MicroBiology MCQs with Answer and Explnation | Chapter 42

Answer: H chain

The portion of an immunoglobulin molecule with a molecular weight around 50,000 is the H chain (Heavy Chain). Each immunoglobulin molecule typically contains two identical H chains and two identical L chains (Light Chains). The H chain is significantly heavier than the L chain, with an approximate molecular weight of 50,000 Da compared to the L chain’s 25,000 Da.

Here’s a brief explanation of the incorrect options:

• Secretory piece: This is a polypeptide chain attached to IgA molecules when they undergo mucosal transport. Its molecular weight is much smaller than 50,000 (~15 kDa).
• L chain (Light Chain): As mentioned earlier, the L chain has a molecular weight of approximately 25,000, half that of the H chain.
• J piece: This is a small sequence of nucleotides that joins the variable (V) and joining (J) regions of the H chain after gene rearrangement during B cell development. It does not have a significant molecular weight.

Answer: It kills all bacteria except thermoduric bacteria

Pasteurization is a heat treatment process used to eliminate or reduce the number of pathogenic microorganisms in food and beverages, particularly those that cause spoilage. Pasteurization does not kill all bacteria, but it reduces their numbers. The process involves heating the substance to a specific temperature for a set period, effectively destroying or inhibiting the growth of most bacteria. However, it does not necessarily kill thermoduric bacteria, which are heat-resistant and may survive the process.

The other options are incorrect:

• It kills bacteria and spores: Pasteurization is not designed to kill bacterial spores, and some spores, particularly thermoduric ones, may survive the process.
• It kills 95% of microorganisms: The effectiveness of pasteurization may vary, and it is not specifically designed to kill a specific percentage of microorganisms. The goal is to reduce microbial load and eliminate or inhibit pathogens.
• Tubercle bacilli are destroyed: While pasteurization may reduce the viability of some bacteria, including Mycobacterium tuberculosis (tubercle bacilli), it may not completely destroy all of them. Specific treatments are required for the complete elimination of tubercle bacilli.

Answer: Ethylene dioxide

Ethylene dioxide: This gas is a highly effective sterilizing agent that penetrates materials like oils and greases, destroying a wide range of microorganisms, including bacteria, viruses, and spores. However, it requires specialized equipment and proper safety protocols due to its toxicity.

The other options are incorrect:

• Hot air oven: While hot air ovens can be used for dry heat sterilization, they are not suitable for oil and grease. The high temperatures required (over 160°C for several hours) can cause the oil or grease to decompose or ignite, posing safety risks. Additionally, hot air may not effectively penetrate the oil’s depth, leaving some microorganisms viable.
• Autoclaving: Autoclaves use saturated steam under pressure for sterilization. They are effective for aqueous materials but are not suitable for oils and greases. The oil would repel the steam, preventing effective sterilization, and could potentially damage the autoclave equipment.
• Irradiation: Gamma irradiation can be used for sterilizing some materials, but it is not commonly used for oils and greases. The effectiveness can vary depending on the type of oil and the radiation dose, and it may not be practical for large quantities due to the required equipment and regulations.

Answer: Liquid paraffin

Hot air ovens are efficient for sterilizing dry heat-resistant materials like glassware, rubber tubes, and even some sharpened instruments. However, liquid paraffin, being a flammable liquid, is not suitable for hot air oven sterilization.

The other options are incorrect:

• Glassware: Most glassware used in laboratories and clinics can be sterilized in hot air ovens at temperatures around 160°C for 2 hours.
• Rubber tubes: Certain heat-resistant rubber tubes can be sterilized in hot air ovens, but temperature and duration should be adjusted based on the specific material.
• Sharp instruments: Some metal surgical instruments can be sterilized in hot air ovens, but careful attention must be paid to the temperature and type of instrument to avoid damage.
• Liquid paraffin: This mineral oil is highly flammable and can easily ignite at the high temperatures used in hot air ovens, posing a significant fire hazard. Therefore, it is strictly not suitable for this sterilization method.

Answer: Cidex

Cidex: This brand name represents a family of high-level liquid chemical sterilants containing glutaraldehyde. These solutions are specifically designed for sterilizing heat-sensitive medical instruments like endoscopes, effectively killing a wide range of microorganisms, including bacteria, viruses, and spores.

The other options are incorrect:

• Autoclaving: While effective for many instruments, autoclaves use high temperatures and pressure (around 121°C and 15 psi) which can damage or deform the delicate materials and electronics in most endoscopes.
• Boiling: Boiling water cannot achieve the necessary temperature for sterilization (100°C is insufficient for destroying spores). While it has limited use for disinfecting non-critical surfaces, it wouldn’t be appropriate for complete sterilization of endoscopes.
• Gamma radiation: Gamma radiation can be effective for sterilizing some medical instruments, but it is not commonly used for endoscopes due to its potential to damage plastic and electronic components. Additionally, the process requires specialized equipment and regulations.

Answer: T cells

Killer (cytotoxic) and Helper (CD4) cells are both types of T cells, which are a crucial component of the immune system. T cells play a key role in the body’s defense against infections and are involved in coordinating and regulating the immune response.

