MicroBiology MCQs with Answer and Explnation | Chapter 64

Answer: Virus

Dengue fever is caused by a virus called the dengue virus. There are four serotypes of the dengue virus, and infection with one can increase your risk of severe illness if infected by a different serotype later.

The other options are incorrect:

• Bacteria: Dengue fever is not caused by bacteria. Bacteria are single-celled organisms that can cause a variety of infections, but dengue fever is caused by a virus, which is much smaller and simpler than a bacterium.
• Fungi: Dengue fever is not caused by fungi. Fungi are eukaryotic organisms that can cause infections like athlete’s foot or ringworm. Dengue fever is caused by a virus, not a fungus.
• Rickettsia: Rickettsia are a type of bacteria that can cause diseases like typhus. While dengue fever can cause flu-like symptoms, it is caused by a virus, not rickettsia.

Answer: Insensitive to interferon

Viruses are insensitive to interferon, which is a protein produced by cells in response to viral infections. Interferon helps to inhibit the replication of viruses within host cells.

The other options are incorrect:

• No growth on inanimate culture media: This characteristic does not specifically relate to viruses. In fact, viruses require a host cell to replicate and do not grow on inanimate culture media like bacteria or fungi.
• Not sensitive to antibiotics: Antibiotics are drugs that target bacteria, not viruses. Viruses do not possess the structures or mechanisms targeted by antibiotics, so they are not sensitive to them.
• No energy producing enzymes: While viruses do not possess their own metabolism for energy production, some viruses do encode enzymes required for certain metabolic processes. However, this characteristic alone is not a defining feature of viruses.

Answer: None of these

Chickenpox is caused by the varicella-zoster virus, also known as VZV. This virus belongs to the herpesvirus family. After a person recovers from chickenpox, the virus lies dormant in nerve cells and can reactivate later in life to cause shingles.

The other options are incorrect:

• Fox virus: There is no known virus called “fox virus.” Foxes can carry various viruses, but none are known to cause chickenpox in humans.
• Mumps virus: Mumps is a separate contagious disease caused by the mumps virus. It causes symptoms like swollen parotid glands, fever, and fatigue.
• Measles virus: Measles is another distinct contagious disease caused by the measles virus. Symptoms include a red rash, fever, cough, and runny nose.

Answer: Both a and b

Rickettsia are bacteria that are difficult to stain due to their small size and thin cell wall. However, two common staining techniques are effective for visualizing them.

• Giemsa stain: This is a widely used stain in microbiology that displays Rickettsia as a characteristic red color against a blue background.
• Castaneda stain: This is a more specific stain for Rickettsia, highlighting them as a red-purple color against a light green background.

The other options are incorrect:

• Macchiavello and Gimenez stains: While these stains are used for diagnosing other infectious diseases caused by intracellular bacteria, they are not typically used for Rickettsia.
• Malachite green: Malachite green is a stain commonly used in histology to differentiate between different types of tissues. It’s not generally used to stain bacteria like Rickettsia.

Answer: Candidiasis

Candidiasis is a fungal infection caused by the fungus Candida albicans. It can affect various parts of the body, including the mouth (thrush), vagina (yeast infection), and skin folds. In immunocompromised individuals like those with AIDS, Candida infections can become severe and widespread.

The other options are incorrect:

• Cryptococcosis: While cryptococcosis is another serious fungal infection that can occur in AIDS patients, it’s less common than candidiasis.
• Tuberculosis: Tuberculosis (TB) is a bacterial infection that becomes a major opportunistic threat in AIDS due to weakened immunity. However, candidiasis is still the most frequent opportunistic infection.
• Aspergillosis: Aspergillosis is a fungal infection caused by Aspergillus mold. It can be a serious complication in AIDS, but it’s less common than candidiasis.

Answer: Pneumocystis carinii pneumonia

Pneumocystis carinii pneumonia (PCP) is the classic opportunistic infection in acquired immune deficiency syndrome (AIDS). It’s a serious lung infection caused by the fungus Pneumocystis jirovecii (formerly called Pneumocystis carinii).

The other options are incorrect:

• Apthous stomatitis: This is a common inflammatory condition causing painful mouth ulcers. While it can occur in people with HIV, it’s not considered a classic opportunistic infection specific to AIDS.
• Tuberculosis (TB): TB is a bacterial infection that becomes a major opportunistic threat in AIDS due to weakened immunity. However, PCP is still considered the classic opportunistic infection.
• Herpetic gingivostomatitis: This is a viral infection causing painful blisters on the gums and mouth. While individuals with HIV might experience more frequent or severe herpes outbreaks, it’s not a classic opportunistic infection specific to AIDS.

Answer: Spore

 Bacterial endospores are dormant structures formed by certain bacteria under stressful conditions. They have a thick outer coat that protects the bacterial DNA from harsh chemicals, including disinfectants and antiseptics.

