MicroBiology MCQs with Answer and Explnation | Chapter 40

Answer: HBs AG

The Australian antigen is another name for HBsAg, which stands for Hepatitis B surface antigen. It is a protein located on the outer surface of the Hepatitis B virus (HBV) and plays a crucial role in viral infectivity and persistence.

The other options are incorrect:

• HB Ag: This could potentially refer to Hepatitis B antigen, which is a broader term encompassing various antigens associated with HBV. However, HBsAg is the most specific and widely used among them.
• HBV: HBV is the entire virus itself, not just a specific antigen. While detecting HBsAg indicates the presence of HBV, they are not interchangeable terms.
• None of the above: This option is incorrect as HBsAg is the established terminology for the Australian antigen

Answer: ELISA followed by western blot technique

The most common method adopted for screening HIV infection is ELISA (Enzyme-Linked Immunosorbent Assay) followed by the Western blot technique. ELISA is a sensitive and high-throughput test used for initial screening. If the ELISA result is positive, the Western blot test is then used for confirmation. This two-step process helps reduce the likelihood of false-positive results.

The other options are incorrect:

• Virus isolation: Virus isolation is not typically used for routine screening of HIV infection. It is a more complex and time-consuming method used in research and specific diagnostic situations.
• Western blot followed by ELISA: The correct sequence is ELISA followed by Western blot. Using Western blot first may not be as efficient for initial screening, as it is a more specific but less sensitive test compared to ELISA.
• Polymerase Chain Reaction (PCR): PCR is a molecular technique used to detect viral genetic material. While it is a valuable tool for diagnosing HIV infection, it is not typically used as the primary screening method. PCR is often used in confirmation or in situations where serological tests may be inconclusive.

Answer: Hepatitis E

Enterically transmitted NANB (Non-A, Non-B) hepatitis refers to hepatitis caused by viruses that are transmitted through the fecal-oral route. Hepatitis E virus (HEV) is the virus associated with enterically transmitted NANB hepatitis.

The other options are incorrect:

• Hepatitis C: Hepatitis C virus (HCV) is not enterically transmitted. It is primarily transmitted through blood-to-blood contact, such as sharing of contaminated needles or through unsafe medical procedures.
• Hepatitis D: Hepatitis D virus (HDV) is a defective virus that requires the presence of hepatitis B virus (HBV) for its replication. It is not primarily enterically transmitted.
• Hepatitis F: Hepatitis F is a hypothetical virus that has not been conclusively identified or confirmed to cause hepatitis. It is not a recognized hepatitis virus.

Answer: Antibody of HBs Ag is associated with resistance to infection

The presence of antibodies against HBsAg (Hepatitis B surface antigen) indicates successful immune response and resistance to future HBV infection. These antibodies neutralize the virus, preventing it from entering and infecting liver cells.

The other options are incorrect:

• Antibody of HBC is not protective: While antibodies against HBC (Hepatitis B core antigen) can be detected after infection, they don’t directly neutralize the virus and don’t provide long-term protection from re-infection.
• Highest titres of anti HBC are found in persistent carriers of HBs Ag: This is true. Carriers have ongoing HBV replication, resulting in high levels of HBC antibodies. However, it’s important to note that this doesn’t imply protection but rather active infection.
• CMI disappears soon after recovery: CMI (Cell-mediated immunity) plays a crucial role in controlling HBV infection by targeting infected liver cells. While it might decrease after recovery, it doesn’t disappear entirely and contributes to long-term immune memory.

Answer: Cytopathic changes in culture cells

The best way of detecting the presence of viruses in the infected cell culture is to assess the presence of viral proteins in the infected monolayer. This can be achieved through various techniques such as immunofluorescence, enzyme-linked immunosorbent assay (ELISA), or Western blot, which specifically detect viral proteins in the infected cells.

The other options are incorrect:

• Cytopathic changes in culture cells: While cytopathic effects (CPE) are observable changes in cell morphology caused by viral infection, they do not directly provide information about the presence of viral proteins. Additional tests are needed for specific protein detection.
• Haemagglutination test: Haemagglutination tests are commonly used for certain viruses, particularly influenza viruses, to detect their ability to agglutinate red blood cells. However, it may not be the most direct method for detecting viral proteins in infected cells.
• Haemagglutination inhibition test: This test is used to assess the ability of antibodies to inhibit the haemagglutination activity of certain viruses, such as influenza viruses. It is not a direct method for detecting viral proteins in infected cells.

Answer: HBV

The Dane particle refers to the complete, intact virion (virus particle) of the hepatitis B virus (HBV). It was first observed in the serum of individuals infected with hepatitis B and is composed of the viral envelope, core, and DNA.

