MicroBiology MCQs with Answer and Explanations | Chapter 72

Answer: Secondary metabolite

Penicillin is a secondary metabolite. Primary metabolites are essential for the growth, development, and basic functions of an organism. Secondary metabolites, on the other hand, are not directly required for these core processes. Instead, they often play ecological roles, such as providing defense mechanisms against other organisms or attracting beneficial ones. Penicillin is an antibiotic produced by fungi like Penicillium chrysogenum, and it helps the fungus compete with bacteria in its environment.

The other options are incorrect:

• Primary metabolite: As explained above, primary metabolites are crucial for the organism’s basic functioning, and penicillin is not essential for the fungus’s core survival processes.
• Tertiary metabolite: The concept of “tertiary metabolite” is not widely used in scientific classification. Secondary metabolites are the generally recognized category encompassing compounds like penicillin.
• None of the above: Since penicillin is a well-characterized secondary metabolite produced by fungi, this option is not accurate.

Answer: Gram positive

Corynebacterium belongs to a group of bacteria with a thick cell wall structure, a characteristic that defines Gram-positive bacteria. This cell wall structure allows them to retain a purple stain during the Gram staining test, used to differentiate bacteria.

The other options are incorrect:

• Resistant to Penicillin: Not all Corynebacterium strains are resistant to penicillin. Their antibiotic susceptibility can vary depending on the specific strain.
• Gram-negative: As explained earlier, Corynebacterium has a Gram-positive cell wall structure.
• Resistant to Chloramphenicol: Similar to penicillin, Corynebacterium susceptibility to chloramphenicol depends on the strain.

Answer: Polymeta phosphate granules

Corynebacterium diphtheriae, the bacteria responsible for diphtheria, stores energy reserves in the form of polymetaphosphate granules. These granules appear bluish-purple when stained with methylene blue, a characteristic used for identification in laboratory settings.

The other options are incorrect:

• Starch granules: Starch is a carbohydrate for energy storage not typically found in bacteria like C. diphtheriae. Bacteria use different energy storage molecules.
• Lipid granules: While some bacteria can store lipids for energy, C. diphtheriae primarily uses polymetaphosphate granules.
• None of these: While other components may be present in the bacteria, polymetaphosphate granules are a defining characteristic for identification.

Answer: 2–4 weeks

The incubation period for diphtheria refers to the time between exposure to the Corynebacterium diphtheriae bacteria and the development of symptoms. In most cases, it falls within the range of 2 to 4 weeks.

The other options are incorrect:

• Upto 2 weeks: While some cases might show symptoms within 2 weeks, it’s not the most common timeframe.
• Upto 1 week: The incubation period is typically longer than 1 week for diphtheria.
• None of these: All the options represent a time frame, though 2-4 weeks is the most accurate range.

Answer: Eleck’s gel precipitation test

Elek’s gel precipitation test, also known as the Elek plate test, is a safe and reliable in vitro (performed in a test tube or dish) method to assess the toxigenicity (toxin-producing ability) of Corynebacterium diphtheriae. It utilizes the principles of immunodiffusion to detect the presence of diphtheria toxin produced by the bacteria.

The other options are incorrect:

• Ascoli’s thermoprecipitation test: This test is used to differentiate between different types of precipitating antibodies in a patient’s serum, not for bacterial virulence testing.
• C.R.P test (C-Reactive Protein test): This test measures inflammation in the body and is not specific to diphtheria diagnosis or virulence testing.
• M.R.T. test (Methyl Red test): This test is a biochemical test used to differentiate between various bacterial groups based on their ability to ferment certain sugars. It’s not used for virulence testing of C. diphtheriae.

Answer: Toxaemia

Diphtheria is a disease caused by the toxin produced by Corynebacterium diphtheriae bacteria. This toxin affects various organs in the body without the bacteria itself necessarily entering the bloodstream. Toxaemia refers to a condition where a toxin produced by an organism (bacteria in this case) is responsible for the illness.

The other options are incorrect:

• Bacteraemia: This refers to the presence of bacteria in the bloodstream, which can be a complication of some infections but isn’t the defining characteristic of diphtheria.
• Pyaemia: This is a specific type of bacteraemia where pus-forming bacteria are present in the bloodstream. Again, not the main feature of diphtheria.
• Septicemia: Septicemia is another term for bloodstream infection, similar to bacteraemia. Diphtheria primarily acts through toxins, not necessarily widespread bacterial presence in the blood.

