MicroBiology MCQs with Answer and Explnation | Chapter 16

Answer: All the above

The rabies virus can multiply in all of the following:

• The central nervous system (CNS): This is the primary site of rabies virus replication. The virus enters the CNS through the peripheral nerves and then spreads to the brain and spinal cord.
• The peripheral nerves: The rabies virus can also replicate in the peripheral nerves. This is how the virus spreads from the bite site to the CNS.
• Muscle tissues: The rabies virus can replicate in muscle tissues, but this is less common.

Answer: Semple vaccine

Neurological complications following rabies vaccines are more commonly associated with the Semple vaccine. This vaccine, which is an inactivated nerve tissue vaccine, has been associated with adverse neurological effects.

The other options are incorrect:

• Chick embryo vaccine: This option is not commonly associated with neurological complications following rabies vaccination.
• HDCS vaccine (Human Diploid Cell Strain): HDCS vaccine is a modern and safer rabies vaccine, and it is not known for causing frequent neurological complications.
• BPL vaccine (Beta-Propiolactone): BPL is a chemical used in the inactivation process of some rabies vaccines, but neurological complications are not commonly associated with BPL itself. The choice of inactivation method doesn’t necessarily correlate with neurological issues; it depends more on the overall formulation and safety measures in vaccine development.

Answer: HDCS vaccine

HDCS vaccine, developed using human diploid cell strains, is considered one of the more modern and effective rabies vaccines recommended by the WHO. It is safer than older vaccines that used nerve tissue (like sheep brain) and offers a high level of protection against rabies.

The other options are incorrect:

• Duck embryo vaccine: Duck embryo vaccine is not a commonly recommended rabies vaccine. Modern cell culture vaccines are preferred over older ones.
• Sheep brain vaccine: Vaccines derived from sheep brain tissue are considered outdated and less safe. Modern alternatives like HDCS vaccine have largely replaced them.
• BPL vaccine (Beta-Propiolactone): Beta-Propiolactone is a chemical used in the inactivation process of some rabies vaccines, but it doesn’t represent a specific type of vaccine. Modern vaccines, including those using BPL, are considered safer than older nerve tissue vaccines, but HDCS vaccines are often preferred.

Answer: Cl. tetani

Tetanus is caused by the bacterium Clostridium tetani. It produces a toxin known as tetanospasmin, which causes the characteristic symptoms of tetanus.

The other options are incorrect:

• Clostridium botulinum: This bacterium causes botulism, not tetanus. Botulism is characterized by muscle paralysis.
• Cl. welchii (Clostridium welchii): Clostridium welchii is an outdated name for Clostridium perfringens, which is not the causative agent of tetanus. It is associated with gas gangrene.
• Cl. perfringens (Clostridium perfringens): Clostridium perfringens is not the causative agent of tetanus. It is associated with various types of food poisoning and gas gangrene.

Answer: Exotoxin in sympathetic system

Tetanus is caused by the action of tetanus neurotoxin, which is an exotoxin produced by the bacterium Clostridium tetani. This neurotoxin primarily affects the central nervous system, particularly the sympathetic nervous system, leading to the characteristic symptoms of tetanus.

The other options are incorrect:

• Exotoxin in the parasympathetic system: Tetanus neurotoxin primarily affects the sympathetic nervous system, not the parasympathetic system.
• Endotoxin in the sympathetic system: Tetanus is not caused by endotoxins; it is caused by the exotoxin produced by Clostridium tetani.
• Endotoxin in the parasympathetic system: Tetanus is not caused by endotoxins, and its primary impact is on the sympathetic nervous system rather than the parasympathetic system.

Answer: Trismus

Trismus, or “lock jaw,” is often the initial symptom of tetanus. It involves the tightening of the jaw muscles, making it difficult to open the mouth. Other symptoms, such as muscle stiffness and spasms, usually follow.

The other options are incorrect:

• Lock jaw: This is another term for trismus, which is indeed an early symptom of tetanus.
• Anorexia: Anorexia, or loss of appetite, is not typically the first symptom of tetanus.
• Dysphagia: Difficulty swallowing (dysphagia) is a symptom that may occur in the later stages of tetanus, but trismus usually precedes it.

Answer: Cl. botulinum

Clostridium botulinum produces botulinum toxin, which is known for its potency. Botulinum toxin is a neurotoxin that causes botulism and is considered one of the most potent toxins known.