The other options are incorrect:

• B cells: These cells produce antibodies, which are proteins that neutralize pathogens. While B cells are critical for the immune system, they are not directly involved in the killing of infected cells, which is the primary function of Killer T cells.
• Monocytes: These are large, circulating white blood cells that eventually mature into macrophages. Macrophages engulf and digest foreign particles and debris, but they primarily act as scavengers and don’t have the specific targeting and killing capabilities of T cells.
• Macrophages: As mentioned above, these are derived from monocytes and primarily function as phagocytes, ingesting and destroying pathogens and cellular debris. While they contribute to the immune response, they lack the antigen-specific recognition and targeted killing functions of T cells.

Answer: Phytohaemagglutinin

Phytohaemagglutinin (PHA) is a lectin protein extracted from the red kidney bean (Phaseolus vulgaris). It binds to specific sugar molecules on the surface of T cells, triggering their activation and proliferation. This makes PHA a potent stimulator of T cell multiplication, commonly used in laboratory studies and testing T cell function.

The other options are incorrect:

• Macrolin: It is an antibiotic with no known effect on T cell multiplication.
• Heat: Excessive heat can damage cells, including T cells, and hinder their multiplication.
• Bovine serum: This blood serum can provide nutrients for T cell growth but doesn’t directly stimulate their multiplication.
• None of the above: While other factors like antigens and cytokines can also stimulate T cell growth, PHA remains the most specific and potent stimulus listed in the options.

Answer: Heterophile antigens

Heterophile antigens are molecules present in different biological species that share structural similarities, allowing them to react with the same antibodies. This can lead to false-positive results in some diagnostic tests, as antibodies generated against one species’ antigen may cross-react with the heterophile antigen in another species.

The other options are incorrect:

• Sequestrated antigens: These are antigens naturally hidden within cells or tissues, not readily accessible to the immune system. While they can be immunogenic under certain circumstances, they don’t share similarities with antigens in other species.
• Isoantigens: These are antigens present within an individual that are recognized as “foreign” by the immune system due to genetic differences. However, they are unique to an individual and not shared with other species.
• Haptens: These are small molecules that are not immunogenic on their own but can become antigenic when conjugated to a larger carrier molecule. However, they generally lack the complex structure and shared features of heterophile antigens.

Answer: Type II

Rh incompatibility is a Type II hypersensitivity reaction because it involves antibody-mediated destruction of target cells (fetal red blood cells). The mother’s immune system mistakenly identifies Rh-positive fetal red blood cells as “foreign” and produces antibodies against them. These antibodies then attack and destroy the fetal red blood cells, leading to hemolytic disease of the newborn (HDN) in severe cases.

The other options are incorrect:

• Type I: This type involves immediate allergic reactions mediated by IgE antibodies and mast cells, triggered by allergens like pollen or food (not relevant to Rh incompatibility).
• Type III: This type involves immune complex formation and inflammation in tissues, often triggered by drugs or infections (not involving direct cell destruction like in Rh incompatibility).
• Type IV: This type involves delayed-cell mediated reactions primarily through T cells, often associated with skin reactions and tissue damage (not involving antibodies targeting circulating cells like in Rh incompatibility).

Answer: Type II

Killer cells, specifically cytotoxic T cells (CD8+ T cells), are associated with the Type II hypersensitivity reaction. In Type II hypersensitivity, antibodies, often IgG or IgM, target specific cells, leading to cell destruction or dysfunction. Cytotoxic T cells can also contribute to cell-mediated cytotoxicity.

The other options are incorrect:

• Type I: Type I hypersensitivity reactions involve immediate, IgE-mediated responses, such as allergies. Killer cells are not directly associated with Type I reactions.
• Type III: Type III hypersensitivity reactions involve immune complex-mediated inflammation, where immune complexes deposit in tissues and cause damage. Killer cells are not primarily associated with Type III reactions.
• Type IV: Type IV hypersensitivity reactions are delayed and involve T cell-mediated responses, such as contact dermatitis. While killer cells (cytotoxic T cells) are involved in cell-mediated immunity, they are not specifically associated with Type IV reactions.

Answer: Auto immune hemolytic anemia

AIHA is the prototype of a Type II hypersensitivity reaction because it directly involves antibodies targeting and destroying the body’s own red blood cells (self-antigens). This leads to anemia and related symptoms. The immune system mistakenly recognizes these cells as “foreign” and produces antibodies that bind to their surfaces, triggering opsonization and phagocytosis by macrophages, leading to cell death.

Incorrect Options and Brief Explanations:

• Arthus reaction: This is a Type III hypersensitivity reaction involving immune complex formation and inflammation in tissues, triggered by high antigen concentrations. While it shares some similarities with AIHA, the target cells and mechanisms involved differ.
• SLE (Systemic Lupus Erythematosus): This is an autoimmune disease with complex pathology involving multiple organ systems and different types of hypersensitivity reactions. While AIHA can be one manifestation of SLE, it doesn’t represent the whole picture and isn’t the sole prototype of Type II.
• Contact dermatitis: This is a Type IV hypersensitivity reaction primarily mediated by T cells and inflammatory responses in the skin. While it shares some features with AIHA in terms of tissue damage, the mechanism and target cells are distinct.

Answer: Gamma rays

Cold sterilization refers to the process of sterilization using ionizing radiation, particularly gamma rays. Gamma rays have high energy and can penetrate materials to kill or inactivate microorganisms, ensuring sterility without the need for high temperatures.

