MicroBiology MCQs with Answer and Explnation | Chapter 43

Answer: When inoculated in experimental animals bacteria may or may not cause disease

One of Koch’s postulates states that the suspected pathogen must be able to consistently produce the disease in healthy, susceptible animals when inoculated with a pure culture. This means that the disease must be reliably replicated in the animal model. Saying that the bacteria “may or may not” cause disease violates this principle by introducing inconsistency.

The other options are incorrect:

• The bacteria should be able to be isolated from a diseased tissue: This is actually the first postulate of Koch and is essential for establishing a link between the suspected pathogen and the disease.
• Pure cultures can be obtained: This is the third postulate and emphasizes the need to isolate the pathogen in pure culture, free from other organisms, to confirm its role in the disease.
• Bacteria should be able to be isolated from the diseased tissue in the experimental animals: This is the fourth postulate and reinforces the first postulate by demonstrating that the pathogen can be re-isolated from the diseased animal, further solidifying its link to the disease.

Answer: Hapten

In penicillin allergy, penicillin itself is not a complete allergen. Instead, it acts as a hapten, a small molecule that can’t induce an immune response on its own. However, when it binds to certain proteins in the body, like serum albumin, it forms a new molecule that the immune system recognizes as foreign. This triggers the production of antibodies and T cells specific to the penicillin-protein complex, leading to an allergic reaction.

The other options are incorrect:

• Carrier: Carriers are large molecules, like proteins, that can bind to haptens and help them elicit an immune response. While penicillin binds to proteins, it doesn’t act as a carrier in the classical sense. It’s the hapten itself that triggers the immune response through the protein complex formation.
• Super antigen: Super antigens are potent antigens that can activate many T cells simultaneously, leading to a strong and uncontrolled immune response. While penicillin allergy involves T cell activation, it doesn’t involve the direct activation of large numbers of T cells like a super antigen would.
• Toxin: Toxins are poisonous substances produced by microorganisms that can cause harm to the body. Penicillin is an antibiotic, not a toxin, and doesn’t directly cause harm through its chemical properties.

Answer: Can kill mycobacterium tuberculosis

Boiling water is not consistently effective in killing Mycobacterium tuberculosis. While boiling can kill many vegetative bacterial cells and some viruses, Mycobacterium tuberculosis, the causative agent of tuberculosis, is more resistant to heat. Sterilizing surgical instruments or reliably killing the spores of certain bacteria may require more rigorous methods such as autoclaving.

The other options are incorrect:

• It can kill hepatitis B virus: Boiling water can be effective in inactivating the hepatitis B virus. However, this does not apply to all viruses, and more reliable methods such as disinfection or autoclaving are often recommended for virus inactivation.
• Used for sterilizing surgical instruments: Boiling water is not a recommended method for the sterilization of surgical instruments. Autoclaving or other methods that achieve higher temperatures and pressure are more suitable for achieving sterilization.
• Can kill vegetative bacterial cells: Boiling water can indeed kill many vegetative bacterial cells by denaturing proteins and disrupting cell membranes. However, it may not be effective against certain bacterial spores or more heat-resistant pathogens.

Answer: short wave lenght

Sunlight is composed of various wavelengths, including visible light, infrared radiation, and UV radiation. The germicidal properties of sunlight come primarily from short-wavelength UV radiation (UVC), typically between 200-280nm. This UV radiation disrupts the DNA and RNA of microorganisms, preventing them from replicating and ultimately killing them.

The other options are incorrect:

• Long wavelength: Longer wavelengths like visible light and infrared radiation in sunlight don’t possess enough energy to damage microbial DNA and RNA effectively.
• Ozone: While ozone in the stratosphere absorbs harmful UV radiation shielding us from its most intense effects, it doesn’t contribute significantly to the sterilizing power of sunlight reaching the Earth’s surface.
• Heat: Although sunlight generates heat, temperatures reached through direct sunlight exposure might not be enough for consistent sterilization across different materials and environments. Additionally, excessive heat can damage surfaces and materials.