The other options are incorrect:

• Mycobacteria: Mycobacteria have a thick waxy cell wall that offers some resistance to certain antiseptics and disinfectants. However, they are not as resistant as spores.
• Prions: Prions are not microbial cells. They are infectious particles composed solely of misfolded proteins. While prions are difficult to inactivate, they are not susceptible to antiseptics and disinfectants designed to target microbial cells.
• Coccidia: Coccidia are a group of parasitic protozoa that can form cysts for survival outside a host. These cysts offer some protection, but they are generally less resistant to antiseptics and disinfectants compared to bacterial spores.

Answer: Flavi viruses

Flaviviruses are a family of single-stranded RNA viruses transmitted by arthropod vectors like mosquitoes and ticks. They cause various diseases, including hepatitis C, dengue fever, yellow fever, and West Nile virus infection.

The other options are incorrect:

• Picornaviruses: Picornaviruses are a different family of single-stranded RNA viruses. They cause various diseases like the common cold, polio, and hand, foot, and mouth disease.
• Herpesviruses: Herpesviruses are a large family of double-stranded DNA viruses. They cause various infections, including herpes simplex virus (cold sores, genital herpes), varicella-zoster virus (chickenpox, shingles), and Epstein-Barr virus (mononucleosis).
• Hepadnaviruses: While the name seems like a close match, Hepadnaviridae is a separate family of viruses. Hepatitis B virus belongs to this family, and it’s the cause of another type of viral hepatitis.

Answer: All of the above

Viruses are fundamentally different from bacteria in several key aspects:

• Presence of either DNA or RNA: While both bacteria and some viruses possess genetic material, bacteria have DNA and often some additional genetic material in a plasmid. Viruses can have either DNA or RNA, but never both.
• Simple structure: Bacteria are single-celled organisms with a complex internal structure, including a cell membrane, cytoplasm, ribosomes, and often a cell wall. Viruses are much simpler. They lack most cellular machinery and consist only of genetic material enclosed in a protein coat.
• Complex multiplication: Bacteria reproduce by binary fission, a well-defined process. Viruses cannot reproduce on their own. They invade host cells, hijack the cellular machinery, and use it to produce new viral particles, eventually lysing (bursting) the host cell.

Answer: Aspergillus

Aspergillus is a genus of fungi that is capable of forming fungal balls, also known as aspergillomas. Fungal balls are masses of fungal hyphae, mucus, and cellular debris that can develop in body cavities, particularly in the lungs, sinuses, or other areas where there is pre-existing tissue damage or inflammation.

The other options are incorrect:

• Penicillium: Penicillium is a genus of fungi known for producing the antibiotic penicillin. While some species of Penicillium can cause respiratory infections in immunocompromised individuals, they are not typically associated with the formation of fungal balls.
• Mucor: Mucor is a genus of fungi that can cause invasive fungal infections known as mucormycosis. However, mucormycosis typically presents as angioinvasive disease rather than the formation of fungal balls.
• Rhizopus: Rhizopus is another genus of fungi that can cause mucormycosis, particularly in immunocompromised individuals. Like Mucor, Rhizopus infections are more commonly associated with invasive disease rather than the formation of fungal balls.

Answer: Sabourauds medium

Sabouraud medium: This is a rich, acidic medium containing peptone and dextrose (sugar) that provides essential nutrients for fungal growth. It also often includes antibiotics to inhibit bacterial growth, allowing fungi to thrive selectively.

The other options are incorrect:

• Tellurite medium: Tellurite medium is selective for bacteria, specifically those that can reduce tellurium to its metallic form. It’s not suitable for growing fungi.
• NNN medium: NNN medium (Neomycin, Natamycin, and Novobiocin) is another selective medium for bacteria, particularly those causing diarrhea. It’s not suitable for fungi.
• Chocolate agar medium: Chocolate agar medium is enriched with blood products to enhance the growth of certain bacteria, particularly those that require additional nutrients. It’s not ideal for most fungi.

Answer: Nails, hair and skin

Dermatophytes, also known as ematophytes, are a group of fungi that thrive on keratin, a protein found in hair, skin, and nails. They invade these structures and cause superficial infections collectively called dermatophytoses or ringworm.

The other options are incorrect:

• Subcutaneous tissue: While some fungal infections can reach the subcutaneous tissue (layer below the skin), dermatophytes typically don’t penetrate that deep.
• Systemic organs: Ematophytes are not equipped to invade and survive in internal organs.
• Superficial skin and deep tissue: While they primarily infect the outermost layers of the skin, hair, and nails, they don’t typically reach deeper tissues.

Answer: Saboraud’s medium

The culture medium commonly used for Candida species is Sabouraud’s agar or Sabouraud’s broth. Sabouraud’s medium is a general-purpose medium designed for the cultivation of fungi. It contains a low pH and high glucose concentration, creating an environment conducive to fungal growth while inhibiting the growth of bacteria.

The other options are incorrect:

• Methylene blue dextrose agar: While Methylene blue can be used in some fungal identification tests, it’s not the primary medium for culturing Candida. SDA is a more complete growth medium for this purpose.
• Pingolevin: Pingolevin agar is a selective medium specifically designed for isolating Trichomonas vaginalis, a parasitic flagellate, not Candida.
• All of the above: While Sabouraud’s is the preferred choice, other media can be used in specific situations. However, the other two options listed are not commonly used for culturing Candida.

