MicroBiology MCQs with Answer and Explnation | Chapter 44

Answer: IgG1

Among the four human IgG subclasses, IgG1 has the highest serum concentration, typically composing around 65-75% of total IgG. This is due to its broad and potent effector functions in neutralizing viruses, activating complement, and opsonizing bacteria for phagocytosis.

The other options are incorrect:

• IgG2: Comprises roughly 20-25% of total IgG. Its primary role is in neutralizing bacterial polysaccharides and activating specific Fc receptors.
• IgG3: Represents only 5-10% of total IgG. It excels in activating the complement system against certain pathogens.
• IgG4: Makes up approximately 4-8% of total IgG. This subclass is involved in allergic responses and immune regulation.

Answer: Autoclaving

Autoclaving is the standard method for sterilizing glassware in a laboratory setting. It utilizes high-pressure steam (typically at 121°C for 15 minutes) to effectively kill all microorganisms, including bacteria, viruses, and spores, which are highly resistant to other methods.

The other options are incorrect:

• Hot air oven: While effective for dry heat sterilization, hot air ovens typically operate at temperatures below 200°C, insufficient for complete sterilization of glassware.
• Incineration: This method involves burning, which can damage or melt glassware and is generally not used for laboratory equipment.
• Formaldehyde: While a potent disinfectant, formaldehyde is primarily used for surfaces and not suitable for sterilizing glassware as it leaves residues and requires proper ventilation due to its toxic fumes.

Answer: All of the above

T-lymphocytes, also known as T cells, are crucial components of the adaptive immune system, playing a multifaceted role in defending the body against infections and diseases. They perform all the functions listed in the options:

• Production of interferon: T cells produce various types of interferons, signaling molecules that activate immune cells and inhibit viral replication.
• Lymphokine production: T cells secrete a diverse range of lymphokines (now called cytokines), which regulate immune responses, activate other immune cells, and direct the overall immune attack.
• Rosette formation: Certain T cell types can form rosettes with sheep red blood cells in a laboratory test used for their identification.

Answer: Carrier required for specific antibody production

Haptane serves as the carrier needed for the production of specific antibodies. In immunology, carriers are substances that are used to attach antigens and enhance the immune response, leading to the production of antibodies.

The other options are incorrect:

• Same as epitopes: While both haptens and epitopes can bind to antibodies, epitopes are specific regions on antigens that trigger an immune response. Haptens, even when attached to a carrier, do not directly induce antibody production.
• High molecular protein: This characteristic defines the carrier molecule, not the hapten itself. Haptens are typically small molecules like drugs, toxins, or environmental chemicals.

Answer: T lymphocytes

The delayed tuberculin skin test (TST) relies on a cell-mediated immune response driven by T lymphocytes. When someone previously encountered the tuberculosis (TB) bacteria, their T cells develop a memory and become sensitized to specific TB antigens. Upon TST administration, these sensitized T cells accumulate at the injection site, leading to a localized inflammatory reaction (redness, swelling) peaking 48-72 hours later. This delayed response signifies past or present TB infection.

The other options are incorrect:

• B lymphocytes: While B cells play a crucial role in generating antibodies, they are not directly involved in the cell-mediated response measured by the TST.
• Monocytes: These immune cells contribute to phagocytosis and antigen presentation, but they are not the primary effector cells in the TST reaction.
• Histiocytes: These are tissue macrophages that can activate T cells, but they are not the main participants in the delayed hypersensitivity response triggered by the TST.

Answer: Slide flocculation test

VDRL stands for Venereal Disease Research Laboratory. It is a slide flocculation test used for the screening of syphilis. In this test, patient serum is mixed with a reagent on a glass slide, and the appearance of flocculation (clumping) is observed.

The other options are incorrect:

• Tube flocculation test: VDRL is specifically a slide flocculation test, not a tube flocculation test.
• Tube agglutination test: VDRL is not a tube agglutination test. It is a slide flocculation test for syphilis screening.
• Latex agglutination test: VDRL is not a latex agglutination test. It is a slide flocculation test used in the diagnosis of syphilis.

Answer: Mucosal epithelium

The secretory piece of IgA, abbreviated as SC, is a crucial component of secretory IgA (sIgA), the most abundant antibody found in mucosal secretions like saliva, tears, and intestinal fluids. Unlike “regular” IgA found in blood, sIgA has an extra layer of protection: the secretory component. This additional layer, formed by the mucosal epithelium lining our body’s cavities and surfaces, shields sIgA from harsh environmental conditions and enzymatic degradation.

The other options are incorrect:

• T-cells: Primarily responsible for cell-mediated immunity, T-cells do not synthesize antibody components like the secretory piece.
• B-cells: While B-cells produce the IgA molecule itself, they don’t synthesize the secretory component. This crucial addition happens in the mucosal epithelium.
• Lymph nodes: Lymph nodes are crucial filtering centers for the immune system but don’t directly synthesize the secretory piece. They play a role in IgA maturation and trafficking, but not its initial construction.