Answer: Three successive days

Tyndallization is a specific sterilization method that relies on the heat resistance and germination properties of bacterial spores. It involves heating the material (usually liquid media) to a temperature just below boiling (e.g., 80-100°C) for 15-30 minutes, followed by incubation at a suitable temperature (e.g., 37°C) for at least 24 hours. This cycle is repeated two more times (hence, three days total) to ensure all spores germinate and are subsequently killed by the next heating phase.

The other options are incorrect:

• One day: One heating cycle wouldn’t be enough to capture and kill all spores, as some might remain dormant and survive.
• Two successive days: While two cycles would offer better effectiveness than one, three is considered the standard protocol for reliable sterilization through Tyndallization.
• 60 minutes: While the heating phase within each cycle may take around 60 minutes, the entire process involves three cycles spanning three days, including incubation periods.

Answer: Type I hypersensitivity

Type I hypersensitivity is a rapid allergic reaction mediated by IgE antibodies attached to mast cells and basophils. When exposed to the specific antigen, these antibodies cross-link, causing the mast cells and basophils to degranulate and release inflammatory mediators like histamine, leading to immediate symptoms like wheezing, skin rash, and anaphylaxis.

The other options are incorrect:

• Type II hypersensitivity: This involves antibody-mediated destruction of host cells coated with antigens. It’s not immediate and doesn’t involve mast cells or basophils.
• Type III hypersensitivity: This involves immune complexes formed from antigen and antibody that activate the complement system and cause inflammation. It’s also not immediate and doesn’t primarily involve mast cells or basophils.
• Type IV hypersensitivity: This involves T-cell-mediated delayed hypersensitivity reactions like contact dermatitis. It’s not immediate and doesn’t involve mast cells or basophils.

Answer: Gamma rays

Gamma rays provide the most effective and reliable sterilization method for disposable syringes. They penetrate deeply, achieving complete sterilization without damaging the plastic components.

The other options are incorrect:

• Hot air oven: While effective for metal instruments, hot air ovens can damage the plastic parts of syringes and may not reach sufficient temperatures for complete sterilization.
• U.V. rays: U.V. rays have limited penetration and are ineffective against bacteria hidden within the syringe barrel. They also require direct line of sight to be effective, making complete sterilization difficult.
• Boiling: Boiling can only partially sterilize syringes and is not reliable for eliminating spore-forming bacteria. It can also damage the plastic and cause warping.

Answer: It has got no deleterious effect on the cement and lenses of instruments

Glutaraldehyde is preferred over formaldehyde because it has no deleterious effect on the cement and lenses of instruments. Unlike formaldehyde, glutaraldehyde is less likely to damage or corrode materials commonly found in medical instruments and equipment.

The other options are incorrect:

• It has got more bactericidal activity: Both glutaraldehyde and formaldehyde have strong bactericidal activity. The choice between them is often based on other factors, such as material compatibility.
• It has got more bacteriostatic activity: Glutaraldehyde and formaldehyde are primarily used for their bactericidal (killing bacteria) rather than bacteriostatic (inhibiting bacterial growth) properties.
• Its application is easier: The ease of application can vary depending on the context and the specific use. However, the preference for glutaraldehyde is more related to its compatibility with materials rather than the ease of application.

Answer: Hot air oven

Liquid paraffin, also known as mineral oil, is a non-aqueous liquid and cannot be effectively sterilized by steam-based methods like autoclaving. Hot air ovens provide a dry heat method suitable for sterilizing liquid paraffin without compromising its properties.

The other options are incorrect:

• Autoclaving: While effective for many materials, autoclaving involves high-pressure steam, which can cause the liquid paraffin to boil and potentially explode.
• UV-Radiation: UV radiation has limited penetration and is ineffective against bacteria within the bulk liquid. It’s also not suitable for sterilizing large volumes of liquid.
• Inspissation: This process involves thickening the liquid by evaporation, which doesn’t achieve sterilization and can even concentrate existing microorganisms.

Answer: Robert koch

While other microbiologists contributed to the development of solid media, Robert Koch is credited with introducing the first practical and widely used method in 1881. He used nutrient gelatin poured onto flat glass plates to isolate and study pure cultures of bacteria, revolutionizing the field of microbiology.

