MicroBiology MCQs with Answer and Explnation | Chapter 33

Answer: I/V

The best route for administering Anti-lymphocytic globulin is intravenous (I/V) because it allows for rapid and direct delivery into the bloodstream, ensuring a quick and effective response.

The other options are incorrect:

• Oral: Oral administration is not suitable for Anti-lymphocytic globulin because it would undergo digestion in the gastrointestinal tract, potentially rendering it ineffective.
• S/C (Subcutaneous): Subcutaneous administration involves injecting the drug under the skin. While this route is suitable for some medications, Anti-lymphocytic globulin is better absorbed and utilized through the intravenous route.
• I/M (Intramuscular): Intramuscular administration involves injecting the drug into a muscle. However, Anti-lymphocytic globulin is typically administered intravenously for optimal and rapid distribution throughout the body. Intramuscular injections may not provide the desired therapeutic effects.

Answer: Gamma

While all other listed interferons (Alpha, Beta, and Delta) are primarily induced by viral infections, Gamma interferon stands apart. Its main production is triggered by activated T cells and natural killer (NK) cells in response to intracellular pathogens like bacteria, parasites, and some fungi. While viruses can also stimulate IFN-γ production, it’s not their primary inducer.

The other options are incorrect:

• Alpha (IFN-α): Primarily produced by plasmacytoid dendritic cells in response to viral infections. Interferes with viral replication and activates immune cells.
• Beta (IFN-β): Mainly produced by various cell types upon viral infection. Inhibits viral replication and induces antiviral state in nearby cells.
• Delta (IFN-δ): Less well-understood than other interferons, but evidence suggests its primary induction by viruses and certain tumor cells. Its functions still require further research.

Answer: Small pox : Guarnieri bodies

Guarnieri bodies are distinctive cytoplasmic inclusions found in infected cells during smallpox infection. They are composed of viral particles and provide a visible diagnostic marker for the disease.

The other options are incorrect:

• Streptococcus : Coagulase test: While the Coagulase test is associated with certain Streptococcus species, it detects the presence of an enzyme that helps bacteria evade the immune system rather than a specific intracellular structure.
• Corynebacterium : Paul Bunnel test: The Paul Bunnel test is used to diagnose mononucleosis caused by the Epstein-Barr virus, not any species of Corynebacterium.
• Vibrio : Schick test: The Schick test is used to assess immunity to diphtheria toxin, not specifically related to Vibrio bacteria.

Answer: Ampicillin

While Ampicillin shares a similar structure with many penicillinase-resistant penicillins, it lacks the specific modification on its side chain that confers resistance to the penicillinase enzyme produced by certain bacteria. This enzyme cleaves the beta-lactam ring of penicillin, rendering it ineffective.

The other options are incorrect:

• Methicillin: The original penicillinase-resistant penicillin, often used as a marker for methicillin-resistant Staphylococcus aureus (MRSA).
• Oxacillin: Another penicillinase-resistant penicillin commonly used to treat penicillin-resistant Staphylococcus aureus (S. aureus) infections.
• Cloxacillin: Similar to Oxacillin, Cloxacillin is a penicillinase-resistant penicillin with activity against penicillin-resistant S. aureus.

Answer: Formaldehyde

Carbol fuchsin used in Ziehl-Neelsen staining is a mixture of basic fuchsin, phenol, and water. Formaldehyde is not a component of carbol fuchsin. Ziehl-Neelsen staining is commonly used in the detection of acid-fast bacteria, including Mycobacterium species, which cause diseases like tuberculosis.

The other options are incorrect:

• Basic fuchsin: Basic fuchsin is a component of carbol fuchsin. It is a red-colored dye that binds to acid-fast organisms.
• Absolute alcohol: Absolute alcohol is used in the staining process to decolorize non-acid-fast bacteria. It is an important component of the Ziehl-Neelsen staining technique.
• Aqueous phenol: Aqueous phenol is a component of carbol fuchsin. It helps in the penetration of the stain and acts as a mordant.

Answer: Penicillin

Step-wise” mutation for drug resistance refers to the gradual acquisition of resistance to a drug through a series of genetic changes. This is commonly seen with antibiotics like penicillin. Bacteria can develop resistance to penicillin through a stepwise process of mutations that confer resistance to the antibiotic.

The other options are incorrect:

• Streptomycin: Streptomycin is an antibiotic, but step-wise mutation for drug resistance is not typically associated with it. It may involve other mechanisms such as the acquisition of resistance genes.
• Garamycin: Garamycin is another name for gentamicin, and while bacteria can develop resistance to gentamicin, the term “step-wise” mutation is more commonly associated with penicillin resistance.
• Kanamycin: Like streptomycin, kanamycin is an antibiotic, but step-wise mutation for drug resistance is not the primary mechanism associated with kanamycin resistance.