The other options are incorrect:

• IgG anti HAV: Immunoglobulin G (IgG) antibodies against hepatitis A virus (HAV) are part of the immune response to HAV infection. However, they are not the Dane particle, which specifically refers to the structure of the hepatitis B virus.
• Delta Virus: Delta virus (HDV) is a defective virus that requires the presence of hepatitis B virus (HBV) for its replication. It is a separate entity from the Dane particle, which is specific to HBV.
• HBC Ag: Hepatitis B core antigen (HBcAg) is a component of the Dane particle, but the term “Dane particle” refers to the entire structure of the hepatitis B virus. It includes the core antigen as well as the envelope and viral DNA.

Answer: 50% chances to have AIDS

A baby born to a mother suffering from AIDS (Acquired Immunodeficiency Syndrome) does not necessarily have a 50% chance of having AIDS. While the risk of transmission from an HIV-positive mother to her baby is present, the actual risk depends on various factors such as the mother’s viral load, use of antiretroviral therapy, and other interventions.

The other options are incorrect:

• Failure to thrive: Babies born to mothers with AIDS may face challenges, including failure to thrive, due to potential complications related to HIV infection. However, it is not universally true for all infants born to HIV-positive mothers.
• Have infections: Infants born to mothers with AIDS may have an increased risk of infections, as their immune systems may be compromised. However, the occurrence of infections is not guaranteed for every baby in this situation.
• 50% chances to have AIDS: This statement is incorrect. The risk of transmission from an HIV-positive mother to her baby can be reduced significantly with appropriate medical interventions, such as antiretroviral therapy and other preventive measures. The actual risk varies and is not a fixed 50%.

Answer: Neurotropic

The rabies virus is classified as a neurotropic virus, meaning it has a special affinity for infecting and replicating within nerve tissue. It travels along nerve pathways to reach the central nervous system (CNS), where it causes fatal inflammation and damage.

The other options are incorrect:

• Cytotropic: This term refers to viruses that preferentially infect any type of cell. While rabies can technically infect some non-neuronal cells, its primary target is still the nervous system.
• Dermatotropic: These viruses have a specific tropism for skin cells, which doesn’t align with the rabies virus’s primary target in the nervous system.
• Chromophilic: This term is typically used in histology to describe cells or structures that stain readily with certain dyes. It doesn’t directly represent a virus’s tropism or target tissue.

Answer: All of the above

While each option contributes to the differences between viruses and bacteria, only “all of the above” encompasses all the key points:

• Presence of either DNA or RNA: Both viruses and bacteria can contain genetic material, but viruses can have either DNA or RNA, while bacteria only have DNA.
• Simple structure: Compared to the complex cellular structure of bacteria, viruses are much simpler. They lack many organelle structures (cell parts) found in bacteria, such as ribosomes and mitochondria
• Complex multiplication: While both can multiply, the process is vastly different. Bacteria typically divide through binary fission, whereas viruses hijack host cells to replicate their genetic material and assemble new viral particles.

Answer: Hepatitis E virus

The faeco-oral route, where contaminated feces enter the mouth and infect the digestive system, is the primary transmission mode for Hepatitis E virus (HEV). It thrives in environments with poor sanitation and hygiene, often spreading through contaminated water and food.

The other options are incorrect:

• Hepatitis B virus (HBV): HBV primarily transmits through bodily fluids like blood and blood products, sexual contact, and from mother to child during childbirth/breastfeeding.
• Hepatitis C virus (HCV): Similar to HBV, HCV spreads through infected blood and body fluids, mainly through sharing needles and syringes or unsafe medical practices.
• Hepatitis D virus (HDV): HDV requires the presence of HBV for its own replication and transmission. It shares the same routes as HBV, like infected blood and bodily fluids.

Answer: Western Blot

The confirmatory test for HIV infection is the Western Blot. While ELISA (Enzyme-Linked Immunosorbent Assay) is commonly used as an initial screening test due to its high sensitivity, Western Blot is used to confirm the presence of specific antibodies against HIV. Western Blot is more specific and helps eliminate false-positive results that may occur with ELISA.

The other options are incorrect:

• ELISA: ELISA is an initial screening test for HIV infection, but it is not confirmatory. False-positive results can occur, and a confirmatory test, such as Western Blot, is required.
• Immunodot: Immunodot assays are similar to Western Blot and are used for the detection of specific antibodies. However, Western Blot is more commonly used as a confirmatory test for HIV.
• RIPA (Radioimmunoprecipitation assay): RIPA is a technique used for immunoprecipitation and is not typically used as a confirmatory test for HIV infection. Western Blot is the preferred confirmatory method.

Answer: Twort and d’herelle

Bacteriophage, a virus that infects bacteria, was discovered independently by Frederick Twort in 1915 and Felix d’Herelle in 1917. Both Twort and d’Herelle observed the phenomenon of bacterial lysis (dissolution) caused by an invisible agent later identified as bacteriophage.