The other options are incorrect:

• Louis Pasteur: While a pioneer in microbiology, Pasteur primarily focused on liquid media and fermentation studies. He contributed to early attempts at solid media but didn’t develop a widely adopted method.
• Hensen: Julius Hansen was a Danish mycologist and botanist who worked with yeasts and molds but didn’t significantly contribute to the development of solid media for bacterial culture.
• Ogston: Alexander Ogston was a British physician who made contributions to understanding wound infections but didn’t develop a specific method for solid media.

Answer: 40% formaldehyde vapour

Disinfection of rooms can be achieved by using 40% formaldehyde vapor. Formaldehyde is a strong disinfectant that has broad-spectrum antimicrobial properties, making it effective for room disinfection by eliminating various pathogens.

The other options are incorrect:

• 20% phenol: While phenol is a disinfectant, its use in rooms is limited due to its strong odor, potential skin irritation, and slower action compared to chlorine gas.
• High efficiency particle arrestors (HEPA): HEPA filters are designed to capture airborne particles, not kill them. They can help prevent the spread of airborne pathogens by filtering contaminated air but don’t disinfect surfaces.
• 40% formaldehyde vapor: Formaldehyde is a potent disinfectant but highly toxic and carcinogenic. Its use in occupied spaces is strictly prohibited due to its health risks.

Answer: Nucleic acids

Nucleic acids, specifically DNA and RNA, are the primary target of UV irradiation for disinfecting bacteria and viruses. UV light damages the structure of these molecules, preventing them from replicating and rendering the microorganisms inactive.

The other options are incorrect:

• Lipids: While lipids are essential components of bacteria and viruses, they are not directly affected by UV irradiation. Damage to lipids might occur as a secondary effect, but it wouldn’t contribute to the initial inactivation.
• Carbohydrates: Similar to lipids, carbohydrates primarily play structural roles and are not significantly affected by UV light. Their damage wouldn’t contribute to microbial inactivation.
• Inorganic salts: These minerals typically don’t absorb UV light and wouldn’t play a role in the inactivation process. They might influence UV penetration through solutions but wouldn’t directly sensitize the microbes.

Answer: Sterilization kills all spores but disinfection does not

The key difference between sterilization and disinfection is that sterilization kills all forms of microbial life, including spores, while disinfection may not necessarily eliminate all spores.

The other options are incorrect:

• Disinfection kills all spores but sterilization does not: Sterilization, not disinfection, is the process that kills all forms of microbial life, including spores.
• Sterilization kills all spores but disinfection does not: This is the correct answer. Sterilization is a more rigorous process that eliminates all microbial life, including spores.
• Sterilization is easier to achieve: Sterilization is generally more challenging to achieve than disinfection because it requires the elimination of all forms of microbial life, including resistant spores.

Answer: Enriched media

Blood agar is an enriched media. It is a type of culture medium that contains nutrients, including whole blood (usually sheep or horse blood), to support the growth of a wide variety of microorganisms. The blood in the agar provides additional nutrients, such as vitamins and growth factors, making it particularly suitable for the cultivation of fastidious bacteria.

The other options are incorrect:

• Simple media: These are basic culture media containing minimal nutrients and are suitable for only a few, non-fastidious organisms. Blood agar, with its enriched blood content, is not considered a simple medium.
• Transport media: These are designed to maintain the viability of microorganisms during transport from the collection site to the laboratory. Blood agar is not specifically designed for this purpose and primarily serves as a growth medium.
• Differential media: These media allow the differentiation of different types of bacteria based on their specific characteristics, such as growth patterns, color changes, or hemolytic activity. While blood agar can be used to differentiate some bacteria based on their hemolytic properties (complete, partial, or no hemolysis), its primary function is as an enriched media for fastidious organisms.

Answer: Internal structures are differentiated in living cells

Phase contrast microscopy is a powerful tool for visualizing unstained, living cells. It enhances contrast by converting slight differences in the refractive index of the cell’s internal structures into variations in brightness, allowing us to see details like organelles, membranes, and even specific molecules. This makes it ideal for studying the morphology and dynamics of living cells, without the need for potentially harmful staining or fixation techniques.

