MicroBiology MCQs with Answer and Explnation | Chapter 41

Answer: Ascomycetes

Ascomycetes are the largest phylum of fungi, encompassing over 64,000 known species. Remarkably, a significant majority of medically important fungi belong to this group, accounting for around 70%. This includes well-known pathogens like Candida albicans (yeast infections), Aspergillus fumigatus (pulmonary infections), and Pneumocystis carinii (pneumonia in immunocompromised individuals).

The other options are incorrect:

• Zygomycetes: While some zygomycetes can cause opportunistic infections, notably Mucormycosis, their overall contribution to medical mycology is significantly lower compared to ascomycetes.
• Basidiomycetes: While including well-known edible and poisonous mushrooms, basidiomycetes are less frequent as pathogens. Some exceptions exist, like Cryptococcus neoformans (meningitis), but they are less common and impactful compared to ascomycetes.
• Deuteromycetes: This term is no longer used in modern taxonomy as it refers to fungi classified based on their reproductive structures rather than evolutionary relationships. Many former deuteromycetes have now been reclassified into other phyla, including ascomycetes and basidiomycetes.

Answer: Allo

An allograft refers to a transplant where the donor and recipient are genetically different individuals. In this case, the mother and daughter, while related, possess distinct sets of genes, making the kidney donation an allograft.

The other options are incorrect:

• ISO: An isograft refers to a transplant between genetically identical individuals, such as identical twins. While a mother and daughter share some genetic material, they are not identical, making this option incorrect.
• Xeno: A xenograft refers to a transplant between individuals from different species. Here, both the mother and daughter are humans, disqualifying this option.
• Auto: An autograft refers to a transplant where the donor and recipient are the same individual. In this scenario, the mother donates her own kidney to her daughter, making this option incorrect.

Answer: Proteins

Proteins are the most potent antigens for stimulating both humoral (antibody-mediated) and cell-mediated immunity. Proteins can elicit a strong immune response because they can be recognized by both B cells (leading to the production of antibodies) and T cells (activating cell-mediated immunity). Many pathogens, including viruses and bacteria, have protein components that serve as antigens.

The other options are incorrect:

• Adjuvant: Adjuvants are substances added to vaccines to enhance the immune response. While important for vaccine efficacy, adjuvants themselves are not antigens. They work by enhancing the immune response to the co-administered antigens.
• Polysaccharides: Polysaccharides are large carbohydrates composed of repeated sugar units. They are generally weaker antigens compared to proteins and are mainly involved in stimulating humoral immunity. Polysaccharides are often used in vaccines against certain bacteria, but they may not effectively stimulate cell-mediated immunity.
• Lipids: Lipids are nonpolar molecules, and they are not as immunogenic as proteins. They typically do not stimulate a robust immune response on their own. While lipids may play a role in immune responses, they are not the most potent antigens for activating both humoral and cell-mediated immunity.

Answer: Malabsorption

Falciparum malaria primarily causes anemia through destruction of red blood cells (hemolysis), sequestration of infected red blood cells in the spleen, and inhibition of red blood cell production in the bone marrow (depression). Malabsorption, however, is not directly involved in the development of anemia in this type of malaria.

The other options are incorrect:

• Hemolysis: As mentioned, hemolysis of both infected and uninfected red blood cells due to parasite activity is a major contributor to anemia in falciparum malaria.
• Spleen sequestration: Infected red blood cells can stick to the lining of the spleen, leading to their removal from circulation and contributing to anemia.
• Bone marrow depression: The malaria parasite can suppress red blood cell production in the bone marrow, further adding to the anemia development.

Answer: Q fever

While other options in the list are indeed transmitted by lice, Q fever has different means of transmission and is not associated with these parasitic insects.

The other options are incorrect:

• Trench fever: This bacterial disease, also known as Rickettsia quintana, is primarily transmitted through body lice and their feces.
• Relapsing fever: Another louse-borne illness, caused by Borrelia bacteria, spreads via the bites and feces of body lice and head lice.
• Epidemic typhus: Similar to the previous two, epidemic typhus, caused by Rickettsia prowazekii, is a louse-borne bacterial infection transmitted through direct contact, bites, and feces of human body lice.

Answer: Gametocyte

Gametocytes are the sexual stage of the parasite that develops in human red blood cells. When a female Anopheles mosquito feeds on the blood of an infected person, it ingests the gametocytes. Inside the mosquito’s gut, gametocytes mature into gametes, leading to the formation of ookinetes and eventually developing into sporozoites, which can then infect a new human host during a mosquito bite.

The other options are incorrect:

• Sporozoite: Sporozoites are the infective stage for humans. When an infected mosquito bites a person, sporozoites are injected into the bloodstream and migrate to the liver, where they infect liver cells.
• Merozoite: Merozoites are released from infected liver cells and red blood cells, leading to the multiplication of the parasite within the human host. They are not the stage that infects mosquitoes.
• Zygote: Zygotes are formed when male and female gametes (gametocytes) fuse in the mosquito’s gut. Zygotes develop into ookinetes, which then penetrate the mosquito’s midgut wall. Zygotes themselves do not directly infect mosquitoes.

Answer: Plasmodium vivax

Schuffner’s dots are small, reddish-purple dots seen in red blood cells under a microscope. They are a characteristic feature of infection with Plasmodium vivax, one of the five species of Plasmodium parasites that cause malaria. These dots are not seen in infections with other Plasmodium species like falciparum, malariae, or ovale.

