NEET-PG 2018 - Microbiology Practice Questions

Q: Sabin Feldman dye test is used for diagnosis of which of the following condition?

Toxoplasmosis. ***Toxoplasmosis*** The **Sabin-Feldman dye test** is a **serological assay** used to detect specific IgG antibodies against *Toxoplasma gondii*, the causative agent of toxoplasmosis. It measures the ability of antibodies in a patient's serum to prevent the cytoplasmic staining of live toxoplasma tachyzoites by methylene blue dye, indicating an **active immune response** to the parasite. This classic test has high sensitivity and specificity for detecting toxoplasma antibodies and is considered the gold standard serological test, though it has been largely replaced by ELISA and IFA in routine practice due to the requirement for live organisms. *Botulism* Botulism is diagnosed through **toxin detection** in serum, stool, or food samples using mouse bioassay, or by culturing *Clostridium botulinum* from clinical specimens. The Sabin-Feldman dye test is not relevant for the diagnosis of botulism, which is a **neuroparalytic disease** caused by botulinum neurotoxin blocking acetylcholine release at neuromuscular junctions. *Sarcoidosis* Sarcoidosis is a multisystem **granulomatous disease** diagnosed primarily by **tissue biopsy** showing non-caseating granulomas along with compatible clinical and radiological findings. Supportive tests include elevated serum ACE levels and Kveim test (historical). There is no serological test like the Sabin-Feldman dye test associated with the diagnosis of sarcoidosis, as it is not an infectious disease requiring antibody detection. *Yellow fever* Yellow fever is a **viral hemorrhagic disease** caused by a flavivirus, diagnosed by detecting viral RNA through RT-PCR or specific IgM antibodies in the acute phase of infection using ELISA or immunofluorescence. The Sabin-Feldman dye test is not used for viral infections like yellow fever, as it specifically targets **toxoplasma antibodies** and has no role in arboviral disease diagnosis.

Q: Which of the following is the carrying agent for Lyme disease?

Ixodes scapularis ticks. ***Ixodes scapularis ticks*** - *Ixodes scapularis* ticks (deer ticks) are the primary **vectors for Lyme disease** (caused by *Borrelia burgdorferi*) in North America [1]. - In Europe, *Ixodes ricinus* is the main vector for Lyme disease. - Lyme disease presents with characteristic **erythema migrans** rash, followed by potential neurological, cardiac, and arthritic complications [1]. - Lyme arthritis commonly affects large joints, particularly the **knee**, causing inflammatory arthritis [1]. *Anopheles* - **Anopheles mosquitoes** are the primary vectors for **malaria**, not Lyme disease [2]. - Malaria is caused by *Plasmodium* parasites and presents with fever, chills, and hemolytic anemia [2]. *Louse* - **Lice** are vectors for diseases such as **epidemic typhus** (caused by *Rickettsia prowazekii*) and **relapsing fever** (caused by *Borrelia recurrentis*) [3]. - They are not associated with the transmission of Lyme disease. *Rat flea* - **Rat fleas** (e.g., *Xenopsylla cheopis*) are the primary vectors for **bubonic plague** (caused by *Yersinia pestis*) and **murine typhus**. - These insects do not transmit Lyme disease. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Infectious Diseases, pp. 389-390. [2] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Infectious Diseases, p. 400. [3] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Infectious Diseases, pp. 392-393.

Q: Urea breath test is used for diagnosis of:

H. pylori. ***H. pylori*** - The **urea breath test** is a common and accurate non-invasive method to detect current **Helicobacter pylori** infection. - H. pylori produces the enzyme **urease**, which breaks down ingested urea into ammonia and carbon dioxide, which is then exhaled and measured. *Campylobacter jejuni* - **Campylobacter jejuni** is a common cause of **bacterial gastroenteritis** and typically diagnosed via **stool culture**. - It does not possess the **urease** enzyme, so a urea breath test would not be positive. *E.coli* - **E. coli** is a diverse group of bacteria, some strains causing gastrointestinal illness, but it is not associated with **urease production** for diagnostic purposes. - Diagnosis for diarrheagenic E. coli strains usually involves **stool culture** and specific toxin assays. *Lactobacillus* - **Lactobacillus** are beneficial bacteria commonly found in the gut and are not typically associated with pathogenic infections requiring a **urea breath test**. - They do not produce the **urease** enzyme in quantities relevant for this diagnostic test.