Answer: 2 light, 2 heavy chains

Immunoglobulins (also known as antibodies) are Y-shaped protein molecules composed of two light chains and two heavy chains. These chains are linked together by disulfide bonds and interact in specific ways to form the antibody’s antigen-binding domain. The combination of two light chains and two heavy chains provides structural stability and flexibility for effective antigen recognition and binding.

The other options are incorrect:

• 1 heavy, 2 light chains: While this arrangement appears logical, it is incorrect. Immunoglobulins always have an equal number of light and heavy chains (2:2).
• 1 light, 1 heavy chain: This configuration results in a much smaller molecule lacking the characteristic Y-shape and antigen-binding ability of antibodies.
• 3 light, 1 heavy chain: This combination is not found in any known type of immunoglobulin. The standard structure remains two light chains and two heavy chains.

Answer: Epitope

The epitope is the precise region on an antigen molecule that specifically interacts with the immune system, particularly with antibodies and T cell receptors. This “docking site” on the antigen determines its immunogenicity and triggers the targeted immune response. Imagine antigens as puzzle pieces, and epitopes are the specific knobs and grooves that antibodies and T cells recognize and bind to.

The other options are incorrect:

• Clone: This refers to a genetically identical population of cells derived from a single ancestor cell. While B cells producing antibodies against a specific epitope can be considered clones, it’s not the epitope itself but rather the result of the immune response to it.
• Idiotope: This is a specific type of epitope found on antibody molecules themselves. Idiotopes can be recognized by other immune cells and play a role in regulating the immune response. However, idiotopes are not the primary target of the immune system but rather a part of the antibody itself.
• Paratope: This is the complementary region on an antibody molecule that specifically fits and binds to an epitope. While crucial for the antigen-antibody interaction, the paratope is the “lock” side, not the “key” represented by the epitope on the antigen.

Answer: Opsonisation

Opsonization is the process where molecules bind to the surface of pathogens (antigens), making them more easily recognizable and engulfable by phagocytes (white blood cells that ingest foreign particles). These opsonizing molecules act like “tags” that signal to phagocytes that the antigen is a target for destruction.

The other options are incorrect:

Incorrect Options:

• Chemotaxis: This refers to the directed movement of immune cells towards a source of chemical attractants, such as those released by infected cells. While chemotaxis helps phagocytes reach the site of infection, it’s not the same as opsonization, which directly enhances their ability to engulf pathogens.
• Decoding: This term doesn’t apply to the immune system or phagocytosis. It might be related to other biological processes like genetic decoding, but it’s not relevant to the given context.
• CFT: This abbreviation could stand for various things, but none of them are directly related to opsonization. It’s important to ensure clarity and context when using abbreviations.

Answer: IgM

The first immunoglobulin produced by the fetus in response to infection is IgM. This usually occurs around 20 weeks of gestation. Unlike IgG, IgM cannot cross the placenta from the mother to the fetus, so the fetus must develop its own immune response to produce it.

The other options are incorrect:

• IgG: This is the most abundant immunoglobulin in the blood and is responsible for long-term immunity. However, it is primarily acquired from the mother through the placenta and not produced by the fetus itself in response to an infection.
• IgA: This immunoglobulin is present in mucosal secretions and plays a role in protecting the respiratory and digestive tracts. While the fetus can produce IgA later in development, it is not the first immunoglobulin produced in response to infection.
• IgD: This immunoglobulin is present in small amounts on the surface of B cells and is involved in B cell activation. It is not typically produced in response to infection, especially not in the fetus.

Answer: Both Involved in multidrug resistance transfer & Involved in conjugation

Plasmids are small, circular DNA molecules that exist within bacteria and some other organisms. They can replicate independently of the host cell’s chromosome and often carry genes that provide beneficial traits. Among these beneficial traits, two key functions stand out:

• Multidrug resistance transfer: Many plasmids harbor genes that encode resistance to antibiotics and other drugs. These genes can be transferred from one bacterial cell to another through a process called conjugation, allowing the recipient cell to acquire resistance as well.
• Conjugation: Plasmids play a crucial role in conjugation, a type of horizontal gene transfer where bacteria physically connect and exchange genetic material. Plasmids often contain specific genes that facilitate the formation of the pilus, a hair-like structure that bridges the gap between two bacterial cells during conjugation.

The other options are incorrect:

• Imparts capsule formation: While some bacterial capsules may be encoded by genes located on plasmids, this is not a universal function of plasmids.
• Imparts pili formation: Similar to capsule formation, not all pili are encoded by plasmids. Some bacteria possess pili encoded by their chromosomal DNA.

Answer: ETO gas

Modern operating theatres are sterilized using ethylene oxide (ETO) gas. This method is highly effective against all types of microorganisms, including bacteria, viruses, and spores, due to its ability to penetrate deeply into medical equipment and materials. ETO sterilization is typically performed in cycles at specific temperatures and humidity levels, ensuring thorough decontamination.

The other options are incorrect:

• Carbolic acid spraying: While once used as a disinfectant, carbolic acid (phenol) is not considered an effective modern method for sterilizing operating theatres due to its limited action spectrum and potentially toxic fumes.
• Washing with soap and water: Washing with soap and water is suitable for basic cleaning but cannot achieve the level of sterilization required for surgical environments.
• Formaldehyde fumigation: While effective against some microbes, formaldehyde fumigation has disadvantages like strong odor, irritation to respiratory system, and prolonged aeration time, making it less suitable for routine sterilization of operating theatres.