The other options are incorrect:

• Plasmodium falciparum: This species causes the most severe form of malaria and does not display Schuffner’s dots.
• Plasmodium malariae: Similar to falciparum, malariae does not exhibit Schuffner’s dots in infected red blood cells.
• Plasmodium ovale: While ovale sometimes presents with Schuffner’s dots, it’s less common and less pronounced compared to vivax. Moreover, the morphology of the dots can be slightly different, making vivax the more definitive option.

Answer: Plasmodium falciparum

The clinical presentation described, including sudden onset high fever, crescent-shaped gametocytes, and dark brown malaria pigment, is indicative of infection with Plasmodium falciparum. Plasmodium falciparum is known for causing severe and potentially life-threatening malaria. The presence of crescent-shaped gametocytes is a characteristic feature of P. falciparum infection.

The other options are incorrect:

• Plasmodium vivax: Gametocytes are round, not crescent-shaped. Malaria pigment is golden brown, not dark brown.
• Plasmodium malariae: This is not a valid species name for malaria parasites.
• Plasmodium ovale: Gametocytes are elliptical, not crescent-shaped. Malaria pigment is light brown, not dark brown.

Answer: Liver

The commonest site of extra-intestinal amoebiasis is the liver. In amoebiasis caused by the protozoan parasite Entamoeba histolytica, the amoebic trophozoites can invade the intestinal mucosa and may also disseminate through the bloodstream to other organs. Hepatic amoebiasis, also known as amoebic liver abscess, is the most frequent form of extra-intestinal involvement. The trophozoites can form abscesses in the liver, leading to symptoms such as fever, right upper quadrant pain, and hepatomegaly.

Incorrect options and brief explanations:

• Brain: Brain involvement with amoebiasis is exceedingly rare, occurring in less than 1% of cases.
• Spleen: Splenic involvement is uncommon and typically associated with disseminated amoebiasis, a severe and rare form.
• Lungs: Pleuropulmonary amebiasis can occur due to spread from liver abscesses, but it’s less frequent than hepatic involvement.

Answer: L. Tropica sore

Delhi boil refers to L. Tropica sore, which is a cutaneous manifestation of infection with the parasite Leishmania tropica. Leishmaniasis is a vector-borne disease transmitted by sandflies. L. tropica causes a skin lesion known as a “Delhi boil” or “Oriental sore.” This ulcerative skin lesion typically occurs in regions where the disease is endemic, including parts of the Middle East, Central Asia, and the Indian subcontinent.

The other options are incorrect:

• Solar Keratosis: Solar keratosis, or actinic keratosis, is a precancerous skin lesion caused by long-term exposure to ultraviolet (UV) radiation from the sun.
• Malignant Pustule: Malignant pustule is a term often associated with cutaneous anthrax, caused by the bacterium Bacillus anthracis. It presents as an ulcer with a central black eschar.
• Venereal Ulcer: A venereal ulcer refers to an ulceration associated with sexually transmitted infections. The term is not specifically related to Leishmania tropica or Delhi boil.

Answer: Chromoblastomycosis

These specific features of sclerotic bodies are highly suggestive of Chromoblastomycosis, a chronic fungal infection affecting the skin and subcutaneous tissues. The size, septation, and color are distinct from other fungal infections with sclerotic bodies.

The other options are incorrect:

• Histoplasmosis: Sclerotic bodies in Histoplasmosis are typically smaller (1-2 µm) and unicellular, not multi-septate. They also have a different morphology and staining pattern.
• Rhinosporodiosis: Rhinosporidiosis doesn’t have true sclerotic bodies. Instead, it has characteristic sporangia with endospores.
• Phaeohypomycosis: Phaeohypomycosis encompasses a variety of fungal infections with diverse microscopic features. Sclerotic bodies, if present, vary in size and morphology depending on the specific fungus involved.

Answer: All of the above

All the methods listed are commonly used for the diagnosis of superficial fungal infections:

• Microscopic Examination of Skin Scrapings: Microscopic examination of skin scrapings involves collecting a sample from the affected area and observing it under a microscope. Fungal elements, such as hyphae or spores, can be visualized, aiding in the identification of the causative organism.
• KOH Staining: Potassium hydroxide (KOH) staining is a technique used to dissolve non-fungal tissues in a sample, leaving behind fungal elements. This facilitates the microscopic examination of fungal structures, making it easier to identify the type of fungus causing the infection.
• Wood Light Examination: Wood light examination involves exposing the affected skin to ultraviolet (UV) light. Some fungi fluoresce under UV light, aiding in the diagnosis. However, not all fungi exhibit fluorescence, and this method is not as specific as direct microscopic examination.

Answer: Candida infection is usually endogenous

Candida albicans is a commensal fungus, meaning it normally resides on the skin and mucous membranes of healthy individuals without causing harm. However, under certain conditions like immune suppression or imbalance in the microbiome, Candida can overgrow and cause infection. This endogenous origin is why Candida infections are common.

The other options are incorrect:

• Dermatophyte infection are exclusively man to animal: While many dermatophytes primarily infect humans, some species can transmit to animals and vice versa. For example, ringworm in pets can be transmitted to humans and vice versa.
• Rhinosporidium causes deep infection in man: Rhinosporidium typically causes a chronic granulomatous infection of the nose and nasopharynx, but it can also involve other areas like the conjunctiva and genitals. These are considered superficial or localized infections, not deep infections.
• albicans is not pathogenic to lab animals: Candida albicans can indeed be pathogenic to lab animals like mice and rabbits, causing infections similar to those it causes in humans. This makes it a valuable model for studying Candida infections and developing antifungal drugs.