Q: Whole blood is used as a sample for which of the following tests?

Interferon Gamma Release Assay (IGRA). ***Interferon Gamma Release Assay (IGRA)*** - IGRAs, such as QuantiFERON-TB Gold, directly measure **interferon-gamma release** from T-lymphocytes stimulated by *Mycobacterium tuberculosis* antigens. - This test requires **fresh whole blood** as the living lymphocytes are essential for the immune response measured. *Blood Culture for Bacteria* - While blood is cultured, the primary goal is to **isolate and identify viable bacteria** from the bloodstream, not to detect an immune response within the whole blood itself. - Blood cultures typically involve placing blood into specific **culture media** to promote bacterial growth. *Genexpert* - The GeneXpert MTB/RIF assay is a **molecular test** used to detect *Mycobacterium tuberculosis* DNA and rifampicin resistance. - This assay is typically performed on **sputum samples** or other bodily fluids, not whole blood, to diagnose active tuberculosis. *Serological Test for Viruses* - Serological tests for viruses detect **antibodies or antigens** in the blood, which circulate in the **plasma or serum** component of blood. - These tests typically use **separated serum or plasma**, rather than whole blood, as the cellular components are not required for antibody or antigen detection.

Q: Most common catheter-related bloodstream infection is due to:

Coagulase-negative Staphylococci (CoNS). ***Coagulase-negative Staphylococci (CoNS)*** - **Coagulase-negative Staphylococci (CoNS)**, particularly *Staphylococcus epidermidis*, are the most common cause of **catheter-related bloodstream infections (CRBSIs)** due to their ability to form **biofilms** on catheter surfaces. - Their ubiquity on the skin, combined with their capacity for **adherence** and **biofilm production**, facilitates their entry and proliferation within the catheter lumen. *Candida species* - While *Candida species* (e.g., *Candida albicans*) are significant causes of CRBSIs, especially in **immunocompromised** patients or those on **broad-spectrum antibiotics**, they are less common overall than CoNS. - Risk factors for *Candida* CRBSIs include prolonged hospitalization, total parenteral nutrition, and **central venous catheters**. *Gram-negative bacilli* - **Gram-negative bacilli** (e.g., *Klebsiella pneumoniae*, *Escherichia coli*, *Pseudomonas aeruginosa*) are important pathogens in CRBSIs, often associated with **severe sepsis** and higher mortality rates. - However, their overall incidence in catheter-induced infections is lower than that of CoNS, though they are more prevalent in certain hospital units like **ICUs**. *Staphylococcus aureus (S. aureus)* - **Staphylococcus aureus** causes clinically significant CRBSIs, often leading to more severe infections, including **endocarditis** and **septic emboli**, than CoNS. - While *S. aureus* infections are serious, CoNS remain the most frequently isolated organism in all CRBSI cases, partly due to the high carriage rate of *S. epidermidis* on human skin.

Q: Which of the following is responsible for the abnormality shown below?