Answer: Incineration

Incineration is the most recommended method for disposing of hospital dressings due to its effectiveness in destroying all types of microorganisms, including bacteria, viruses, and spores. This is crucial for preventing the spread of infections and protecting public health.

The other options are incorrect:

• Dumping: This is highly irresponsible and dangerous. Dumping hospital waste can contaminate the environment and potentially expose people to harmful pathogens.
• Autoclaving: While effective for sterilizing instruments and reusable materials, autoclaving is not suitable for disposing of contaminated waste like dressings. It’s an energy-intensive process and doesn’t fully destroy all pathogens.
• Burying: Burying contaminated waste can potentially contaminate soil and groundwater, posing environmental and health risks. Additionally, some pathogens may survive burial and resurface later.

Answer: Sarcina

Only Sarcina bacteria are typically arranged in cubical packets of eight cocci. This specific arrangement is often referred to as a “sarcina packet” or “packet cocci.”

The other options are incorrect:

• Staphylococcus: These cocci typically cluster in grape-like bunches or irregular groups, not specifically in cubical packets.
• Micrococcus: While also cocci, Micrococcus usually appears in tetrads (four) or pairs, not cubical packets of eight.
• Aerococcus: These cocci form pairs or tetrads, and may sometimes form chains, but not the characteristic cubical packets of Sarcina.

Answer: Stationary phase

Sporulation, the process by which certain bacteria form highly resistant spores for survival under harsh conditions, typically occurs in the stationary phase of bacterial growth. During this phase, nutrients become limited, and cell growth slows down or stops. To cope with these unfavorable conditions, some bacteria like Bacillus and Clostridium undergo sporulation, transforming into dormant spores that can remain viable for extended periods.

The other options are incorrect:

• Lag phase: This is the initial phase of growth when bacteria adapt to the new environment and prepare for active replication. Sporulation doesn’t usually occur during this phase.
• Log phase: This is the phase of rapid exponential growth, and most bacteria are focused on multiplying, not forming spores.
• Decline phase: This is the final phase when nutrients are depleted and cell death increases. While some spores may have already formed in the stationary phase, sporulation itself doesn’t predominantly occur in this phase.

Answer: T-lymphocytes

Graft versus host disease (GVHD) is a serious complication that can occur after a stem cell or bone marrow transplant. In this procedure, healthy cells from a donor are introduced into the recipient’s body to replace diseased or damaged ones. However, sometimes the donor’s T-lymphocytes (a type of white blood cell) can mistakenly attack the recipient’s tissues, mistaking them for foreign invaders. This reaction is known as GVHD.

The other options are incorrect:

• B-Lymphocytes: While B-cells play a role in the immune system, they are not directly involved in the cell-mediated attack characteristic of GVHD. They primarily produce antibodies to fight pathogens.
• Monocytes: These cells are phagocytes that engulf and digest foreign particles, but they are not the primary effector cells in GVHD.
• Leukocytes: This is a broader term encompassing all white blood cells, including lymphocytes, monocytes, and neutrophils. While all play a role in the immune system, T-lymphocytes specifically are responsible for the attack in GVHD.

Answer: Spirochetes

Smith-Noguchi medium is a specific type of bacterial culture media designed to support the growth of spirochetes, a group of spiral-shaped bacteria. These bacteria typically require rich and complex media containing fresh animal tissue, like rabbit kidney, spleen, or testes, to provide essential nutrients for their growth. Smith-Noguchi medium fulfills this requirement and is primarily used to isolate and cultivate various pathogenic and non-pathogenic spirochete species,

The other options are incorrect:

• Salmonella: While belonging to the same bacterial domain as spirochetes, Salmonella are different in their growth requirements and are typically cultured on different media like MacConkey agar or Hektoen enteric agar.
• Klebsiella: These are rod-shaped bacteria belonging to the genus Klebsiella and require different media suitable for their specific nutritional needs, like lactose agar or blood agar.
• Bacillus: These are also rod-shaped bacteria belonging to the genus Bacillus and often grow on simple media like nutrient broth or tryptic soy agar. They don’t require the complex and enriched environment provided by Smith-Noguchi medium.

Answer: Borrelia

Noguchi’s medium is a specific type of culture media enriched with fresh animal tissue. It’s specifically designed to support the growth of microaerophilic and anaerobic bacteria, particularly spirochetes. Borrelia, a genus of spirochete bacteria, includes the infamous B. burgdorferi, the causative agent of Lyme disease. Therefore, Noguchi’s medium is primarily used for isolating and cultivating Borrelia species.

The other options are incorrect:

• Bordetella: While Bordetella are also microaerophilic bacteria, they belong to a different genus and have different nutritional requirements. Standard Bordet-Gengou medium, not Noguchi’s, is used for their isolation.
• Brucella: Brucella are facultative intracellular bacteria, not microaerophilic like Borrelia. They require different culture media enriched with specific nutrients, like Farrell’s agar or trypticase soy agar.