The other options are incorrect:

• Cl. tetani (Clostridium tetani): This bacterium produces tetanus toxin, which is potent but not as powerful as botulinum toxin.
• Cl. welchii (Clostridium perfringens): Clostridium perfringens does not produce a neurotoxin as potent as botulinum toxin. It is associated with gas gangrene and food poisoning.
• Cl. septicum (Clostridium septicum): Clostridium septicum produces toxins associated with tissue destruction, but they are not as potent as botulinum toxin in terms of their neurotoxic effects.

Answer: Botulinum

The toxin produced by Clostridium botulinum is known as botulinum toxin. It causes botulism and is one of the most potent toxins known, leading to muscle paralysis.

The other options are incorrect:

• Tetanospasmin: This toxin is produced by Clostridium tetani and causes tetanus, not botulism.
• Tetanolysin: This is a hemolysin produced by Clostridium tetani, but it is not the primary neurotoxin responsible for the symptoms of tetanus.
• Cholera toxin: This toxin is associated with Vibrio cholerae, the bacterium that causes cholera, and is not produced by Clostridium botulinum.

Answer: Staphylococcus aureus

Toxic shock syndrome (TSS) is often associated with the production of toxic shock syndrome toxin-1 (TSST-1), which is produced by certain strains of Staphylococcus aureus bacteria.

The other options are incorrect:

• Streptococcus pyogenes: While Streptococcus pyogenes can cause various infections, it is not typically associated with toxic shock syndrome.
• Vibrio cholerae: Vibrio cholerae is associated with cholera, not toxic shock syndrome.
• Candida: Candida is a type of yeast and is not known to cause toxic shock syndrome. TSS is more commonly linked to bacterial toxins.

Answer: T. pallidum

The causative agent of syphilis is Treponema pallidum. It is a spiral-shaped bacterium that is transmitted through direct contact with a syphilitic sore, known as a chancre. Syphilis is a sexually transmitted infection (STI) that can also be transmitted from mother to child during pregnancy or childbirth.

The other options are incorrect:

• Treponema pertenue is the causative agent of yaws, a tropical skin disease that is endemic in parts of Africa, Southeast Asia, and the Pacific Islands.
• Treponema carateum is the causative agent of pinta, a skin disease that is endemic in parts of Central and South America.
• Treponema endemicum is the causative agent of bejel, a skin disease that is endemic in parts of Africa and the Middle East.

Answer: FTA

The specific test for syphilis is FTA-ABS (fluorescent treponemal antibody absorbed) test. It is a highly accurate test that can detect antibodies to Treponema pallidum, the bacteria that causes syphilis, even in early stages of the infection when other tests may be negative.

The other options are incorrect:

• VDRL test (Venereal Disease Research Laboratory): This is a non-treponemal antibody test that can also detect antibodies to other bacteria, so it is not as specific as FTA-ABS.
• ELISA (enzyme-linked immunosorbent assay): This is another non-treponemal antibody test that is similar to VDRL.
• RPR (rapid plasma reagin): This is a non-treponemal antibody test that is the least specific of the three tests. It is often used as a screening test because it is quick and easy to perform. However, a positive RPR test should always be confirmed with a more specific test, such as FTA-ABS.

Answer: Slide flocculation test

The VDRL test is a slide flocculation test for syphilis. This means that it detects antibodies in the blood that clump together when mixed with a special reagent. The clumping reaction is visible as a change in the color of the mixture.

The other options are incorrect:

• Agglutination test: Agglutination tests detect antibodies that clump together with antigens (foreign substances) in the blood. The VDRL test does not use antigens, so it is not an agglutination test.
• Precipitation test: Precipitation tests detect antibodies that cause soluble antigens to precipitate (form a solid deposit) in the blood. The VDRL test does not cause antigens to precipitate, so it is not a precipitation test.

Answer: Air borne infection

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Out of the given options, the character that is false about Neisseria gonorrhoeae is “Air borne infection”. Neisseria gonorrhoeae is a sexually transmitted bacterium and is not typically transmitted through the air. It is spread through direct contact with the mucous membranes of the genitals, rectum, or mouth.

The other options are correct:

• Gram-negative, aerobic bacteria: Neisseria gonorrhoeae is a gram-negative bacterium, which means that it has a thin cell wall and does not retain the Gram stain. It is also an obligate aerobe, which means that it requires oxygen to grow.
• Non-motile diplococci: Neisseria gonorrhoeae is a non-motile organism, which means that it cannot move on its own. It is also a diplococcus, which means that it appears as pairs of bacteria in a microscope.
• Oxidase positive organisms: Neisseria gonorrhoeae is oxidase positive, which means that it produces an enzyme that can oxidize certain chemicals. This is a useful test for identifying Neisseria gonorrhoeae in the laboratory.