Answer: Blastomeres seen in isolates

Candida albicans reproduces asexually through budding, where a small daughter cell (bud) forms from the parent cell. These daughter cells are called blastospores, not blastomeres. Blastomeres are the early embryonic cells formed during cell division in multicellular organisms.

The other options are incorrect:

• Yeast-like fungus: This is true. Candida albicans is a type of fungus that exhibits characteristics similar to yeast, including single-celled growth and asexual reproduction through budding.
• Forms Chlamydospores: This is true. Chlamydospores are thick-walled resting structures Candida albicans can form under stressful conditions.
• Seen in immunocompromised and causes meningitis in them: This is true. Candida albicans is an opportunistic pathogen, meaning it can cause infections in individuals with weakened immune systems.

Answer: All of the above

An opportunistic infection is caused by organisms that typically wouldn’t cause disease in a healthy person with a functioning immune system. These organisms, including some fungi, bacteria, and viruses, can take advantage of a weakened immune system to establish an infection.

• Penicillium: Some Penicillium species can cause opportunistic infections in immunocompromised individuals.
• Mucor: Mucor belongs to a group of fungi called mucormycosis, which are known for causing opportunistic infections.
• Aspergillus: Aspergillus is another fungus that can cause opportunistic infections in people with weakened immune systems.

Answer: Candida albicans

The Reynolds-Braude phenomenon refers to the transformation of Candida albicans from its yeast form to a filamentous form (hyphae) during a germ tube test. This transition is believed to be a virulence factor, aiding Candida albicans in penetrating host tissues.pen_spark

The other options are incorrect:

• Mucor: Mucor species do not exhibit the Reynolds Braude phenomenon. They are a group of fungi belonging to the order Mucorales, and their morphological characteristics differ from those of Candida albicans.
• Cryptococcus: Cryptococcus species, such as Cryptococcus neoformans, do not demonstrate the Reynolds Braude phenomenon. Cryptococcus is encapsulated yeast known for causing cryptococcal infections, particularly in immunocompromised individuals.
• Aspergillus: Aspergillus species do not exhibit the Reynolds Braude phenomenon. Aspergillus is a genus of filamentous fungi known for producing conidiophores and conidia (asexual spores) rather than germ tubes.

Answer: Periodic acid schiff stain

Periodic acid-Schiff (PAS) stain is a commonly used technique for highlighting carbohydrate structures in tissues. Candida albicans cell walls contain carbohydrates, making PAS stain ideal for visualizing the fungal elements, including hyphae, within a sample.

The other options are incorrect:

• Van Gieson’s stain: This stain is typically used to differentiate between collagen and cytoplasm in tissue sections. While it might provide some background detail, it wouldn’t specifically target fungal components like PAS stain.
• Masson Trichrome stain: Similar to Van Gieson’s stain, Masson Trichrome is used for differentiating connective tissue elements. It wouldn’t be the primary choice for highlighting fungal structures.
• Toluidine blue stain: Toluidine blue can be used for various purposes, including staining mast cells and certain bacteria. However, it’s not commonly used for specifically visualizing fungal elements like hyphae.

Answer: Noncapsulated fungus infecting man

Cryptococcus neoformans is a defining characteristic of this fungus. It possesses a thick polysaccharide capsule that plays a crucial role in its virulence and immune evasion.

The other options are incorrect:

• Causes meningitis: This is true. Cryptococcus neoformans is a major cause of fungal meningitis, particularly in immunocompromised individuals.
• Melanin production related to virulence: This is true. Melanin production in C. neoformans is associated with increased resistance to environmental stress and phagocytosis by immune cells, contributing to its virulence.
• Basidiomycetes yeast: This is true. Cryptococcus neoformans belongs to the phylum Basidiomycota and exhibits a yeast form during its asexual reproduction cycle.

Answer: Bifido bacteria

Bifidobacteria are a type of bacteria commonly found in the gut microbiome and considered a probiotic organism. Probiotics are live microorganisms that offer health benefits when consumed in adequate amounts. Bifidobacteria are believed to aid digestion, support the immune system, and contribute to a healthy gut environment.

The other options are incorrect:

• E. coli: While some strains of E. coli are part of the normal gut flora, most strains are not beneficial and can even cause illness.
• Staphylococcus: Similar to E. coli, most Staphylococcus species are not considered probiotics. Some can be part of the skin microbiome, but others can cause infections.
• Salmonella: Salmonella is a pathogenic bacterium known for causing foodborne illness. It is definitely not a probiotic organism.

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 nontuberculous mycobacterium (NTM) that can contaminate injectable medications, including vaccines, leading to localized abscess formation at the injection site.

The other options are incorrect:

• M. Kansasii: While M. Kansasii is another NTM, it’s less commonly associated with injection site abscesses compared to M. chelonae.
• M. ulcerans: This NTM is known for causing chronic skin ulcers and wouldn’t be a typical cause of injection abscesses.
• M. smegmatis: This NTM is part of the normal skin flora and typically doesn’t cause infections unless introduced into a sterile site like during an injection.