Answer: India ink preparation

Negative staining techniques highlight the background, leaving the target specimen unstained and visible. While the other options involve applying stains directly to the specimen, India ink preparation utilizes a negative stain, usually a dark ink, to fill the background around unstained organisms like bacteria. This creates a clear contrast for visualizing their morphology under a microscope.

The other options are incorrect:

• Gram’s staining: This is a differential staining technique, employing a series of dyes to categorize bacteria based on their cell wall composition. Both Gram-positive and Gram-negative bacteria take up specific stains, making them directly visible.
• Fontana’s staining: This method uses silver nitrate to stain spirochete bacteria, like Treponema pallidum, the causative agent of syphilis. The spirochetes appear dark and twisted against a light background, similar to India ink, but the stain directly interacts with the organism, not just the surrounding space.
• Ziehl-Neelsen staining: This technique specifically targets acid-fast bacteria, like Mycobacterium tuberculosis, using a fuchsin dye and a strong acid-alcohol decolorizer. The bacteria retain the red stain, appearing bright against a blue background, again a direct staining method, not negative staining.

Answer: Lophotrichate

Bacteria can be categorized based on the number and arrangement of their flagella, the hair-like appendages responsible for locomotion. Lophotrichate describes bacteria with a tuft of flagella at one end of their cell. This tuft can resemble a pom-pom or plume, contributing to their characteristic swimming patterns.

The other options are incorrect:

• Monotrichate: These bacteria have a single flagellum located at one end. While similar to lophotrichate in location, the presence of only one flagellum distinguishes them.
• Peritrichate: These bacteria have numerous flagella distributed randomly over their entire surface, creating a “fuzzy” appearance. The distribution pattern differentiates them from lophotrichate, which concentrates flagella in a single tuft.
• Bipolar: This descriptor refers to an arrangement where flagella are present at both ends of the bacteria, not just one. This distinction helps differentiate them from lophotrichate, where the tuft remains focused at a single pole.

Answer: Increased Virulence

Exaltation refers to an increase in the virulence or pathogenicity of a microorganism. When a microbe undergoes exaltation, it becomes more potent in causing disease. This may involve an enhancement of factors such as the ability to invade host tissues, evade the host immune system, or produce toxins.

The other options are incorrect:

• Decreased Virulence: This is the opposite of what exaltation signifies. While some mutations might indeed decrease virulence, the term “exaltation” itself implies an enhancement.
• No Change: Again, not consistent with the meaning of exaltation, which indicates a change in state, specifically towards greater potentiality.
• None: This doesn’t provide any specific information about the relationship between exaltation and virulence.

Answer: IgM

During a primary immune response, IgM is the first immunoglobulin class produced by B cells in response to exposure to a new antigen. This means it’s the first antibody released to fight an infection or vaccine.

The other options are incorrect:

• IgD: IgD plays a role in B cell development and maturation, but it’s not typically found in high amounts in the bloodstream after primary immunization.
• IgE: IgE is primarily involved in allergic reactions and defense against parasites. While it can be present in small amounts after primary immunization, it’s not the dominant antibody class.
• IgG: IgG is the predominant antibody class in the blood and provides long-term immunity. However, it takes longer than IgM to reach significant levels after first exposure to an antigen.

Answer: Orally administered

The BCG vaccine is not administered orally. It is given either intradermally (injection into the skin) or intravesically (injection into the bladder).

The other options are incorrect:

• Live vaccine: This is true. The BCG vaccine contains a weakened strain of live bacteria called Mycobacterium bovis.
• T.B vaccine: This is true. BCG stands for Bacillus Calmette-Guérin, and it is used to prevent tuberculosis (TB).
• All of the above: This is false because the BCG vaccine is not given orally.

Answer: using Bacillus stearo thermo philus

Bacillus stearothermophilus (often abbreviated as B. stearo) is the standard biological indicator for moist heat sterilization in laboratories. This means it’s a microorganism that is highly resistant to heat and whose death within the autoclave confirms that the sterilization process was effective.

The other options are incorrect:

• Using non-pathogenic strain of Clostridium tetani: While Clostridium tetani spores are also heat-resistant, they are not as resistant as B. stearo. Using them as indicators could give false positives (thinking sterilization is successful when it’s not).
• Using chemical indicator: Chemical indicators like melt strips or spore strips can be used as additional checks, but they only confirm that the proper temperature was reached, not that all microorganisms have been killed. B. stearo provides a more direct test for sterility.
• Using methylene blue: Methylene blue is a dye used to stain dead cells, not a sterility indicator. It can’t differentiate between live and dead bacteria, making it unreliable for verifying sterilization.

Answer: activate complement by the alternate pathway

Endotoxins are lipopolysaccharides (LPS) found in the outer membrane of the cell wall of Gram-negative bacteria. One of their characteristics is the ability to activate the complement system, primarily by the alternate pathway. This activation can contribute to the host’s immune response and inflammation.