Answer: Sexually transmitted venereal disease

Gonorrhea is a sexually transmitted infection (STI) caused by the bacterium Neisseria gonorrhoeae. It is primarily transmitted through sexual contact with an infected person and is not classified as an airborne or waterborne disease. The correct answer is “Sexually transmitted venereal disease.”

Answer: Gonococcus

Bartholin cysts are caused by a blockage in the Bartholin gland ducts, which are two small glands that are located on either side of the vaginal opening. The blockage can be caused by a number of things, including:

• Infection with bacteria, such as E. coli, Staphylococcus aureus, or Streptococcus
• Sexually transmitted infections (STIs), such as gonorrhea or chlamydia
• Injury to the vaginal area

The most common type of bacteria that causes Bartholin cysts is Gonococcus, which is the bacteria that causes gonorrhea. Gonorrhea is an STI that is transmitted through sexual contact.

The other options are incorrect:

• Candida: Candida is a fungus and is not a typical cause of Bartholin cysts. These cysts are usually related to glandular duct obstruction rather than fungal infections.
• Streptococcus: While infections can occur in Bartholin cysts, Streptococcus is not a common causative agent. The primary cause is usually ductal obstruction.
• Staphylococcus: Similar to Streptococcus, Staphylococcus is not a typical causative agent for Bartholin cysts. The obstruction of the gland duct is the primary factor leading to cyst formation.

Answer: All of the above

Neisseria gonorrhoeae is the bacterium that causes gonorrhea, a sexually transmitted infection (STI). Gonorrhea can infect several parts of the body, including the urethra, the conjunctiva of the eyes, and the joints.

• Urethritis is an inflammation of the urethra, which is the tube that carries urine out of the body. In men, gonorrhea is the most common cause of urethritis. In women, gonorrhea can also cause urethritis, but it is more common to cause vaginitis, which is an inflammation of the vagina.
• Conjunctivitis is an inflammation of the conjunctiva, which is the lining of the eyelids and eyeball. Gonorrheal conjunctivitis is a serious eye infection that can cause blindness if not treated promptly.
• Arthritis is an inflammation of the joints. Gonorrheal arthritis is a rare complication of gonorrhea that can cause severe joint pain and damage.

Answer: Pili

Pili, also known as fimbriae, are hair-like appendages on the surface of bacteria. In Neisseria gonorrhoeae, pili play a crucial role in virulence. They are involved in the attachment of the bacterium to host cells, facilitating colonization and the establishment of infection. Pili contribute to the ability of the bacterium to evade host defenses and establish a successful infection. Therefore, in the case of Neisseria gonorrhoeae, virulence is often attributed to the presence and functionality of pili.

The other options are incorrect:

• Cell membrane: The cell membrane of Neisseria gonorrhoeae is composed of a unique lipopolysaccharide (LPS) that helps the bacterium to resist phagocytosis by immune cells.
• Its cellular location: Neisseria gonorrhoeae is an intracellular pathogen, which means that it lives inside of host cells. This allows the bacterium to evade the immune system and to replicate more easily.
• Cyclic enzymes: Neisseria gonorrhoeae produces a number of cyclic enzymes that help it to cause disease. These enzymes include proteases, which break down proteins, and lipases, which break down fats.

Answer: Arbo Viruses

Japanese encephalitis is primarily caused by the Japanese encephalitis virus (JEV), which belongs to the family Flaviviridae. JEV is transmitted through mosquito vectors, making it an arbovirus.

The other options are incorrect:

• Toga Viruses: This is not the correct term for the family that includes Japanese encephalitis virus. The family is Flaviviridae.
• Para myxo Viruses: Japanese encephalitis is not caused by paramyxoviruses. Paramyxoviruses are a different family of viruses.
• Ortho myxo Viruses: Japanese encephalitis is not caused by orthomyxoviruses. Orthomyxoviruses include influenza viruses, not JEV.

Answer: Culex vishnui

The primary vector of Japanese encephalitis virus (JEV) in India is Culex vishnui, and it was first isolated from this species. Culex tritaeniorhynchus is also an important vector of JEV in various regions where Japanese encephalitis is prevalent. Culex annulirostris is a species found in other parts of the world, particularly Australia. Therefore, in the context of India, the correct answer is “Culex vishnui.”

The other options are incorrect:

• Culex tritaeniorhynchus: While Culex tritaeniorhynchus is an important vector for Japanese encephalitis in various regions, it was not the species from which JEV was first isolated in India.
• Culex annulirostris: Culex annulirostris is a mosquito species found in Australia, and it is not associated with the first isolation of Japanese encephalitis virus in India.