The other options are incorrect:

• Robert Koch: While known for his contributions to germ theory and identifying causative agents for several infectious diseases, Koch did not discover bacteriophage.
• Menkin: Valy Menkin was a pathologist who studied inflammation and immune responses, but his research did not involve bacteriophages.
• Metchinkoff: Elie Metchnikoff made significant contributions to understanding phagocytosis (white blood cell engulfment of foreign particles), but his work doesn’t directly correlate to bacteriophage discovery.

Answer: Hepatitis B surface antigen in acute hepatitis

Australia antigen is an earlier term for the Hepatitis B surface antigen (HBsAg). This protein found on the surface of the Hepatitis B virus (HBV) plays a crucial role in the virus’s infectivity and is a key marker for diagnosing acute hepatitis B infection.

The other options are incorrect:

• AIDS: HIV (Human Immunodeficiency Virus) causes AIDS, not Hepatitis B virus. While HBV and HIV can co-infect individuals, Australia antigen specifically relates to HBV.
• Chronic leukemia: While some studies have looked at possible associations between HBV and certain cancers, Australia antigen isn’t directly linked to chronic leukemia.
• Basal cell carcinoma: Although HBV has been implicated in the development of some cancers, basal cell carcinoma isn’t currently considered a primary association with Australia antigen

Answer: in a week and reach a peak in 3 weeks

After exposure to the Herpes Simplex Virus (HSV), antibodies start to develop within a week and reach their peak level around 3 weeks later. These antibodies play a crucial role in managing future HSV infections and reducing their severity.

The other options are incorrect:

• Only after one year: While it might take several months for antibody levels to stabilize, they begin appearing much earlier within a week.
• No antibodies are present in primary HSV: Even in the initial infection, antibody production starts within a week, although it takes time to reach peak levels.
• Antibodies are present in recurrent and chronic apthous stomatitis: This statement confuses HSV with apthous stomatitis, a different condition with no known involvement of HSV antibodies.

Answer: 6 hours

The half-life of free HIV in plasma is significantly less than 24 hours. Studies have shown a range of around 28-110 minutes, averaging approximately 6 hours. This means that half of the circulating HIV virions in the blood are cleared within 6 hours.

The other options are incorrect:

• 24 hours: This is too long for the half-life of free HIV in plasma.
• 12 hours: While closer to the actual value, it’s still slightly overestimated.
• 3 months: This is significantly longer than the actual half-life and inaccurate.

Answer: Chorio allantoic membrane

The culture media used for the cultivation of Herpes Simplex Virus (HSV) is the chorioallantoic membrane. The chorioallantoic membrane is a highly vascularized membrane found in the eggs of developing chick embryos. It provides a suitable environment for the growth of some viruses, including HSV.

The other options are incorrect:

• Chocolate agar: Chocolate agar is not typically used for the cultivation of HSV. It is a specialized growth medium primarily used for the isolation of fastidious bacteria.
• Robertson’s cooked-meat broth: Robertson’s cooked-meat broth is a nutrient-rich liquid medium often used for the cultivation of anaerobic bacteria. It is not commonly used for HSV.
• Sabouraud’s agar: Sabouraud’s agar is a selective medium used for the cultivation of fungi. It is not suitable for the cultivation of HSV, which is a virus.

Answer: Hepatitis E

While all the other listed infections (HIV, Hepatitis B, and Hepatitis C) can be transmitted through contaminated dental instruments, Hepatitis E is primarily transmitted through the fecal-oral route and not typically associated with dental procedures.

The other options are incorrect:

• HIV: HIV can be transmitted through contaminated dental instruments if proper sterilization protocols are not followed. This includes instruments touching blood, saliva, or other bodily fluids of an infected individual.
• Hepatitis B: Similar to HIV, Hepatitis B can be transmitted through contaminated instruments due to its highly infectious nature and ability to survive on surfaces for extended periods.
• Hepatitis C: While less common than Hepatitis B, transmission of Hepatitis C through dental instruments is still possible, although primarily through needlestick injuries or inadequate sterilization of reusable instruments.

Answer: Saliva

While HIV can be present in saliva, the viral load is typically too low to cause transmission through casual contact like sharing utensils or kissing. Therefore, saliva is not considered a significant route of HIV transmission.

The other options are incorrect:

• Needle prick injury: Contaminated needles or syringes used for injections or other procedures pose a high risk of HIV transmission due to direct introduction of the virus into the bloodstream.
• Blood transmission: Direct contact with infected blood, such as through open wounds or sharing blood products, is a major route of HIV transmission.
• Sexual intercourse: Unprotected vaginal, anal, and oral sex are the most common ways HIV is transmitted due to the exchange of bodily fluids containing the virus.