The other options are incorrect:

• Are proteins: Endotoxins are not proteins; they are complex molecules composed of lipids and polysaccharides.
• Are heat labile: Endotoxins are heat-stable, unlike many exotoxins that can be inactivated by heat.
• Are highly antigenic: Endotoxins are generally considered to be less antigenic than exotoxins. Exotoxins are proteins and are often highly immunogenic, while endotoxins are less so.

Answer: membrane

Membrane: Detergents are amphiphilic molecules, meaning they have both hydrophilic (water-loving) and hydrophobic (water-hating) ends. The hydrophobic ends disrupt the phospholipid bilayer of the cell membrane, causing leakage of cellular contents and ultimately cell death. This is the primary mechanism by which detergents kill bacteria.

The other options are incorrect:

• Wall: While some detergents can damage the cell wall in some bacteria, it’s not their primary target and not as effective for killing. The cell wall is a less critical structure compared to the membrane, and some bacteria lack it altogether.
• Nucleus: Detergents don’t typically target the nucleus directly. The nucleus houses the genetic material of the bacteria, and damaging it wouldn’t necessarily lead to immediate cell death.
• Capsule: Capsule is an outermost layer in some bacteria and may be affected by detergents, but it’s not the main site of action for their bactericidal effect. The capsule is primarily a protective barrier and doesn’t play a crucial role in bacterial survival.

Answer: Arthus reaction

Arthus reaction, also known as Type III hypersensitivity, is a delayed-type hypersensitivity reaction not primarily mediated by histamine release. Instead, it involves immune complexes formed by antigen-antibody interactions, resulting in inflammation and tissue damage. Although histamine might be involved to some extent, it’s not the main driving force of the reaction.

The other options are incorrect:

• Urticaria: While some forms of urticaria (hives) can be non-immunological and not involve histamine, most types, including allergic urticaria, are classified as Type I hypersensitivity reactions, heavily reliant on histamine release from mast cells and basophils.
• Asthma: The most common form of asthma, allergic asthma, falls under Type I hypersensitivity and similarly hinges on IgE-mediated histamine release and airway constriction.
• Anaphylaxis: This severe, potentially life-threatening reaction belongs to Type I hypersensitivity and is characterized by a rapid release of histamine and other inflammatory mediators from mast cells.

Answer: CH2 domian

The binding site for the complement protein C1q on the IgG molecule is located in the CH2 domain of the Fc region. This domain, specifically residues within it, forms specific interactions with C1q, triggering the classical complement activation pathway.

The other options are incorrect:

• VL domain: The VL domain belongs to the variable region of the antibody responsible for antigen binding, not complement activation.
• CL domain: The CL domain also lies within the variable region and doesn’t participate in complement binding.
• CH1 domain: While the CH1 domain plays a role in Fc receptor binding, it doesn’t interact with C1q.

Answer: IgA

Secretory immunoglobulin A (sIgA) is the most abundant antibody class found in mucosal secretions, such as tears, saliva, colostrum, and mucus lining the respiratory, gastrointestinal, and urogenital tracts. It plays a crucial role in the first line of defense against pathogens at these mucosal surfaces.

The other options are incorrect:

• IgE: IgE is primarily involved in allergic reactions and defense against parasites. While it can be present in small amounts in mucosal secretions, it’s not the dominant antibody class and doesn’t have the same protective functions as sIgA.
• IgM: IgM is the first antibody produced in a primary immune response, but it’s not the main antibody found in mucosal secretions. sIgA is more suitable for long-term protection at mucosal surfaces due to its unique properties
• IgD: IgD is mainly involved in B cell development and maturation. It’s not found in significant amounts in mucosal secretions and doesn’t contribute significantly to mucosal immunity.

Answer: Systemic arthus reaction

Systemic arthus reaction: This type III hypersensitivity reaction is triggered by immune complexes formed between antigen and antibody, similar to what happens in serum sickness. These complexes deposit in various tissues, leading to inflammation, fever, rash, and joint pain. Both are delayed-type reactions occurring several days after exposure.

The other options are incorrect:

• Anaphylactic: This is a type I hypersensitivity reaction caused by immediate and massive release of histamine and other inflammatory mediators from mast cells. While serum sickness can have severe symptoms, it doesn’t involve the same rapid mast cell degranulation as anaphylaxis.
• Angioneurotic edema: This can be a symptom of both anaphylaxis and serum sickness, but it’s not the defining characteristic of either. It refers to localized swelling of tissues due to fluid accumulation.
• Cell-mediated immunity: This type of immune response involves T cells directly attacking infected cells or foreign agents. Serum sickness, however, is primarily driven by humoral immunity (antibodies) and immune complexes.

Answer: Plasma cells

Immunoglobulins, also known as antibodies, are secreted by plasma cells. These are specialized B lymphocytes that have transformed and matured to become antibody-producing factories. After B cells encounter an antigen and undergo activation, they differentiate into plasma cells that can churn out large quantities of specific antibodies tailored to attack that particular antigen.

The other options are incorrect:

• Macrophages: These are phagocytic cells, which engulf and destroy pathogens, but they don’t produce antibodies.
• T-cells: These are lymphocytes involved in cell-mediated immunity, directly attacking infected cells but not secreting antibodies.
• Neutrophils: These are another type of phagocytic cell involved in the early stages of inflammation, but also don’t produce antibodies.