Answer: Aedes aegypti

Dengue virus is transmitted from man to man by the Aedes aegypti mosquito. Aedes aegypti is a daytime-biting mosquito that is found in tropical and subtropical regions around the world. It is the primary vector of dengue virus, and it is estimated to be responsible for transmitting the virus to over 390 million people each year.

The other options are incorrect:

• Sand fly: Sand flies are vectors of other diseases, such as leishmaniasis and sandfly fever, but they do not transmit dengue virus.
• Ticks: Ticks are vectors of other diseases, such as Lyme disease and Rocky Mountain spotted fever, but they do not transmit dengue virus.
• Culex: Culex mosquitoes are vectors of other diseases, such as West Nile virus and St. Louis encephalitis virus, but they are not primary vectors of dengue virus.

Answer: Arbo virus

Yellow fever is caused by the yellow fever virus, which is an arthropod-borne virus (arbovirus). The virus is primarily transmitted to humans through the bite of infected mosquitoes, particularly the Aedes aegypti mosquito. The term “arbovirus” refers to viruses that are transmitted to humans through arthropod vectors, such as mosquitoes and ticks.

The other options are incorrect:

• Bunya virus: Bunyaviruses are a different family of viruses and are not associated with yellow fever.
• Calci virus: There is no virus known as “Calci virus” associated with yellow fever.

Answer: Sand fly

The primary vector of leishmaniasis is the sand fly. Sand flies are small, biting insects that are found in tropical and subtropical regions around the world. They are responsible for transmitting various leishmaniasis diseases, including cutaneous leishmaniasis, mucocutaneous leishmaniasis, and visceral leishmaniasis.

The other options are incorrect:

• Tick: Ticks are blood-feeding arachnids that are found in various habitats worldwide. They are vectors of diseases such as Lyme disease, Rocky Mountain spotted fever, and tick-borne relapsing fever. However, they do not transmit leishmaniasis.
• Mite: Mites are small arachnids that are closely related to ticks. They are found in various habitats, including soil, plants, and animal nests. Some mites are parasitic and can cause skin diseases, but they do not transmit leishmaniasis.
• Tsetse fly: Tsetse flies are large, biting flies that are found in sub-Saharan Africa. They are the vectors of African sleeping sickness, a parasitic disease caused by the protozoan Trypanosoma brucei. Tsetse flies do not transmit leishmaniasis.

Answer: All of these

Splenomegaly is the enlargement of the spleen, an organ located in the upper left side of the abdomen. It is a common manifestation of several diseases, including Kala-azar (visceral leishmaniasis), typhoid fever, and malaria.

• In Kala-azar, the spleen enlarges as it tries to fight off the infection caused by the Leishmania parasite. The parasite invades immune cells in the spleen, causing them to rupture and release their contents into the bloodstream. This triggers an inflammatory response that leads to the enlargement of the spleen.
• In typhoid fever, the spleen enlarges as it responds to the infection caused by Salmonella typhi bacteria. The bacteria invade the spleen’s red pulp, where they multiply and release toxins that damage the spleen’s tissue. This can lead to the release of inflammatory substances that cause the spleen to enlarge.
• In malaria, the spleen enlarges as it tries to filter out infected red blood cells. The malaria parasite infects red blood cells and multiplies inside them. As the infected cells are destroyed, they release their contents into the bloodstream, including the parasite and its waste products. The spleen filters out these infected cells and debris, but it can become overwhelmed, leading to enlargement.

Answer: Spleen

Kala-azar, also known as visceral leishmaniasis, is characterized by the severe involvement of the spleen. The protozoan parasite Leishmania donovani primarily affects the reticuloendothelial system, leading to enlargement and dysfunction of the spleen.

The other options are incorrect:

• Liver: While the liver can be affected in Kala-azar, it is not typically the most severely affected organ. Splenomegaly (enlarged spleen) is a hallmark feature.
• Adrenal gland: The adrenal gland is not a primary target of Leishmania donovani in Kala-azar. The main organs affected are the spleen, liver, and bone marrow.
• Bone marrow: The bone marrow is indeed affected in Kala-azar, but the spleen is generally the organ most severely affected, leading to complications such as anemia and immune suppression.

Answer: Anophels culicifacies.

In India, malaria most often spreads by Anopheles culicifacies. It is the most common vector of malaria in India and is responsible for transmitting the disease to over 80% of cases. Anopheles culicifacies is a daytime-biting mosquito that is found in rural areas and along water bodies. It is a highly efficient vector of malaria, meaning that it is very good at transmitting the parasite to humans.