Answer: Caused by Calymmatobacterium granulomatis

Donovanosis, also known as granuloma inguinale, is a sexually transmitted infection caused by the bacterium Calymmatobacterium granulomatis. It primarily affects the genital and perineal regions, causing painless ulcers that may be mistaken for other sexually transmitted infections.

The other options are incorrect:

• Lymphadenopathy is remarkable & diagnostic: Lymphadenopathy (swollen lymph nodes) is not typically a prominent feature of donovanosis. While it can occur in some cases, it is not a characteristic finding that distinguishes donovanosis from other sexually transmitted infections.
• Penicillin is drug of choice: Penicillin is not the drug of choice for treating donovanosis. Tetracycline antibiotics, such as doxycycline, or macrolide antibiotics, such as azithromycin, are commonly used for treatment. Penicillin is not effective against Calymmatobacterium granulomatis.
• Characterized by painful genital ulcers: Genital ulcers caused by donovanosis are typically painless, not painful. This is an important clinical feature that can help differentiate donovanosis from other sexually transmitted infections, such as genital herpes.

Answer: India ink preparation

India ink preparation is a rapid and simple staining technique used for detecting encapsulated yeasts, particularly Cryptococcus neoformans, in cerebrospinal fluid (CSF). The carbon particles in the ink cannot penetrate the capsule, creating a clear halo around the yeast cell when viewed under a microscope.

The other options are incorrect:

• Methanamine silver stain: This stain is used for visualizing various microorganisms, including bacteria and fungi. However, it’s not the preferred choice for specifically detecting encapsulated yeasts like Cryptococcus neoformans in CSF.
• Ziehl-Neelsen stain: This stain is specific for identifying acid-fast bacilli, such as Mycobacterium tuberculosis. It wouldn’t be used for detecting encapsulated yeasts.
• Pyte-ferraco stain: This stain is used for visualizing fungi in tissue sections and wouldn’t be the primary choice for examining CSF for encapsulated yeasts.

Answer: Q fever

Q fever is caused by the bacterium Coxiella burnetii. This bacterium is most commonly transmitted through inhalation of aerosolized contaminated particles from infected animals (cattle, sheep, goats) or their birthing products. Lice are not involved in the transmission of Q fever.

The other options are incorrect:

• Trench fever: This bacterial infection is transmitted by human body lice (Pediculus humanus corporis). The infected louse feces are deposited on the skin, and the bacteria enter the body when the person scratches.
• Relapsing fever: Several species of bacteria belonging to the Borrelia genus cause relapsing fever. These bacteria are transmitted through the bites of lice (body lice or head lice) or ticks (the soft tick Ornithodoros erraticus).
• Epidemic typhus: Similar to trench fever, epidemic typhus is caused by Rickettsia prowazekii bacteria and transmitted through the feces of infected human body lice.

Answer: L. Tropica sore

Delhi boil refers to L. tropica sore, which is caused by the parasitic protozoan Leishmania tropica. It is characterized by a painless, ulcerated lesion on the skin, typically on exposed areas such as the face and hands. Delhi boil is a form of cutaneous leishmaniasis and is transmitted by the bite of infected sandflies.

The other options are incorrect:

• Solar Keratosis: This is a precancerous skin lesion caused by chronic sun exposure and wouldn’t be associated with a parasitic infection like Delhi boil.
• Malignant Pustule: This refers to a severe skin ulcer caused by Bacillus anthracis, the bacterium responsible for anthrax. While it can cause a pustule, it’s not related to leishmaniasis.
• Venereal Ulcer: This is a general term for ulcers on the genitals, often caused by sexually transmitted infections (STIs). Delhi boil wouldn’t be considered a sexually transmitted disease.

Answer: Chromoblastomycosis

Sclerotic bodies measuring 3-5 micrometers (µm) in size, multi-septate (having multiple internal divisions), and chestnut brown in color are characteristic of Chromoblastomycosis. These structures are diagnostic features of the fungal infection caused by dematiaceous fungi.

The other options are incorrect:

• Histoplasmosis: Sclerotic bodies in Histoplasmosis are typically smaller (1-2 µm) and lack the distinct chestnut brown color.
• Rhinosporidiosis: This fungal infection doesn’t involve sclerotic bodies.
• Phaeohypomycosis: While dematiaceous fungi causing Phaeohypomycosis can produce dark structures, they wouldn’t typically have the specific characteristics mentioned in the prompt (size, septation, color). They might be larger or have different pigmentation.

Answer: All of the above

A combination of methods is often used for diagnosing superficial fungal infections to increase accuracy and rule out other possibilities. Here’s a brief explanation of each method.

• Microscopic examination of skin scrapings: This involves collecting a sample of skin flakes or scales from the infected area and examining them under a microscope for fungal elements like hyphae and spores.
• KOH staining: Potassium hydroxide (KOH) is a solution that dissolves skin cells but leaves fungal elements intact. KOH preparations can be helpful in visualizing fungal structures and differentiating them from other elements.
• Wood light examination: A Wood’s lamp emits ultraviolet (UV) light. Some fungal species have a characteristic fluorescence when viewed under Wood’s light, aiding in diagnosis.