Answer: hypersensitivity

Most fungal diseases are caused by hypersensitivity reactions to fungal components, not by direct tissue damage or toxin production. These reactions, triggered by the immune system, can range from mild (skin rashes) to severe (allergic bronchopulmonary aspergillosis) depending on the type of fungus and the individual’s sensitivity.

Incorrect Options:

• Exotoxin production: While some fungi produce exotoxins that can damage host cells, this is not the primary mechanism for most fungal diseases.
• Lecithinase production: Lecithinase is an enzyme produced by some fungi that can break down lecithin, a phospholipid found in cell membranes. While it might contribute to tissue damage in specific situations, it doesn’t explain the widespread nature of hypersensitivity-based fungal diseases.
• Coagulase production: This enzyme, associated with certain bacteria like Staphylococcus aureus, helps form clots, which is irrelevant to the mechanisms of fungal disease.

Answer: Aspergillus

Aspergillus species are known for their ability to form fungal balls, also known as aspergillomas. These fungal balls are masses of fungal elements, inflammatory cells, and debris that can develop in pre-existing cavities, such as lung cavities. Aspergillomas are often associated with conditions like chronic pulmonary aspergillosis.

The other options are incorrect:

• Penicillium: Penicillium is a genus of fungi known for producing the antibiotic penicillin. It is not typically associated with the formation of fungal balls.
• Mucor: Mucor is a genus of fungi that includes species causing mucormycosis. However, the formation of fungal balls is more commonly associated with Aspergillus than with Mucor.
• Rhizopus: Rhizopus is a genus of fungi that includes species causing rhinocerebral mucormycosis. Similar to Mucor, the formation of fungal balls is not a characteristic feature of infections caused by Rhizopus.

Answer: Acute infection

A rise in anti-HBc immunoglobulin (antibodies to hepatitis B core antigen) in a patient typically indicates an acute infection with the hepatitis B virus (HBV). Anti-HBc antibodies are produced in response to the core antigen of the virus during the early phase of infection.

The other options are incorrect:

• Carrier state: A rise in anti-HBc antibodies is more indicative of an acute infection rather than a carrier state. Chronic carriers may have detectable anti-HBc antibodies, but an increase is more suggestive of acute infection.
• Prodromal phase: The prodromal phase is an early phase of a disease that precedes the appearance of specific symptoms. While anti-HBc antibodies may be detectable during the prodromal phase, a rise in their levels is more indicative of acute infection.
• Convalescence: Convalescence refers to the period of recovery after an illness or medical treatment. An increase in anti-HBc antibodies is more associated with the active phase of infection rather than the convalescent phase.

Answer: Virus

Cytopathic effect (CPE) refers to visible changes in host cells caused by viral infection. These changes can include cell rounding, lysis (bursting), syncytia formation (fusion of multiple cells), and inclusion bodies (viral protein aggregates). Bacteria, spirochetes, and anaerobes are not directly capable of causing CPE because they lack the ability to invade and manipulate host cells in the same way viruses do.

The other options are incorrect:

• Bacteria: While some bacteria can damage host cells and cause disease, they typically do so through mechanisms that don’t result in the classic CPE seen with viruses.
• Spirochetes: Similar to bacteria, spirochetes are single-celled organisms that interact with host cells differently than viruses and rarely cause CPE.
• Anaerobe: This term refers to a microorganism that can grow without oxygen. While some anaerobes can contribute to infections, they are not directly responsible for the CPE associated with viral infections.

Answer: Fall in to the general size range of 200-3000 angstrom unit

This is the only option that truly reflects a general property of viruses. While other listed characteristics may apply to some specific viruses, they are not universally true for all virus types.

The other options are incorrect:

• New virus particle arises directly (by division) from preexisting viruses: This is not universally true. While some viruses replicate through binary fission, others use more complex replication cycles that do not involve direct division.
• Contain equal proportions of protein, lipo polysaccharide and nucleic acids: This is not accurate. The composition of viruses varies greatly across different types. Lipo polysaccharides, for example, are not present in all viruses.
• Contain DNA but no RNA: This is not true for all viruses. Some viruses contain DNA, while others contain RNA, and some even have double-stranded or single-stranded forms of these nucleic acids.

Answer: Candidiasis

While all the listed infections are commonly associated with AIDS, candidiasis takes the top spot. This fungal infection, also known as thrush, can affect various parts of the body, including the mouth, throat, esophagus, vagina, and skin. The weakened immune system in people with AIDS makes them highly susceptible to opportunistic infections like candidiasis.