The other options are incorrect:

• Ultra violet rays: Ultraviolet (UV) rays have lower energy compared to gamma rays and are not generally used for cold sterilization. UV rays are often used for disinfection rather than sterilization.
• Ultrasonic vibrations: Ultrasonic vibrations are not typically used for cold sterilization. They are more commonly employed in cleaning processes and certain medical applications.
• Infrared rays: Infrared rays are associated with heat, and they do not possess the ionizing capability required for sterilization. Infrared is more commonly used for applications like heating or drying.

Answer: Isograft

In this scenario, the woman receives an ovary transplant from her identical twin sister. This is considered an isograft, which is a type of tissue transplant where the donor and recipient have genetically identical tissues. Identical twins share the same genetic makeup, making their tissues compatible and minimizing the risk of rejection.

The other options are incorrect:

• Xenograft: This refers to a transplant between different species, which is not the case here as both individuals are human.
• Autograft: This refers to a transplant where tissue is taken from the same individual and placed elsewhere in their body. While the donor and recipient are the same person, the transplant in this case involves a different individual (the sister).
• Allograft: This refers to a transplant between genetically different individuals of the same species. While the sisters are still genetically related, they are not identical, so it wouldn’t be considered an allograft.

Answer: IgE

Type I hypersensitivity, also known as immediate hypersensitivity, is primarily mediated by the immunoglobulin IgE. This type of antibody binds to FcεRI receptors on the surface of mast cells and basophils, triggering the release of inflammatory mediators like histamine and leukotrienes. These mediators cause the immediate allergic symptoms associated with Type I reactions, such as hay fever, asthma, and anaphylaxis.

The other options are incorrect:

• IgA: IgA mainly targets mucosal surfaces and plays a role in preventing infections. It is not typically involved in Type I hypersensitivity reactions.
• IgG: IgG is the most abundant immunoglobulin and is involved in various immune functions, including antibody-dependent cytotoxicity and opsonization. However, it plays a primary role in Type II hypersensitivity reactions, not Type I.
• IgM: IgM is the first antibody produced in a primary immune response and can activate the complement system. While it can contribute to some aspects of Type I reactions, it’s not the primary mediator.

Answer: Antitoxins

Active artificial immunization involves exposing the body to weakened or inactive forms of pathogens (bacteria, viruses) or their toxins to stimulate the immune system to develop antibodies and memory cells. This allows the body to mount a quicker and stronger response upon encountering the actual pathogen later.

The other options are incorrect:

• Bacterial products: These can include weakened or dead bacteria, attenuated (weakened) bacterial toxins, or even specific bacterial components like polysaccharides. All of these can be used in vaccines to induce active immunity.
• Toxoids: These are inactivated toxins that retain their antigenicity but have lost their toxicity. They are commonly used in vaccines against diseases like tetanus and diphtheria.
• Vaccines: This is the most common method of inducing active artificial immunity. Vaccines contain weakened or inactive pathogens, their toxins, or specific components, triggering the immune system to generate protective antibodies.

Answer: Passive acquired immunity

The immunity transferred from mother to fetus through IgG and IgA antibodies is passive acquired immunity. This type of immunity involves the transfer of pre-formed antibodies from an immunized individual to a non-immunized individual, providing immediate protection against specific pathogens.

Incorrect Options and Brief Explanations:

• Active acquired immunity: This immunity develops when an individual encounters a pathogen or vaccine and their own immune system produces antibodies and memory cells. While the fetus has immune organs, they are not fully functional until after birth, so it cannot actively generate its own immunity during this period.
• Natural active immunity: This immunity develops after an individual naturally encounters a pathogen and recovers from the infection. The fetus is still within the sterile environment of the womb and has not encountered any natural pathogens to trigger its own immune response.
• Passive natural immunity: This immunity is also acquired passively but usually comes from breast milk, which contains IgA antibodies specific to the mother’s recent exposures. While some IgA does cross the placenta, IgG is the predominant antibody transferred and is more associated with passive acquired immunity during pregnancy.

Answer: IgA antibodies

Breast milk provides a plethora of protective benefits for infants, and IgA antibodies play a crucial role in this. IgA antibodies are specifically adapted to mucosal surfaces, which line the respiratory and digestive tracts of infants. These antibodies bind to pathogens and prevent them from attaching to the mucosal lining, thereby hindering their entry and potential infection.

The other options are incorrect:

• IgM antibodies: While IgM are the first antibodies produced in an immune response, they are not predominant in breast milk and have limited effectiveness against mucosal pathogens.
• Lysozyme: This enzyme is present in breast milk and has antimicrobial properties, but its main function is breaking down bacterial cell walls, not directly preventing attachment.
• Mast cells: These cells are not found in breast milk and are not involved in the specific protective mechanisms of IgA antibodies against mucosal pathogens.

Answer: Activated macrophages

During inflammation, IL-1 and TNF-α are primarily secreted by activated macrophages. These are phagocytic white blood cells that play a crucial role in inflammation and immune responses. Upon encountering pathogens or tissue damage, macrophages become activated, producing and releasing various inflammatory mediators, including IL-1 and TNF-α. These cytokines recruit other immune cells, amplify inflammatory processes, and promote tissue repair.

The other options are incorrect:

• Plasma cells: These cells are specialized antibody-producing lymphocytes and generally don’t secrete IL-1 and TNF-α in significant amounts.
• Lymphocytes: While some T lymphocytes can produce IL-1 and TNF-α under specific conditions, activated macrophages remain the primary source of these cytokines during inflammation.
• Platelets: These blood cells are primarily involved in blood clotting and wound healing and don’t contribute significantly to cytokine production in inflammation.