The other options are incorrect:

• Anopheles fluviatis: Anopheles fluviatis is a malaria vector that is found in mountainous regions of India. It is not as common as Anopheles culicifacies, but it can be a significant vector in some areas.
• Anopheles stephensi: Anopheles stephensi is a malaria vector that is found in urban areas of India. It is less common than Anopheles culicifacies, but it can be a significant vector in some areas.
• Anopheles minimus: Anopheles minimus is a malaria vector that is found in both rural and urban areas of India. However, it is not as common as Anopheles culicifacies and is not considered to be a major vector of malaria.

Answer: Filaria

In the case of filariasis, caused by filarial parasites such as Wuchereria bancrofti, Brugia malayi, and Brugia timori, humans serve as the intermediate host. Mosquitoes are the vectors that transmit the infective larvae (microfilariae) from one human to another during a blood meal.

The other options are incorrect:

• Guinea Worm: Humans are the definitive host for the Guinea worm (Dracunculus medinensis), not the intermediate host. Water fleas (cyclops) serve as the intermediate host.
• Malaria: Humans are the definitive host for the malaria parasite (Plasmodium species). Mosquitoes are the vectors that transmit the malaria parasites between humans during blood meals.
• Kala-azar: Humans are the definitive host for the parasite Leishmania donovani, which causes Kala-azar (visceral leishmaniasis). Sandflies serve as the vectors, transmitting the parasite between humans during blood meals.

Answer: P.vivax

Plasmodium vivax exhibits a preference for infecting reticulocytes, which are immature red blood cells. It has a unique feature among the malaria parasites by being able to invade both reticulocytes and mature red blood cells. This characteristic contributes to the distinctive biology and clinical features of P. vivax malaria.

The other options are incorrect:

• P. ovale: P. ovale primarily infects mature red blood cells.
• P. falciparum: P. falciparum prefers to invade mature red blood cells but can also infect reticulocytes to some extent.
• P. malariae: P. malariae typically infects mature red blood cells.

Answer: P. malariae

Plasmodium malariae is unique among the four major species of Plasmodium that infect humans in that it lacks a true exoerythrocytic stage. In other words, it does not form hypnozoites, dormant liver stages that can cause relapses, as seen in Plasmodium vivax and Plasmodium ovale. Instead, P. malariae has a more straightforward life cycle, progressing directly from the liver stage to the blood stage.

The other options are incorrect:

• P. ovale: P. ovale has a dormant liver stage called hypnozoites, allowing it to cause relapses.
• P. vivax: Similar to P. ovale, P. vivax forms hypnozoites in the liver, leading to relapses.
• P. falciparum: P. falciparum, like P. vivax and P. ovale, has an exoerythrocytic stage in the liver, but it does not form hypnozoites.

Answer: Induces antibodies

Sporozoite vaccines aim to induce an immune response, particularly the production of antibodies, against the sporozoite stage of the malaria parasite. By targeting this stage, the vaccine seeks to prevent the parasite from establishing infection in the liver and progressing to the blood stage.

The other options are incorrect:

• Prevents only asexual forms with reproduction: False, sporozoite vaccines target the sporozoite stage, which is the first asexual form of the parasite. However, they can also have some effect on later stages of the lifecycle.
• No effects on clinical illness: False, sporozoite vaccines can reduce the severity of clinical illness by preventing the parasite from infecting the liver and progressing to the clinical stages of malaria.

Answer: P. falciparum

Plasmodium falciparum, the parasite responsible for falciparum malaria, tends to sequester and seclude itself within the deep vascular beds, particularly in the microvasculature of organs like the brain. This sequestration of infected red blood cells helps the parasite evade the spleen’s filtration and is associated with the severity of P. falciparum malaria. As a result, the characteristic stages of trophozoites and schizonts are less commonly observed in peripheral blood smears compared to other malaria species.

The other options are incorrect:

• P. vivax: Trophozoites and schizonts of P. vivax are more commonly observed in peripheral blood smears.
• P. ovale: Similar to P. vivax, P. ovale shows trophozoites and schizonts in peripheral blood.
• P. malariae: Trophozoites and schizonts of P. malariae can be seen in the peripheral blood but at a lower frequency compared to other species.

Answer: Type of parasite

Thin blood smears are prepared by spreading a small drop of blood in a thin, even layer on a microscope slide. This method allows for better visualization of individual malaria parasites and their different stages, including trophozoites, schizonts, and gametocytes. By carefully examining the characteristics of the parasites, such as the appearance of the infected red blood cells and the morphology of the parasites, laboratory technicians can identify the specific species of Plasmodium causing the infection.