Answer: Landsteiner

In 1900, Karl Landsteiner discovered the ABO blood group system, the foundation of modern blood transfusion safety. His groundbreaking research identified the presence of antigens A and B on red blood cells, leading to the classification of blood types and understanding of incompatible reactions.

The other options are incorrect:

• Richet: Charles Richet was a French physiologist who shared the 1913 Nobel Prize in Physiology or Medicine for his work on anaphylaxis, a severe allergic reaction. While his research contributed to immunology, it wasn’t directly related to blood groups.
• Metchnikoff: Elie Metchnikoff, a Russian microbiologist, received the 1908 Nobel Prize in Physiology or Medicine for his discoveries related to phagocytosis, the process by which immune cells engulf and destroy pathogens. Although he made significant contributions to immunology, blood group discovery wasn’t his area of expertise.
• Jenner: Edward Jenner is best known for developing the smallpox vaccine in the late 18th century. His work paved the way for vaccination and immunology, but it wasn’t directly related to the discovery of blood groups.

Answer: Mycobacterium tuberculosis is more acid-fast than Mycobacterium leprae

The acid-fastness of mycobacteria is a characteristic related to their cell wall composition, specifically the presence of mycolic acids. Mycobacterium tuberculosis, which causes tuberculosis, is more acid-fast than Mycobacterium leprae, the causative agent of leprosy. This difference in acid-fastness is due to variations in the cell wall structure of these two Mycobacterium species.

The other options are incorrect:

• Mycobacterium leprae is more acid-fast than Mycobacterium tuberculosis: This statement is incorrect. Mycobacterium tuberculosis is more acid-fast than Mycobacterium leprae.
• Both are equally acid-fast: The acid-fastness of Mycobacterium tuberculosis and Mycobacterium leprae is not equal. There are variations in acid-fastness due to differences in their cell wall compositions.
• Both are acid-fast but not acid-alcohol-fast: Both Mycobacterium tuberculosis and Mycobacterium leprae are acid-fast and acid-alcohol-fast. The acid-fastness is a key characteristic used in the laboratory staining procedures for their identification.

Answer: Plasmids

Bacterial resistance to antibiotics is often transmitted by plasmids. Plasmids are small, circular DNA molecules separate from the bacterial chromosomal DNA. They can carry genes that confer resistance to antibiotics. These resistance genes may be transferred horizontally from one bacterium to another through processes like conjugation, allowing the spread of antibiotic resistance within bacterial populations.

The other options are incorrect:

• Transduction: Transduction involves the transfer of genetic material between bacteria by bacteriophages (viruses). While it can contribute to genetic variability, it is not the primary mechanism for the transmission of antibiotic resistance.
• Transformation: Transformation is the process by which bacteria take up foreign genetic material from their environment. While this can contribute to genetic diversity, it is not the primary mechanism for the transmission of antibiotic resistance.
• Mutation: Mutation is a random, spontaneous change in the DNA sequence. While mutations can lead to antibiotic resistance, they are not the primary means of transmitting resistance between bacteria. Horizontal gene transfer mechanisms, like those involving plasmids, are more significant in the spread of resistance.

Answer: Virus

Ramsay Hunt Syndrome is caused by a virus. Specifically, it is typically associated with the Varicella-zoster virus (VZV), the same virus responsible for chickenpox and shingles. Ramsay Hunt Syndrome, also known as herpes zoster oticus, manifests with facial paralysis, ear pain, and a rash affecting the ear and mouth. It occurs when the Varicella-zoster virus reactivates in the geniculate ganglion.

The other options are incorrect:

• Bacteria: While bacteria can cause infections of the ear and face, they are not involved in Ramsay Hunt Syndrome.
• Chlamydia: Chlamydia is a sexually transmitted bacteria that can cause various infections, but it is not associated with Ramsay Hunt Syndrome.
• Fungus: Fungal infections can affect the ear and face, but they are not typically responsible for Ramsay Hunt Syndrome.

Answer: Reovirus

Reoviruses are double-stranded RNA viruses belonging to the Reoviridae family. They are relatively common and can cause a variety of mild illnesses, including respiratory infections, gastroenteritis, and febrile illness in children.

The other options are incorrect:

• Hepatitis A and B: Both are double-stranded DNA viruses belonging to the Hepadnaviridae and Orthohepadnaviridae families, respectively. They cause liver inflammation and disease.
• Polio: The poliovirus is a single-stranded RNA virus belonging to the Picornaviridae family. It primarily affects the nervous system and can cause paralysis.

Answer: 0.005 nm

In electron microscopy, the wavelength of electrons is extremely small. The correct value is approximately 0.005 nm (nanometers). Electron microscopes use electron beams instead of light to achieve much higher resolution compared to light microscopes. The short wavelength of electrons allows for the visualization of smaller details in specimens.