The other options are incorrect:

• Internal structures are differentiated in dead cells: While phase contrast can still reveal some internal structures in dead cells, the lack of metabolic activity and movement can limit the level of detail compared to living cells.
• Internal metabolic activities can be observed: While some dynamic changes can be seen in real-time, phase contrast is primarily focused on visualizing the static structure of the cell. It doesn’t directly reveal metabolic processes like enzyme activity or molecule movement.
• External capsule formation can be observed: Phase contrast can indeed capture the presence and morphology of an external capsule, if present, but its primary focus is on internal structures within the cell.

Answer: Protein compound

Exotoxins are toxic proteins produced and secreted by living bacteria. These potent toxins play a crucial role in bacterial pathogenesis, allowing them to harm host cells and tissues, contributing to disease symptoms. The protein structure of exotoxins enables them to bind to specific receptors on host cells, triggering various detrimental effects like pore formation, enzyme inhibition, or disruption of essential cellular processes.

The other options are incorrect:

• Lipid-polysaccharide complex: This describes the structure of endotoxins, another type of bacterial toxin released upon cell death. Unlike exotoxins, endotoxins are not actively secreted and have a different mechanism of action, triggering inflammatory responses rather than specific cellular damage.
• Lipoprotein: Some exotoxins contain a small lipid component attached to the protein, technically classifying them as lipoproteins. However, the protein portion is the key functional element responsible for their toxicity, making “protein compound” the most accurate overall description.
• None: This is incorrect as exotoxins are a well-established and crucial category of bacterial toxins with diverse types and modes of action.

Answer: Stationary phase

The stationary phase is characterized by a zero net growth rate. This means the rate of cell division is equal to the rate of cell death, resulting in a stable population size.

The other options are incorrect:

• Lag phase: While the growth rate is slow in the lag phase due to cells adapting to the new environment, there is still some increase in cell numbers.
• Exponential growth phase: This phase is defined by rapidly increasing cell numbers due to optimal conditions, resulting in a positive growth rate.
• Decline phase: In the decline phase, the death rate exceeds the division rate, leading to a decreasing population size and negative growth rate.

Answer: Culture media

Hot air ovens rely on dry heat to kill microorganisms. While this method is effective for instruments and some materials like glassware and metal, it is not suitable for culture media. Culture media typically contain nutrients and agar, which can melt, burn, or alter their composition at the high temperatures required for hot air sterilization (around 160°C to 180°C). This can render the media unusable for its intended purpose of growing and supporting microorganisms.

The other options are incorrect:

• Clothes: Hot air ovens can be used to sterilize clothes at high temperatures (around 120°C to 140°C) for extended periods (around 30 minutes to 2 hours). This is effective for removing dust mites and some bacteria.
• Instruments: Hot air ovens are a common method for sterilizing heat-resistant instruments like scalpels, forceps, and glassware in medical and laboratory settings.
• Needles: Similar to instruments, needles can be sterilized in hot air ovens, especially those made of heat-resistant materials like stainless steel.

Answer: CD4

T-cells have CD4 receptors on their surface. CD4 is a glycoprotein that serves as a co-receptor along with the T-cell receptor (TCR) for the recognition of antigens presented by major histocompatibility complex class II (MHC-II) molecules. CD4 receptors play a crucial role in the activation of T-helper cells.

The other options are incorrect:

• Ig A: This is an antibody, a type of protein produced by B-cells, not T-cells.
• Ig G: Similar to Ig A, this is another antibody type specific to B-cells.
• Prostaglandins: These are signaling molecules involved in inflammation and other cellular processes, not receptors.

Answer: IgE

In patients with asthma due to an allergic cause, the serum levels of immunoglobulin E (IgE) increase. IgE is involved in allergic reactions and is particularly associated with conditions such as asthma, hay fever, and other allergic responses. Elevated IgE levels indicate an increased sensitivity to allergens.

The other options are incorrect:

• IgD: IgD plays a role in B-cell activation but is not significantly elevated in allergic asthma.
• IgM: IgM is the first antibody produced in response to an infection and is not typically associated with allergies.
• IgA: IgA defends against mucosal pathogens and protects body surfaces but is not a primary player in allergic asthma.

Answer: IgG

IgG is the most abundant immunoglobulin in human serum, constituting approximately 70-80% of all circulating antibodies. This high concentration reflects its crucial role in long-term humoral immunity against various pathogens.