The other options are incorrect:

• Plasmodium: Thin blood smears can indeed be used to identify Plasmodium species, but the more specific answer is identifying the type of parasite.
• Gametocytes: Both thin and thick blood smears can be used to identify gametocytes, the sexual stage of the malaria parasite.
• Schizont: Thin blood smears can also help identify schizonts, which are the stage of the parasite where multiple nuclear divisions have occurred, leading to the formation of daughter parasites.

Answer: Exo-erythrocytic phase

Radical treatment in malaria involves eliminating the liver-stage parasites (exo-erythrocytic phase) to prevent relapses. This is achieved by using drugs that specifically target the hypnozoites (dormant liver-stage parasites) in the case of Plasmodium vivax and Plasmodium ovale. This step is crucial for preventing the recurrence of the infection.

The other options are incorrect:

• Gametocyte: Gametocytes are the sexual stage of the malaria parasite and are not the primary target for radical treatment. However, drugs used for radical treatment may also have an impact on gametocytes.
• Erythrocytic phase: The erythrocytic phase involves the multiplication of the parasite in red blood cells, causing symptoms of malaria. Radical treatment primarily focuses on eliminating the liver-stage parasites, but some drugs may also target the erythrocytic phase.

Answer: Malaise & Anorexia

Aflatoxins are a group of poisonous compounds produced by fungi of the Aspergillus genus. They can contaminate a wide variety of food products, including peanuts, corn, and grains. Acute aflatoxicosis is a severe form of aflatoxin poisoning that can occur within a few days of consuming contaminated food.

The other options are incorrect:

• Osteogenic sarcoma: Aflatoxin exposure is not associated with the development of osteogenic sarcoma. Osteogenic sarcoma is a type of bone cancer and is not directly linked to aflatoxin toxicity.
• Lymphatic leukemia: Aflatoxin exposure is not directly associated with the development of lymphatic leukemia. Aflatoxins are known for their hepatotoxic (liver-damaging) effects and are more commonly linked to liver-related issues

Answer: A. ochraceus

Penicillic acid is a mycotoxin produced by Aspergillus ochraceus, a fungus known to contaminate various food commodities such as grains and coffee. It is considered a potential health risk as it has been associated with nephrotoxicity (kidney damage) and may contribute to food spoilage.

The other options are incorrect:

• P. puberulum: Penicillic acid is not primarily associated with P. puberulum. Different fungi may produce different mycotoxins, and in this case, A. ochraceus is the known producer of penicillic acid.
• Both A. ochraceus and P. puberulum: Penicillic acid is specifically associated with A. ochraceus, not P. puberulum.

Answer: Candida albicans

Candidiasis refers to infections caused by various species of the Candida genus, with Candida albicans being the most common culprit. Candida albicans is a type of yeast that is naturally present in the human body, but it can overgrow and cause infections under certain conditions, such as a weakened immune system or changes in the normal balance of microorganisms.

The other options are incorrect:

• Aspergillus spp.: Aspergillus spp. can cause different types of fungal infections, but they are not the primary cause of candidiasis.
• E. floccosum: Epidermophyton floccosum is a dermatophyte fungus that can cause skin infections like ringworm, but it is not associated with candidiasis.
• M. audouinii: Microsporum audouinii is another dermatophyte fungus that can cause ringworm, particularly in the scalp. It is not the cause of candidiasis

Answer: Multicellular forms

Candida albicans, a type of yeast, has the ability to exist in different forms, including single cells (yeast form), pseudohyphae, and true hyphae. These various forms contribute to its versatility and its ability to adapt to different environments within the human body. The transition between yeast and hyphal forms is associated with the pathogenicity of Candida albicans.

The other options are incorrect:

• Single cells: Candida albicans can exist in a single-cell (yeast) form, but it is not limited to this form.
• Pseudomonas: Pseudomonas is a type of bacteria and is not directly related to Candida albicans.

Answer: A. fumigatus

Aspergillus fumigatus is a species of fungus that is known to cause infections in humans. It is the most common cause of invasive aspergillosis, a serious and often life-threatening condition. While other Aspergillus species like A. niger, A. flavus, and A. oryzae can also cause diseases, A. fumigatus is particularly associated with respiratory infections in immunocompromised individuals.

The other options are incorrect:

• A. niger: Aspergillus niger can cause infections, but it is not the primary species associated with invasive aspergillosis.
• A. flavus: Aspergillus flavus is another species that can cause infections, but A. fumigatus is more commonly linked to invasive disease.
• A. oryzae: Aspergillus oryzae is used in the food industry for fermentation processes and is generally not associated with human infections.