The other options are incorrect:

• 0.005 μ: This is the same value as the correct answer but incorrectly expressed in micrometers (μ). The wavelength of electrons in electron microscopy is in the nanometer range, not micrometers.
• 0.5 μ: This value is expressed in micrometers (μ), and it is larger than the correct wavelength of electrons. The correct value is in the nanometer range.
• 0.05 nm: This value is smaller than the correct answer. The wavelength of electrons in electron microscopy is approximately 0.005 nm, not 0.05 nm.

Answer: Absence of aromatic amino acids

Gram-positive bacteria are characterized by several features, including having a thicker peptidoglycan layer in their cell wall, the absence of an outer membrane, and the presence of teichoic acids. However, they do not necessarily have an absence of aromatic amino acids.

The other options are incorrect:

• Thicker: Gram-positive bacteria have a thicker peptidoglycan layer in their cell wall compared to gram-negative bacteria. This is a characteristic feature of gram-positive bacteria.
• Absent lipids: Gram-positive bacteria do have lipids, but the lipid composition of their cell membrane is different from that of gram-negative bacteria. They lack an outer membrane.
• Absent Teichoic acid: Gram-positive bacteria are characterized by the presence of teichoic acids in their cell wall. Teichoic acids are important components of the gram-positive bacterial cell wall.

Answer: Lysosomes

Lysosomes are membrane-bound organelles functioning as the “digestive system” of the cell. They contain a variety of hydrolytic enzymes capable of breaking down carbohydrates, proteins, lipids, and nucleic acids.

The other options are incorrect:

• Mitochondria: Primarily responsible for energy production through oxidative phosphorylation and do not contain significant amounts of hydrolytic enzymes.
• Golgi bodies: Mainly involved in protein modification, sorting, and packaging for secretion or transport within the cell, not digestion.
• Ribosomes: Responsible for protein synthesis and do not contain hydrolytic enzymes.

Answer: Principle sites of respiratory enzymes

While mesosomes were initially thought to be involved in various cellular processes, including respiration, they are no longer considered a normal part of bacterial cell structure. They are actually artifacts formed during chemical fixation techniques used to prepare bacteria for electron microscopy.

The other options are incorrect:

• A kind of Ribosome: Ribosomes are responsible for protein synthesis, and mesosomes have no role in this process.
• A part of cell wall: Mesosomes are not part of the bacterial cell wall, which is composed mainly of peptidoglycan.
• Formed during cell lysis: Cell lysis refers to the destruction of a cell, and mesosomes are not formed during this process. They arise as an artifact during specific fixation methods.

Answer: United Kingdom

Bovine Spongiform Encephalopathy (BSE), also known as Mad Cow Disease, first emerged in the United Kingdom in 1986. The disease quickly spread, impacting cattle throughout the country and eventually reaching other parts of the world.

The other options are incorrect:

• France: While France did experience some cases of BSE later, it was not the initial location of the outbreak.
• Canada: The first diagnosed case of BSE in North America occurred in Canada in 1993, but it likely originated from imported cattle infected in the UK.
• Pakistan: Pakistan has not reported any confirmed cases of BSE to date.

Answer: Avian leukosis

The COFAL (Complement Fixation for Avian Leukosis) test is specifically designed to detect the presence of antibodies against the group antigen of avian leukosis viruses (ALVs) in the blood serum of poultry. It is a valuable tool for identifying birds infected with ALVs, which can cause various tumors and immunosuppression in chickens.

The other options are incorrect:

• A. Equine infectious anemia: This viral disease affecting horses is diagnosed with different methods like Coggins test and ELISA, not the COFAL test.
• B. AIDS: Human immunodeficiency virus (HIV), the cause of AIDS, is diagnosed through different tests like ELISA and Western blot, not the COFAL test specific to avian viruses.
• D. Bovine leukosis: While bovine leukosis virus (BLV) exists, the COFAL test is not suitable for its detection due to differences in viral antigens and diagnostic approaches

Answer: Caprine arthritis encephalitis virus

While CAEV is a retrovirus and can infect goats, it is not directly linked to tumor formation. Its primary effects are inflammation of the joints and nervous system, leading to arthritis and neurological disorders.

The other options are incorrect:

• Bovine leukemia virus (BLV): BLV is known to cause a type of cancer called enzootic bovine leukosis in cattle.
• Avian leukosis virus (ALV): ALVs are a group of retroviruses responsible for various tumors in chickens, including lymphomas and myeloblastosis.
• Feline leukemia virus (FeLV): FeLV can cause several types of tumors in cats, including lymphoma and leukemia.

Answer: DIg E and Ig D

Immunoglobulin classes IgM, IgG, and IgA can manifest antiviral activity. They play essential roles in the immune response against viral infections. IgM is involved in the early stages of infection, IgG provides long-term immunity, and IgA is crucial at mucosal surfaces.