Answer: Tuberculous cavity of the lung

A tuberculous cavity in the lung is a hollow space formed due to the destruction of lung tissue by Mycobacterium tuberculosis, the bacteria that causes tuberculosis. These cavities provide a favorable environment for the bacteria to multiply due to the presence of oxygen and nutrients.

The other options are incorrect:

• Large sized tuberculomas: While tuberculomas are collections of immune cells surrounding the bacteria, they might not always harbor the highest number of bacilli compared to cavities.
• Miliary tuberculosis: This refers to a widespread infection with tiny tubercles throughout the lungs and other organs. The individual tubercles might not contain as many bacilli as a large cavity.
• Tuberculous lymphadinitis: This is inflammation of lymph nodes due to tuberculosis. Lymph nodes might have some bacilli, but the concentration wouldn’t be as high as a lung cavity.

Answer: Paronchia

Streptococcus pyogenes, also known as Group A Streptococcus (GAS), is known to cause various skin infections, including impetigo contagiosa (a superficial skin infection), erysipelas (a superficial cellulitis), and boils (furuncles). However, paronchia, which is an infection around the nail fold, is typically caused by other bacteria or fungi, not Streptococcus pyogenes.

The other options are incorrect:

• Impetigo contagiosa: Impetigo contagiosa is a common skin infection caused by Streptococcus pyogenes and/or Staphylococcus aureus.
• Erysipelas: Erysipelas is a superficial form of cellulitis caused by Streptococcus pyogenes, characterized by redness, swelling, and warmth of the skin.
• Boil: Boils, or furuncles, can be caused by bacterial infections, including those by Streptococcus pyogenes, leading to localized inflammation and pus formation.

Answer: Stre. pyogens

Scarlet fever is a bacterial illness characterized by a red rash. It’s caused by Streptococcus pyogenes, also known as group A Streptococcus (GAS). This bacteria produces toxins that trigger the distinctive rash.

The other options are incorrect:

• Staphylococcus aureus: This bacteria is a common cause of skin infections like boils and impetigo, but it doesn’t typically cause scarlet fever.
• Streptococcus viridans: This type of Streptococcus is usually found in the mouth and throat and isn’t known to cause scarlet fever.
• None of these: While other bacteria can cause skin infections, Streptococcus pyogenes is the specific culprit behind scarlet fever.

Answer: Str. pyogenes

Rheumatic fever is an autoimmune complication that can develop after an untreated infection caused by Streptococcus pyogenes (group A Streptococcus). While the bacteria itself doesn’t directly cause rheumatic fever, the body’s immune response to the infection triggers inflammation in various tissues.

The other options are incorrect:

• Str. viridans: Streptococcus viridans is a type of bacteria commonly found in the mouth and throat. It’s not typically associated with causing rheumatic fever.
• Stph. aures (Staphylococcus aureus): Staphylococcus aureus is another type of bacteria known for causing skin infections like boils and impetigo. It’s not a common cause of rheumatic fever.
• None of these: While other factors may contribute to rheumatic fever, Streptococcus pyogenes is the primary bacterial trigger.

Answer: Pneumomnia

Streptococcus pneumoniae (Str. pneumoniae) is a major cause of bacterial pneumonia. It’s a common and potentially serious infection that inflames the lungs’ air sacs.

The other options are incorrect:

• Septicaemia: While Str. pneumoniae can sometimes enter the bloodstream and cause septicemia (blood poisoning), it’s not the most common outcome of infection with this bacteria.
• Paronychia: This is an infection around the fingernails or toenails, and Str. pneumoniae is not a typical causative agent. It’s more commonly caused by Staphylococcus aureus or Pseudomonas aeruginosa.
• None of these: Pneumonia is a well-established consequence of Str. pneumoniae infection.

Answer: Capsular polysaccharide

The capsular polysaccharide is a key virulence factor for Streptococcus pneumoniae. It’s a sugary coat surrounding the bacteria that helps it evade the immune system’s phagocytes (white blood cells). This allows the bacteria to colonize the respiratory tract and potentially cause infections like pneumonia.