Answer: P.notatum

Penicillium notatum is not typically considered a pathogenic species. Instead, it is historically significant as the source from which Sir Alexander Fleming discovered penicillin, the first widely used antibiotic.

The other options are incorrect:

• P. commune: Penicillium commune is not generally considered a pathogenic species. It is commonly found in the environment and is not known for causing infections in humans.
• P. bicolor: Penicillium bicolor is also not recognized as a pathogenic species. It is often associated with food spoilage and environmental contamination.
• P. glaucum: Penicillium glaucum is more commonly associated with food spoilage and is not known as a significant human pathogen.

Answer: Malassezia furfur

Tinea versicolor, also known as pityriasis versicolor, is a superficial fungal infection of the skin caused by the yeast Malassezia furfur (formerly known as Pityrosporum orbiculare and Pityrosporum ovale). This yeast is a normal component of the skin flora but can overgrow and cause skin discoloration in individuals predisposed to the condition.

The other options are incorrect:

• Candida albicans: Candida albicans is a yeast that is more commonly associated with candidiasis, a fungal infection that can affect various mucosal surfaces in the body, but it is not the causative agent of tinea versicolor.
• Aspergillus niger: Aspergillus niger is a fungus, but it is not associated with tinea versicolor. Tinea versicolor is caused by Malassezia furfur.

Answer: Exophiala werenekii

Tinea nigra is a superficial fungal infection of the skin characterized by the development of brown to black macules or patches. The fungus Exophiala werneckii is responsible for this condition.

The other options are incorrect:

• Malassezia furfur: Malassezia furfur is associated with tinea versicolor, a different fungal infection that causes discolored patches on the skin.
• Candida albicans: Candida albicans is commonly associated with candidiasis, a fungal infection that can affect mucosal surfaces.
• Aspergillus flavus: Aspergillus flavus is not typically associated with Tinea nigra. Tinea nigra is specifically caused by Exophiala werneckii.

Answer: Histoplasma duboissi

Histoplasma duboisii is a species of fungus that can cause a form of histoplasmosis known as African histoplasmosis. This type of histoplasmosis is primarily found in tropical and subtropical regions of Africa. It is important to note that the more common cause of histoplasmosis, particularly in the Americas, is Histoplasma capsulatum.

The other options are incorrect:

• Histoplasma capsulatum: While Histoplasma capsulatum is a significant cause of histoplasmosis, it is not the causative agent of African histoplasmosis.
• Aspergillus niger: Aspergillus niger is a species of fungus, but it is not the causative agent of histoplasmosis. Aspergillus species are generally associated with other fungal infections.
• Aspergillus flavus: Similar to Aspergillus niger, Aspergillus flavus is not the causative agent of histoplasmosis. It is associated with other fungal infections and mycotoxin production.

Answer: Bacteriostatic

Bacteriostatic agents inhibit the growth and reproduction of bacteria without necessarily killing them. When the agent is removed, the bacterial colony can resume growth. This is in contrast to bactericidal agents that directly kill bacteria.

The other options are incorrect:

Bactericidal: Bactericidal agents kill bacteria rather than just inhibiting their growth.
Antibiotic: An antibiotic is a type of antimicrobial substance that can be either bacteriostatic or bactericidal.
Antiseptic: Antiseptics are substances used to disinfect living tissues and are generally bactericidal or bacteriostatic, depending on the concentration and specific agent.

Answer: Penicillium griseofluvin

Griseofulvin is an antifungal medication used to treat fungal infections of the skin and nails. It was originally isolated from the fungus Penicillium griseofulvum. The name of the fungus itself reflects the source of the compound.

The other options are incorrec:

• Penicillium notatum: Penicillium notatum is the fungus from which penicillin, the first antibiotic, was isolated. It is not the source of griseofulvin.
• Streptomyces griseus: Streptomyces griseus is a bacterium, and it is not the source of griseofulvin.

Answer: Penicillin

Penicillin is a class of antibiotics that contain the characteristic β-lactam ring in their chemical structure. The β-lactam ring is essential for the antibacterial activity of penicillins. It plays a crucial role in inhibiting bacterial cell wall synthesis by interfering with the formation of peptidoglycan, a key component of the bacterial cell wall.

The other options are incorrect:

• Erythromycin: Erythromycin is a macrolide antibiotic and does not contain a β-lactam ring.
• Tetracyclins: Tetracyclines are a class of antibiotics that do not contain a β-lactam ring.
• Chloramphenicol: Chloramphenicol is an antibiotic that also lacks a β-lactam ring.