Answer: Whip worm

The common name for Trichuris trichura is Whipworm. The name “whipworm” is derived from the characteristic whip-like appearance of the adult worm, with a thin anterior portion and a thicker posterior end.

The other options are incorrect:

• Round worm: While Trichuris trichura is indeed a type of roundworm (nematode), it’s not the most specific or descriptive common name. Other roundworms like Ascaris lumbricoides (common roundworm) have different shapes and characteristics.
• Tape worm: Tapeworms are flat, segmented worms that don’t resemble Trichuris trichura in shape or anatomy. They also have a different life cycle and mode of infection.
• Seat woman: This is not a recognized common name for Trichuris trichura and is considered offensive and inappropriate. It’s important to use respectful and accurate terminology when discussing medical topics.

Answer: KOH wet mount

Rapid evaluation of fungal hyphae and spores can be achieved with a KOH (Potassium Hydroxide) wet mount. When clinical samples (such as skin scrapings or fluid specimens) are treated with KOH, the fungal elements are digested, leaving behind fungal structures like hyphae and spores. The process clears the sample, making it easier to observe under a microscope for the presence of fungal elements.

The other options are incorrect:

• Grocott Gomori Methenamine silver (GMS): While GMS is a highly sensitive stain for fungi, it requires tissue processing and staining steps, making it slower than KOH wet mount for rapid evaluation.
• Hematoxylin and Eosin (H&E): H&E is a standard stain used in pathology, but it doesn’t highlight fungal elements specifically. While fungal structures might be visible, identification can be challenging and less clear compared to KOH.
• Periodic-acid Schiff (PAS): PAS stains carbohydrates and can highlight fungal cell walls, but it also stains other structures like basement membranes and mucus. This can make identifying fungal elements amidst background noise more difficult compared to the targeted visualization of KOH.

Answer: NNN

NNN medium is a rich, complex medium specifically formulated for cultivating Leishmania promastigotes, the motile, extracellular form of the parasite. It contains a variety of nutrients, including blood, serum, and agar, that provide the Leishmania with the necessary conditions to grow and multiply.

The other options are incorrect:

• Chocolate agar: This medium is typically used for culturing bacteria, not parasites like Leishmania. While they share some features, their nutritional requirements differ significantly.
• Tellurite: This is a selective agent used to inhibit the growth of bacteria, not a growth medium for parasites. It wouldn’t provide the necessary nutrients for Leishmania to thrive.
• Sabouraud’s: This medium is commonly used for culturing fungi, not protozoa like Leishmania. While some specialized Sabouraud’s-based media can support Leishmania growth, NNN remains the preferred choice for routine culture.

Answer: Terminal nuclei absent

The statement that is false about Wuchereria bancrofti is “Terminal nuclei absent.” Wuchereria bancrofti, the causative agent of lymphatic filariasis, does have terminal nuclei. The adult worms are thread-like and have nuclei at both ends, making them distinctive in microscopic examinations.

The other options are incorrect:

• Causes Filariasis: True. Wuchereria bancrofti is one of the main nematodes responsible for causing lymphatic filariasis, a tropical disease transmitted through the bites of infected mosquitoes.
• Body is Slender and Long: True. Wuchereria bancrofti has a slender and long body, typical of filarial nematodes.
• Man and Anopheles Mosquito are Hosts: True. Wuchereria bancrofti completes part of its life cycle in humans (as the definitive host) and another part in Anopheles mosquitoes (as the intermediate host). The mosquitoes transmit the infection to humans during a blood meal.

Answer: Syphilis

The Kolmer test, also known as the Kolmer complement fixation test (KFT), was a historical serological test used to diagnose syphilis. It detected antibodies produced by the body in response to the Treponema pallidum bacteria, the causative agent of syphilis. While no longer commonly used due to the availability of more sensitive and specific tests, the Kolmer test played a significant role in syphilis diagnosis for many decades.

The other options are incorrect:

• Tuberculosis: The Kolmer test was not specific for tuberculosis and could give false positive results in individuals with the condition. Diagnosis of tuberculosis relies on different types of tests, including chest X-rays, sputum smears, and blood tests like the QuantiFERON-TB Gold test.
• Gonorrhea: Similar to tuberculosis, the Kolmer test was not specific for gonorrhea and could produce false positive results. Gonorrhea diagnosis typically involves specific tests like Gram stain and culture of urethral or cervical discharge.
• Lymphoma: The Kolmer test is not used for diagnosing lymphoma, a type of cancer of the lymphatic system. Lymphomas are diagnosed through a combination of tests, including blood tests, bone marrow biopsies, and imaging studies like CT scans and PET scans.

Answer: T. Solium

ysticercosis cellulosae is a parasitic infection caused by the larval stage (cysticercus) of the pork tapeworm, Taenia solium. Humans become infected by ingesting eggs of T. solium passed in the stool of an infected person. These eggs hatch and release larvae that migrate through the body and form cysts in various tissues, most commonly the brain, muscles, and eyes.