The other options are incorrect:

• Cryptococcosis: This serious fungal infection involving the brain and meninges can occur in AIDS, but its prevalence is lower than candidiasis.
• Tuberculosis: This bacterial infection is indeed a major threat to people with AIDS, but it’s typically not considered the most common opportunistic infection.
• Aspergilosis: Similar to cryptococcosis, aspergilosis is a less common fungal infection compared to candidiasis in AIDS patients.

Answer: Blood agar

Viruses require living cells to replicate and cannot grow on nutrient media like blood agar, which is designed for bacterial growth.

The other options are incorrect:

• Chick embryo: Viruses can be cultured in chick embryos through a technique called chorioallantoic membrane (CAM) inoculation. The virus infects the developing chick embryo, allowing for its replication and detection.
• Guinea pigs: Some viruses can be cultured in live animals like guinea pigs, primarily those that cause specific diseases in these animals. This method, however, has ethical and practical limitations.
• Cell culture: This is the most common method for culturing viruses. Different types of cells are used depending on the specific virus, and specialized culture media provides the necessary nutrients and environment for viral replication.

Answer: The time lapse between the infection and detection of viral antibodies

The window period in HIV infection refers to the time between the initial exposure to the virus and the moment when a blood test can reliably detect the presence of HIV antibodies. This is because it takes some time for the body to produce these antibodies in response to the infection.

The other options are incorrect:

• The time lapse between the infection and development of AIDS: While HIV infection can eventually lead to AIDS if untreated, the window period specifically refers to the detection of antibodies, not the development of AIDS. AIDS is a later stage of HIV infection that can take years to develop.
• The time lapse between obtaining the sample and detection of virus in the lab: This refers to the processing time of the test itself, which is typically very short (hours or even minutes) and not considered part of the window period.

Answer: Helper T lymphocytes (CD4)

HIV primarily infects and destroys helper T lymphocytes (CD4), a type of white blood cell crucial for the immune system’s functioning. This weakens the immune system’s ability to fight off infections and diseases, making individuals with HIV more susceptible to various opportunistic infections and eventually leading to AIDS if untreated.

The other options are incorrect:

• Red blood cells: HIV does not typically infect red blood cells. They lack the necessary receptors for HIV to enter and replicate.
• Fibroblasts: These are connective tissue cells involved in wound healing and other functions. While HIV can potentially infect some types of fibroblasts under specific conditions, it’s not its primary target and not the main concern in HIV infection.
• Mast cells: These cells are also part of the immune system but are not significantly affected by HIV. Their role in the immune response differs from helper T lymphocytes, and HIV focuses on targeting those crucial for CD4-mediated immunity.

Answer: Pneumocystis carinii pneumonia

While all listed infections can occur in AIDS, Pneumocystis carinii pneumonia (PCP) was historically and remains a classic opportunistic infection associated with the disease. This fungal infection of the lungs, caused by the Pneumocystis jirovecii organism, was a major threat to people with AIDS before the widespread use of antiretroviral therapy (ART).

The other options are incorrect:

• Apthous stomatitis: This ulcerative condition can occur in both HIV-positive and HIV-negative individuals, and its association with AIDS is less prominent compared to PCP.
• Tuberculosis: While a significant concern in AIDS, tuberculosis (TB) is not strictly an opportunistic infection as it can affect individuals with healthy immune systems as well.
• Herpetic gingivostomatitis: This infection caused by the herpes simplex virus can happen in individuals with both normal and compromised immune systems and is not specifically characteristic of AIDS.

Answer: Orthomyxo virus, which is a RNA virus

Influenza is caused by Orthomyxoviruses, which are RNA viruses. The influenza virus has a segmented RNA genome, and it belongs to the family Orthomyxoviridae. There are three types of influenza viruses: A, B, and C, with influenza A being the most common cause of seasonal flu outbreaks in humans.

The other options are incorrect:

• Paramyxo virus, which is a DNA virus: Paramyxoviruses are RNA viruses, not DNA viruses. Influenza is caused by Orthomyxoviruses, not Paramyxoviruses.
• Paramyxo virus, which is an RNA virus: While Paramyxoviruses are RNA viruses, they do not cause influenza. Influenza is caused by Orthomyxoviruses.
• Orthomyxo virus, which is a DNA virus: This is incorrect. Influenza viruses (Orthomyxoviruses) have RNA genomes, not DNA genomes.

Answer: Banana

Sporozoites of Plasmodium falciparum, the parasite responsible for the deadliest form of malaria, have a characteristic elongated, curved shape often described as banana-shaped. This specific shape is important for their movement and ability to invade host cells.

The other options are incorrect:

• Dot: Sporozoites are elongated and not round like a dot.
• Comma: While they are curved, the curvature is more pronounced than a simple comma shape.
• Sickle: While falciparum malaria is sometimes called sickle cell malaria due to specific red blood cell changes, the sporozoites themselves are not sickle-shaped.