Answer: Interferons

Interferons are signaling proteins produced by virus-infected cells to alert nearby cells and induce an antiviral state. They play a crucial role in the body’s defense against viruses by inhibiting viral replication and promoting the immune response. Interferons can also contribute to the programmed cell death (apoptosis) of infected cells, preventing the spread of the virus.

The other options are incorrect:

• Macrophages: While macrophages can engulf and destroy some infected cells, they are not the primary killers in this scenario. Interferons play a key role in activating macrophages for this task.
• Neutrophils: These are white blood cells primarily involved in fighting bacterial infections. While they can contribute to clearing some viral infections, they are not the main killers of virus-infected cells.
• Autolysis: This refers to the self-destruction of a cell, but it’s not typically triggered by viral infection. Interferons can induce cell death in some cases, but it’s a controlled and programmed process, not random autolysis.

Answer: Excess antibody

The prozone phenomenon occurs when there are excess antibodies present in a sample relative to the antigen. This abundance of antibodies leads to the formation of large immune complexes, which are unable to agglutinate (clump together) and are therefore not detected by the test. This results in a false-negative result, even though the antigen is actually present.

The other options are incorrect:

• Disproportionate antigen antibody levels: While the relative concentrations are crucial, specifically excess antibodies are the main culprit in the prozone phenomenon.
• Excess antigen: This can potentially mask the antigen and hinder its detection, but it wouldn’t lead to the formation of large immune complexes that prevent agglutination.
• Hyper immune reaction: This term doesn’t accurately describe the mechanism behind the prozone phenomenon, which is a specific issue with immune complex formation and agglutination, not a general exaggeration of the immune response.

Answer: Radioimmuno Assay

This is difficult to definitively state without knowing the specific antigen in question. However, Radioimmunoassay (RIA) often ranks among the most sensitive tests for antigen detection, particularly for low-abundance antigens. It utilizes radioactive isotopes to label antibodies, allowing for highly sensitive detection of antigen-antibody binding.

The other options are incorrect:

• ELISA: While Enzyme-linked Immunosorbent Assay (ELISA) is a versatile and widely used technique, its sensitivity can vary depending on the specific antigen and ELISA format. Generally, it’s considered less sensitive than RIA for low-abundance antigens.
• Immunofluorescence: This technique can be highly sensitive for visualizing antigen localization in cells or tissues, but its overall sensitivity for antigen detection in solution is generally lower than RIA.
• Passive hemaglutination: This is a relatively simple and rapid technique, but its sensitivity is generally lower than RIA, ELISA, and immunofluorescence. It’s often used for qualitative detection rather than quantitative measurement of antigen levels.

Answer: IgG & igM

Immunoglobulin classes IgG and IgM can bind to antigens and initiate the classical pathway of the complement system. The classical pathway is a cascade of events that leads to the activation of complement proteins, contributing to the immune response against pathogens.

The other options are incorrect:

• IgG & IgA: IgA primarily functions in mucosal immunity and doesn’t effectively activate the classical pathway.
• IgG & IgD: IgD is mainly involved in B cell maturation and signaling and doesn’t play a significant role in classical pathway activation.
• IgD & IgE: Neither IgD nor IgE are capable of activating the classical pathway. IgD functions as described above, and IgE is primarily involved in Type I hypersensitivity reactions.

Answer: Acts as a mucosal barrier for infection

Acts as a mucosal barrier for infection: IgA is the most abundant antibody found in mucosal secretions, such as saliva, tears, and breast milk. It plays a crucial role in preventing pathogens from entering the body through mucosal surfaces. IgA neutralizes pathogens by agglutination (clumping) and preventing their attachment to epithelial cells. Additionally, IgA can activate complement and recruit immune cells to further enhance the immune response at mucosal sites.

The other options are incorrect:

• Circulating antibody: While IgA can be found in small amounts in the blood, its primary function is not as a circulating antibody. IgG is the predominant antibody in the blood and plays a more significant role in systemic immune responses.
• Kills virus infected cells: IgA mainly neutralizes pathogens by preventing their attachment and entry, rather than directly killing infected cells. This function is primarily carried out by other immune cells like cytotoxic T lymphocytes.
• Activates macrophages: While IgA can indirectly contribute to macrophage activation through complement cascade engagement, its main function is not directly activating these cells. Other factors like cytokines and chemokines play a more significant role in macrophage activation.

Answer: Paratope

The antigen combining site of the antibody is called the paratope. This specialized region on the antibody molecule is uniquely shaped to bind with specific parts of an antigen (epitope). The fit between the paratope and the epitope is like a lock and key, allowing the antibody to recognize and neutralize specific pathogens or foreign particles.

The other options are incorrect:

• Idiotope: This refers to a region on the antibody molecule itself that can be recognized by other immune cells. It’s not the site for antigen binding.
• Epitope: This is the specific part of an antigen that the paratope binds to. It’s not the antibody site itself.
• Hapten: This is a small molecule that can bind to an antibody but cannot trigger an immune response on its own. It cannot form the specific and complementary fit required for the antigen combining site.