The other options are incorrect:

• Specific soluble substance: This term is too vague to pinpoint a specific virulence factor.
• Vi-antigen: Vi-antigen is another polysaccharide capsule found in some strains of Salmonella enterica. It’s not a common virulence factor for Streptococcus pneumoniae.
• Forsmann antigen: This is a protein antigen found in sheep red blood cells and not relevant to Streptococcus pneumoniae virulence.

Answer: Brucellosis

Brucella is a genus of bacteria that causes brucellosis, a zoonotic disease. This means it can be transmitted from animals to humans. Brucellosis affects various organs and can cause flu-like symptoms, fatigue, and joint pain.

The other options are incorrect:

• Pertussis: This is caused by Bordetella pertussis bacteria and results in whooping cough, a respiratory illness characterized by severe coughing spells.
• Plague: Caused by Yersinia pestis bacteria, plague is a serious infectious disease with symptoms like fever, chills, and swollen lymph nodes.
• None of these: Brucella is the specific cause of brucellosis.

Answer: Brucella

Brucella is a type of bacteria that can cause a disease called brucellosis, which has symptoms similar to Mediterranean fever, including fever, fatigue, and abdominal pain. Mediterranean fever, however, is a genetic disorder and not caused by an infectious agent.

The other options are incorrect:

• M. tuberculosis: This bacterium causes tuberculosis, a respiratory illness with symptoms like cough, fever, and night sweats, but not typically the abdominal pain seen in Mediterranean fever.
• S. typhi: This bacterium causes typhoid fever, characterized by fever, headache, and intestinal issues, but not the recurrent attacks of inflammation associated with Mediterranean fever.
• C. neoformans: This fungus can cause cryptococcal meningitis, a fungal infection of the brain and meninges, with symptoms like headache, fever, and confusion, which are not typical of Mediterranean fever.

Answer: Castaneda strip

he Castaneda strip test is a specific agglutination test used to detect antibodies against Brucella bacteria, indicating a current or past infection with brucellosis.

The other options are incorrect:

• Frei test: This test detects past exposure to Mycobacterium tuberculosis, the bacteria that causes tuberculosis, not Brucella.
• Weil-Felix test: This test, though no longer commonly used, can detect antibodies to several bacteria including Rickettsia (causing typhus fever) but not Brucella specifically.
• Rose Bengal test: While this test is also used for Brucellosis diagnosis, it’s not as specific as the Castaneda strip test and can sometimes show false positives.

Answer: Anthrax

A malignant pustule is the characteristic skin lesion associated with anthrax infection. It’s caused by the bacteria Bacillus anthracis.

The other options are incorrect:

• Tetanus: Tetanus is caused by the bacterium Clostridium tetani and affects the nervous system, leading to muscle stiffness and spasms. It doesn’t cause skin lesions like malignant pustules.
• Diphtheria: Diphtheria, caused by Corynebacterium diphtheriae, primarily affects the respiratory system and can cause a thick membrane to form in the throat. While skin lesions can occur rarely in diphtheria, they are not the hallmark feature and wouldn’t resemble a malignant pustule.
• None of these: While other agents can cause skin lesions, none are typically referred to as a “malignant pustule” which is strongly linked to anthrax infection.

Answer: Cutaneous

Cutaneous anthrax occurs when anthrax spores enter the body through a cut or scrape on the skin. It is the most common form of anthrax infection and affects the skin and surrounding tissue.

The other options are incorrect:

• Alimentary: This refers to the digestive system. While anthrax can be contracted through contaminated food (gastrointestinal anthrax), it is less common than cutaneous anthrax.
• Pulmonary: This refers to the lungs. Inhalation anthrax occurs when spores are inhaled, but it’s less frequent than cutaneous infection.
• Hepatic: This refers to the liver. Anthrax does not primarily target the liver.

Answer: Cl. tetani

Clostridium tetani is a spore-forming bacterium found in soil and dust. When spores enter the body through a wound, they can germinate and produce a toxin called tetanospasmin. This toxin causes muscle stiffness and painful contractions, which are the hallmarks of tetanus.