Zika virus. ***Zika virus*** - The image depicts a newborn with **microcephaly**, characterized by a significantly smaller head circumference than expected, which is a hallmark congenital abnormality associated with **Zika virus infection** during pregnancy. - Zika virus is a **teratogen** that primarily targets neural progenitor cells, leading to severe brain malformations and microcephaly in developing fetuses. *Human parvovirus B19* - This virus is known to cause **erythema infectiosum** (fifth disease) in children and can lead to **hydrops fetalis**, severe anemia, and cardiac failure in fetuses if transmitted during pregnancy. - It does not typically cause microcephaly as its primary congenital manifestation. *HHV6* - Human Herpesvirus 6 (HHV6) is the causative agent of **roseola infantum** (exanthem subitum) in young children. - While it can cause febrile seizures and encephalitis, it is not primarily associated with congenital microcephaly or other severe birth defects when acquired prenatally. *EBV* - Epstein-Barr virus (EBV) is responsible for **infectious mononucleosis** and is linked to various malignancies. - Congenital EBV infection is rare and has been associated with a range of non-specific outcomes, but it is not a recognized cause of microcephaly.

Q: The following organism is called:

Cestode. ***Cestode*** - The image displays a long, **segmented, ribbon-like worm**, which is characteristic morphology of a **tapeworm (cestode)**. - Cestodes typically possess a head (scolex) for attachment and a body composed of repeating segments called **proglottids**. *Nematode* - **Nematodes** are generally **unsegmented**, cylindrical, and elongated worms, often described as roundworms. - They lack the distinct proglottids and flattened, ribbon-like appearance seen in the image. *Trematode* - **Trematodes**, also known as flukes, are typically **leaf-shaped** and **unsegmented**. - They are much broader and flatter than the organism shown, and do not have the visible segmentation. *Annelid* - **Annelids** are segmented worms like earthworms and leeches, but they have a **cylindrical body** with visible external ring-like segments. - Unlike cestodes, annelids have a complete digestive system and lack the flat, ribbon-like morphology and internal proglottid structure characteristic of tapeworms.

Q: Which of the following life cycle is shown below?

Diphyllobothrium latum. ***Diphyllobothrium latum*** - The diagram clearly illustrates a life cycle involving **freshwater fish** as a second intermediate host, where **plerocercoid larvae** are found, and humans ingesting these fish. The presence of **procercoid** and **plerocercoid larvae** in the depicted stages is characteristic of *Diphyllobothrium latum*. - The description mentions that humans are infected by ingesting fish containing **plerocercoid larvae**, which become adults in the intestine and discharge eggs from **gravid proglottides**, which is consistent with the life cycle of the **fish tapeworm**. *Echinococcus granulosus* - This parasite's life cycle involves **dogs as definitive hosts** and **sheep or humans as intermediate hosts** developing **hydatid cysts**, which is distinctly different from the fish-involved cycle shown. - Infection occurs through ingestion of **eggs passed in dog feces**, and not through contaminated fish. *Taenia solium* - *Taenia solium* (pork tapeworm) involves **pigs as intermediate hosts** and humans as definitive hosts, or humans as intermediate hosts in the case of **cysticercosis**. - Its life cycle does not involve **fish** or the **plerocercoid/procercoid larval stages** as depicted. *Clonorchis sinensis* - While *Clonorchis sinensis* (Chinese liver fluke) also involves **freshwater fish** as an intermediate host, it is a **fluke, not a tapeworm**, and its larval stages are **cercariae** and **metacercariae**, not procercoid or plerocercoid larvae. - The adult worm primarily infects the **biliary ducts (liver)**, not maturing in the intestine with proglottids as shown for the tapeworm in the diagram.

Q: Which of the following life cycle is shown below?

Clonorchiasis. ***Clonorchiasis*** - The diagram displays metacercariae (infective stage) in freshwater fish being ingested by a human host, a defining characteristic of the Clonorchis sinensis life cycle. - The life cycle involves freshwater snails (first intermediate host) and freshwater fish (second intermediate host), which aligns with the image showing cercariae encysting in fish. *Diphylobothrium latum* - The infective stage for *Diphylobothrium latum* (fish tapeworm) is the **plerocercoid larva** in raw or undercooked freshwater fish, not metacercariae. - While it also involves freshwater fish, its larval forms and overall life cycle stages are distinct from what is depicted. *Echinococcus granulosus* - This parasite causes **hydatid disease** and has a life cycle involving canids (definitive host) and herbivores (intermediate host), with humans being accidental intermediate hosts. - The life cycle does not involve freshwater fish or metacercariae for human infection. *Tenia solium* - The human is the definitive host for **Taenia solium** (pork tapeworm), acquiring infection by ingesting undercooked pork containing **cysticerci**. - The intermediate host is pigs, and the life cycle does not involve freshwater fish or metacercariae.