The other options are incorrect:

• IgA: While IgA plays a vital role in mucosal immunity, its overall concentration is lower than IgG.
• IgD: IgD is primarily involved in B-cell activation and has a very low serum concentration.
• IgM: IgM is the first antibody produced in response to infections, but its levels decline after initial exposure and remain lower than IgG in the long term.

Answer: Leumenhoek

Antonie van Leumenhoek is credited with coining the term “animalcules” to refer to the microscopic organisms, including many oral microorganisms, that he observed through his self-made microscopes in the late 17th century. His detailed sketches and descriptions paved the way for early microbiology.

The other options are incorrect:

• Wd Miller: While W.D. Miller was a prominent dental researcher in the late 19th century, he did not introduce the term “animalcules.” He focused on studying the role of bacteria in dental caries.
• Robertson: M.A. Robertson made significant contributions to oral microbiology in the 20th century, focusing on streptococci and their connection to various oral diseases. He did not, however, coin the term “animalcules.”
• Socranci: G. Socransky was another key figure in 20th-century oral microbiology, exploring the composition and ecology of the oral microbiome. He was not associated with the term “animalcules.”

Answer: Ig G

Among the given options, only IgG possesses the necessary molecular size and structure to effectively cross the placenta and provide passive immunity to the fetus. It binds to a specific receptor on placental cells, facilitating its transport to the fetal circulation.

The other options are incorrect:

• IgM: IgM molecules are too large and complex to efficiently traverse the placenta. They primarily function in the early stages of immune response and are not essential for fetal protection.
• IgA: While IgA is important for mucosal immunity, its structure and distribution render it ineffective for placental transfer. Its primary focus is on protecting mucosal surfaces in the lungs, gut, and other areas rather than the bloodstream.
• IgD: IgD has negligible presence in serum and mainly functions as a receptor on B cells. It plays a limited role in humoral immunity and does not contribute to placental antibody transfer.

Answer: Deactivate all spores and dill pathogenic organism

Sterilization is a process in which all forms of microbial life, including spores, are deactivated or killed. The goal of sterilization is to eliminate or destroy all viable microorganisms, including bacteria, viruses, fungi, and their spores, to achieve asepsis.

The other options are incorrect:

• Kill all pathogenic micro-organisms: This only addresses a portion of the target population. Sterilization needs to eliminate all microbes, not just those known to cause harm.
• Kill all non-pathogenic micro-organisms in the environment: While this might seem desirable in some situations, it disrupts the natural microbial balance and can have unintended consequences for the environment and ecosystem.
• Deactivate all pathogens not spores: Deactivating pathogens means temporarily rendering them inactive, but it doesn’t guarantee they won’t become active again under favorable conditions. Spores, in particular, can remain dormant for years and still pose a threat.

Answer: Erythrocytes

While erythrocytes (red blood cells) are crucial for transporting oxygen throughout the body, they play no role in the acquired immune response. The acquired immune system, developed over time and specific to encountered pathogens, relies on specialized cell types like lymphocytes and antigen-presenting cells (APCs) to recognize, target, and eliminate foreign invaders.

The other options are incorrect:

• B lymphocytes: These cells produce antibodies, highly specific proteins that neutralize pathogens and mark them for destruction by other immune cells.
• T lymphocytes: These cells come in several types, including cytotoxic T cells that directly kill infected cells and helper T cells that activate other immune cells.
• Antigen-presenting cells (APCs): These cells, such as dendritic cells and macrophages, engulf and process pathogens, displaying fragments (antigens) on their surface. APCs then present these antigens to T lymphocytes, triggering the specific immune response.

Answer: C3

The common pathway of the complement system begins with complement factor C3. C3 is a central component in the complement cascade and plays a crucial role in both classical and alternative pathways of complement activation. Activation of C3 leads to the formation of C3 convertase, which is a key step in the amplification of the complement cascade.

The other options are incorrect:

• C5: While C5 is part of the complement system, the common pathway begins with the activation of C3.
• C2: C2 is involved in the classical pathway of complement activation, but it is not the starting point of the common pathway.
• Protein B: Protein B is associated with the alternative pathway of complement activation, and it is not the factor through which the common pathway begins.