Answer: Alanine

Cycloserine is a cyclic analog of D-alanine, meaning it has a similar structure to D-alanine but with a ring closure. D-alanine is an amino acid that plays a crucial role in bacterial cell wall synthesis. Cycloserine interferes with this process, making it an effective antibiotic.

The other options are incorrect:

• Serine: Serine is an amino acid with a linear structure, unlike the cyclic structure of cycloserine. It is involved in various biological processes, including protein synthesis and metabolism.
• Aspergine: Aspergine is an amino acid found in plants and animals. It is involved in various metabolic pathways, including nitrogen fixation and protein synthesis. Its structure is also different from cycloserine.

Answer: Streptomycin

Streptomycin is one of the first-line antibiotics used in the treatment of tuberculosis (TB). It is effective against Mycobacterium tuberculosis, the bacterium that causes TB. Streptomycin is often used in combination with other anti-TB drugs as part of a multidrug regimen to prevent the development of drug resistance.

The other options are incorrect:

• Penicillin: Penicillin is not the primary antibiotic used for the treatment of tuberculosis. Penicillins are not effective against Mycobacterium tuberculosis.
• Chloramphenicol: Chloramphenicol is not a first-line drug for tuberculosis treatment. The mainstay of TB therapy involves drugs like streptomycin, isoniazid, rifampin, and others, depending on the regimen.
• Cycloserine: Cycloserine is an antibiotic used in the treatment of tuberculosis, particularly in cases of drug-resistant TB. However, it is not typically the main antibiotic used in standard TB therapy.

Answer: Cell wall synthesis

Penicillin exerts its antibacterial action by inhibiting the synthesis of bacterial cell walls. It specifically targets enzymes called penicillin-binding proteins (PBPs), which are involved in the cross-linking of peptidoglycan chains during the formation of the bacterial cell wall. The inhibition of these enzymes leads to weakened cell walls, making bacteria susceptible to osmotic lysis and ultimately causing cell death.

The other options are incorrect:

• Cell membrane permeability: Penicillin primarily affects cell wall synthesis, not cell membrane permeability.
• DNA synthesis: Penicillin does not directly interfere with DNA synthesis. Its main target is the bacterial cell wall.
• Protein synthesis: Penicillin does not directly inhibit protein synthesis. It primarily disrupts the synthesis of the bacterial cell wall.

Answer: Bacitracin

Bacillus subtilis is a bacterium known for producing the antibiotic bacitracin. Bacitracin is effective against Gram-positive bacteria and is commonly used as a topical antibiotic. It interferes with bacterial cell wall synthesis by inhibiting the dephosphorylation of bactoprenol, a lipid carrier involved in the transport of peptidoglycan precursors.

The other options are incorrect:

• Vancomycin: Vancomycin is not produced by Bacillus subtilis. It is produced by the bacterium Amycolatopsis orientalis.
• Both Vancomycin and Bacitracin: This option is incorrect because Bacillus subtilis produces Bacitracin, not Vancomycin. Vancomycin is produced by a different bacterium, Amycolatopsis orientalis.

Answer: Group ‘A’ Streptococci

The bacitracin sensitivity test is commonly used to differentiate between beta-hemolytic streptococci, specifically to identify whether the bacteria belong to Group A Streptococcus (GAS). Streptococcus pyogenes, a significant pathogen responsible for various infections, including pharyngitis (strep throat), is sensitive to bacitracin. Other beta-hemolytic streptococci, such as Group B Streptococcus (GBS), are resistant to bacitracin.

The other options are incorrect:

• Pneumococci: Bacitracin sensitivity testing is not typically performed for pneumococci. Pneumococci are often identified using other methods, such as optochin sensitivity testing.
• Gonococci: Bacitracin sensitivity testing is not relevant for gonococci. Neisseria gonorrhoeae, the bacterium causing gonorrhea, is not routinely tested for bacitracin sensitivity.
• Staphylococci: Bacitracin sensitivity testing is not used for staphylococci. Staphylococci are commonly identified using other methods, such as coagulase testing.

Answer:

Antibiotics can have various mechanisms of action, and they may target different components of bacterial cells. The three options mentioned encompass key mechanisms:

• Inhibition of cell-wall synthesis: Antibiotics like penicillins and cephalosporins interfere with the synthesis of bacterial cell walls, weakening the cell structure and leading to cell lysis.
• Damage to the cytoplasmic membrane: Some antibiotics, such as polymyxins, disrupt the integrity of bacterial cell membranes, causing leakage of cellular contents and eventual cell death.
• Inhibition of nucleic acid and protein synthesis: Antibiotics like quinolones and rifamycins interfere with the processes of DNA replication, RNA transcription, and protein synthesis, disrupting essential cellular functions.