The other options are incorrect:

• Echinococcus granulosus: This parasite causes hydatid cyst disease, a different type of parasitic infection with distinct features and life cycle. E. granulosus cysts typically grow in the liver and lungs, unlike C. cellulosae which can involve various organs.
• T. Saginata: This is the beef tapeworm and while humans can become infected by ingesting its eggs, it does not cause cysticercosis. T. saginata larvae remain confined to the intestine and don’t form cysts in other tissues.
• nana: This is a misspelling of the species name “Hymenolepis nana,” a dwarf tapeworm found in humans. H. nana does not cause cysticercosis and its life cycle doesn’t involve forming cysts in humans.

Answer: Haematin-globin pigment

Malaria pigment, also known as hemozoin, is composed of haematin-globin pigment. It is a byproduct of the digestion of hemoglobin by the malaria parasite within infected red blood cells. As the parasite metabolizes hemoglobin, it produces hemozoin crystals, which accumulate in the form of pigment granules within the parasite.

The other options are incorrect:

• Bilurubin: Bilurubin is another breakdown product of hemoglobin, but it is formed by the liver and not by the Plasmodium parasite. Additionally, it doesn’t have the same characteristic dark brown color as malaria pigment.
• Haemoglobin: Haemoglobin is the intact protein molecule that carries oxygen in red blood cells. While it is the starting point for the formation of malaria pigment, it doesn’t represent the final product.
• Iron: Iron is the central element within haematin, but it doesn’t encompass the entire pigment structure, which also includes other components derived from hemoglobin.

Answer: Sporozoite

In the transmission of malaria, a mosquito bite transfers the sporozoites from an infected mosquito to a human host. Sporozoites are the infective form of the malaria parasite (Plasmodium) that resides in the salivary glands of infected mosquitoes. When an infected mosquito takes a blood meal from a human, it injects sporozoites into the bloodstream. These sporozoites then travel to the liver, where they infect liver cells and initiate the next stage of the malaria life cycle.

Incorrect Options and Brief Explanations:

• Merozoite: Merozoites are the stage of the parasite that invades and multiplies within red blood cells, causing malaria symptoms. They are not transmitted by mosquito bites but are released from schizonts inside the liver.
• Hypnozoite: Hypnozoites are a dormant stage of the Plasmodium parasite that can remain in the liver for months or even years before reactivating and causing relapses in certain types of malaria. They are also not transmitted by mosquito bites.
• Gametocyte: Gametocytes are the sexual stage of the parasite that develops in red blood cells. They are only infective for mosquitoes, who ingest them during a blood meal. Once inside the mosquito, they mature into sporozoites, which are then transmitted back to humans during the next bite.

Answer: Trophozoites in the pus

Amoebic liver abscess can be diagnosed by demonstrating trophozoites in the pus aspirated from the abscess. The trophozoite is the active, motile form of the amoeba, and its presence in the abscess material confirms the diagnosis of amoebic liver abscess.

The other options are incorrect:

• Cysts in the sterile pus: This is unlikely, as pus is typically not sterile and the presence of any cysts wouldn’t necessarily pinpoint Entamoeba histolytica as the cause.
• Trophozoites in the feces: While trophozoites can be found in the feces of individuals with intestinal amebiasis, their presence doesn’t confirm liver involvement.
• Cysts in the intestine: Finding cysts in the intestine indicates intestinal amebiasis but not necessarily a liver abscess.

Answer: Eosinophils

While all types of white blood cells can be involved in inflammatory responses, parasitic infections typically trigger a predominantly eosinophilic response. This means that the inflamed tissue shows a higher proportion of eosinophils compared to other white blood cell types.

The other options are incorrect:

• Lymphocytes: While lymphocytes are important components of the immune system, in the context of parasitic inflammation, eosinophils are typically more prominent.
• Neutrophils: Neutrophils are the primary white blood cells involved in the acute inflammatory response, especially to bacterial infections. However, in parasitic inflammation, eosinophils are often more predominant.
• Basophils: Basophils are a type of white blood cell involved in allergic reactions and immune responses, but they are not as commonly associated with the immune response against parasites as eosinophils are.

Answer: Fish tapeworm

Megaloblastic anemia is caused by the deficiency of vitamin B12 (cobalamin) or folic acid. In the context of the options provided, megaloblastic anemia is associated with the Fish Tapeworm (Diphyllobothrium latum). The fish tapeworm can compete with the host for vitamin B12, leading to its deficiency and the development of megaloblastic anemia.

The other options are incorrect:

• Dog Tapeworm: The dog tapeworm (Echinococcus granulosus) is not associated with megaloblastic anemia. It is known for causing hydatid disease.
• Hookworm: Hookworms (Ancylostoma duodenale, Necator americanus) can cause iron-deficiency anemia by feeding on blood in the intestinal tract, but they are not linked to megaloblastic anemia.
• Threadworm: Threadworms, also known as pinworms (Enterobius vermicularis), are not associated with megaloblastic anemia. They commonly cause gastrointestinal and perianal infections.

Answer: Kalahazar

L.D. bodies, also known as Leishman-Donovan bodies, are intracellular parasites present in macrophages. Their presence is considered a diagnostic hallmark of visceral leishmaniasis, commonly known as kala-azar. They are not typically seen in the other listed diseases.

The other options are incorrect:

• Toxoplasmosis: While macrophages are also involved in toxoplasmosis infection, the parasite resides within cysts and doesn’t form the characteristic L.D. bodies.
• Malaria: Malaria parasites invade red blood cells, not macrophages, and therefore wouldn’t exhibit L.D. bodies in these cells.
• Sleeping sickness: African sleeping sickness caused by Trypanosoma brucei gambiense or rhodesiense also involves parasite presence in macrophages. However, the parasite morphology and associated cellular changes differ from Leishmania, and L.D. bodies are not observed.