The other options are incorrect:

• IgM: The first antibody produced in response to an infection, IgM can neutralize viruses by agglutination (clumping) and activating the complement system.
• IgG: The most abundant antibody, IgG also neutralizes viruses through various mechanisms, including opsonization (facilitating phagocytosis) and antibody-dependent cellular cytotoxicity (ADCC).
• IgA: Secretory IgA found in mucosal surfaces (respiratory, gastrointestinal) neutralizes viruses by preventing their attachment and entry into epithelial cells.

Answer: Edward Jenner

While many brilliant minds have contributed to the field of vaccinations, the term “vaccine” itself was coined by English physician Edward Jenner in 1798. He used the word in the title of his groundbreaking paper, “An Inquiry into the Causes and Effects of the Variolae Vacciniae,” describing his discovery of the smallpox vaccine derived from cowpox.

The other options are incorrect:

• Robert Koch: A renowned German microbiologist, Koch discovered the specific bacteria responsible for several diseases including anthrax and tuberculosis. However, he wasn’t directly involved in coining the term “vaccine.”
• Louis Pasteur: Another French scientist and pioneer in microbiology, Pasteur developed vaccines for rabies and anthrax based on Jenner’s and others’ works. He did not, however, originate the term “vaccine.”
• Needham: John Needham was an English microscopist known for his early observations of microorganisms. He wasn’t involved in vaccination or coining the term.
• F. Redi: Francesco Redi, an Italian physician, performed early experiments challenging spontaneous generation theories but wasn’t involved in vaccination or coining the term.

Answer: Vibrio

Among the options provided, Vibrio bacteria have a single curve. Vibrio species are curved, rod-shaped bacteria that exhibit a single, gentle curve. The curved shape is distinctive and contributes to their classification within the Vibrio genus.

The other options are incorrect:

• Borrelia: Borrelia bacteria are characterized by a helical or spiral shape rather than a single curve. They are responsible for diseases such as Lyme disease and relapsing fever.
• Treponema: Treponema bacteria are spiral-shaped and often exhibit a corkscrew or helical morphology. Treponema pallidum, for example, is the causative agent of syphilis.
• Pasteurella: Pasteurella bacteria typically have a straight or slightly curved rod shape. They are not known for a single curve; rather, their morphology is more straight or slightly curved.

Answer: Carbol fuchsin

Albert’s stain, utilized for staining metachromatic granules in bacteria like Corynebacterium diphtheriae, is composed of two solutions: Albert’s A and Albert’s B. Neither of these solutions contains carbol fuchsin.

The other options are incorrect:

• Toluidine blue: This is a key component of Albert’s A solution, specifically chosen for its metachromatic staining properties where color changes depending on concentration.
• Malachite green: Another crucial component of Albert’s A solution, malachite green adds counterstaining for the background and enhances differentiation between granules and the bacterial body.
• Acetic acid: Glacial acetic acid also plays a vital role in Albert’s A solution. It acts as a mordant, facilitating dye penetration and intensifying the staining.

Answer: Azure II staining

While various techniques can visualize bacterial cell walls, Azure II staining is not commonly used for this purpose. It primarily stains nucleic acids (DNA and RNA) in bacteria, making them appear blue or purple under a light microscope.

The other options are incorrect:

• Silver impregnation technique: This technique, like the Gram stain, uses silver nitrate to deposit metallic silver particles on the cell wall, making it visible under a light microscope.
• Ultraviolet microscopy: While not commonly used for visualizing bacterial cell walls, ultraviolet light can excite certain molecules in the cell wall, allowing for their detection in specialized microscopes.
• Electron microscopy: This powerful technique uses a beam of electrons to create highly detailed images of bacterial cells, including their cell walls.

Answer: Anionic detergents

Gram-positive bacteria are more susceptible to certain antimicrobial agents, including sulfonamides (sulfas) and penicillin. These agents target components of the bacterial cell wall, which is more prominent in Gram-positive bacteria.

The other options are incorrect:

• Sulfas and Penicillin: Gram-positive bacteria are more susceptible to sulfonamides (sulfas) and penicillin. These antibiotics target cell wall synthesis, which is a more effective strategy against Gram-positive bacteria due to the thicker peptidoglycan layer in their cell walls.
• Basic Dyes: Basic dyes, which are positively charged, tend to bind more readily to the negatively charged components of bacterial cells. This includes the cell wall components of both Gram-positive and Gram-negative bacteria.

Answer: Not influenced by environment

While genotypic variations are typically stable and heritable, they can be influenced by the environment through various mechanisms, making option “Not influenced by the environment” incorrect.

