane pore formation. *C1* - The **C1 complex** (C1q, C1r, C1s) is synthesized in the liver and initiates the classical complement pathway. - C1q recognizes antibody-antigen complexes (IgG or IgM bound to antigen). - **C1 deficiency** is associated with severe **SLE-like syndromes** and recurrent infections. **Note:** From a purely biochemical standpoint, all major complement components are produced primarily by hepatocytes in the liver, though some can also be synthesized by macrophages and other cells. This question reflects the specific context of the original examination.

Q: Which of the following is the most common yeast pathogen?

Candida. ***Candida*** - **Candida** species, particularly *Candida albicans*, are the **most common cause of fungal infections** worldwide, ranging from superficial mucocutaneous infections to invasive systemic candidiasis. - They are part of the normal human microbiota and opportunistic pathogens, thriving in conditions like **immunocompromise**, antibiotic use, or presence of medical devices. *Mucor* - **Mucor** is a genus of mold, not yeast, and is known to cause **mucormycosis**, a severe and rapidly progressive fungal infection. - While dangerous, mucormycosis is **much rarer** compared to candidiasis. *Rhizopus* - **Rhizopus** is also a genus of mold, not yeast, and is another causative agent of **mucormycosis**, particularly in immunocompromised individuals. - Like Mucor, infections caused by Rhizopus are **less common** than those caused by Candida. *Cryptococcus* - **Cryptococcus neoformans** is a significant yeast pathogen, primarily causing **cryptococcosis**, which often manifests as meningoencephalitis in immunocompromised patients. - Although it is an important pathogen, its overall incidence is **lower than that of Candida** species.

Q: Which cells are known to cause rosette formation with sheep red blood cells?

T cells. ***T cells*** - **T cells** are the classic cells known to form rosettes with sheep red blood cells, a phenomenon called **E-rosette formation** - This interaction is mediated by the **CD2 receptor** on human T cells binding to **CD58 (LFA-3)** on sheep red blood cells - E-rosette formation was historically used as a diagnostic test to identify and enumerate T cells before the advent of flow cytometry - This is a characteristic feature of **mature T cells** and was widely used in immunology laboratories *NK cells* - **NK cells** do NOT typically form rosettes with sheep red blood cells - NK cells lack the specific CD2-mediated interaction required for classical E-rosette formation - NK cells are identified by other markers such as CD16 and CD56, and by their ability to kill target cells without prior sensitization *Monocytes* - **Monocytes** do not form rosettes with sheep red blood cells - Their primary functions include phagocytosis, antigen presentation, and cytokine production - They are identified by surface markers like **CD14** and their characteristic morphology (large size, kidney-shaped nucleus) *All types of T cells* - While this option is technically correct since all mature T cells express CD2 and can form E-rosettes, the more conventional answer is simply **"T cells"** - Both CD4+ helper T cells and CD8+ cytotoxic T cells possess the CD2 receptor and can participate in rosette formation - The distinction between "T cells" and "All types of T cells" is subtle, but "T cells" is the standard textbook answer

Q: Acute Infective Endocarditis with abscess formation is most commonly associated with

Staphylococcus. ***Staphylococcus*** - **_Staphylococcus aureus_** is the most common cause of **acute infective endocarditis (AIE)** and is particularly virulent, leading to rapid valve destruction and **abscess formation**. - Its ability to adhere to damaged endothelium and produce various toxins contributes to its high pathogenicity and propensity for complicated infections. *Listeria* - **_Listeria monocytogenes_** is a gram-positive rod known to cause meningitis and gastrointestinal infections, especially in immunocompromised individuals. - While it can rarely cause endocarditis, it is not typically associated with the majority of AIE cases or abscess formation. *Streptococcus* - **_Streptococcus_ species**, particularly **_Viridans streptococci_**, are commonly associated with **subacute infective endocarditis (SIE)** on previously damaged valves. - They generally cause a more indolent course and are less frequently linked to rapid valve destruction or abscess formation compared to _Staphylococcus aureus_. *Enterococcus* - **_Enterococcus_ species** are a common cause of endocarditis, especially in older patients, those with healthcare-associated infections, or urinary tract procedures. - While they can cause serious infections, **_Staphylococcus aureus_** remains the predominant pathogen for acute infective endocarditis with abscess formation.

Q: Which virus has the highest chance of transmission to the newborn during delivery?