Q: Which of the following parasite is shown below?

Echinococcus granulosus. ***Echinococcus granulosus*** - The image displays a **hydatid cyst**, characterized by its thick, laminated outer wall (ectocyst) and an inner germinal layer (endocyst) from which **brood capsules** and **protoscolices** (seen as invaginations) bud off. - This morphology is pathognomonic for **Echinococcus granulosus**, the causative agent of **cystic echinococcosis** (hydatid disease). *Cysticercosis cellulosae* - Cysts of *Cysticercus cellulosae* (larval stage of *Taenia solium*) typically appear as a fluid-filled bladder with a single **invaginated scolex** lacking the complex brood capsule arrangement seen in the image. - They also generally have a thinner cyst wall compared to *Echinococcus* cysts. *E. Histolytica* - *Entamoeba histolytica* is a **protozoan parasite** that causes amoebiasis, presenting as trophozoites or cysts; it does not form macroscopic cysts with complex internal structures like the one shown. - Amoebic abscesses are typically necrotic lesions, not true cysts with parasitic structures within. *Fasciola hepatica* - *Fasciola hepatica* is a **trematode (fluke)**, and its larval stages or adult worms do not form cysts with this characteristic morphology. - Liver flukes would appear as tissue sections of the flatworm itself in infected organs, not as a large, spherical cyst with internal budding structures.

Question 1

Sabin Feldman dye test is used for diagnosis of which of the following condition?

Accepted Answer

Toxoplasmosis

Answer

Botulism

Answer

Sarcoidosis

Answer

Yellow fever

Question 2

Which of the following is the carrying agent for Lyme disease?

Accepted Answer

Ixodes scapularis ticks

Answer

Anopheles

Answer

Louse

Answer

Rat flea

Question 3

Urea breath test is used for diagnosis of:

Accepted Answer

H. pylori

Answer

E. coli

Answer

Lactobacillus

Answer

Campylobacter jejuni

Question 4

Whole blood is used as a sample for which of the following tests?

Accepted Answer

Interferon Gamma Release Assay (IGRA)

Answer

Genexpert

Answer

Blood Culture for Bacteria

Answer

Serological Test for Viruses

Question 5

Most common catheter-related bloodstream infection is due to:

Accepted Answer

Coagulase-negative Staphylococci (CoNS)

Answer

Candida species

Answer

Gram-negative bacilli

Answer

Staphylococcus aureus (S. aureus)

Question 6

Which of the following is responsible for the abnormality shown below?

Accepted Answer

Zika virus

Answer

Human parvovirus B19

Answer

HHV6

Answer

EBV

Question 7

The following organism is called:

Accepted Answer

Cestode

Answer

Nematode

Answer

Trematode

Answer

Annelid

Question 8

Which of the following life cycle is shown below?

Accepted Answer

Diphyllobothrium latum

Answer

Echinococcus granulosus

Answer

Taenia solium

Answer

Clonorchis sinensis

Question 9

Which of the following life cycle is shown below?

Accepted Answer

Clonorchiasis

Answer

Diphylobothrium latum

Answer

Echinococcus granulosus

Answer

Tenia solium

Question 10

Which of the following parasite is shown below?

Accepted Answer

Echinococcus granulosus

Answer

Cysticercosis cellulosae

Answer

E. Histolytica

Answer

Fasciola hepatica

NEET-PG 2018 — Microbiology