Answer: Parasitic in nature

Hydatid cysts are caused by the larvae of a tapeworm species called Echinococcus. These larvae develop into fluid-filled sacs (cysts) within organs like the liver or lungs. The infection is called echinococcosis, also known as cystic hydatid disease.

The other options are incorrect:

• Fungal: Fungal infections do not cause hydatid cysts. Fungal infections typically involve fungal growth in tissues or cavities, unlike the parasitic cyst formation seen in hydatid disease.
• Congenital: Congenital refers to conditions present at birth and not transmitted after birth. Hydatid cysts are acquired after birth through exposure to infected animals or their feces.
• Viral: Viruses also do not cause hydatid cysts. Viral infections involve viral replication within host cells, leading to various cellular and tissue changes, not the specific cyst formation associated with parasites.

Answer: Mycetoma

While Candida albicans can cause endocarditis, meningitis, and oral thrush, it is not typically associated with mycetoma. Mycetoma is a chronic infection of the skin and subcutaneous tissue, primarily caused by bacteria and some specific fungi (Madurella, Actinomadura, Nocardia). Candida albicans, though a fungus, doesn’t have the specific characteristics to cause this type of localized, chronic infection.

The other options are incorrect:

• Endocarditis: Candida albicans, especially in individuals with weakened immune systems or specific risk factors, can cause fungal endocarditis, an infection of the inner lining of the heart.
• Meningitis: Candida albicans can also cause fungal meningitis, although it’s less common than bacterial meningitis. This infection involves inflammation of the membranes surrounding the brain and spinal cord.
• Oral thrush: Candida albicans is the most common cause of oral thrush, a fungal infection of the mouth causing white patches on the tongue and inner cheeks.

Answer: Thrush

Candida, particularly Candida albicans, is the most common cause of thrush, a fungal infection that affects the mucous membranes of the mouth, throat, and sometimes the vagina. It causes white patches to form on these surfaces, accompanied by burning, discomfort, and difficulty swallowing in severe cases.

The other options are incorrect:

• Conjunctivitis: While Candida can occasionally cause conjunctivitis, it’s a much less common cause compared to bacterial and viral conjunctivitis.
• Tenea capitis: Tenea capitis, also known as ringworm of the scalp, is caused by fungal infections of the hair follicles, not Candida but by dermatophyte fungi like Trichophyton and Microsporum.
• Desert rheumatism: Desert rheumatism, also known as Pontiac fever, is a bacterial disease caused by Legionella bacteria, not Candida.

Answer: Candida albicans

Pseudohyphae are seen in Candida albicans. Candida albicans is a yeast-like fungus that can exist in two forms: yeast cells and pseudohyphae. Pseudohyphae are elongated chains of yeast cells with constrictions between the cells, resembling true hyphae. They are a characteristic feature of Candida albicans during certain phases of its growth and are observed in conditions such as candidiasis.

The other options are incorrect:

• Alternaria: Alternaria is a genus of fungi known for producing airborne spores. Pseudohyphae are not a characteristic feature of Alternaria.
• Aspergillus: Aspergillus is a genus of fungi that typically forms septate hyphae, not pseudohyphae. Pseudohyphae are not a common feature in Aspergillus species.
• Osporium: It seems there might be a typographical error, and “Osporium” is likely meant to be “Sporothrix.” However, neither Osporium nor Sporothrix typically show pseudohyphae. Sporothrix species usually produce conidia.

Answer: porangiospores

A sporangium is a sac-like structure in various organisms, specifically plants, fungi, and some protists, that contains spores for asexual reproduction. These spores, produced within the sporangium, are called sporangiospores. Their primary function is to disperse and germinate into new individuals upon landing in suitable conditions.

The other options are incorrect:

• Spherules: Spherules are characteristic of certain fungal infections, especially aspergillosis. They are thick-walled structures containing numerous fungal spores called ascospores, not sporangiospores.
• Chlamydospores: Chlamydospores are thick-walled, dormant spores produced by several fungal species, but they are not formed within sporangia. They serve as survival structures under harsh conditions and don’t directly participate in sporangium-based reproduction.
• Oidia: Oidia are short, oval, yeast-like cells that detach from fungal hyphae (filamentous structures). While they can contribute to fungal propagation, they aren’t specifically produced within sporangia like sporangiospores.

Answer: Aspergillus flavus

Aflatoxins are a group of toxic fungal metabolites primarily produced by Aspergillus flavus. These toxins can contaminate various food crops like corn, peanuts, and grains, posing health risks due to their carcinogenic and hepatotoxic (liver-damaging) properties.

The other options are incorrect:

• Aspergillus niger: While this fungus is known for producing the citric acid used in food and industrial applications, it doesn’t produce significant amounts of aflatoxins.
• Aspergillus fumigatus: This species is a common cause of invasive aspergillosis, a fungal infection, but it isn’t a major producer of aflatoxins.
• All of the above: Although all three species belong to the genus Aspergillus, only Aspergillus flavus possesses the specific biochemical pathways necessary for aflatoxin production.

Answer: Candida albicans

Germ tube formation, a rapid phenotypic test, is a characteristic feature of Candida albicans. Under specific conditions (warm temperature, serum in the medium), C. albicans readily converts from its yeast form to elongated, tube-like structures called germ tubes. This ability is primarily associated with its virulence and tissue invasion potential.