Answer: cats

Toxoplasma gondii is carried by cats. Cats are the definitive hosts of Toxoplasma, meaning the parasite can complete its sexual life cycle within the cat’s digestive system. Humans and other animals can become infected with Toxoplasma through ingestion of oocysts shed in the feces of infected cats or by consuming undercooked or raw meat containing cysts.

The other options are incorrect:

• Dogs: Toxoplasma gondii is not primarily carried by dogs. While dogs can become infected, they are not the primary hosts for the completion of the parasite’s life cycle.
• Rats: Rats are not the carriers of Toxoplasma gondii. The definitive hosts are cats, where the sexual reproduction of the parasite occurs.
• Cow: Cows are not the primary carriers of Toxoplasma gondii. The primary source of infection for humans is contact with cat feces or consumption of contaminated meat.

Answer: T. Saginata

Taenia saginata, commonly known as the beef tapeworm, is the longest among the options listed. Adult tapeworms of Taenia saginata can grow to lengths of several meters in the human intestine.

The other options are incorrect:

• T. Solium: Taenia solium, the pork tapeworm, is also a large tapeworm, but T. saginata is typically longer.
• Hookworm: Hookworms are intestinal parasites, but they are not as long as tapeworms. They are much smaller in size.
• A. Lumbricoides: Ascaris lumbricoides, the giant roundworm, is a nematode and can grow to a considerable length. However, in comparison to tapeworms, it is not as long.

Answer: Enterobius

Threadworm is another name for Enterobius vermicularis, a parasitic nematode commonly known as pinworm. Enterobius vermicularis is a type of roundworm that infects the human colon and rectum.

The other options are incorrect:

• Ancylostoma: Ancylostoma refers to a genus of hookworms, which are different from pinworms (Enterobius).
• Ascaris: Ascaris lumbricoides is a giant roundworm, not a threadworm. It is one of the largest intestinal parasites that infect humans.
• Necator: Necator americanus is a hookworm species, not a threadworm. It is another type of hookworm that infects the small intestine of humans.

Answer: Hook worm

Hookworm infection, particularly Ancylostoma and Necator species, is a major contributor to anemia in tropical regions. This is because hookworms attach to the intestinal wall and feed on blood, leading to iron deficiency and ultimately anemia.

The other options are incorrect:

• Thread worm: While Enterobius can cause some intestinal discomfort, it doesn’t significantly contribute to iron deficiency or anemia.
• Ascaris: Ascaris lumbricoides, the common roundworm, can cause nutritional deficiencies but primarily affects vitamin A and protein absorption. While they may contribute to overall malnutrition, iron deficiency and anemia are less typical consequences.
• Guinea worm: Dracunculus medinensis, the guinea worm, causes significant tissue damage and discomfort but doesn’t directly feed on blood or cause iron deficiency. Its primary impact is unrelated to anemia.

Answer: Ascariasis

The “Medusa lock” appearance, characterized by multiple, intertwined, curvilinear shadows on an X-ray, is most commonly associated with Ascariasis, an intestinal infection caused by the roundworm Ascaris lumbricoides.

The other options are incorrect:

• Tapeworm: While tapeworms can be seen on X-rays in some cases, their appearance generally differs from the characteristic “Medusa lock” seen in Ascariasis. They often appear as single, elongated, radiolucent (darker) shadows within the intestines.
• Hook worm: Hookworms are smaller intestinal parasites and typically wouldn’t show up as distinct radiographic findings like the “Medusa lock.”
• Ascariasis and tapeworm: While both can potentially appear on an X-ray, the specific “Medusa lock” pattern is primarily associated with Ascariasis and doesn’t necessarily indicate co-infection with tapeworm.

Answer: Saboraud’s medium

The culture medium commonly used for the cultivation of Candida species is Saboraud’s medium. It is a selective and differential medium designed to promote the growth of fungi while inhibiting the growth of bacteria. Saboraud’s medium typically contains peptones, dextrose, and agar.

The other options are incorrect:

• Methylene blue dextrose agar: This is not a commonly used culture medium for Candida. Methylene blue dextrose agar is more commonly associated with bacterial culture.
• Pingolevin: There is no widely known culture medium called Pingolevin. It might be a term or typo not commonly used in microbiology.
• All of the above: While Saboraud’s medium is a suitable culture medium for Candida, the inclusion of “Methylene blue dextrose agar” and “Pingolevin” is incorrect. These are not standard or widely recognized culture media for Candida.

Answer: Seen in immunocompromised and causes meningitis in them

While Candida albicans can cause meningitis in immunocompromised individuals, it’s not as common as other types of infections associated with this fungus. It primarily causes superficial infections like oral thrush, vaginal yeast infections, and skin infections.