Answer: Candida infection is usually endogenous

Candida albicans is a commensal fungus, meaning it can live on the skin and mucous membranes of healthy individuals without causing harm. However, under certain conditions like weakened immune system or antibiotic use, Candida can overgrow and cause infections.

The other options are incorrect:

• Dermatophyte infection are exclusively man to animal: While some dermatophytes primarily infect humans, others can infect both humans and animals (zoonosis).
• Rhinosporidium causes deep infection in man: Rhinosporidiosis is a chronic infection primarily affecting the mucous membranes of the upper respiratory tract (nose) and can sometimes involve the eyes. It wouldn’t be classified as a deep fungal infection.
• Candida albicans is not pathogenic to lab animals: Although Candida albicans might not cause infections as readily in healthy lab animals compared to humans, it can still be pathogenic under certain conditions that compromise their immune system.

Answer: KOH wet mount

KOH (Potassium hydroxide) wet mount is a rapid and simple technique for visualizing fungal elements like hyphae and spores in a clinical setting. A KOH solution dissolves host cells but leaves fungal structures relatively intact, allowing for quick observation under a microscope. This provides valuable information for initial diagnosis of fungal infections.

The other options are incorrect:

• Grocott-Gomori Methenamine Silver (GMS): This is a sensitive and specific stain used for detecting fungi in tissue sections. While it provides excellent detail, it requires more processing time compared to a KOH wet mount.
• Hematoxylin and Eosin (H&E): This is a routine stain used in histology for general tissue examination. While it might reveal some fungal elements, it’s not specific for fungi and wouldn’t be the preferred choice for rapid evaluation.
• Periodic Acid-Schiff (PAS): This stain highlights carbohydrate structures and can be used to visualize fungal elements in tissue sections. However, similar to GMS, it requires more processing time than a KOH wet mount.

Answer: NNN

NNN medium is the most commonly used medium for culturing Leishmania parasites. It provides a rich nutrient environment with sheep blood, which is essential for Leishmania growth.

The other options are incorrect:

• Chocolate agar: This medium is enriched with blood but isn’t specifically formulated for Leishmania and lacks some necessary components.
• Tellurite: Tellurite is an antibiotic sometimes added to media to inhibit bacterial growth. While it might be used in some selective media for Leishmania, it’s not the complete culture medium itself.
• Sabouraud’s: While Sabouraud’s dextrose agar (SDA) is a good medium for growing fungi, it’s not ideal for Leishmania cultivation. It lacks essential nutrients and blood components needed by Leishmania parasites.

Answer: Syphilis

The Kolmer test, along with other tests like the Wassermann and Kahn tests, were historically used as serological tests for syphilis. These tests detected antibodies produced by the body in response to the syphilis bacterium Treponema pallidum.

The other options are incorrect:

• Tuberculosis: Tuberculosis diagnosis typically relies on tests like chest X-rays, sputum analysis, and interferon gamma release assays (IGRA), not serological tests like the Kolmer test.
• Gonorrhea: Similar to tuberculosis, Gonorrhea diagnosis involves tests like smears, cultures, and nucleic acid amplification tests (NAATs) to detect the causative bacteria Neisseria gonorrhoeae.
• Lymphoma: Lymphoma is a cancer of the lymphatic system, and diagnosis usually involves procedures like lymph node biopsy, blood tests, and imaging studies. Serological tests like the Kolmer test wouldn’t be used for diagnosing lymphoma.

Answer: Kalahazar

L.D. bodies are amastigotes (a developmental stage of the parasite) of Leishmania Donovani, the causative agent of visceral leishmaniasis, also known as kala-azar. These amastigotes are found within macrophages, white blood cells infected by the parasite. Examining tissue samples or bone marrow aspirates for L.D. bodies is a diagnostic tool for kala-azar.

The other options are incorrect:

• Toxoplasmosis: Toxoplasmosis is caused by a different parasite, Toxoplasma gondii. While it can also infect macrophages, the diagnostic stages and structures wouldn’t be L.D. bodies.
• Malaria: Malaria is caused by Plasmodium parasites, which have a different life cycle and wouldn’t form structures like L.D. bodies within human cells.
• Sleeping sickness: This disease is caused by Trypanosoma parasites. While they can also infect the bloodstream and central nervous system, their diagnostic stages wouldn’t be L.D. bodies.

Answer: Parasitic in nature

Hydatid cysts are caused by the larval stage of tapeworms belonging to the genus Echinococcus. These tapeworms are parasitic worms that live in the intestines of definitive hosts (dogs, foxes) and form cysts in the intermediate hosts (sheep, humans) where the larval stage develops.