The other options are incorrect:

• Candida stellatoidea: While closely related to C. albicans, C. stellatoidea exhibits limited germ tube formation, making it unreliable for this diagnostic test.
• Candida tropicalis: Similarly, C. tropicalis generally doesn’t form germ tubes and relies on other morphologies for identification.
• Candida pseudotropicalls: This species also demonstrates a weak and inconsistent ability to form germ tubes, making it unsuitable for reliable identification through this method.

Answer: Mycosis

“Mycosis” is the preferred term for fungal infections in humans. It comes from the Greek word “mykēs” meaning “fungus”. It broadly encompasses various types of fungal infections affecting different body parts, such as skin, nails, hair, lungs, and even internal organs.

The other options are incorrect:

• Mucorsis: This term specifically refers to a severe fungal infection caused by theMucoralesorder, typically involving the sinuses, lungs, or gastrointestinal tract. It’s a type of mycosis, but not a general term for all fungal infections.
• Fungosis: While sometimes used colloquially, “fungosis” is not a widely recognized or accepted medical term for fungal infections. “Mycosis” is the preferred and more accurate terminology.
• Micromia: This term isn’t related to fungal infections. It typically refers to a condition with abnormally small bones or muscles.

Answer: Trophozoites can be visualized in the pus

In amoebic liver disease, trophozoites of the amoeba Entamoeba histolytica can be visualized in the pus obtained from the abscess. Amoebic liver abscess is characterized by the presence of these trophozoites, which are the active, motile forms of the parasite, in the aspirated pus.

The other options are incorrect:

• Left lobe of the liver is commonly involved: This statement is incorrect. Amoebic liver abscesses can occur in any part of the liver and are not limited to the left lobe.
• Portal system is the main filtration system: This statement is incorrect. The portal system is not the main filtration system for amoebic liver abscess. The infection typically occurs through the ingestion of contaminated food or water, and the trophozoites travel to the liver via the bloodstream.
• Non-suppurative form is the serious form of extra-intestinal amoebiasis: This statement is incorrect. The suppurative (pus-forming) form of amoebic liver abscess is generally considered more serious than the non-suppurative form. The presence of pus is a characteristic feature of amoebic liver abscess

Answer: Cholera

Cholera is not a live attenuated vaccine. It is an inactivated vaccine, meaning the bacteria responsible for the disease (Vibrio cholerae) are killed during the vaccine preparation process. This inactivated form can still trigger an immune response but cannot cause the disease itself.

The other options are incorrect:

• Tuberculosis (BCG): This is a live attenuated vaccine, meaning the bacteria causing tuberculosis (Mycobacterium tuberculosis) are weakened but still alive in the vaccine. This allows them to trigger a strong immune response without causing the full-blown disease.
• Typhoid: This is also a live attenuated vaccine, using weakened strains of Salmonella Typhi bacteria to stimulate immunity against typhoid fever.
• Varicella Zoster virus: This vaccine contains a weakened strain of the varicella-zoster virus, which causes chickenpox and shingles. Similar to BCG, it provides immunity through a controlled exposure to the weakened virus.

Answer: Ninhydrin stain

Ninhydrin stain is used to make the wetted area of a filter paper strip more visible. Ninhydrin reacts with amino acids, particularly those present in fingerprints, and produces a visible purple or red color. This staining technique is commonly used in forensic science to visualize and enhance the visibility of latent fingerprints on paper.

The other options are incorrect:

• Eosin stain: Eosin stain is commonly used in histology and cytology for the staining of tissues, but it is not used for visualizing wetted areas on filter paper.
• Haemotoxin stain: There is a typographical error, and the correct term is likely “hematoxylin stain.” Hematoxylin is used as a nuclear stain in histology, and it is not employed for visualizing wetted areas on filter paper.
• Blue stain: “Blue stain” is a generic term, and there are various blue stains used in different applications. However, none of them are specifically used for making the wetted area of a filter paper strip more visible.

Answer: Severe reaction following the injection of protein solution in a sensitized individual

Anaphylaxis is a life-threatening allergic reaction involving rapid release of chemicals from immune cells, triggered by exposure to an allergen that the individual is already sensitized to. This means it requires prior sensitization (previous exposure) to the protein.

The other options are incorrect

• Severe reaction following primary injection of Protein solutions: Not all individuals react badly to their first exposure to protein solutions. Anaphylaxis requires prior sensitization.
• State of immunity developed by repeated injections of any foreign substance: This describes the general concept of immunization, not anaphylaxis, which is an allergic reaction, not a protective one.
• Severe reaction resulting from sensitivity to common allergens: While anaphylaxis can be triggered by common allergens like peanuts or insect stings, the question specifies protein solutions, implying a medical context where prior sensitization through injections is more likely.

Answer: 100% alcohol

100% alcohol is not commonly used as a disinfectant. While alcohol, particularly isopropyl alcohol or ethanol, is widely used as a disinfectant, it is typically used in solutions with lower concentrations (e.g., 70-90%). High-concentration alcohol (100%) evaporates rapidly and may not provide sufficient contact time to effectively eliminate microorganisms.

The other options are incorrect:

• 1-2% cetrimide: Cetrimide is a quaternary ammonium compound and is commonly used as a disinfectant in concentrations ranging from 1-2%. It has antiseptic properties and is used in various healthcare and household applications.
• 2% Lysol: Lysol, which often contains various disinfectant agents, including phenolics, is used as a disinfectant. In this context, 2% Lysol refers to a solution with a disinfecting concentration.
• 5% chloroxylene: Chloroxylenol, commonly known as Dettol, is used as a disinfectant. However, the percentage mentioned (5%) is not a standard concentration for this disinfectant. Standard concentrations are often lower, typically around 0.5-1%.