Answer: Both IgG & IgM

Both IgG & IgM: Both IgG and IgM antibodies can participate in opsonization, although they have slightly different roles. IgG is the most abundant antibody in the blood and efficiently binds to C3b protein of the complement system, marking the pathogen for phagocytosis by macrophages and neutrophils. IgM, with its pentameric structure, can effectively bind to multiple antigen sites, enhancing the efficiency of opsonization by C3b binding.

The other options are incorrect:

• IgA: Primarily found in mucosal secretions and not as efficient in opsonization compared to IgG and IgM.
• IgE: Primarily involved in Type I hypersensitivity reactions and not significantly involved in opsonization.

Answer: Gram +ve bacteria

Endotoxins are lipopolysaccharides (LPS) found in the outer membrane of Gram-negative bacteria. These toxins cause a strong inflammatory response when released into the bloodstream, potentially leading to fever, shock, and organ damage.

The other options are incorrect:

• Fungi: Fungi typically produce mycotoxins, which have different structures and effects compared to endotoxins.
• Gram-positive bacteria: Gram-positive bacteria have a different cell wall structure and do not contain LPS. They may produce exotoxins, which are secreted proteins with various toxic effects.
• Virus: Viruses are not cellular organisms and do not produce endotoxins. They can, however, trigger an immune response that can have inflammatory consequences.

Answer: Proteus

The Weil-Felix test utilizes antigenic cross-reactivity between specific strains of Proteus bacteria and rickettsial pathogens. The test uses suspensions of Proteus OX19, OX2, and OXK strains to detect antibodies against Rickettsiae in a patient’s serum.

The other options are incorrect:

• Pseudomonas: While some Pseudomonas species can express antigens cross-reacting with specific pathogens, they are not used in the Weil-Felix test.
• coli: Escherichia coli (E. coli) is a Gram-negative bacterium not related to Proteus or Rickettsiae and doesn’t share relevant antigenic similarities for the Weil-Felix test.
• Staphylococcus: Staphylococcus aureus is a Gram-positive bacterium with distinct antigenic properties not related to the Rickettsiae-Proteus cross-reactivity utilized in the Weil-Felix test.

Answer: Mutation

Mutations in bacterial DNA are the primary driver of drug resistance in most cases. These mutations can alter genes or regulatory regions, affecting enzymes and other proteins involved in drug uptake, target binding, or metabolic pathways. This altered functionality can render the drug ineffective, allowing resistant bacteria to survive and even thrive under drug pressure.

The other options are incorrect:

• Transduction: While transduction involves horizontal gene transfer via phages, it’s not as frequent as mutations and contributes to a smaller portion of drug resistance cases.
• Transformation: Transformation refers to the uptake of external DNA by bacteria, again less common than mutations and not the main driver of drug resistance. Acquired genes may not necessarily confer resistance traits.
• Conjugation: Conjugation is a direct cell-to-cell transfer of plasmids, which can harbor resistance genes. While it plays a role in spreading resistance, it doesn’t directly create new resistance through mutations.

Answer: Both Glutaraldehyde & Formaldehyde

Both Glutaraldehyde and Formaldehyde are effective disinfectants for spores.

• Glutaraldehyde: It is a high-level disinfectant and sterilant that can inactivate bacterial spores, making it suitable for use in healthcare settings to sterilize medical instruments.
• Formaldehyde: It is a disinfectant and sterilant that can kill bacterial spores. It is used in various forms, including formalin solutions, for the sterilization of equipment and materials.

The other options are incorrect:

• Betapropiolactone: This is another sporicidal agent, but its use has declined due to concerns regarding its toxicity and potential carcinogenicity.
• Hexachlorophene: While this has some antimicrobial activity, it’s not considered a reliable sporicide and is not commonly used for spore disinfection.

Answer: 72° for 15 – 20 Sec

Flash pasteurization, also known as high-temperature short-time (HTST) pasteurization, is typically done at a temperature of 72°C for 15–20 seconds. This process helps in reducing microbial load in milk while preserving its sensory and nutritional qualities.

The other options are incorrect:

• 125°C for new seconds: This temperature is much higher than what is used in flash pasteurization and would significantly change the milk’s properties. It would fall under Ultra-High Temperature (UHT) pasteurization, which requires different conditions.
• 60°C for 15 minutes: This temperature is too low to effectively kill all harmful bacteria and falls below the minimum requirements for flash pasteurization.
• 72° for 5 minutes: While 72°C is the correct temperature, 5 minutes is a shorter holding time than the recommended 15-20 seconds for effective bacterial inactivation.

Answer: 25°C to 40°C

Mesophilic organisms are those that thrive in moderate temperatures, neither too hot nor too cold. Their optimal growth range typically falls between 25°C and 40°C. This range aligns with the average temperatures found in many temperate environments, making these organisms the most common type found in nature and human surroundings.

The other options are incorrect:

• -20°C to -7°C: This range falls within the psychrophilic category, representing organisms adapted to cold environments.
• -7°C to +20°C: While some mesophiles might have a slightly lower optimal temperature, they generally prefer warmer temperatures within the 25°C to 40°C range.
• 55°C to 80°C: This range falls within the thermophilic category, representing organisms adapted to high temperatures.

Answer: Transduction

Transduction is the mechanism of genetic transfer where a phage (virus that infects bacteria) serves as a vehicle, carrying and delivering bacterial DNA from one host cell to another. Phages can accidentally package bacterial DNA during their replication cycle and then transfer it to new bacterial cells they infect. This can introduce new genetic material into the recipient cell, potentially altering its traits.