Answer: Candida albicans

Gram stain is a differential staining technique that classifies bacteria into two groups based on their cell wall composition. While the other three listed organisms are bacteria with cell walls, Candida albicans is a fungus. Fungi lack the peptidoglycan layer in their cell walls that interacts with the Gram stain components, making them non-reactive to the stain.

The other options are incorrect:

• Actinomyces israelii: This gram-positive bacterium has a thick peptidoglycan layer that retains the crystal violet dye, staining it blue-purple.
• Mycobacterium tuberculosis: This gram-positive bacterium has a waxy cell wall with a unique lipid composition that requires additional staining steps after Gram staining to visualize it.
• Streptococcus mutan: This gram-positive bacterium has a typical bacterial cell wall with peptidoglycan that readily takes up the crystal violet dye, appearing blue-purple.

Answer: Different refractive indices of object

Phase contrast microscopy utilizes the variations in the refractive indices of objects within the specimen to create contrast and visualize unstained, transparent structures. Light passing through materials with different refractive indices experiences slight changes in its phase (wavelength speed). This principle allows phase contrast microscopes to convert these invisible phase shifts into visible differences in brightness, revealing details otherwise invisible with traditional brightfield microscopy.

The other options are incorrect:

• Different reflective indices of objects: While reflective index plays a role in some microscopy techniques, it’s not the key principle underlying phase contrast. Phase contrast focuses on the interaction of light with the refractive index of the specimen itself, not its reflection.
• Light scattering: Light scattering is a phenomenon that can occur in microscopy but isn’t the primary principle behind phase contrast. Phase contrast specifically uses controlled phase shifts caused by refractive index differences to enhance image contrast.
• Light attenuation: This refers to the absorption or weakening of light as it passes through a material. While some light attenuation may occur in phase contrast microscopy, it’s not the main mechanism for creating contrast. The key feature is the conversion of phase shifts into brightness variations.

Answer: Smallest antigenic determinant

An epitope is the smallest specific region of an antigen molecule that can be recognized and bound by antibodies or T cell receptors. It’s like a “keyhole” on the antigen that only certain antibodies (the “keys”) can fit into. It’s important to note that an antigen can have multiple epitopes, each recognized by different antibodies, triggering different immune responses.

The other options are incorrect:

• Complete antigen molecule: While the entire antigen molecule triggers an immune response, the epitope is the specific part that interacts with the antibody. It’s like saying the whole door is the keyhole, whereas the epitope is the actual slot where the key fits.
• Hapten: A hapten is a small molecule that can bind to antibodies but cannot trigger an immune response on its own. It needs to be attached to a carrier molecule, like a protein, to elicit an immune reaction. While an epitope can be small, it has the ability to induce an immune response by itself.
• Immunogen: An immunogen is any substance that can trigger an immune response, including antigens, adjuvants, and even some vaccines. While epitopes are essential for antigen recognition, not everything that causes an immune response needs to have an epitope. For example, adjuvants enhance the immune response without having specific epitopes.

Answer: Type III hypersensitivity

Post-streptococcal acute glomerulonephritis (PSGN) is primarily caused by an immune complex reaction, which is a hallmark of Type III hypersensitivity. In PSGN, immune complexes containing streptococcal antigens and antibodies deposit in the glomeruli (tiny filtering units in the kidneys), triggering inflammation and damage that impair kidney function.

The other options are incorrect:

• Type I hypersensitivity: This type involves immediate allergic reactions mediated by IgE antibodies and mast cells. It’s not involved in PSGN, which is a delayed immune response.
• Type II hypersensitivity: This type involves antibody-mediated damage to cells or tissues. While PSGN involves antibodies, they target immune complexes rather than directly attacking kidney cells.
• Type IV hypersensitivity: This type involves delayed-onset cell-mediated reactions through T cells. It’s not directly involved in PSGN, even though T cells participate in the inflammatory response to some extent.

Answer: Mitochondria

Bacterial cells are prokaryotic, meaning they lack a true nucleus and membrane-bound organelles like mitochondria. They manage vital cellular functions differently than eukaryotic cells like animal and plant cells. While bacteria have their own mechanisms for energy production, they do not rely on mitochondria for respiration like most eukaryotes.