Answer: NK Cells

NK cells, or natural killer cells, are a crucial component of the innate immune system specifically active against viral cells. They recognize and destroy virus-infected cells without prior specific antigen exposure, hence their “natural” name. They function by directly lysing infected cells or triggering apoptosis (programmed cell death) within them.

The other options are incorrect:

• Cytotoxic T cells: These powerful lymphocytes belong to the adaptive immune system and play a key role in eliminating infected cells, but only after undergoing specific activation upon encountering a specific antigen.
• B cells: Primarily responsible for humoral immunity through antibody production, B cells are also part of the adaptive immune system and require antigen exposure for activation.
• Memory B cells: Derived from activated B cells after prior antigen exposure, memory B cells provide rapid antibody production against previously encountered pathogens but are not directly involved in initial antiviral defense.

Answer: IL-8

IL-8 (Interleukin-8) is a chemotactic cytokine. It plays a crucial role in the recruitment and activation of neutrophils to the site of infection or inflammation. IL-8 is produced by various cell types, including macrophages and epithelial cells, in response to infection or tissue damage. Its primary function is to attract and activate neutrophils, promoting their migration to the site where they can help eliminate pathogens.

The other options are incorrect:

• IL-1 (Interleukin-1): IL-1 is a pro-inflammatory cytokine involved in various immune responses, including fever induction and the activation of lymphocytes. It is not specifically classified as a chemotactic cytokine.
• IL-6 (Interleukin-6): IL-6 is a multifunctional cytokine with roles in inflammation, immune response, and hematopoiesis. While it has various functions, it is not primarily known as a chemotactic cytokine.
• TNF (Tumor Necrosis Factor): TNF is a pro-inflammatory cytokine involved in inflammation and immune regulation. Similar to IL-1 and IL-6, TNF is not primarily classified as a chemotactic cytokine.

Answer: Culture

Antibiotic sensitivity and resistance of microorganisms are primarily determined by culture. In the laboratory, microorganisms are isolated and grown in cultures, and then susceptibility testing is performed to assess their response to different antibiotics. The process involves exposing the cultured microorganisms to various antibiotics and observing their growth or inhibition, helping to identify effective antibiotics for treatment.

The other options are incorrect:

• Direct microscopy: Direct microscopy involves the examination of samples under a microscope without the need for culturing. While it can provide information about the presence and morphology of microorganisms, it does not determine antibiotic sensitivity.
• ELISA (Enzyme-Linked Immunosorbent Assay): ELISA is a technique used to detect the presence of specific antigens or antibodies. It is not directly involved in determining antibiotic sensitivity but is more commonly used for immunological assays.
• DNA probe: DNA probes are used for the detection of specific nucleic acid sequences. They are not typically used for assessing antibiotic sensitivity but may be employed for identifying specific pathogens based on their genetic material.

Answer: Mycoplasma

Mycoplasma bacteria are unique in that they completely lack a cell wall. This characteristic sets them apart from other bacteria, which typically have a rigid cell wall composed of peptidoglycan. Lacking a cell wall allows Mycoplasma to be extremely flexible and resistant to certain antibiotics that target cell wall synthesis.

The other options are incorrect:

• Rickettsiae: While Rickettsiae are also intracellular bacteria like Mycoplasma, they do possess a thin cell wall containing a different type of peptidoglycan compared to most bacteria.
• Chlamydiae: Similar to Rickettsiae, Chlamydiae also have a cell wall, albeit a complex one that undergoes significant rearrangement during their life cycle.
• Ehrlichiae: These bacteria also possess a typical bacterial cell wall composed of peptidoglycan.

Answer: Passive

A negative phase in immunity refers to a temporary period where an individual might be more susceptible to a specific infection due to a recent exposure to an antigen. This phenomenon is primarily observed in passive immunity, where antibodies are transferred from another source, like a mother to her child through breast milk or through vaccination.

The other options are incorrect:

• Active immunity: This type of immunity develops after exposure to an antigen and the body’s own immune system produces antibodies. No negative phase is associated with active immunity.
• Herd immunity: This refers to the protection of a community against a disease due to a high level of vaccination or immunity within the population. It doesn’t involve a negative phase in individual immunity.
• Local immunity: This refers to the specific immune response in a particular tissue or organ, and there’s no specific association with a negative phase.

Answer: Arthus phenomenon

The Arthus phenomenon, also known as the Arthus reaction, is a localized, necrotizing reaction that occurs when an antigen is injected into an already sensitized individual. In this case, the first injection of horse serum sensitizes the rabbit’s immune system by priming it to recognize horse serum proteins as foreign. When the second injection is given a few weeks later, the sensitized immune system reacts violently at the injection site, leading to localized tissue damage and necrosis.

The other options are incorrect:

• Atopy: This is a type of allergic reaction due to genetic predisposition, typically involving IgE antibodies and airway inflammation. It is not specific to horse serum and wouldn’t involve necrosis as a main feature.
• Anaphylaxis: This is a systemic, life-threatening allergic reaction involving widespread histamine release and anaphylactic shock. While it can be triggered by horse serum, the characteristic rapid onset and systemic symptoms differentiate it from the localized Arthus reaction.
• Serum sickness: This is a delayed hypersensitivity reaction to foreign serum, typically occurring 7-10 days after the initial exposure. It presents with systemic symptoms like fever, rash, and joint pain, rather than the localized necrosis of the Arthus phenomenon.