The other options are incorrect:

• Clostridium botulinum: This bacterium produces botulinum toxin, which causes botulism, a different disease characterized by muscle weakness and paralysis.
• Cl. welchii (Clostridium perfringens): This bacterium can cause gas gangrene, a serious infection that affects muscle tissue. However, it is not the causative agent of tetanus.
• Cl. perfringens (already mentioned): We can remove the repetition by keeping only one entry for Clostridium perfringens.

Answer: Exotoxin in sympathetic system

Tetanus is caused by the spread of the exotoxin produced by Clostridium tetani bacteria within the sympathetic nervous system. This neurotoxin, known as tetanospasmin, travels via retrograde axonal transport from the site of infection to the central nervous system, specifically targeting neurons involved in motor control.

The other options are incorrect:

• Exotoxin in parasympathetic system: Tetanus is not caused by the spread of exotoxin within the parasympathetic nervous system. It primarily affects the sympathetic nervous system.
• Endotoxin in sympathetic system: Endotoxins are components of the outer membrane of certain bacteria and are not involved in the pathogenesis of tetanus. Tetanus is caused by the exotoxin produced by Clostridium tetani within the sympathetic nervous system.
• Endotoxin in parasympathetic system: Similar to the previous option, endotoxins are not implicated in the development of tetanus, and the parasympathetic nervous system is not the primary target of tetanus neurotoxin.

Answer: Cl. botulism

Clostridium botulinum produces some of the most potent bacterial toxins known, called botulinum neurotoxins (BoNTs). These toxins are extremely effective at blocking neurotransmitter release, leading to muscle paralysis.

The other options are incorrect:

• Cl. tetani: While tetanus toxin (tetanospasmin) produced by Cl. tetani is potent and causes severe muscle rigidity, botulinum neurotoxins are generally considered more powerful due to their ability to cause complete muscle paralysis even at very low doses.
• Cl. welchii (Clostridium perfringens): This bacterium produces several toxins, but none are neurotoxins. Clostridium perfringens is associated with gas gangrene, a serious tissue infection.
• Cl. septicum: This bacterium also produces toxins, but they primarily cause tissue damage and inflammation, not neurotoxicity.

Answer: Botulin

Clostridium botulinum produces a group of toxins called botulinum neurotoxins (BoNTs). “Botulin” is a simpler term often used to refer to these toxins collectively.

The other options are incorrect:

• Tetanospasmin: This toxin is produced by Clostridium tetani and is responsible for tetanus.
• Tetanolysin: This is not a known toxin produced by Clostridium botulinum.
• Cholaragen: Cholaragen is a toxin produced by Vibrio cholerae, the bacterium that causes cholera. It has a different mechanism of action compared to botulinum toxin.

Answer: T. pallidum

Treponema pallidum is a spiral-shaped bacterium, the sole cause of syphilis.

The other options are incorrect:

• T. pertenue: Treponema pertenue is the causative agent of yaws, a tropical skin disease with some similarities to syphilis but distinct characteristics.
• T. carateum: Treponema carateum causes pinta, another tropical skin disease with clinical features that differ from syphilis.
• T. endemicum: Treponema endemicum is not a well-established species and isn’t currently associated with any known human disease.

Answer: Penicillin

Penicillin is the first-line antibiotic treatment for most spirochete infections, including syphilis, leptospirosis, and early Lyme disease. It’s highly effective against these bacteria due to its ability to interfere with cell wall synthesis.

The other options are incorrect:

• Chloramphenicols: While chloramphenicol is a broad-spectrum antibiotic, its effectiveness against spirochetes can be variable depending on the specific strain. It’s not typically the preferred treatment for these infections.
• Erythromycin: Erythromycin is another broad-spectrum antibiotic, but similar to chloramphenicol, its efficacy against spirochetes can be less reliable compared to penicillin.
• Tetracyclines: Tetracyclines can be a good alternative to penicillin for some spirochete infections, particularly Lyme disease in adults. However, penicillin remains the preferred choice for many spirochetal illnesses.

Answer: Air borne infection

Neisseria gonorrhoeae is not transmitted through airborne means. It is a sexually transmitted infection (STI) spread through vaginal, oral, or anal sex.