HSV. ***HSV*** - **Herpes Simplex Virus (HSV)** has the **highest transmission rate during vaginal delivery** if the mother has active genital lesions, with transmission rates of **30-50% for recurrent infection** and up to **85-90% for primary infection**. - Neonatal herpes can lead to severe disseminated disease, central nervous system involvement, or mucocutaneous lesions with high morbidity and mortality. - **Cesarean section is indicated** if active lesions are present at the time of labor to prevent transmission. *CMV* - **Cytomegalovirus (CMV)** is primarily transmitted **congenitally (in utero)** rather than during delivery. - While perinatal transmission can occur through cervical secretions or blood during delivery, the rate is **much lower** than HSV and most postnatal transmission occurs through **breastfeeding**. - Intrapartum transmission, when it occurs, generally causes less severe disease compared to congenital infection. *VZV* - **Varicella-Zoster Virus (VZV)** transmission to the newborn occurs primarily when maternal infection develops **within 5 days before to 2 days after delivery**. - This can cause severe neonatal varicella, but the **overall intrapartum transmission rate is lower** than HSV. - Most severe fetal effects occur with **congenital varicella syndrome** (first or second trimester infection). *Rubella* - **Rubella** is almost exclusively transmitted **congenitally during early pregnancy**, leading to **congenital rubella syndrome**. - There is **no significant transmission during delivery** itself. - The critical period for fetal damage is during the first trimester, not at the time of birth.

Q: Most common bacterial cause of acute parotitis -

Staphylococcus Aureus. ***Staphylococcus Aureus*** - **_Staphylococcus aureus_** is the most frequent bacterial pathogen isolated in cases of **acute bacterial parotitis**. [2] - It often causes ascending infection from the oral cavity, leading to inflammation and suppuration of the parotid gland. [1] *Streptococcus Pneumonia* - While **_Streptococcus pneumoniae_** can cause various infections, it is not the primary cause of acute bacterial parotitis. - Its infections more commonly manifest as **pneumonia**, otitis media, or meningitis. *Klebsiella* - **_Klebsiella_** species are typically associated with **nosocomial infections**, particularly urinary tract infections and pneumonia. - They are a relatively uncommon cause of acute parotitis compared to _S. aureus_. *Streptococcus Viridans* - **_Streptococcus viridans_** group bacteria are common commensal organisms of the oral cavity and are often implicated in **dental caries** and **endocarditis**. - They are not a usual cause of acute bacterial parotitis.

Q: An 18-year-old girl presents with watery diarrhea. Most likely causative agent -

V. cholerae. ***V. cholerae*** - *Vibrio cholerae* is a classic cause of **acute, severe watery diarrhea** that can lead to rapid dehydration. - While other agents can cause watery diarrhea, *V. cholerae* is primarily associated with large-scale outbreaks of this symptom. *Rota virus* - While rotavirus causes **watery diarrhea**, it primarily affects **infants and young children** and is less common as the most likely cause in an 18-year-old in many settings due to widespread vaccination programs. - The diarrhea, though watery, is often accompanied by **fever and vomiting**. *Salmonella* - *Salmonella* typically causes **inflammatory diarrhea** (dysentery-like symptoms with blood/mucus in stool) or **food poisoning**, with diarrhea that may be watery but is often not as profuse or severe as cholera. - It is more commonly associated with **fever and abdominal cramps**. *Shigella* - *Shigella* causes **bacillary dysentery**, characterized by **bloody, mucoid stools**, abdominal cramps, and fever. - It is not typically associated with solely profuse watery diarrhea.

Q: Ehrlichia chaffeensis is the causative agent of -

HME. ***HME (Human Monocytic Ehrlichiosis)*** - **Ehrlichia chaffeensis** is the primary causative agent of **Human Monocytic Ehrlichiosis**, a tick-borne illness. - This bacterium primarily infects **monocytes** and macrophages, leading to characteristic intracellular inclusions called **morulae**. *Glandular fever* - Glandular fever, also known as **infectious mononucleosis**, is predominantly caused by the **Epstein-Barr virus (EBV)**. - It is characterized by fever, sore throat, lymphadenopathy, and fatigue, and is not caused by bacteria. *HGE (Human Granulocytic Ehrlichiosis)* - **Human Granulocytic Ehrlichiosis (HGE)** is caused by **Anaplasma phagocytophilum**, not *Ehrlichia chaffeensis*. - HGE primarily targets **neutrophils** (granulocytes), differentiating it from HME which targets monocytes. *None of the options* - This option is incorrect because *Ehrlichia chaffeensis* is indeed the causative agent of HME, as described above.