The other options are incorrect:

• Yeast-like fungus: Candida albicans is classified as a yeast-like fungus due to its ability to reproduce through budding.
• Forms Chlamydospores: Chlamydospores are thick-walled spores produced by Candida albicans under certain conditions, allowing it to survive adverse environments.
• Blastomeres seen in isolates: Blastomeres are the yeast form of Candida albicans and are commonly observed in clinical isolates.

Answer: All of the above

All three listed fungi, Penicillium, Mucor, and Aspergillus, can act as opportunistic pathogens, causing infections in individuals with weakened immune systems. While each has its own specific characteristics and risk factors, they all share the potential to exploit compromised immunity.

Answer: Kerion

Kerion is the term for the specific inflammatory type of tinea capitis, characterized by the features you described: a painful, circumscribed, boggy, and indurated lesion. It results from a strong immune response to the fungal infection combined with secondary bacterial involvement.

The other options are incorrect:

• Alopecia areata: This is an autoimmune disorder causing patchy hair loss but lacks the inflammatory features and secondary infection typical of kerion.
• Pilomatrixoma: This is a benign skin tumor originating from hair follicles and doesn’t have the infectious or inflammatory aspects of kerion.
• Tenia incognito: This is a fictional parasite mentioned in the video game “Bloodborne” and has no relation to human scalp infections.

Answer: Candida albicans

The Reynolds Braude phenomenon refers to the characteristic formation of germ tubes by Candida albicans when grown in specific conditions, like serum-supplemented media. Germ tubes are elongated, filamentous structures considered virulence factors that aid adhesion and penetration into host tissues.

The other options are incorrect:

• Mucor: Mucor species generally don’t exhibit germ tube formation and are known for their characteristic fungal hyphae with broad, non-septate branches.
• Cryptococcus: Cryptococcus neoformans, another fungal pathogen, also lacks germ tube formation and typically appears as round, budding yeast cells with a capsule.
• Aspergillus: While some Aspergillus species possess the ability to form elongated conidia (spores), these structures differ from the true germ tubes seen in Candida albicans and arise through a distinct reproductive process.

Answer: Periodic acid schiff stain

PAS stain is the gold standard for visualizing fungal elements, including Candida hyphae, in tissue sections. It highlights polysaccharides in the fungal cell wall, rendering them bright red against the blue background of hematoxylin-stained tissue. This allows for clear identification and differentiation of Candida hyphae from host cells and other microorganisms.

The other options are incorrect:

• Van Gieson’s stain: This stain is primarily used to differentiate collagen (red) from muscle fibers (yellow) and is not effective for visualizing fungi.
• Masson Trichrome stain: This stain provides a more detailed view of connective tissue by differentiating collagen (blue), muscle fibers (red), and nuclei (black). However, it doesn’t specifically highlight fungal elements.
• Toluidine blue stain: This stain is commonly used in plant histology and can stain fungal hyphae, but it is less specific than PAS and may also stain other tissue components, making visualization less clear.

Answer: Noncapsulated fungus infecting man

While Cryptococcus neoformans can exist in a noncapsulated form during its mating cycle, its characteristic feature and primary virulence factor is the thick polysaccharide capsule surrounding its yeast cells. This capsule plays a crucial role in evading the immune system and facilitating infection.

The other options are incorrect:

• Causes meningitis: Cryptococcus neoformans is a well-known cause of cryptococcal meningitis, particularly in immunocompromised individuals.
• Melanin production related to virulence: Melanin pigments produced by Cryptococcus neoformans contribute to its ability to withstand oxidative stress and resist phagocytosis by immune cells, thereby enhancing its virulence.
• Basidiomycete yeast: Cryptococcus neoformans belongs to the phylum Basidiomycota, making it a basidiomycete yeast.

Answer: 2:1

The normal ratio of CD4 (T4) to CD8 (T8) lymphocytes in the peripheral blood is approximately 2:1. This ratio is commonly used in immunological assessments to evaluate the balance between T-helper (CD4) and T-cytotoxic/suppressor (CD8) cells.

The other options are incorrect:

• 1:2: This ratio is the reverse of the normal CD4:CD8 ratio. In a healthy individual, the CD4 count is typically higher than the CD8 count.
• 3:1: This ratio is not the usual normal ratio of CD4 to CD8. The normal ratio is closer to 2:1.
• 1:3: This ratio is also the reverse of the normal CD4:CD8 ratio. In a healthy immune system, the CD4 count is higher than the CD8 count.

Answer: Caecum and large intestine

Lesions caused by Entamoeba histolytica predominantly involve the caecum and large intestine. Entamoeba histolytica is the pathogenic amoeba responsible for amoebic dysentery and can cause ulceration and inflammation in the colonic mucosa, leading to symptoms such as bloody diarrhea.