The other options are incorrect:

• Gram-negative, aerobic bacteria: This is true. Neisseria gonorrhoeae are bacteria with a gram-negative cell wall and require oxygen for growth (aerobic).
• Non-motile diplococci: This is true. These bacteria appear in pairs (diplococci) and lack flagella for movement (non-motile).
• Oxidase positive organisms: This is true. Neisseria gonorrhoeae possess an enzyme called oxidase, allowing them to use oxygen in electron transport for energy production.

Answer: Pili

Virulence in gonococcus (Neisseria gonorrhoeae) is primarily due to pili, also known as fimbriae. Pili are hair-like structures protruding from the surface of the bacterium that facilitate adherence to host cells and tissues, allowing N. gonorrhoeae to colonize and infect the mucous membranes of the genital tract and other sites. P

The other options are incorrect:

• Cell membrane: While the cell membrane plays a general role in bacterial survival and function, it’s not the specific virulence factor in this case.
• Cellular location: Neisseria gonorrhoeae’s location within the host (e.g., urogenital tract) is important for establishing an infection, but it’s not a virulence factor itself.
• Cyclic enzymes: Cyclic enzymes are not a known virulence factor associated with Neisseria gonorrhoeae.

Answer: All of the above

Penicillium species produce a variety of mycotoxins, and all three listed options (citrinin, patulin, and penicillic acid) are considered important due to their potential health risks.

• Citrinin: This toxin can cause kidney damage and has been linked to chronic nephropathy in animals.
• Patulin: It can cause gastrointestinal problems and has been associated with genotoxicity (potential to damage DNA).
• Penicillic acid: This toxin can have neurotoxic and hepatotoxic effects (damaging the nervous system and liver, respectively).

Answer: Both a and b

Penicillic acid can be produced by several Penicillium species, and both A. ochraceus and P. puberulum are known to produce it.

The other options are incorrect:

• None of the above: Since both A. ochraceus and P. puberulum have been documented to produce penicillic acid, this option is incorrect.

Answer: Both a and b

• Moulds: These are multicellular fungi that grow in thread-like filaments called hyphae. These hyphae collectively form a network called mycelium. Moulds are visible to the naked eye and often appear fuzzy or cottony.
• Filamentous fungi: This is a broader term encompassing fungi that grow long, thread-like hyphae. Moulds are a type of filamentous fungi, but not all filamentous fungi are moulds. Some filamentous fungi may not grow in the fluffy, visible structures we associate with moulds.

The other options are incorrect:

• Yeasts: Yeasts are unicellular fungi and do not produce mycelium. They reproduce through budding and typically appear as single-celled organisms.

Answer: Candida albicans

Candida albicans is the most common fungal species responsible for candidiasis infections. It’s a type of yeast that naturally lives on the skin and mucous membranes in small amounts. However, an overgrowth of Candida albicans can lead to infections in various body areas.

The other options are incorrect:

• Aspergillus spp.: Aspergillus species are molds that can cause different fungal infections, but not candidiasis.
• E. floccosum (Escherichia coli): E. coli is a bacterium commonly found in the intestines and can cause various infections, but not candidiasis. Candidiasis is caused by a fungus, not a bacterium.
• M. audouinii (Microsporum audouinii): This fungus causes a type of scalp ringworm infection called tinea capitis. While it affects the skin, it’s a different condition than candidiasis.

Answer: Multicellular forms

Candida albicans is a dimorphic fungus, meaning it can exist in both unicellular (yeast) and multicellular (hyphae) forms. This ability to switch shapes is crucial for its virulence and biofilm formation.

The other options are incorrect:

• Single cells: While C. albicans can exist as single yeast cells, it’s not limited to this form.
• Pseudomonas: This is a completely different type of bacteria, not a form that C. albicans can take.
• None of these: This is incorrect because C. albicans can indeed form multicellular forms.

Answer: A. fumigatus

Aspergillus fumigatus is a specific type of fungus known to cause aspergillosis, a respiratory infection.

The other options are incorrect:

• A. niger: This is another Aspergillus species, but it’s not commonly associated with aspergillosis infections in humans.
• A. flavus: This Aspergillus species can produce aflatoxins, which are carcinogenic toxins that contaminate food. It doesn’t typically cause infections.
• A. oryzae: This Aspergillus species is used in the production of sake, miso, and other fermented foods. It’s not known to cause infections in humans.