The other options are incorrect:

• Fungal: Hydatid cysts are not caused by fungi. Fungi are eukaryotic organisms that lack the complex life cycle involving multiple hosts seen in parasitic infections.
• Congenital: Hydatid cysts are not typically congenital (present at birth). Infection usually occurs later in life through accidental ingestion of parasite eggs.
• Viral: Viruses are much smaller than parasites and wouldn’t form macroscopic structures like cysts. They also don’t have a complex life cycle involving multiple hosts.

Answer: Mycetoma

While Candida albicans can cause a variety of infections, mycetoma is typically caused by other organisms, primarily filamentous fungi and some bacteria actinomycetes. Mycetoma is a chronic granulomatous infection that affects the subcutaneous tissue, bones, and sometimes muscles, often involving the foot.

The other options are incorrect:

• Endocarditis: Candida albicans can cause fungal endocarditis, an infection of the inner heart lining. This is a serious complication, particularly for immunocompromised individuals with intravascular catheters.
• Meningitis: Candida albicans can also cause meningitis, an inflammation of the meninges (membranes surrounding the brain and spinal cord). This is another potential complication in immunocompromised patients.
• Oral thrush: Oral thrush is a common fungal infection caused by Candida albicans, particularly in immunocompromised individuals or infants. It manifests as white patches on the tongue and inner cheeks.

Answer: Thrush

Candida albicans is the most common fungal species responsible for causing thrush, also known as oropharyngeal candidiasis. It affects the mucous membranes of the mouth and tongue, leading to characteristic white patches.

The other options are incorrect:

• Conjunctivitis: While Candida can occasionally cause conjunctivitis (eye inflammation), it’s a less frequent manifestation compared to thrush. Bacteria and viruses are more common causes of conjunctivitis.
• Tinea capitis: This is a fungal scalp infection caused by dermatophytes, a different group of fungi compared to Candida albicans.
• Desert rheumatism: This is not a well-defined medical term. It’s possible you might be referring to a specific fungal or parasitic infection, but Candida albicans wouldn’t be the primary culprit.

Answer: Candida albicans

Candida albicans can exhibit both yeast and hyphal growth forms. Pseudohyphae are elongated yeast cells with constrictions at the septum (division points), which is a characteristic intermediate stage between yeast and true hyphae. Candida albicans is known for its ability to form these pseudohyphae.

The other options are incorrect:

• Alternaria: This is a mold fungus and wouldn’t typically exhibit pseudohyphae. It primarily reproduces asexually through spores.
• Aspergillus: This is another mold fungus that reproduces by forming spores and wouldn’t typically show pseudohyphae.
• Osporium: This is a less common fungal genus, and information on its growth morphology might be limited. However, based on current knowledge, most filamentous fungi wouldn’t exhibit true pseudohyphae like Candida albicans.

Answer: porangiospores

A sporangium is a sac-like structure in fungi and some other organisms that contains spores for asexual reproduction. These spores, called sporangiospores, develop and mature within the sporangium until they are released for dispersal and germination into new individuals.

The other options are incorrect:

• Spherules: Spherules are spherical structures that can contain multiple spores or other reproductive elements. While some fungi might produce spores within spherules, it’s not the defining characteristic of a sporangium.
• Chlamydospores: These are thick-walled resting spores produced by some fungi under stress conditions. They wouldn’t be contained within a sporangium.
• Oidia: Oidia are another type of asexual spore produced by some fungi, particularly yeasts like Candida albicans. They are formed by fragmentation of hyphae and wouldn’t be produced within a sporangium.

Answer: Aspergillus flavus

Aflatoxins are produced by Aspergillus flavus, as well as Aspergillus parasiticus. These toxic secondary metabolites are carcinogenic and are commonly found in various food crops, especially maize, peanuts, cottonseed, and tree nuts, under conditions of high humidity and temperature. Aflatoxin contamination poses significant health risks to humans and animals if ingested in contaminated food products.

The other options are incorrect:

• Aspergillus niger: Aspergillus niger is a common mold species known for its role in industrial applications, such as citric acid production. However, it is not a significant producer of aflatoxins. A. niger is more commonly associated with the production of citric acid, enzymes, and other metabolites.
• Aspergillus fumigatus: Aspergillus fumigatus is a medically important species known for causing invasive aspergillosis in immunocompromised individuals. While it produces various secondary metabolites, aflatoxins are not typically associated with A. fumigatus.

Answer: Candida albicans

Germ tube formation is a characteristic feature used in the laboratory to differentiate Candida albicans from other Candida species. Candida albicans readily forms germ tubes, which are elongated, unbranched projections arising from yeast cells under specific incubation conditions (often involving serum).

The other options are incorrect:

• Candida stellatoidea: While some strains of Candida stellatoidea might exhibit weak or rudimentary germ tube formation, it’s not a reliable feature for identification.
• Candida tropicalis: This species typically does not form germ tubes.
• Candida pseudotropicallis: Similar to Candida tropicalis, Candida pseudotropicallis generally does not form germ tubes.

Answer: Mycosis

Mycosis is the scientific term for a fungal infection in humans. It refers to any disease caused by a fungus, encompassing various types of infections that can affect the skin, nails, hair, mucous membranes, internal organs, and even the central nervous system.