The other options are incorrect:

• Stable: Genotypic variations, such as mutations in DNA sequences, generally persist within individual cells and can be passed on to offspring through cell division or reproduction.
• Heritable: These variations can be transmitted from parents to offspring through gametes (sperm and egg cells), influencing the genotype and potentially the phenotype of the next generation.
• Influenced by the environment: Environmental factors like exposure to chemicals, radiation, or certain diseases can cause mutations, altering the DNA sequence and thus the genotype. Additionally, environmental factors can interact with existing genetic variations and influence their expression, leading to phenotypic changes.

Answer: Fungi imperfecti

Fungi imperfecti, also known as Deuteromycetes, are fungi that lack a known sexual stage in their life cycle. They reproduce solely through asexual means, typically by producing spores through mitosis. This differentiates them from other fungal groups like Phycomycetes, Ascomycetes, and Basidiomycetes, which all possess distinct and readily observable sexual stages.

The other options are incorrect:

• Phycomycetes: This fungal group exhibits sexual reproduction through the formation of zygospores or gametangia.
• Ascomycetes: These fungi reproduce sexually through the formation of asci, specialized structures containing ascospores.
• Basidiomycetes: This group is characterized by the presence of basidia, club-shaped structures that produce basidiospores during sexual reproduction.

Answer: Loeffler’s methylene blue

The counterstain used in Zeihl-Neelsen staining is Loeffler’s Methylene Blue. Zeihl-Neelsen staining is a special staining technique used for the detection of acid-fast bacteria, particularly Mycobacterium species. The primary stain used is Carbol Fuchsin, and Loeffler’s Methylene Blue is employed as a counterstain to visualize non-acid-fast structures.

The other options are incorrect:

• Carbol Fuchsin: Carbol Fuchsin is the primary stain used in Zeihl-Neelsen staining for acid-fast bacteria. It is not the counterstain.
• Gentian Violet: Gentian Violet is not used as a counterstain in Zeihl-Neelsen staining. It is a basic dye used in other staining techniques, such as the Gram stain.
• Gram’s Iodine: Gram’s Iodine is part of the Gram staining technique and is not used as a counterstain in Zeihl-Neelsen staining.

Answer: Single stranded RNA

11Hepatitis A virus (HAV) belongs to the family Picornaviridae and is classified as a single-stranded RNA virus,

The other options are incorrect:

• Double stranded DNA: HAV and other picornaviruses do not possess double-stranded DNA. Their genetic material is composed of a single strand of RNA.
• Single stranded DNA: Some viruses use single-stranded DNA as their genetic material, but HAV is not one of them.
• Double stranded RNA: This is also not common in viruses that infect humans. Double-stranded RNA is more typically found in certain fungal viruses.

Answer: Chemosynthetic heterotrophs

Staphylococcus bacteria are heterotrophs, meaning they need organic compounds for energy and growth. They are also chemosynthetic, meaning they obtain their energy from chemical reactions, not from sunlight. Therefore, chemosynthetic heterotrophs is the correct answer.

The other options are incorrect:

• Photosynthetic autotrophs: These organisms use sunlight and inorganic compounds to make their own organic compounds. Staphylococcus bacteria are not photosynthetic and are heterotrophs, so this option is incorrect.
• Chemosynthetic autotrophs: These organisms obtain their energy from chemical reactions and use inorganic compounds to make their own organic compounds. While Staphylococcus bacteria are chemosynthetic, they are heterotrophs and rely on organic compounds from their environment, making this option incorrect.
• Photosynthetic heterotrophs: These organisms are not a well-defined group, as photosynthesis typically creates enough organic compounds for the organism’s needs. It’s also contradictory to be both photosynthetic and heterotrophic. Therefore, this option is incorrect.

Answer: Single stranded RNA

Rhinoviruses belong to the Picornaviridae family, all of which are single-stranded RNA viruses. Their genetic material exists as a single strand of ribonucleic acid, not DNA.

The other options are incorrect:

• Double stranded DNA: This type of genetic material is typical of eukaryotes like plants and animals, and some bacteria. Rhinoviruses, being RNA viruses, do not possess double-stranded DNA.
• Single stranded DNA: While some viruses do have single-stranded DNA, rhinoviruses specifically belong to the group with single-stranded RNA. DNA viruses have different characteristics and replication mechanisms compared to RNA viruses.
• Double stranded RNA: Double-stranded RNA is less common than single-stranded RNA in viruses, and rhinoviruses are not among the types with this genetic structure. Some viruses like rotaviruses have double-stranded RNA, but rhinoviruses have just one strand.

Answer: Surface water

Surface water is generally considered the most contaminated form of water among the options provided. Surface water includes rivers, lakes, and ponds, and it is more susceptible to contamination from various sources such as industrial discharges, agricultural runoff, and human activities.