Answer: P.notatum

P. notatum (currently known as Penicillium chrysogenum) is the famous fungus that produces penicillin, a life-saving antibiotic. It’s generally not considered pathogenic to humans.

The other options are incorrect:

• P. commune: This species can be opportunistic pathogens, meaning they can cause infections in individuals with weakened immune systems.
• P. bicolor: Similar to P. commune, it can act as an opportunistic pathogen.
• P. glaucum: This is an older name sometimes used for various Penicillium species, including some with potential to cause opportunistic infections.

Answer: Malassezia furfur

Tinea versicolor is a fungal infection caused by an overgrowth of a yeast called Malassezia furfur, which naturally lives on human skin in small amounts.

The other options are incorrect:

• Candida albicans: This is a different type of fungus that can cause yeast infections like thrush. While it can sometimes be found on the skin, it’s not the primary culprit behind tinea versicolor.
• Aspergillus niger: This is a mold species not typically associated with skin infections like tinea versicolor. It’s more commonly linked to food spoilage.
• None of these: This is incorrect because Malassezia furfur is the established cause of tinea versicolor.

Answer: Histoplasma duboissi

African histoplasmosis is a specific fungal disease caused by a variant of Histoplasma capsulatum known as Histoplasma capsulatum var. duboisii. This variant is distinct from the more common Histoplasma capsulatum var. capsulatum, which causes American histoplasmosis.

The other options are incorrect:

• Histoplasma capsulatum: This is the general name for the fungus, but the specific variety responsible for African histoplasmosis is var. duboisii.
• Aspergillus niger: This is a mold species not associated with histoplasmosis infections. It’s more commonly linked to food spoilage.
• Aspergillus flavus: Similar to A. niger, this Aspergillus species doesn’t cause histoplasmosis. It’s known for producing aflatoxins, carcinogenic toxins.

Answer: Actinomyces irraeli

Sun ray fungus is a common nickname for Actinomyces israelii, a type of bacteria that causes actinomycosis, a chronic infection.

The other options are incorrect:

• Chromoblastomycosis: This refers to a fungal infection, not a specific bacteria.
• Streptomyces griseus: This is another type of bacteria, but it’s not known to cause the characteristic “sun ray” appearance associated with Actinomyces israelii infections.
• Cryptococcosis: This is a fungal infection caused by Cryptococcus species, not bacteria.

Answer: Bacteriostatic

A bacteriostatic agent slows down or halts the growth and reproduction of bacteria, but doesn’t necessarily kill them. Once the agent is removed, the bacteria can resume growth if there are enough viable cells remaining.

The other options are incorrect:

• Bactericidal: This refers to an agent that kills bacteria altogether. If a bactericidal agent is effective, the colony wouldn’t regrow after removal.
• Antibiotic: This is a type of antimicrobial agent that can be either bacteriostatic or bactericidal. The answer focuses on the mechanism of action, so “bacteriostatic” is the more specific term.
• Antiseptic: This is an agent that kills or inhibits the growth of microorganisms on living tissue. While it can have some effect on bacterial colonies, it’s not typically used in the context you described. Antiseptics are usually applied to surfaces or skin to prevent infections.

Answer: Penicillium griseofluvin

Griseofulvin is an antifungal medication specifically produced by the fungus Penicillium griseofulvum.

The other options are incorrect:

• Penicillium notatum: This is the famous fungus that produces penicillin, a different type of antibiotic effective against bacteria, not fungi.
• Streptomyces griseus: This is a type of bacteria known for producing various antibiotics, but not griseofulvin.
• None of these: Griseofulvin is indeed obtained from a specific Penicillium species.

Answer: Cl. tetani

Tetanus is caused by the bacterium Clostridium tetani. “Cl. tetani” is an abbreviation commonly used in scientific contexts.

The other options are incorrect:

• Clostridium botulinum: This bacterium is responsible for botulism, a different kind of neuroparalytic illness caused by a toxin.
• Cl. welchii (Clostridium perfringens): This bacterium can cause various foodborne illnesses, but not tetanus.
• Cl. perfringens (Clostridium perfringens): This is the same bacteria listed as Cl. welchii. It’s included twice here but isn’t the cause of tetanus.