Answer: Cytotoxic / cytolytic type

Type II hypersensitivity, also known as cytotoxic or cytolytic hypersensitivity, involves antibody-mediated damage to host cells or tissues. Antibodies directly bind to cell surface antigens, activating pathways that lead to cell destruction through mechanisms like complement activation or antibody-dependent cell-mediated cytotoxicity.

The other options are incorrect:

• Anaphylaxis: This is a severe, rapidly occurring allergic reaction mediated by IgE antibodies and mast cell degranulation. It is categorized as Type I hypersensitivity, not Type II.
• Delayed hypersensitivity: This is a broad term encompassing several types of immune responses characterized by delayed (48-72 hours) reactions after antigen exposure. Type IV hypersensitivity (cell-mediated hypersensitivity) falls under this category, but it differs from Type II in lacking direct antibody-mediated cell damage.
• Immune complex mediated: This is Type III hypersensitivity, where preformed antigen-antibody complexes activate complement and attract inflammatory cells, causing tissue damage. While it overlaps with some aspects of Type II, the mechanisms and target cells differ.

Answer: Acid Fast Stain

The description of the papule turning into an ulcer in an abattoir worker points towards a potential infection with Mycobacterium tuberculosis, the bacteria causing tuberculosis. Acid Fast Stain is a specific test used to identify Mycobacterium species, including M. tuberculosis, by highlighting their unique cell wall composition. Therefore, it is the most appropriate diagnostic tool in this case.

The other options are incorrect:

• Trichrome Methylene Blue: This stain is used for general tissue differentiation and is not specific for Mycobacterium. It would not be helpful in diagnosing tuberculosis.
• Carbol Fuschin: This stain is also used for general tissue differentiation and bacterial identification but is not specific for Mycobacterium. It would not be the best choice for diagnosing tuberculosis.
• Calcoflour White: This stain is used for identifying fungal infections, which is not the case here. It would not be helpful in diagnosing tuberculosis.

Answer: CD7+ Pro-T-Cells

The earliest identifiable cells of T-cell lineage during maturation are CD7+ Pro-T-Cells. T-cell development begins in the bone marrow with the generation of pro-T-cells that express CD7. These cells then migrate to the thymus, where further maturation and differentiation occur.

The other options are incorrect:

• CD5+ Pre-T-Cells: CD5 is expressed on mature T cells, not on early precursor cells. Pre-T-cells at an early stage express CD7.
• CD8+ Pro-T-Cells: CD8 is a marker associated with mature cytotoxic T cells. Pro-T-cells at the earliest stage express CD7 and not CD8.
• CD8+ Pre-T-Cells: Similar to the explanation for CD8+ Pro-T-Cells, CD8 is not expressed at the early stages of T-cell development. CD7 is a more relevant marker for pro-T-cells.

Answer: IgE

Short Explanation:

IgE is the immunoglobulin least involved in complement activation. While other immunoglobulins like IgM, IgG, and IgA can initiate the complement cascade under specific circumstances, IgE plays a primarily effector role in allergic responses and lacks the necessary structural features for efficient complement fixation.

The other options are incorrect:

• IgM: IgM is highly efficient in activating the classical complement pathway through its pentameric structure, which facilitates binding to C1q protein.
• IgA: While IgA is less efficient than IgM in classical pathway activation, it can activate the alternative pathway, particularly when bound to mucosal surfaces.
• IgG: IgG subclasses IgG1, IgG2, and IgG3 can activate the classical pathway, while IgG4 is less efficient. Some IgG subclasses also participate in alternative pathway activation.

Answer: IgE

The reaginic antibody is IgE, specifically the IgE2 subclass. These antibodies are associated with allergic reactions and parasitic infections. They bind to antigens on parasites and allergens, stimulating mast cells and basophils to release histamine and other inflammatory mediators, leading to the characteristic symptoms of allergy or parasite expulsion.

The other options are incorrect:

• IgG: While IgG is the most abundant immunoglobulin and plays a crucial role in immune defense, it is not specifically associated with the term “reaginic antibody.”
• IgA: IgA is essential for protecting mucosal surfaces in the respiratory and digestive tracts but doesn’t have the “reaginic” property for specific allergic or parasitic responses.
• IgD: IgD functions primarily as a surface receptor on B cells and is not directly involved in the classic allergic or parasitic reactions associated with reaginic antibodies.

Answer: IgG

The secondary immune response is primarily mediated by IgG (Immunoglobulin G). During a secondary immune response, memory B cells are activated upon re-exposure to the same antigen. These memory B cells rapidly differentiate into plasma cells, producing a more significant and faster production of antibodies. IgG antibodies are the most abundant class of antibodies in the secondary immune response and play a crucial role in providing effective and rapid protection against previously encountered pathogens.

The other options are incorrect:

• IgA: IgA is predominantly associated with mucosal immunity and is found in mucosal secretions such as saliva, tears, and breast milk. It is not the main antibody involved in the secondary immune response.
• IgM: IgM is the primary antibody produced during the primary immune response. While it is present in the secondary response, its role diminishes compared to IgG, which becomes the predominant antibody in the secondary response.
• IgE: IgE is involved in allergic reactions and immediate hypersensitivity responses. It is not the primary mediator of the secondary immune response.