INI-CET 2023 - Microbiology PYQs Practice Questions

Q: A person handling cat feces is at risk of transmitting an infection. Which of the following is the infective stage of the organism transmitted through cat feces?

Oocyst. ***Oocyst*** - The **oocyst** is the infective stage of *Toxoplasma gondii* that is shed in cat feces. - Cats are the definitive host where sexual reproduction occurs in the intestinal epithelium, producing oocysts. - Humans can become infected by ingesting these **oocysts** directly from contaminated cat litter or soil, or indirectly through contaminated food or water. - Oocysts become infective (sporulated) after 1-5 days in the environment. *Bradyzoite* - **Bradyzoites** are slow-growing forms of *Toxoplasma gondii* found within tissue cysts, particularly in muscle and brain tissue. - While they can be infective if undercooked meat containing cysts is consumed, they are not present in cat feces. - This represents a different route of transmission (foodborne via tissue cysts). *Tachyzoite* - **Tachyzoites** are rapidly multiplying forms of *Toxoplasma gondii* responsible for acute infection and tissue damage. - They are found within host cells during active infection and are not shed in cat feces. - They can cross the placenta causing congenital toxoplasmosis. *Gametocyte* - While **gametocytes** (sexual stages) do develop in the cat's intestinal epithelium during *Toxoplasma gondii* reproduction, they are not the stage shed in feces. - The product of sexual reproduction—the **oocyst**—is what gets excreted and serves as the infective stage. - In contrast, gametocytes of *Plasmodium* species remain in blood and are relevant for malaria transmission. [Practice more Microbiology PYQs on OnCourse]

Q: A man has undergone renal transplant and is taking immunosuppressant drug. On biopsy there was presence of budding cells with pseudohyphae. Identify the organism?

Invasive candidiasis. ***Invasive candidiasis*** - The presence of **budding cells** and **pseudohyphae** on biopsy is a classic histological finding for *Candida* species. - Individuals who have undergone **renal transplant** and are on **immunosuppressant drugs** are at high risk for opportunistic fungal infections, including invasive candidiasis. *Pneumocystis* - *Pneumocystis jirovecii* typically causes pneumonia and is characterized by cysts or trophic forms in lung tissue, not budding cells and pseudohyphae. - While common in immunocompromised patients, its microscopic morphology is distinctly different from *Candida*. *Invasive aspergillosis* - *Aspergillus* species are characterized by **septate hyphae with acute angle branching** (typically 45-degree angles) on microscopy. - They do not form budding cells or pseudohyphae, which are characteristic of *Candida*. *Histoplasmosis* - *Histoplasma capsulatum* appears as **small, oval-shaped yeast cells** (2-4 µm) often found within macrophages. - It does not form pseudohyphae or large budding cells as described in the question. [Practice more Microbiology PYQs on OnCourse]

Q: A peculiar organism has resistance to azithromycin, but is sensitive to ticarcillin, clavulanic acid, cotrimoxazole. Identify the organism?

Stenotrophomonas. ***Stenotrophomonas*** - *Stenotrophomonas maltophilia* is intrinsically **resistant to azithromycin** and other macrolides due to its efflux pumps. - It is known to be sensitive to **ticarcillin-clavulanic acid** (a beta-lactam/beta-lactamase inhibitor combination) and **cotrimoxazole** (trimethoprim-sulfamethoxazole), which are common treatment options. *Pseudomonas* - *Pseudomonas aeruginosa* is generally **resistant to macrolides like azithromycin** but can exhibit varying sensitivity to antibiotics. - However, it often shows resistance to cotrimoxazole and ticarcillin-clavulanic acid is not a first-line agent, and it would typically be sensitive to other antipseudomonal beta-lactams (e.g., piperacillin-tazobactam, carbapenems). *Staphylococcus* - Many *Staphylococcus* species, particularly **MRSA**, are resistant to azithromycin. - However, *Staphylococcus* species are typically sensitive to other antibiotics like **vancomycin**, and are generally not sensitive to ticarcillin-clavulanic acid, and their susceptibility to cotrimoxazole varies depending on the species and resistance mechanisms. *Mycoplasma* - *Mycoplasma* species are **intrinsically resistant to beta-lactam antibiotics like ticarcillin** because they lack a cell wall, which is the target of these drugs. - They are typically sensitive to macrolides like azithromycin and also to cotrimoxazole. [Practice more Microbiology PYQs on OnCourse]

Q: CD40 deficiency in a person signifies?