Answer: Treponema

A darkfield microscope is specifically useful for visualizing Treponema bacteria, which are motile and have a characteristic spiral shape. This makes them ideal candidates for darkfield microscopy, where unscattered light illuminates the organism against a dark background, enhancing its visibility.

The other options are incorrect:

• Actinomyces: While these bacteria can be seen under a microscope, they are not motile and their morphology wouldn’t be significantly enhanced by darkfield microscopy.
• Streptococcus: These bacteria are typically non-motile and appear as cocci (clusters) under a microscope, not benefiting from darkfield visualization.
• Mycobacterium: Mycobacteria are often weakly staining and require specific staining techniques for proper visualization. They are generally not motile and wouldn’t benefit significantly from darkfield microscopy.

Answer: Vegetative forms

Disinfection is the process of eliminating or reducing the number of microorganisms on a surface to a level that is considered safe. It primarily targets vegetative forms of microorganisms, which include actively growing and reproducing bacteria, viruses, and fungi. Disinfection does not necessarily eliminate spores.

The other options are incorrect:

• Spore forms: Disinfection is generally not as effective against spore forms as it is against vegetative forms. Spores are more resistant and often require specialized techniques or agents for their elimination.
• Both of the above: While disinfection primarily targets vegetative forms, it is generally less effective against spore forms. The statement “both of the above” is not accurate in the context of general disinfection.
• None of the above: Disinfection is specifically aimed at eliminating or reducing vegetative forms of microorganisms on surfaces.

Answer: Placental transfer of antibodies

Placental transfer of antibodies is a prime example of naturally acquired passive immunity. During pregnancy, maternal antibodies pass through the placenta and into the developing fetus, providing the newborn with temporary protection against various infections until their own immune system matures. This passive immunity can last for several months after birth, shielding the infant from potential pathogens.

The other options are incorrect:

• Hepatitis vaccination: This is an example of active immunity, where the body actively produces its own antibodies against the hepatitis virus in response to the vaccine.
• Gamma globulin injection: This is a form of artificial passive immunity, where pre-made antibodies are injected into a person to provide immediate protection against a specific disease.
• Immune blood transfusion: This is also a form of artificial passive immunity, where blood containing antibodies from an immune donor is transfused into a recipient to provide immediate protection against a specific disease.

Answer: Selenite F Broth

Enrichment media are designed to selectively encourage the growth of specific microorganisms while inhibiting the growth of others. Selenite F Broth is an example of an enrichment medium commonly used for the isolation of Salmonella and Shigella from clinical samples. It contains selective agents that help in suppressing the growth of normal flora and favor the growth of the target pathogens.

The other options are incorrect:

• Blood agar: Blood agar is a differential medium that supports the growth of a wide range of microorganisms, including many bacteria. However, it is not typically considered an enrichment medium.
• MacConkey agar: MacConkey agar is a selective and differential medium that is commonly used for the isolation of Gram-negative bacteria, particularly Enterobacteriaceae. While it is selective, it is not classified as an enrichment medium.
• Nutrient broth: Nutrient broth is a general-purpose medium that supports the growth of a wide variety of microorganisms. It is not designed to selectively enrich specific bacteria and is not considered an enrichment medium.

Answer: Endoplasmic reticulum

The endoplasmic reticulum, specifically the rough ER, is the primary site of antibody synthesis in plasma cells. It houses ribosomes that translate the mRNA instructions for antibody production into protein chains. These chains then undergo folding and modification in the ER before being transported to the Golgi apparatus for further processing and packaging for secretion.

The other options are incorrect:

• Golgi body: The Golgi apparatus plays a crucial role in processing and packaging mature antibody molecules for secretion, but it’s not the initial site of synthesis. It receives the already-made antibody chains from the ER and modifies them with carbohydrates and other molecules.
• Nucleus: The nucleus houses the DNA blueprint for antibody production, but it doesn’t directly synthesize the proteins. It transcribes the DNA into mRNA, which then moves to the ER for translation into protein chains.
• Mitochondria: Mitochondria are responsible for energy production in the cell, not protein synthesis. They have no role in antibody production.

Answer: IgE

Immunoglobulin E (IgE) is the main immunoglobulin implicated in atopy and anaphylaxis. Its role involves binding to allergens and triggering mast cell degranulation, releasing inflammatory mediators causing the characteristic symptoms of these conditions.

The other options are incorrect:

• IgM: IgM is primarily involved in early immune responses and agglutination (clumping) of pathogens. While elevated IgM levels can sometimes be associated with allergies, it’s not the key player in atopy and anaphylaxis.
• IgG: IgG is the most abundant immunoglobulin and plays a crucial role in opsonization and antibody-dependent cell-mediated cytotoxicity (ADCC). While some IgG subclasses can contribute to allergic inflammation, IgE plays the central role in the immediate hypersensitivity reactions like those seen in atopy and anaphylaxis.
• IgA: IgA is primarily found in mucosal secretions and protects against infections at mucosal surfaces. While some IgA subclasses can be involved in allergic reactions, especially food allergies, their role is less prominent compared to IgE in atopy and anaphylaxis.