The other options are incorrect:

• Mucorsis: This is a specific type of fungal infection caused by the mucormycetes group of fungi. While it’s an example of mycosis, it doesn’t represent the general term for all fungal infections.
• Fungosis: This term is not commonly used in modern medical terminology. Mycosis is the preferred and more widely accepted term for fungal infections.
• Micromia: This term doesn’t refer to fungal infections. It’s a very rare medical term that might have historical use but lacks a clear definition in current medical practice.

Answer: 100% alcohol

100% alcohol is not typically used as a disinfectant. While alcohol, particularly ethanol and isopropyl alcohol, is commonly used as a disinfectant at lower concentrations (usually around 70-90%), pure 100% alcohol is less effective as a disinfectant due to its rapid evaporation and reduced ability to denature proteins and disrupt microbial membranes.

The other options are incorrect:

• 1-2% cetrimide: Cetrimide is a quaternary ammonium compound commonly used as a disinfectant and antiseptic. It is effective against a wide range of bacteria, fungi, and some viruses. Solutions containing 1-2% cetrimide are often used for disinfection purposes.
• 2% Lysol: Lysol is a brand of disinfectant products that contain various active ingredients, including quaternary ammonium compounds and phenolic compounds. Lysol solutions are used for disinfecting surfaces and controlling microbial growth in various settings.
• 5% chloroxylene: Chloroxylenol, often marketed under the brand name Dettol, is an antiseptic and disinfectant commonly used in household and medical settings. Solutions containing chloroxylenol are used for disinfecting wounds, skin, and surfaces

Answer: Culture

Antibiotic sensitivity and resistance of microorganisms are determined primarily by culture-based methods. In this process, the microorganism of interest is isolated and grown in a culture medium under controlled conditions. Once the organism has been cultured, susceptibility testing is performed to determine its response to various antibiotics. This testing involves exposing the microorganism to different antibiotics and assessing its growth or inhibition.

The other options are incorrect:

• Direct microscopy: While direct microscopy can be used to identify microorganisms, it wouldn’t provide information on their antibiotic susceptibility.
• ELISA (Enzyme-Linked Immunosorbent Assay): ELISA is a versatile technique used for various purposes, but it’s not typically used for routine antibiotic susceptibility testing.
• DNA probe: DNA probe technology can be used for rapid identification of specific microorganisms or resistance genes. However, it wouldn’t necessarily involve culturing the organism and determining its response to different antibiotics across a concentration range.

Answer: Mycoplasma

Mycoplasma are bacteria that lack a cell wall, making them cell wall deficient. Instead of a rigid cell wall, Mycoplasma species are surrounded by a three-layered cell membrane. This unique feature allows them to be more flexible in shape and enables them to pass through filters typically used to trap bacteria with cell walls. Mycoplasma species are responsible for various infections in humans and animals, including respiratory and genital tract infections.

The other options are incorrect:

• Rickettsiae: Rickettsiae are small, obligate intracellular bacteria that possess a cell wall. They are responsible for diseases such as Rocky Mountain spotted fever, typhus, and Q fever.
• Chlamydiae: Chlamydiae are obligate intracellular bacteria that possess a cell wall. They cause diseases such as chlamydia, which is one of the most common sexually transmitted infections worldwide.
• Ehrlichiae: Ehrlichiae are obligate intracellular bacteria that possess a cell wall. They are transmitted by ticks and cause diseases such as ehrlichiosis, which can manifest as mild to severe flu-like symptoms.

Answer: It kills all bacteria except thermoduric bacteria

Pasteurization is a heating process designed to eliminate harmful bacteria from food and beverages, primarily milk. It uses a specific temperature range and holding time to kill most pathogens (disease-causing microorganisms) while minimizing changes to the product’s taste and nutritional value. However, pasteurization doesn’t destroy all bacteria.

The other options are incorrect:

• It kills bacteria and spores: While pasteurization kills most bacteria, it doesn’t eliminate spores, which are the dormant reproductive stages of some bacteria. Spores are highly resistant to heat and other harsh conditions.
• It kills 95% of microorganisms: This statement lacks precision. Pasteurization effectiveness varies depending on the specific process parameters and the targeted microorganisms. It can achieve a much higher reduction in microbial load than 95%.
• Tubercle bacilli are destroyed: Tubercle bacilli, which cause tuberculosis, are highly heat-resistant. Standard pasteurization conditions are not sufficient to destroy them.

Answer: Gram -ve bacteria

Endotoxins are a specific type of toxin integral to the outer membrane of Gram-negative bacteria. They are complex molecules composed of lipopolysaccharides (LPS) and are released when the bacteria die or lyse (cell wall bursts).

The other options are incorrect:

• Fungi: Fungi do not produce endotoxins. They can produce other types of toxins, but these are structurally and functionally different.
• Gram-positive bacteria: Gram-positive bacteria have a different cell wall structure compared to Gram-negative bacteria and do not contain endotoxins. They may produce other toxins called exotoxins, which are secreted by living bacteria.
• Virus: Viruses are not living organisms and don’t have cellular structures like bacteria. They cannot produce endotoxins.