The other options are incorrect:

• Underground Water: Underground water, sourced from aquifers, is often less prone to contamination compared to surface water. It is naturally filtered as it percolates through the soil.
• Rainwater: Rainwater, in its pure form, is relatively clean. However, it can pick up contaminants from the atmosphere as it falls. Harvested rainwater can be a valuable source when collected and stored properly.
• Water Stored in Ice Caps: Water stored in ice caps, such as glaciers, is typically considered pure and free from contamination. However, accessing this water involves melting the ice, and contamination can occur during that process.

Answer: Treponema

Treponema is a genus of bacteria that is highly sensitive to heat. Treponema species, including Treponema pallidum (the causative agent of syphilis), are heat-sensitive and can be easily killed by exposure to elevated temperatures.

The other options are incorrect:

• Staphylococcus: Staphylococcus bacteria are relatively heat-resistant. Some strains, like Staphylococcus aureus, can survive exposure to moderate heat.
• Pseudomonas: Pseudomonas bacteria are known for their resilience and resistance to various environmental conditions, including heat. They are more heat-resistant compared to Treponema.
• Clostridia: Clostridia bacteria, including Clostridium botulinum and Clostridium tetani, are spore-forming bacteria that can survive harsh conditions, including heat. They are more heat-resistant than Treponema.

Answer: Incineration

Incineration is the preferred method for destroying soiled dressings due to its complete and efficient eradication of all potential pathogens, including bacteria, viruses, and spores. This is crucial for preventing the spread of infections and ensuring patient safety.

The other options are incorrect:

• Hot Air Oven: Hot air ovens use dry heat for sterilization but may not be effective for destroying soiled dressings as they lack the immediate and intense heat of incineration.
• Autoclaving: Autoclaving involves steam under pressure and is effective for sterilizing instruments and materials that can withstand moisture and high temperatures. It may not be the optimal method for destroying soiled dressings.
• Boiling: Boiling is a method of disinfection but may not be sufficient for the complete destruction of soiled dressings, especially if they are contaminated with infectious agents.

Answer: Non-toxigenic strains of Clostridium tetani

The spores of non-toxigenic strains of Clostridium tetani are used as a microbiological test of dry heat efficiency. This test is known as the “spore strip test” or “Bacillus stearothermophilus spore test.” The rationale is that the spores of Clostridium tetani are highly resistant to heat, and their destruction serves as an indicator of the effectiveness of dry heat sterilization processes.

The other options are incorrect:

• Toxigenic Strains of E. coli: Toxigenic strains of Escherichia coli are not typically used in dry heat efficiency tests. E. coli is more commonly associated with water and foodborne infections.
• Toxigenic Strains of Clostridium tetani:Toxigenic strains of Clostridium tetani are not used in dry heat efficiency tests. The focus is on non-toxigenic strains for this purpose.
• Non-toxigenic Strains of Proteus: Proteus bacteria are not commonly used in dry heat efficiency tests. The spores of Clostridium tetani are more widely recognized for their resistance to dry heat.

Answer: Both “Fleming’s Nigrosin method” and “Dry India ink film method”

Both Fleming’s Nigrosin method and the Dry India ink film method are direct staining techniques used to visualize bacterial capsules. They work by contrasting the unstained capsule (appearing clear) with a dark background of nigrosin or India ink, allowing for easy identification under a microscope.

The other options are incorrect:

• Fleming’s Nigrosin Method: This is part of the correct answer. It is a direct staining method for bacterial capsules.
• Dry India Ink Film Method: This is part of the correct answer. It is a direct staining method for bacterial capsules.
• Welch Method: The Welch method is not a direct stain for bacterial capsules. It is not specifically used for visualizing capsules.

Answer: DNA

The major mechanism of the lethal effect of UV light on bacteria is attributed to its effect on DNA. UV light disrupts the structure of DNA molecules, causing mutations, deletions, and ultimately preventing cell replication and growth. This damage can be direct, where the light directly interacts with DNA bases, or indirect, where reactive oxygen species generated by UV light cause DNA damage.

The other options are incorrect:

• Ribosome: Ribosomes are responsible for protein synthesis, and while UV light can damage them to some extent, it’s not the primary target and wouldn’t lead to immediate cell death.
• Lysosome: Lysosomes are organelles involved in intracellular digestion and waste disposal. They are not directly affected by UV light and wouldn’t be the primary cause of cell death.
• Mesosome: Mesosomes are folds in the bacterial inner membrane. They play a role in cell division and respiration, but they are not essential for cell survival. UV light damage to mesosomes wouldn’t necessarily be fatal.

Answer: 50% glycerine

Koch’s old tuberculin (OT) is a purified protein derivative (PPD) extracted from Mycobacterium tuberculosis cultures. It’s primarily used in the Mantoux test to diagnose tuberculosis infection. To retain its stability and effectiveness, OT is preserved in 50% glycerine.