The other options are incorrect:

• Transformation: This involves the uptake of free DNA by a bacterial cell, not mediated by a phage.
• Conjugation: This involves direct cell-to-cell contact for plasmid transfer, not phages.
• Lysogeny: This describes the phage life cycle where the viral DNA integrates into the host chromosome, it doesn’t involve transfer of bacterial DNA to another cell.

Answer: Mycobacterium

Dorset’s egg medium is specifically formulated for the cultivation of Mycobacterium species, including Mycobacterium tuberculosis and Mycobacterium leprae. Its unique composition, containing coagulated egg yolk and glycerol, provides the rich nutrients and fatty acids required for the slow growth of these fastidious bacteria.

The other options are incorrect:

• Staphylococcus: While some Staphylococcus species can potentially grow on Dorset’s egg medium, it’s not an ideal or preferred medium for their cultivation. Other media like Mannitol Salt Agar are more commonly used for Staphylococcus identification.
• Streptococcus: Similar to Staphylococcus, Streptococci generally have different growth requirements and are not routinely cultured on Dorset’s egg medium. Blood agar or selective media like Bile Esculin Agar are more suitable for isolating Streptococci.
• Gonococcus: Neisseria gonorrhoeae, the causative agent of gonorrhea, is another fastidious bacterium but requires different nutrients and conditions for growth. Chocolate agar or Thayer-Martin agar are typically used for isolating and identifying Gonococcus.

Answer: Loefflers serum slope

Loeffler’s serum slope is a specialized culture medium used for the cultivation of Corynebacterium diphtheriae, the bacterium responsible for causing diphtheria. This medium provides a suitable environment for the growth of the pathogen and is commonly used in the laboratory for the isolation and identification of Corynebacterium diphtheriae.

The other options are incorrect:

• McConkey agar: This medium is commonly used for differentiating lactose-fermenting and non-fermenting Gram-negative bacteria. It’s not suitable for growing C. diphtheriae, which is Gram-positive and doesn’t ferment lactose.
• Saboraud agar: This medium is primarily used for cultivating fungi and some yeasts. C. diphtheriae is a bacterium and has different nutritional requirements, making Sabouraud agar unsuitable for its growth.
• Lowenstein-Jensen medium: This medium is commonly used for isolating Mycobacterium species, including the causative agents of tuberculosis and leprosy. While it can support the growth of some Corynebacterium species, it’s not specifically optimized for C. diphtheriae and provides suboptimal conditions for its isolation.

Answer: Chlorhexdine

Chlorhexidine is considered one of the best skin disinfectants. It is a broad-spectrum antimicrobial agent effective against bacteria, viruses, and fungi. Chlorhexidine is commonly used for preoperative skin preparation, surgical hand disinfection, and general skin antisepsis due to its persistent and residual activity.

The other options are incorrect:

• Alcohol: While effective against some bacteria, it evaporates quickly and doesn’t have lasting power. It can also dry out and irritate the skin.
• Savlon: Savlon is a combination of chlorhexidine and another disinfectant, but the concentration of chlorhexidine is usually lower than in dedicated chlorhexidine solutions.
• None of the above: Since chlorhexidine is the most effective option for general skin disinfection, this is not the best answer.

Answer: 2%

The most common concentration of agar used in agar medium for general microbiological purposes is 2%. This provides a firm gel with suitable porosity for diffusion of nutrients and movement of microorganisms. Higher concentrations (like 10% or 15%) would result in a very stiff gel, hindering diffusion and impacting microbial growth. Lower concentrations (like 5%) would create a softer gel, potentially making it difficult to handle and affecting its ability to hold its shape.

The other options are incorrect:

• 10% and 15%: These concentrations are too high and would result in a very stiff gel, hindering diffusion and affecting microbial growth.
• 5%: This concentration is slightly lower than the optimal range and might lead to a softer gel that’s less stable and affects handling.

Answer: Introduction of complex media

While Louis Pasteur made significant contributions in various fields, introducing complex media for bacterial cultures wasn’t one of them. He primarily focused on studying microorganisms responsible for fermentation and disease, developing vaccines, and disproving theories like spontaneous generation. Complex media, containing a variety of nutrients and organic compounds, were developed later by other microbiologists like Martin Emil Hansen and Walter Hesse.

The other options are incorrect:

• Discovery of Rabies Vaccine: Pasteur famously developed the first rabies vaccine in 1885, making it a groundbreaking achievement in his career.
• Discovery of M. Tuberculosis: Robert Koch, not Louis Pasteur, is credited with discovering and identifying Mycobacterium tuberculosis as the causative agent of tuberculosis in 1882.
• Disproved spontaneous regression theory: Pasteur’s famous swan-necked flask experiment helped disprove the theory of spontaneous generation, not “spontaneous regression theory.” The term “spontaneous regression” is more commonly used in medical contexts to describe the unexpected disappearance of disease symptoms without medical intervention.

Answer: Robertson cooked meat medium

Robertson cooked meat medium is specifically designed for culturing anaerobic bacteria. It provides a rich source of nutrients, including carbohydrates, proteins, and blood, and contains reducing agents like sodium thioglycolate to scavenge oxygen and create an anaerobic environment. This makes it ideal for growing a diverse range of anaerobic bacteria.