The other options are incorrect:

• DNA: Both prokaryotic and eukaryotic cells contain DNA as their genetic material, albeit organized differently. Bacteria have a single circular chromosome in the cytoplasm, while eukaryotes have linear chromosomes inside a membrane-bound nucleus.
• Ribosome: Bacterial cells contain ribosomes, the essential components for protein synthesis. Though slightly different in structure and composition from eukaryotic ribosomes, they fulfill the same crucial function.
• Cell wall: Bacteria have a unique cell wall consisting of peptidoglycan, providing structural support and protection against external stresses. Unlike plant cell walls, it differs in composition and function.

Answer: Gamma-Rays

The manufacturing unit of surgical needles and sutures is often sterilized using gamma-rays. Gamma-ray sterilization is a method that utilizes ionizing radiation to eliminate microorganisms and achieve sterility. This process is effective in ensuring that the surgical instruments and materials are free from viable microorganisms.

The other options are incorrect:

• X-Rays: X-rays are not commonly used for the sterilization of surgical needles and sutures. X-rays have lower energy compared to gamma-rays and are primarily used for imaging purposes.
• Autoclaving: Autoclaving involves the use of steam under pressure to achieve sterilization. While it is a widely used method, it may not be suitable for certain heat-sensitive materials, such as some types of sutures.
• Boiling: Boiling is not considered a reliable method for the sterilization of surgical instruments. It is not as effective as methods involving higher temperatures and pressures.

Answer: Spore formers

The purpose of sterilization is to eliminate all forms of microbial life, including spore formers. Sterilization is a process that aims to achieve complete destruction or inactivation of all viable microorganisms, including bacteria, viruses, fungi, and their spores, to create a sterile environment.

The other options are incorrect:

• Bacteria: While sterilization targets bacteria, it is not limited to eliminating bacteria alone.
• Viruses: Sterilization is designed to eliminate viruses along with other microorganisms, ensuring a complete absence of viable infectious agents.
• Fungus: Sterilization is effective against fungi as well, ensuring the elimination of fungal spores and other forms of fungal life.

Answer: Mycoplasma

Cell wall deficient bacteria lack the rigid cell wall structure typical of most bacteria. This makes them unique and presents both advantages and disadvantages for their survival. While some cell wall deficient bacteria can arise from other bacteria through various mechanisms, Mycoplasma is a distinct group of bacteria that naturally lack cell walls.

The other options are incorrect:

• Escherichia coli: Escherichia coli (E. coli) is a Gram-negative bacterium with a well-defined cell wall.
• Staphylococci: Staphylococci, including Staphylococcus aureus, are Gram-positive bacteria with a cell wall.
• Spirochetes: Spirochetes, such as Treponema pallidum (causing syphilis) and Borrelia burgdorferi (causing Lyme disease), have a cell wall. They are not considered cell wall-deficient.

Answer: IgG

In multiple myeloma, the type of immunoglobulin most commonly increased is IgG. Multiple myeloma is a cancer of plasma cells, and these abnormal plasma cells produce excessive amounts of a monoclonal (single type) immunoglobulin, often IgG. Elevated levels of IgG in the blood are a characteristic feature of multiple myeloma.

The other options are incorrect:

• IgA: While IgA can be elevated in some multiple myeloma cases (around 20%), it is significantly less common than IgG.
• IgM: IgM elevation is rare in multiple myeloma, occurring in less than 5% of patients.
• IgD: IgD is normally present in very low levels and is practically undetectable in most people. Its increase in multiple myeloma is even rarer.

Answer: Antigen recognition by B cells

While the exact function of IgD is still under investigation, its primary role is believed to be antigen recognition by B cells. It acts as a co-receptor alongside IgM on immature B cells, aiding in the selection and maturation of B cells that can recognize specific antigens.

The other options are incorrect:

• Localization protection in external secretion: While IgD can be present in some external secretions, its primary function is not related to localization or protection.
• Complement activation: IgD does not directly activate the complement system, although it can indirectly influence it through its interactions with B cells.
• Reagin activity: Reagin activity refers to the ability of certain antibodies to bind to non-specific antigens like cardiolipin. IgD does not typically exhibit this type of activity.