The other options are incorrect:

• 70% Formalin: Formalin (formaldehyde solution) is a strong disinfectant and fixative but is not commonly used as a preservative for tuberculins.
• 2% Phenol: Phenol is an antiseptic and disinfectant, but it is not typically used as a preservative for tuberculins.
• Absolute Alcohol: Absolute alcohol is a dehydrating agent and may not serve as a suitable preservative for tuberculins.

Answer: Contamination

The turbidity test for milk specifically detects the presence of contamination, not pasteurization, sterilization, Lactobacillus content, or simply being cloudy. This test relies on the principle that when milk is contaminated with bacteria or other microorganisms, it can become cloudy or turbid due to the increased scattering of light by bacterial cells and their products.

The other options are incorrect:

• Pasteurization: The turbidity test is not specifically used to detect pasteurization. Pasteurization is a heat treatment process to reduce the microbial load in milk.
• Sterilization: The turbidity test is not used to detect sterilization. Sterilization involves the complete elimination of all microorganisms and spores, which goes beyond the scope of the turbidity test.
• Lactobacillus Contents: The turbidity test is not specifically designed to detect Lactobacillus contents. It is a general test for overall milk quality and contamination.

Answer: Opsonization

Microorganisms can be phagocytosed after opsonization. This process involves coating the microbes with specific molecules called opsonins that act as flags, making them recognizable and attractive targets for phagocytes (cells like macrophages and neutrophils) which then engulf them.

The other options are incorrect:

• Hydrolysis: This refers to the breakdown of large molecules into smaller ones, often through the action of enzymes. While phagocytosis involves ingestion, hydrolysis is not a prerequisite for opsonization and subsequent phagocytosis.
• Cytolysis: This describes the process of cell death and breakdown. While phagocytes can engulf dead cells, opsonization primarily targets live microorganisms for phagocytosis.
• Ingestion: While ingestion means “to take in food or drink,” in the context of phagocytosis, it’s the final step after opsonization where the phagocyte engulfs the microorganism. Opsonization comes before and facilitates this ingestion.

Answer: Red, blue

Acid-fast bacteria are stained with carbol fuchsin, a red dye, and then decolorized with acid alcohol. This process allows them to retain the red color, while non-acid fast bacteria lose the carbol fuchsin and are subsequently stained with a counterstain, typically methylene blue, giving them a blue color.

The other options are incorrect:

• Blue, red: This reverses the colors for acid-fast and non-acid-fast bacteria.
• Red, black: Black is not commonly used as a counterstain in acid-fast staining. Acid-fast bacteria appear bright red, not dark red or black.
• Black, purple: These options are entirely off the mark for the typical colors observed in acid-fast staining.

Answer: Bluish black, green

In Albert’s staining, the volutin granules (metachromatic granules) are stained bluish-black against a green background. This staining technique is commonly used for the demonstration of metachromatic granules, which are storage structures found in certain bacteria.

The other options are incorrect:

• Pink, Green: This is not the correct combination. In Albert’s staining, the volutin granules are stained bluish-black, not pink.
• Green, Black: This is not the correct combination. The volutin granules are stained bluish-black, and the background is green in Albert’s staining.
• Bluish, Purple: This is not the correct combination. The volutin granules are stained bluish-black, not bluish-purple, against a green background in Albert’s staining.

Answer: 70

A 70% solution of ethanol is commonly used for disinfection. This concentration is considered more effective than higher concentrations (e.g., 80% or 90%) because the presence of water in the solution helps enhance the denaturation of proteins in microorganisms. The water content facilitates the penetration of ethanol into the microbial cells, leading to better disinfection.

The other options are incorrect:

• 30: A 30% ethanol solution is relatively weak and may not be as effective for disinfection as higher concentrations.
• 80: An 80% ethanol solution is higher than the commonly used 70% concentration. While it still has disinfectant properties, 70% ethanol is often preferred for its enhanced effectiveness.
• 90: A 90% ethanol solution is a high concentration and may evaporate too quickly, reducing the contact time needed for effective disinfection. 70% ethanol is often considered more suitable for this purpose.

Answer: Autoclaving

The most effective practical way of sterilization is autoclaving. Autoclaving involves the use of steam under pressure, which achieves high temperatures (usually around 121 degrees Celsius or 250 degrees Fahrenheit). This combination of high temperature and pressure is highly effective in killing a wide range of microorganisms, including bacteria, viruses, and spores.

The other options are incorrect:

• Boiling: Boiling is a simple method of disinfection rather than sterilization. It may not reliably kill spores and is less effective than autoclaving for achieving sterility.
• Alpha Rays: Alpha rays are a type of ionizing radiation. While they can be used for sterilization, practical applications are limited, and they may pose safety concerns.
• Gamma Rays: Gamma rays are also a form of ionizing radiation used for sterilization, but they require specialized equipment and are not as commonly used in practical settings as autoclaving.