The other options are incorrect:

• L-J medium: This medium is used for culturing Legionella pneumophila, a fastidious bacterium that requires specific conditions for growth. While it can be used in an anaerobic chamber, it’s not specifically designed for anaerobic bacteria.
• Loeffler’s medium: This medium is primarily used for culturing Corynebacterium diphtheriae, the causative agent of diphtheria. It contains serum and egg yolk, but lacks the reducing agents necessary for anaerobic growth.
• Sabouraud’s agar: This medium is used for culturing fungi and yeasts. It’s acidic and low in nutrients, making it unsuitable for most anaerobic bacteria.

Answer: Protein polysaccharide complex

Exotoxins are pure proteins, not protein-polysaccharide complexes. Polysaccharides are complex carbohydrates, and their presence would alter the properties and functions of exotoxins, making them less efficient and specific.

The other options are incorrect:

• Heat labile: Most exotoxins are indeed heat labile, meaning they lose their activity when exposed to high temperatures. This is because heat can denature the protein structure, disrupting its ability to bind to target cells and cause harm.
• Highly potent: Exotoxins are some of the most potent toxins known, able to cause severe illness and death even in small amounts. Their high potency makes them effective weapons for bacteria to compete and evade host defenses.
• Has specific tissue affinity: Exotoxins have evolved to target specific tissues and disrupt their functions. This specificity arises from their protein structure and how it interacts with receptor molecules on target cells.

Answer: Widal reaction

The Widal reaction detects antibodies against Salmonella typhi, the causative agent of typhoid fever. Unlike the other options, it does not involve heterophil antigens. Heterophil antigens are molecules present in different species that share structural similarities, leading to cross-reactions between antibodies produced against one species and antigens from another.

The other options are incorrect:

• Forssman antigen antibody reaction: This reaction detects antibodies against Forssman antigen, found in various animal and plant tissues. It can be non-specific and interfere with other serological tests.
• Weil-Felix reaction: This reaction detects antibodies against Proteus bacteria, which share antigenic similarities with Rickettsia, the causative agent of typhus fever. It is a classic test for diagnosing typhus.
• Paul bunnel reaction: This reaction detects heterophile antibodies produced in response to Epstein-Barr virus infection, a common cause of infectious mononucleosis. It is a commonly used diagnostic test for this condition.

Answer: Increase antigenicity

Adjuvants are ingredients added to vaccines alongside antigens to boost the immune response. They do this by stimulating the immune system in various ways, leading to the production of more antibodies and immune cells specific to the vaccine antigen. This heightened immunity translates to better protection against the corresponding disease. Therefore, adjuvants increase the antigenicity of the vaccine, not decrease it.

The other options are incorrect:

• Increase toxigenicity: Adjuvants are designed to enhance the immune response against harmless antigens from vaccines, not amplify the toxicity of any potential toxins present.
• Reduce the antigenicity: This goes against the core purpose of adjuvants, which is to strengthen the immune response to the antigen. Weakening the antigenicity would essentially diminish the vaccine’s effectiveness.
• Reduce the toxigenicity: While some adjuvants might possess anti-inflammatory properties that indirectly influence toxin effects, their primary role is not to directly reduce toxigenicity.

Answer: 4

There are four subclasses of IgG in humans: IgG1, IgG2, IgG3, and IgG4. Each subclass has slightly different properties in terms of binding to Fc receptors, activating complement, and half-life in the bloodstream.

Incorrect Options:

• 1: IgG has four subclasses, not one. The subclasses are IgG1, IgG2, IgG3, and IgG4.
• 2: IgG has more than two subclasses. The correct number of subclasses for IgG is four.
• 3: IgG has four subclasses, not three. The subclasses are IgG1, IgG2, IgG3, and IgG4.

Answer: antigenic and non-toxic

Toxoids are derived from toxins, which are harmful substances produced by bacteria. However, during the process of creating a toxoid, the toxin is treated with chemicals or heat to neutralize its toxic properties while preserving its antigenic structure. This means the toxoid can still trigger the immune system to produce antibodies specific to the original toxin, but it cannot cause the harmful effects associated with the active toxin.

The other options are incorrect:

• Non-antigenic and toxic: This would negate the purpose of a toxoid, which is to stimulate an immune response.
• Non-antigenic and non-toxic: This wouldn’t be a very useful molecule at all, as it wouldn’t provide any benefit in terms of immunity or detoxification.
• Antigenic and toxic: This describes the original toxin, not the altered toxoid used in vaccines.

Answer: Structural differences

Human immunoglobulins, or antibodies, are divided into different classes (IgM, IgG, IgA, IgD, and IgE) based on structural differences. Each class has distinct structural characteristics, including the type of heavy chains (e.g., IgG has γ heavy chains, IgM has μ heavy chains) and functional differences, contributing to their specific roles in the immune system.

The other options are incorrect:

• Functional differences: While different immunoglobulin classes have distinct functions, these variations stem from their structural differences. The type of heavy chain dictates how the antibody interacts with antigens, complement proteins, and immune cells.
• Complement fixation: Complement fixation is a specific function associated with some immunoglobulin classes, particularly IgM and IgG. However, it’s not the basis for classifying all immunoglobulins.
• None of the above: While other factors like antigen specificity and light chain type can influence antibody function, the primary classification system relies on structural differences, specifically the heavy chain type.