IgM increase. ***IgM increase*** - A deficiency in **CD40**, or its ligand **CD40L** (found on T helper cells), disrupts **T-cell-dependent B cell activation** and **class switching**. - Without proper signaling through CD40/CD40L, B cells cannot undergo **isotype switching** from **IgM** to IgG, IgA, or IgE, leading to elevated IgM levels and deficiencies in other antibody classes. *IgG increase* - **IgG levels** would likely be **decreased** in CD40 deficiency due to the impaired ability of B cells to undergo **class switching** from IgM to other antibody isotypes. - The primary role of CD40/CD40L interaction is to facilitate this class switching process. *T cell absent* - **CD40 deficiency** does not directly cause the absence of **T cells**; rather, it affects the ability of T cells to adequately activate B cells. - T-cell absence or severe dysfunction would be indicative of a different primary immunodeficiency, such as **SCID (Severe Combined Immunodeficiency)**. *B cell absent* - **CD40 deficiency** does not result in the absence of **B cells**; B cells are present but are dysfunctional in terms of antibody class switching. - Conditions like **X-linked agammaglobulinemia (XLA)** are characterized by the absence or severe deficiency of B cells. [Practice more Microbiology PYQs on OnCourse]

Q: CD 40 marker is absent in the person. Which of the following would be seen?

Impaired B cell function. ***Impaired B cell function*** - The **CD40 receptor** on B cells is crucial for receiving co-stimulatory signals from **CD40 ligand (CD40L)**, primarily expressed on activated T cells. - Absence of CD40 on B cells prevents proper **T-cell dependent antibody class switching** and germinal center formation, leading to impaired B cell activation, immunoglobulin production, and immune responses. - This condition is seen in **Hyper-IgM Syndrome Type 3** (very rare autosomal recessive disorder). *Impaired Macrophage function* - While macrophages express CD40, its absence would primarily affect their ability to be fully activated by T cells and present antigens, but the most direct and profound impact of absent CD40 is on B cells themselves. - Macrophages have other activation pathways not directly dependent on CD40. *Impaired NK cell function* - **Natural killer (NK) cells** primarily recognize and kill target cells lacking MHC class I molecules or those expressing activating ligands, independent of CD40 signaling. - NK cell function is not directly regulated by the CD40-CD40L interaction. *Impaired T cell function* - While **T cells express CD40L** (the ligand for CD40), the question specifies the absence of the **CD40 marker** itself, which is expressed on B cells, not T cells. - T cell function involves antigen recognition, activation, and cytokine production, which are not directly mediated by CD40 expression on T cells. - T-cell function would be indirectly affected due to the lack of proper B cell help and antigen presentation, but the direct impact of absent CD40 is on the cell expressing it (B cells). [Practice more Microbiology PYQs on OnCourse]

Question 1

A person handling cat feces is at risk of transmitting an infection. Which of the following is the infective stage of the organism transmitted through cat feces?

Accepted Answer

Oocyst

Answer

Bradyzoite

Answer

Tachyzoite

Answer

Gametocyte

Question 2

A man has undergone renal transplant and is taking immunosuppressant drug. On biopsy there was presence of budding cells with pseudohyphae. Identify the organism?

Accepted Answer

Invasive candidiasis

Answer

Pneumocystis

Answer

Invasive aspergillosis

Answer

Histoplasmosis

Question 3

A peculiar organism has resistance to azithromycin, but is sensitive to ticarcillin, clavulanic acid, cotrimoxazole. Identify the organism?

Accepted Answer

Stenotrophomonas

Answer

Pseudomonas

Answer

Staphylococcus

Answer

Mycoplasma

Question 4

CD40 deficiency in a person signifies?

Accepted Answer

IgM increase

Answer

IgG increase

Answer

T cell absent

Answer

B cell absent

Question 5

CD 40 marker is absent in the person. Which of the following would be seen?

Accepted Answer

Impaired B cell function

Answer

Impaired Macrophage function

Answer

Impaired NK cell function

Answer

Impaired T cell function

Question 6

With the lack of CD40 in B cells, which immunological abnormality is seen?

Accepted Answer

Decreased IgG and increase in IgM

Answer

Total lack of NK cells

Answer

Lack of CD8 mediated cytotoxicity

Answer

Inability of neutrophil against infections

Question 7

Which of the following microorganisms will be resistant to meropenem and aminoglycosides but sensitive to piperacillin tazobactam and cotrimoxazole?

Accepted Answer

Stenotrophomonas

Answer

Pseudomonas

Answer

Acinetobacter

Answer

Burkholderia cepacia

INI-CET 2023 — Microbiology