Answer: Exotoxin in sympathetic system

Tetanus is caused by the spread of tetanospasmin, an exotoxin produced by the bacterium Clostridium tetani. Tetanospasmin affects the nervous system by blocking the release of inhibitory neurotransmitters, leading to uncontrolled muscle contractions and spasms characteristic of tetanus.

The other options are incorrect

• Exotoxin in parasympathetic system: Tetanus toxin primarily affects the sympathetic nervous system, not the parasympathetic nervous system. The spread of tetanospasmin leads to excessive stimulation of the motor neurons, resulting in muscle rigidity and spasms, which are characteristic features of tetanus.
• Endotoxin in sympathetic system: Endotoxins are lipopolysaccharides found in the cell walls of Gram-negative bacteria and are not associated with tetanus. Tetanus is caused by an exotoxin produced by Clostridium tetani, not an endotoxin.
• Endotoxin in parasympathetic system: Similar to the previous option, endotoxins are not associated with tetanus.
• a

Answer: Cl. botulism

Clostridium botulinum produces one of the most potent toxins known, botulinum neurotoxin. This toxin is significantly more powerful than the tetanospasmin toxin produced by Cl. tetani.

The other options are incorrect:

• Cl. tetani: While tetanospasmin is a potent neurotoxin and causes severe illness, botulinum toxin is much more toxic.
• Cl. welchii (Clostridium perfringens): This bacterium doesn’t produce a neurotoxin. It’s known for causing foodborne illnesses through different toxins.
• Cl. septicum: This bacterium produces toxins that can cause gas gangrene, but these toxins are not neurotoxins and wouldn’t be classified as the most powerful neurotoxin among clostridia.

Answer: Botulin

The toxin produced by C. botulinum is simply called botulin. It’s also sometimes referred to as botulinum toxin or botulinum neurotoxin for more specificity.

The other options are incorrect:

• Tetanospasmin: This is the toxin produced by Clostridium tetani, the causative agent of tetanus.
• Tetanolysin: This is not a well-established toxin associated with C. botulinum.
• Cholaragen: This is a toxin produced by Vibrio cholerae, the bacterium responsible for cholera, a diarrheal illness.

Answer: Staphylococcus aureus

Toxic shock syndrome (TSS) is primarily caused by toxins produced by Staphylococcus aureus bacteria. Specifically, it is often associated with the production of toxic shock syndrome toxin-1 (TSST-1) by certain strains of Staphylococcus aureus. TSS is a rare but potentially life-threatening condition characterized by fever, rash, low blood pressure, and multiple organ dysfunction.

The other options are incorrect

• Streptococcus pyogenes: While Streptococcus pyogenes can cause severe infections such as necrotizing fasciitis and streptococcal toxic shock syndrome, TSS is primarily associated with Staphylococcus aureus.
• Vibrio cholerae: Vibrio cholerae is the bacterium responsible for causing cholera, a diarrheal disease characterized by severe dehydration. It does not produce toxins associated with toxic shock syndrome.
• Candida: Candida species are yeasts that can cause various infections in humans, including candidiasis.

Answer: T. pallidum

Syphilis is caused by the bacterium Treponema pallidum. “T. pallidum” is an abbreviation commonly used in scientific contexts.

The other options are incorrect:

• T. pertenue: This is Treponema pertenue, a related bacterium that causes yaws, a tropical skin disease with some similarities to syphilis but considered a distinct condition.
• T. carateum: This is Treponema carateum, another related bacterium that causes pinta, a skin disease also with some resemblance to syphilis but classified differently.
• T. endemicum: This is not a well-established Treponema species associated with human diseases.

Answer: Air borne infection

Neisseria gonorrhoeae is not transmitted through airborne means. It is a sexually transmitted infection (STI) spread through direct contact with infected mucous membranes.

The other options are incorrect:

• Gram-negative, aerobic bacteria: This is a true statement. N. gonorrhoeae has a gram-negative cell wall and requires oxygen for growth (aerobic).
• Non-motile diplococci: This is true as well. N. gonorrhoeae appears in pairs (diplococci) and doesn’t have flagella for movement (non-motile).
• Oxidase positive organisms: This is another true statement. N. gonorrhoeae possesses the enzyme oxidase, allowing it to use oxygen in its metabolic processes.