Answer: 1 Month

IgG antibodies have a relatively long half-life compared to other immunoglobulin classes. The half-life of IgG antibodies is approximately 1 month. This extended half-life contributes to their effectiveness in providing prolonged immunity and protection against infections.

The other options are incorrect:

• 1 hour: The half-life of IgG antibodies is longer than 1 hour.
• 1 day: The half-life of IgG antibodies is longer than 1 day. They persist in the bloodstream for an extended duration.
• 1 week: While closer to the correct timeframe, the half-life of IgG antibodies is longer than 1 week. It is approximately 1 month.

Answer: Induration

Delayed-type hypersensitivity (DTH) skin tests are used to assess the body’s cell-mediated immune response to a specific antigen. A positive DTH reaction indicates that the body has been previously exposed to the antigen and has developed memory T cells that can react to it. The hallmark feature of a positive DTH reaction is induration, which is a palpable, firm, raised area at the injection site. This induration is caused by the accumulation of T cells and other immune cells around the antigen.

The other options are incorrect:

• Erythema: While redness (erythema) may be present around the injection site in both positive and negative DTH reactions, it is not specific enough to distinguish a positive test.
• Necrosis: Tissue death (necrosis) is not a typical feature of a positive DTH reaction and may indicate a severe allergic reaction or infection.
• Vasculitis: Inflammation of blood vessels (vasculitis) is not a characteristic feature of DTH reactions.

Answer: Sabouraud’s agar

Sabouraud’s agar is a specific medium designed for the growth and isolation of fungi. It provides a well-balanced combination of nutrients, like carbohydrates and nitrogen sources, with an acidic pH (around 5.6) that inhibits the growth of most bacteria. This makes it ideal for most fungi, which generally prefer acidic environments and readily utilize simple sugars like glucose for growth.

The other options are incorrect:

• Blood agar: This medium is primarily used for growing bacteria, as it contains red blood cells which some bacteria require for growth. Fungi typically don’t require blood-derived nutrients and may not grow well on this medium.
• Tissue culture: This technique is used for growing animal cells under controlled conditions in a laboratory. It generally uses specialized nutrient mixtures and is not suitable for most fungi.
• Thioglycollate medium: This medium is designed for culturing a wide range of bacteria, including anaerobic bacteria, and contains ingredients like sodium thioglycollate to scavenge oxygen. While some fungi can tolerate low oxygen conditions, this medium is not specifically formulated for fungal growth and may not support optimal growth for most species.

Answer: Clostridia

Robertson’s cooked meat medium is best suited for the cultivation of anaerobic bacteria, particularly Clostridia. It is a solid medium containing pieces of cooked meat and is used for the isolation and identification of anaerobic organisms.

The other options are incorrect:

• S. epidermidis: This is a common skin commensal bacterium and a facultative anaerobe. While it can tolerate anaerobic conditions, it prefers microaerophilic (low oxygen) or aerobic environments and wouldn’t specifically benefit from Robertson’s cooked meat medium.
• Choleria: This is a genus of Gram-negative, facultative anaerobic bacteria. They typically grow well on general-purpose media like blood agar and wouldn’t require the specific conditions offered by Robertson’s cooked meat medium.
• Mycobacterium: These are slow-growing bacteria with specific nutritional requirements. While some Mycobacterium species are facultative anaerobes, they require specialized media enriched with fatty acids and other unique components, not provided by Robertson’s cooked meat medium.

Answer: Oxidation

Dry heat denatures and damages cells through a process called oxidation. At high temperatures, dry heat reacts with the lipids and proteins in microorganisms, causing them to oxidize and lose their functionality. This disrupts essential cellular processes and ultimately leads to the death of the organism.

The other options are incorrect:

• Lysis: Lysis refers to the bursting of a cell caused by damage to its membrane. While high enough temperatures can eventually cause cell lysis, it is not the primary mechanism of action for dry heat sterilization.
• Hydrolysis of DNA: Hydrolysis involves the breakdown of a molecule with water. While heat can contribute to DNA damage, it primarily acts through oxidation rather than direct hydrolysis.
• Coagulation of proteins: Coagulation describes the process where proteins lose their solubility and form aggregated clumps. While this can occur under high heat, it’s not directly responsible for microbial death in dry heat sterilization. Oxidation causes more widespread and detrimental damage to cell components.

Answer: Epinephrine

Anaphylaxis is a severe, life-threatening allergic reaction requiring immediate intervention. Epinephrine is the first-line treatment because it can rapidly reverse the symptoms by constricting blood vessels, increasing heart rate, and opening airways. It acts directly on the body’s response to the allergen, mitigating the immediate and potentially fatal effects.

The other options are incorrect:

• Steroids: While steroids can reduce inflammation and help manage long-term allergic reactions, they are not effective in the immediate life-threatening phase of anaphylaxis. Their action takes time, making them unsuitable for the urgent need of anaphylaxis treatment.
• Antihistamines: Antihistamines counteract the effects of histamine, a chemical released during allergic reactions. They can alleviate symptoms like hives, itching, and swelling, but they don’t address the critical issues like airway constriction and circulatory collapse that occur in anaphylaxis. They can be used as adjunctive therapy after epinephrine to manage remaining symptoms.
• Antibiotics: Antibiotics target bacteria and have no effect on allergic reactions or the immune system response involved in anaphylaxis. They are completely irrelevant in this context.