Answer: Proteus

The antigen used in the Weil-Felix test is obtained from the bacterium Proteus. This test is primarily used to diagnose rickettsial infections such as typhus and other related diseases. The test relies on the cross-reactivity of antibodies produced against various Proteus strains with certain rickettsial antigens, leading to agglutination reactions.

The other options are incorrect:

• Pseudomonas: Pseudomonas is a different genus of bacteria and does not possess the specific antigens required for the Weil-Felix test.
• Escherichia coli (E. coli): E. coli is another type of bacteria commonly found in the gut. It doesn’t share the necessary antigens with Rickettsia.
• Staphylococcus: Staphylococcus is a group of Gram-positive bacteria, while the Weil-Felix test utilizes antigens from Gram-negative Proteus bacteria.

Answer: Mutation

Most drug resistance in bacteria occurs due to mutations. Mutations can lead to changes in bacterial genes, including those responsible for antibiotic targets or mechanisms of resistance. These mutations can confer resistance to antibiotics, allowing bacteria to survive and proliferate even in the presence of these drugs.

The other options are incorrect:

• Transduction: Transduction is a specific mechanism for horizontal gene transfer where viral vectors carry bacterial DNA between cells. While it can transfer genes for drug resistance, it’s not the most common cause of mutations leading to resistance.
• Transformation: Transformation is the process where a free-floating DNA fragment is taken up by a bacterium and incorporated into its genome. Similar to transduction, it can introduce resistance genes, but mutations are a more frequent source.
• Conjugation: Conjugation is another horizontal gene transfer mechanism where bacteria directly exchange plasmids (circular DNA molecules) containing genes, including those for drug resistance.

Answer: 25°C to 40°C

Mesophiles are organisms that thrive in moderate temperatures, neither too hot nor too cold. Their optimal growth range typically falls between 20°C and 45°C (68°F and 113°F). This temperature range aligns with many environments where life is abundant, including the human body (around 37°C).

The other options are incorrect:

• -20°C to -7°C: This range represents very cold temperatures. Psychrophiles, organisms adapted to cold environments, would grow best in this range.
• -7°C to + 20°C: While some mesophiles might survive or even grow slowly in this range, it’s on the cooler side of their optimal range.
• 55°C to 80°C: This range represents high temperatures suitable for thermophiles, organisms that thrive in hot environments. Mesophiles wouldn’t grow well or at all at these temperatures.

Answer: Transduction

Transduction is the mechanism of genetic transfer where a bacteriophage (phage) serves as a vehicle to transfer genetic material from one bacterium to another. During the lytic cycle of a bacteriophage, the phage can accidentally package bacterial DNA instead of its own genome.

The other options are incorrect:

• Transformation: Transformation involves the uptake of free DNA from the environment by a bacterial cell, leading to genetic alteration of the recipient bacterium. It does not involve the use of a phage as a vehicle for genetic transfer.
• Translation: Translation is the process of protein synthesis where mRNA is decoded by ribosomes to produce a specific polypeptide chain. It is not a mechanism of genetic transfer.
• Conjugation: Conjugation involves the direct transfer of genetic material between bacterial cells through cell-to-cell contact, typically mediated by a plasmid. It does not involve the use of a phage as a vehicle for genetic transfer.

Answer: Mycobacterium

Dorset’s egg medium is a specific culture medium designed for the cultivation of Mycobacterium species, particularly Mycobacterium tuberculosis, the causative agent of tuberculosis. This medium is enriched with egg yolk, which provides essential nutrients for the slow-growing Mycobacterium bacteria.

The other options are incorrect:

• Staphylococcus: Staphylococcus species are generally cultivated on less specific media like blood agar or tryptic soy agar. They don’t require the specialized conditions provided by Dorset’s egg medium.
• Streptococcus: Similar to Staphylococcus, Streptococcus can be grown on various routine culture media. Dorset’s egg medium isn’t typically used for their cultivation.
• Gonococcus: Gonococcus (Neisseria gonorrhoeae) has different growth requirements and is usually cultivated on specific media containing selective antibiotics to inhibit other bacteria.

Answer: Loefflers serum slope

Loeffler’s serum slope is a specialized culture medium enriched with serum (usually sheep or horse serum) and solidified with agar. This medium provides the specific nutrients and moist environment required for optimal growth of Corynebacterium diphtheriae, the bacteria that causes diphtheria.

The other options are incorrect:

• McConkey Agar: This is a differential and selective medium used to differentiate lactose-fermenting from lactose-non-fermenting bacteria. It’s not specifically designed for C. diphtheriae.
• Sabouraud Dextrose Agar (SDA): This medium is commonly used for cultivating fungi and some yeasts. While some bacteria can grow on SDA, it’s not ideal for C. diphtheriae.
• Lowenstein-Jensen medium: This medium is specifically formulated for the cultivation of Mycobacterium tuberculosis and other slow-growing mycobacteria. C. diphtheriae has different growth requirements.