Answer: Pili

Virulence in Neisseria gonorrhoeae, the bacterium that causes gonorrhea, is primarily due to pili (also known as fimbriae). Pili are hair-like structures on the surface of the bacterial cell that facilitate attachment to host cells and colonization of the mucosal surfaces of the urogenital tract.

The other options are incorrect:

Cell membrane: While the cell membrane plays a general role in protecting the bacteria and regulating some functions, it’s not the specific virulence factor in this context. Its cellular location: The location within the host (urogenital tract) is important for gonococcal survival and transmission, but it’s not a virulence factor the bacteria itself controls. Cyclic enzymes: Cyclic enzymes are not a well-established virulence factor associated with Neisseria gonorrhoeae.

Answer: Moulds

Fungi that produce mycelium, which is a network of thread-like structures called hyphae, are commonly referred to as moulds. Moulds typically grow as multicellular filaments and form visible colonies on substrates such as food, soil, or decaying organic matter.

The other options are incorrect:

• Filamentous fungi: While filamentous fungi accurately describe the morphology of moulds, the term “filamentous fungi” is more general and can include other types of fungi that produce filamentous structures, such as some yeasts and certain types of fungal pathogens. Therefore, it is not as specific as “moulds.”
• Both a and b: This option is redundant since both “moulds” and “filamentous fungi” essentially describe the same group of fungi that produce mycelium. It does not provide additional information beyond the correct answer.
• Yeasts: Yeasts are unicellular fungi that typically reproduce by budding rather than by forming mycelium. While some yeasts may form pseudohyphae (elongated chains of budding cells), they do not produce true mycelium.

Answer: Candida albicans

Candida albicans is the most common fungal species responsible for candidiasis infections. It naturally lives on the skin and mucous membranes in small amounts but can overgrow under certain conditions, leading to infection.

The other options are incorrect:

• Aspergillus spp.: These are different fungal species that can cause aspergillosis, a respiratory illness. While some Aspergillus species can rarely cause skin infections, they are not the primary culprit behind candidiasis.
• E. floccosum: This refers to Entamoeba floccosum, a parasitic amoeba that causes intestinal amoebiasis, not a fungal infection like candidiasis.
• M. audouinii: This is Microsporum audouinii, a fungus that causes tinea capitis, a type of fungal scalp infection (ringworm). It’s distinct from Candida albicans, which can cause candidiasis in various body locations.

Answer: Multicellular forms

Candida albicans is a dimorphic fungus, meaning it can exist in two different forms:

• Unicellular form: This is the yeast form, consisting of single oval cells.
• Multicellular form: This is the hyphal form, where the fungus grows long, thread-like filaments that can branch out.

The other options are incorrect:

• Single cells: While C. albicans can exist as single yeast cells, it’s not limited to this form.
• Pseudomonas: This is a completely different type of bacteria, not a form that C. albicans can take.
• None of these: This is incorrect because C. albicans can indeed form multicellular forms (hyphae).

Answer: A. fumigatus

Aspergillus fumigatus is a fungus and cannot infect another fungus. The other options listed (A. niger, A. flavus, and A. oryzae) are also Aspergillus species. Fungi can infect other organisms like plants or animals, but not typically other fungi.

The other options are incorrect:

• A. niger: This fungus is known for producing black mold and can cause spoilage in food and other materials.
• A. flavus: This species can produce aflatoxins, which are carcinogenic toxins that can contaminate food products like grains and nuts.
• A. oryzae: This fungus is used in the production of some fermented foods like sake (Japanese rice wine) and miso (soybean paste).

Answer: P.notatum

Penicillium notatum is the specific species from which the first antibiotic penicillin was derived. It’s not typically considered pathogenic (disease-causing) in humans.

The other options are incorrect:

• P. commune: This species can cause spoilage in food and may be allergenic to some individuals.
• P. bicolor: This fungus can also be involved in food spoilage and might have some allergenic potential.
• P. glaucum: This is a complex of multiple Penicillium species, some of which can cause opportunistic infections in immunocompromised individuals.