Answer: 121°C 15 mts. x 15 lbs pr.

The standard conditions for autoclave sterilization involve exposing the items to a temperature of 121°C (250°F) for 15 minutes at a pressure of 15 pounds per square inch (psi). This combination of time, temperature, and pressure ensures the destruction of a wide range of microorganisms, including spores.

The other options are incorrect:

• 140°C x 2 hrs. x 10 lbs pressure: While higher temperatures can reduce sterilization time, 140°C is unnecessarily high and could damage heat-sensitive materials.
• 121°F x 15 mts. x 15 lbs pressure: The temperature needs to be in Celsius for sterilization in an autoclave. 121°F is equivalent to 49°C and insufficient for proper sterilization.
• 121°F x 15 sec. x 15 lbs pressure: 15 seconds is far too short a time for effective sterilization even at the correct temperature.

Answer: Spleen and the lymph nodes

The production of antibodies occurs in specialized immune cells called B lymphocytes, or B cells. These cells mature in the bone marrow and then migrate to peripheral lymphoid organs, where they further differentiate and produce antibodies. The spleen and lymph nodes are crucial sites for the activation, proliferation, and differentiation of B cells, leading to the production of antibodies in response to antigens.

The other options are incorrect:

• Heart and the liver: These organs are crucial for other functions like circulation and metabolism but don’t play a primary role in antibody production.
• Brain and the meninges: The brain, protected by the meninges, is responsible for the nervous system but hasn’t been identified as a major site for antibody production.
• Thymus and the appendix: The thymus plays a vital role in developing T lymphocytes, another type of immune cell, but is not involved in antibody production. The appendix has functions in the digestive system and lacks significant antibody production activity.

Answer: Lysozyme

Lysozyme is the primary antibacterial substance present in both eggs and saliva. It’s an enzyme that attacks the cell walls of bacteria, specifically Gram-positive bacteria, by breaking down their peptidoglycan layer. This weakens and disrupts the bacterial structure, leading to cell death.

The other options are incorrect:

• Secretozyme: This term isn’t a specific biological molecule. It might be used vaguely to refer to any enzyme secreted by cells, but it doesn’t have a well-defined meaning like lysozyme.
• Albumin: Albumin is a protein found in both eggs and saliva, but it doesn’t have antibacterial properties. Its main function is transporting various molecules throughout the body.
• Isozyme: Isozymes are different forms of the same enzyme with slight variations in their structure and function. While lysozyme does have isozymes, the term itself doesn’t specifically point to the antibacterial property.

Answer: Remove microbes

While soap can have some antimicrobial properties, its primary function as an antiseptic lies in its ability to physically remove microbes from the skin’s surface. The soapy lather helps trap and suspend dirt, oils, and microorganisms, allowing them to be rinsed away with water. This mechanical removal significantly reduces the number of microbes on the skin, thereby reducing the risk of infection.

The other options are incorrect:

• Kill microbes: While some soaps do contain ingredients with antimicrobial properties, these are often not effective against all types of microorganisms and may require longer contact times than simply washing with soap and water. Additionally, overuse of such soaps can contribute to antimicrobial resistance.
• Inhibit microbial growth: Although some soap components can slow down the growth of certain bacteria, their effect is usually temporary and not as effective as physically removing the microbes.
• Dehydrate microbial cells: While soap can disrupt the outer membranes of some microorganisms, it’s not the primary mechanism of its action. The physical removal through lather and rinsing is still the main factor in reducing microbial load.

Answer: Resistance transfer factor (RTF)

Resistance transfer factor (RTF) is a genetic element in bacteria that plays a role in the transfer of multiple drug resistance genes between bacterial cells. It is associated with the ability of bacteria to acquire resistance to various antibiotics and is a key factor in the development of multiple drug resistance.

The other options are incorrect:

• Colicigenic factor (Col): Colicigenic factors are plasmids that carry genes for the production of colicins, which are bacteriocins toxic to other bacteria. They are not specifically associated with multiple drug resistance.
• Fertility factor (F+): Fertility factors (F plasmids) are involved in bacterial conjugation, facilitating the transfer of genetic material between bacterial cells. While conjugation can contribute to the spread of resistance genes, F plasmids are not directly associated with multiple drug resistance in the same way as RTF.
• All of the above: This option is incorrect because not all factors mentioned (Col and F+) are directly associated with multiple drug resistance. The major factor involved in multiple drug resistance is the Resistance transfer factor (RTF).

Answer: Disinfectant

The Rideal-Walker test was historically used to determine the disinfecting power of a given substance, specifically compared to phenol, a standard disinfectant. It measured the relative ability of the test substance to kill Salmonella typhi under specific conditions.