Q: Hanging drop method is used for:

Trichomonas. ***Trichomonas*** - The **hanging drop method** is a highly effective technique for visualizing the characteristic **motility** of *Trichomonas vaginalis*. - This method allows for the observation of living, unstained organisms directly from clinical samples, making it valuable for rapid diagnosis. *Toxoplasma* - **Toxoplasma gondii** is an intracellular parasite best identified through serological tests for **antibodies** or molecular diagnostics like **PCR**. - It does not exhibit characteristic motility in a hanging drop preparation that would aid in its direct identification. *Cryptosporidium* - **Cryptosporidium** species are typically identified by detecting **oocysts** in stool samples, often using **acid-fast staining** or **immunofluorescence assays**. - Their small size and lack of distinctive motility under a hanging drop method make this technique unsuitable for their diagnosis. *Plasmodium* - **Plasmodium** species, the causative agents of malaria, are diagnosed by visualizing **parasites within red blood cells** on **Giemsa-stained blood smears**. - The hanging drop method would not effectively identify these intracellular parasites for malaria diagnosis.

Q: All of the following cause Fournier's gangrene except:

Clostridium. ***Clostridium*** - While *Clostridium* species (especially *C. perfringens*) **CAN be isolated** from Fournier's gangrene cases and contribute to gas formation and tissue necrosis, they are **less commonly identified as primary pathogens** compared to other organisms. - In the context of this question, *Clostridium* is considered the "except" option because it is **relatively less frequently implicated** in Fournier's gangrene compared to the other listed organisms, though it is NOT entirely excluded from the microbiology of this condition. - *Clostridium* species are more classically associated with **gas gangrene (clostridial myonecrosis)** in traumatic wounds and deep muscle tissue. *Bacteroides* - ***Bacteroides fragilis*** and other **anaerobic gram-negative bacilli** are among the **most commonly isolated organisms** in Fournier's gangrene. - They produce enzymes that facilitate tissue destruction and contribute significantly to the **polymicrobial synergistic necrotizing infection**. - Essential component of the typical microbial flora in perianal and genital infections. *Streptococcus* - ***Streptococcus pyogenes*** (Group A Streptococcus) and other streptococcal species are **frequently isolated** from Fournier's gangrene. - They produce toxins and enzymes causing **rapid necrotizing fasciitis** with systemic toxicity. - Major contributor to the aggressive nature and rapid progression of the infection. *Staphylococcus* - ***Staphylococcus aureus*** (including MRSA) is **commonly found** in polymicrobial Fournier's gangrene infections. - Contributes to local tissue destruction through toxin production and enzyme activity. - Often isolated from perianal and genital skin flora, facilitating its involvement in these infections.

Question 1

Which complement proteins are formed in the liver?

Accepted Answer

C2, C4

Answer

C3, C6

Answer

C5, C8

Answer

C1

Question 2

Which of the following is the most common yeast pathogen?

Accepted Answer

Candida

Answer

Mucor

Answer

Rhizopus

Answer

Cryptococcus

Question 3

Which cells are known to cause rosette formation with sheep red blood cells?

Accepted Answer

T cells

Answer

Monocytes

Answer

NK cells

Answer

All types of T cells

Question 4

Acute Infective Endocarditis with abscess formation is most commonly associated with

Accepted Answer

Staphylococcus

Answer

Listeria

Answer

Streptococcus

Answer

Enterococcus

Question 5

Which virus has the highest chance of transmission to the newborn during delivery?

Accepted Answer

HSV

Answer

CMV

Answer

VZV

Answer

Rubella

Question 6

Most common bacterial cause of acute parotitis -

Accepted Answer

Staphylococcus Aureus

Answer

Klebsiella

Answer

Streptococcus Viridans

Answer

Streptococcus Pneumoniae

Question 7

An 18-year-old girl presents with watery diarrhea. Most likely causative agent -

Accepted Answer

V. cholerae

Answer

Rotavirus

Answer

Salmonella

Answer

Shigella

Question 8

Ehrlichia chaffeensis is the causative agent of -

Accepted Answer

HME

Answer

Glandular fever

Answer

HGE

Answer

None of the options

Question 9

Hanging drop method is used for:

Accepted Answer

Trichomonas

Answer

Toxoplasma

Answer

Cryptosporidium

Answer

Plasmodium

Question 10

All of the following cause Fournier's gangrene except:

Accepted Answer

Clostridium

Answer

Bacteroides

Answer

Streptococcus

Answer

Staphylococcus

NEET-PG 2012 — Microbiology