Answer: Basic dyes

Due to the acidic nature of their protoplasm, bacteria have an affinity for basic dyes. Basic dyes are positively charged and are attracted to the negatively charged components of bacterial cells, such as the nucleic acids (DNA and RNA) and certain proteins. The interaction between basic dyes and bacterial components results in the staining of bacterial cells.

The other options are incorrect:

• Acidic Dyes: Acidic dyes are negatively charged and are repelled by the negatively charged bacterial cells. They are not typically used for staining bacterial cells.
• Neutral Dyes: Neutral dyes have no net charge and are not as effective in staining bacterial cells. They do not show a strong affinity for the negatively charged components of bacteria.
• All of the Above: The correct answer is basic dyes. While basic dyes have an affinity for bacterial cells, acidic and neutral dyes do not show the same level of affinity. Therefore, the statement “All of the Above” is not accurate in this context.

Answer: Histamine

While other options like cytokines (IL-1, IL-6, TNF-α), C3b (complement fragment), and γ-IFN (interferon gamma) all stimulate phagocyte activity, histamine does not.

The other options are incorrect:

• Cytokines: Certain cytokines, particularly pro-inflammatory ones like IL-1, IL-6, and TNF-α, act as chemical messengers that activate and recruit phagocytes to sites of infection.
• C3b: This fragment of the complement system binds to pathogens, opsonizing them for phagocytosis and triggering the release of chemotactic factors that attract phagocytes.
• γ-IFN: This interferon stimulates phagocytes to increase their antimicrobial activity and antigen presentation capabilities.

Answer: Immune response

The immunogenicity of an antigen is primarily related to the immune response it elicits in the host organism. An antigen’s ability to induce an immune response, particularly the production of antibodies and activation of T cells, determines its immunogenicity. Factors such as foreignness and chemical nature contribute to an antigen’s ability to provoke an immune response.

The other options are incorrect:

• Foreignness: Foreignness is a contributing factor to immunogenicity. However, the immune response is the ultimate determinant of an antigen’s immunogenicity.
• Chemical Nature: The chemical nature of an antigen influences its immunogenicity, but the key factor is the subsequent immune response it triggers.

Answer: Sweating

Sweating is not a typical sign of inflammation. The classical signs of inflammation, known as the four cardinal signs, are pain, swelling, redness, and heat. These signs are associated with the body’s response to tissue injury or infection.

The other options are incorrect:

• Pain: Pain is a common sign of inflammation and is often associated with the release of inflammatory mediators and the activation of pain receptors.
• Swelling: Swelling, also known as edema, is a common manifestation of inflammation. It results from increased permeability of blood vessels, allowing fluid and immune cells to enter the affected tissue.
• Redness: Redness, or erythema, is a visible sign of increased blood flow to the inflamed area. It is caused by the dilation of blood vessels.

Answer: Passive immunity

Natural transfer of Igs from mother to fetus involves the passive transfer of antibodies from the mother’s circulation to the fetus. This provides the newborn with immediate protection against various pathogens before their own immune system fully develops.

The other options are incorrect:

• Active immunity: Active immunity occurs when the body actively responds to an antigen and produces its own antibodies. This process doesn’t happen in the fetus, as it receives pre-made antibodies from the mother.
• Non-specific: While the transferred antibodies may provide some non-specific protection against various pathogens, their primary function is specific to the antigens they were originally generated against.
• Artificial immunity: Artificial immunity is acquired through vaccination, which doesn’t occur in this natural transfer process.

Answer: IgG

The most common antibody in the serum is IgG (Immunoglobulin G). IgG is the predominant antibody class in the bloodstream and plays a crucial role in providing long-term immunity. It is involved in neutralizing toxins, opsonization (enhancing phagocytosis), and providing protection against a wide range of pathogens.

Incorrect Options:

• IgA: IgA is primarily found in mucosal secretions such as saliva, tears, and breast milk. While important for mucosal immunity, it is not the most common antibody in the serum.
• IgD: IgD is found on the surface of B cells and is involved in the activation of B cells. It is not the most abundant antibody in the serum.
• IgM: IgM is the first antibody produced during an initial immune response. While it is present in serum, IgG surpasses IgM in terms of abundance in the bloodstream over

Answer: IgM

IgM is a type of specific antibody, while the other options are all examples of nonspecific defense mechanisms. Nonspecific defenses target any and all pathogens, whereas specific defenses develop in response to a specific encounter with a particular pathogen.

The other options are incorrect:

• Lacrimal apparatus: Produces tears, which contain lysozyme (an enzyme that breaks down bacterial cell walls) and antibodies, contributing to eye defense.
• Sweat gland: Secretes sweat, which contains lysozyme and defensins (antimicrobial peptides), providing some antibacterial and antifungal activity.
• Mucus: Traps and eliminates pathogens in the respiratory and digestive tracts, acting as a physical barrier.