The other options are incorrect:

• Moist heat sterilization: Moist heat sterilization uses saturated steam under pressure to kill all forms of microbial life, including bacteria, viruses, and spores. The Rideal-Walker test doesn’t assess the effectiveness of sterilization methods themselves.
• Antibiotics: Antibiotics are drugs that target and inhibit the growth or kill specific bacteria. The Rideal-Walker test measures the broad-spectrum disinfectant activity against a specific organism under defined conditions, not the targeted action of antibiotics.
• Dry heat sterilization: Dry heat sterilization uses hot air at high temperatures to kill microorganisms. Similar to moist heat sterilization, the Rideal-Walker test doesn’t directly assess the effectiveness of this specific method.

Answer: All pathogenic and non-pathogenic microorganisms killed

Sterilization is a process that completely eliminates all forms of life, including bacteria, viruses, fungi, and their spores. This means it destroys both pathogenic microorganisms (those that cause disease) and non-pathogenic ones (those that don’t cause disease).

The other options are incorrect:

• Pathogens killed but spores are not affected: This is disinfection, not sterilization. While disinfection can kill many pathogens, it may not be effective against all microorganisms, especially highly resistant spores.
• Only pathogenic micro-organisms killed: This is selective decontamination, a process targeting specific harmful microorganisms while leaving beneficial ones intact. However, it doesn’t achieve complete elimination of all life forms.
• Non-pathogenic killed: This is inaccurate as sterilization aims to eliminate all microorganisms, regardless of their potential to cause harm.

Answer: Time-consuming

Dry heat sterilization is generally more time-consuming compared to autoclaving. Autoclaves use steam under pressure to achieve high temperatures quickly, which is more effective for sterilizing a variety of materials. In contrast, dry heat sterilization relies on hot air and requires a longer exposure time to achieve the same level of microbial destruction.

The other options are incorrect:

• Less effective: While dry heat sterilization may take longer, it can be equally effective in achieving sterilization under the right conditions.
• Causes instruments to rust: Dry heat sterilization is less likely to cause rusting of instruments compared to steam-based methods like autoclaving. Rusting is more commonly associated with exposure to moisture.
• Causes sharp instruments to dull: Sterilization methods, whether dry heat or autoclaving, should not cause instruments to dull if proper procedures and conditions are followed. Dulling can be associated with factors such as improper cleaning or handling.

Answer: Delayed reaction

Anaphylaxis is characterized by a rapid onset and progression of severe allergic symptoms involving multiple organ systems. It typically occurs within minutes to seconds of exposure to the allergen. Therefore, a delayed reaction is not a feature of anaphylaxis.

The other options are incorrect:

• Immediate reaction: As previously mentioned, anaphylaxis is characterized by its rapid onset and progression.
• Passive transfer by serum: Antibodies specific to the allergen can be transferred from an anaphylactic individual to a non-sensitized individual, inducing anaphylaxis in the recipient. This demonstrates the involvement of circulating antibodies in the reaction.

Answer: Autoclave

An autoclave is a device that uses steam under pressure to achieve high temperatures, typically around 121-132°C, which is effective in destroying bacterial spores. Autoclaving is a widely used method for sterilization in laboratories, hospitals, and other settings where complete microbial elimination is required.

The other options are incorrect:

• Boiling at 100°C: Boiling at 100°C is not sufficient to consistently destroy bacterial spores. While it may kill vegetative bacteria, spores are more resistant to heat.
• Disinfection by hypochlorite solution: Disinfection with hypochlorite solution is effective against many microorganisms, but bacterial spores, especially those of certain species, can be resistant to chemical disinfection.
• Pasteurization: Pasteurization involves heating at temperatures below those used in autoclaving and is primarily aimed at reducing the number of vegetative bacteria and pathogens, not necessarily destroying bacterial spores.

Answer: IgA

Immunoglobulin A (IgA) is the class of immunoglobulins found in exocrine secretions, including tears, saliva, mucus, and breast milk. It plays a crucial role in mucosal immunity, providing protection against infections at mucosal surfaces. IgA exists in two forms: IgA1 and IgA2, and it can be found as a dimer (secretory IgA) in secretions.

The other options are incorrect:

• IgG: While the most abundant immunoglobulin in blood, IgG is not well-suited for exocrine secretions due to its susceptibility to proteases.
• IgD: Primarily involved in B cell activation and signaling, IgD is not abundant in exocrine secretions.
• IgM: Mainly present in blood and lymph, IgM plays a role in early immune response but is not well-adapted for exocrine environments.

Answer: CLED Agar

CLED Agar (Cystine-Lactose-Electrolyte-Deficient Agar) is the best medium for urine culture. It is a selective and differential medium designed to inhibit the swarming of Proteus species and to differentiate between lactose-fermenting and non-lactose-fermenting bacteria commonly found in urine.

The other options are incorrect:

• Blood Agar: Blood Agar is a general-purpose medium used for the cultivation of a wide variety of microorganisms. It is not specific for urine culture, and it does not provide the selectivity needed for urine pathogens.
• Nutrient Agar: Nutrient Agar is a basic medium that supports the growth of a wide range of microorganisms. However, it lacks the selectivity required for urine culture, making it less suitable compared to specialized media.
• Chocolate Agar: Chocolate Agar is enriched with heat-treated blood and is commonly used for the growth of fastidious bacteria, particularly Haemophilus species. It is not the best choice for urine culture as it does not provide the selective conditions necessary.