The other options are incorrect:

• Duodenum: Entamoeba histolytica primarily affects the large intestine, and involvement of the duodenum is not characteristic of amoebic infection.
• Stomach: Amoebic lesions do not typically involve the stomach. The primary site of infection is the lower gastrointestinal tract.
• Jejunum and Ileum: Entamoeba histolytica predominantly affects the caecum and large intestine rather than the small intestine (jejunum and ileum). The large intestine is the primary site of amoebic colonization and pathology.

Answer: Bifido bacteria

Bifidobacteria are generally considered safe and beneficial bacteria found naturally in the gut microbiome of healthy humans. They play a crucial role in maintaining gut health by suppressing harmful bacteria, aiding digestion, and promoting nutrient absorption.

The other options are incorrect:

• E. coli: While some specific strains of E. coli may have probiotic properties, most strains are associated with foodborne illness and shouldn’t be considered beneficial bacteria.
• Staphylococcus: Some Staphylococcus strains are beneficial skin commensals, but others can cause various infections. It’s not a typical probiotic organism.
• Salmonella: This is a harmful bacteria responsible for food poisoning and shouldn’t be consumed as a probiotic.

Answer:  Tsetse fly

Sleeping sickness, also known as Human African Trypanosomiasis (HAT), is caused by parasitic protozoans of the genus Trypanosoma brucei. These parasites are exclusively transmitted to humans by the bite of infected tsetse flies. The two main subspecies responsible for HAT are Trypanosoma brucei gambiense and Trypanosoma brucei rhodesiense.

The other options are incorrect:

• House fly: While house flies can mechanically transmit certain diseases on their legs and mouthparts, they are not known to play a role in spreading sleeping sickness.
• Tick: Ticks transmit various diseases like Lyme disease and Rocky Mountain spotted fever, but not sleeping sickness.
• Reduvid bug: Reduvid bugs (also known as kissing bugs) transmit Chagas disease in the Americas, but not sleeping sickness.

Answer: M. chelonae

Injection abscesses due to the use of contaminated vaccines can occur in infections caused by Mycobacterium chelonae. M. chelonae is a rapidly growing mycobacterium that is associated with skin and soft tissue infections. Contaminated vaccines or injection equipment can introduce the bacteria, leading to abscess formation.

The other options are incorrect:

Prevalence: Certain species might be more likely to be present in specific geographic regions or contexts.
Vaccine type: Different vaccines might be linked to higher risks of contamination with specific mycobacteria depending on their manufacturing processes and storage requirements.
Specific characteristics of the contamination: The bacterial load and viability in the contaminated vaccine would also play a role in the development of an abscess.

Answer: Caused by Calymmatobacterium granulomatis

Donovanosis is a sexually transmitted infection caused by the bacterium Calymmatobacterium granulomatis (formerly known as Klebsiella granulomatis). It is characterized by painless, beefy red, granulomatous genital ulcers. Donovanosis primarily affects the genital and perineal regions.

The other options are incorrect:

• Lymphadenopathy is remarkable & diagnostic: Lymphadenopathy is not a characteristic feature of Donovanosis. It is more associated with syphilis and chancroid.
• Penicillin is the drug of choice: Tetracyclines, such as doxycycline, are the preferred antibiotics for treating Donovanosis, not penicillin.
• Characterized by painful genital ulcers: Donovanosis is characterized by painless genital ulcers. Painful genital ulcers are more commonly associated with other sexually transmitted infections, such as herpes simplex virus infection.

Answer: 500

The normal CD4 count in a healthy adult is approximately 500 cells/mm³. The CD4 count is a measure of the number of CD4-positive T lymphocytes in a sample of blood and is an important indicator of immune function.

The other options are incorrect:

• 200: This is significantly below the normal range and can be indicative of a weakened immune system or HIV infection.
• 1000: While above the lower limit of the normal range, 1000 is slightly higher than the typical average and might warrant further investigation depending on other health factors.
• 300: Similar to 200, this is well below the normal range and raises concerns about potential immune system issues.

Answer: India ink preparation

The staining technique most commonly employed to detect the presence of capsulated yeast in cerebrospinal fluid is the India ink preparation. India ink is used to visualize the capsules surrounding certain yeast, such as Cryptococcus neoformans. The capsule appears as a clear halo around the yeast cells against the dark background of the ink.

The other options are incorrect:

• Methenamine silver stain: This stain is used for the detection of fungi, particularly Pneumocystis jirovecii, and is not commonly employed for visualizing yeast capsules.
• Ziehl-Neelsen stain: Ziehl-Neelsen stain is used for acid-fast bacteria, such as Mycobacterium tuberculosis, and is not suitable for staining yeast capsules.
• Pyte-ferraco stain: Pyte-ferraco stain is used for the detection of Treponema pallidum in syphilis and is not used for visualizing yeast capsules.