Answer: One Fc fragment and two Fab fragments

Cleavage of the IgG molecule by the enzyme papain results in the generation of one Fc (Fragment crystallizable) fragment and two Fab (Fragment antigen-binding) fragments. The Fc fragment is involved in effector functions, while the Fab fragments contain the antigen-binding sites responsible for recognizing and binding to specific antigens.

The other options are incorrect:

• One Fc fragment and four Fab fragments: This is not the result of cleavage by papain. The correct ratio is one Fc fragment and two Fab fragments.
• Two Fc fragments and two Fab fragments: Cleavage by papain does not produce two Fc fragments; it results in one Fc fragment and two Fab fragments.
• Two Fc fragments and one Fab fragment: The correct result of papain cleavage is one Fc fragment and two Fab fragments, not two Fc fragments and one Fab fragment.

Answer: Joeph Lister

While all the listed individuals were prominent figures in medicine and microbiology, Joseph Lister is credited with discovering the concept of antiseptic surgery, which laid the foundation for modern physical sterilization practices. He pioneered the use of carbolic acid (phenol) to disinfect surgical instruments and dressings, significantly reducing post-operative infections and saving countless lives.

The other options are incorrect:

• Robert Koch: He was a German microbiologist who identified the bacteria responsible for tuberculosis and cholera. While his contributions to germ theory were crucial, he didn’t directly discover physical sterilization.
• John Hunter: A Scottish surgeon and anatomist, he made significant contributions to understanding surgical techniques and wound healing. However, he predates the discovery of antisepsis and didn’t employ systematic sterilization methods.
• Alexander Fleming: He discovered penicillin, the first antibiotic, which revolutionized the treatment of bacterial infections. However, antibiotics primarily address existing infections, while physical sterilization focuses on preventing microbial growth.

Answer: Autoclaving

Autoclaving uses high-pressure steam (typically 121°C for 15 minutes) to destroy all forms of microbial life, including bacteria, viruses, and fungal spores. This thorough and reliable method ensures sterility without affecting the properties of the dressing powder.

The other options are incorrect:

• Hot air oven: While dry heat can be effective for sterilizing certain instruments, it requires much higher temperatures (approximately 180°C for 2 hours) for dressing powders, potentially making them unusable due to degradation of components.
• Inspissation: This technique involves heating liquid media to concentrate it, not achieving true sterilization. It only reduces the number of viable organisms and would be inadequate for dressing powders.
• Tyndallization: This method involves repeated cycles of heating and cooling, designed to kill spore-forming bacteria. However, it’s time-consuming, may not be effective for all microorganisms, and is generally not suitable for powders.

Answer: Coxiella burnetti

Moist heat, typically in the form of autoclaving, is a highly effective sterilization method that destroys all forms of microbial life, including bacteria, viruses, fungi, and spores. However, Coxiella burnetti possesses unique characteristics that make it resistant to standard moist heat sterilization procedures. It can survive in a dormant spore-like state, allowing it to withstand temperatures of up to 100°C for extended periods.

The other options are incorrect:

• Brucella: These bacteria are susceptible to moist heat and can be effectively sterilized at temperatures exceeding 70°C for a sufficient duration.
• Mycobacterium: This group includes bacteria like Mycobacterium tuberculosis (causing TB), which can be eradicated by moist heat at temperatures exceeding 121°C for a specific time frame.
• Salmonella: These common foodborne pathogens are readily destroyed by moist heat sterilization at temperatures exceeding 75°C for a sufficient duration.

Answer: Thymus

The thymus gland is a vital organ located in the chest, responsible for the maturation and development of T cells, a crucial component of the adaptive immune system. T cells originate in the bone marrow as immature precursors and migrate to the thymus where they undergo a rigorous selection process.

The other options are incorrect:

• Payer’s patches: These are lymphoid tissue patches located in the small intestine, responsible for the maturation of B cells, another type of immune cell.
• Lymph node: While lymph nodes play a role in T cell activation and proliferation, they are not the primary site of T cell maturation.
• Bursa of Fabricius: This is a lymphoid organ in birds that serves a similar function to the thymus in mammals, specifically for B cell maturation. It’s not present in humans.

Answer: MHC II

CD4 cells, also known as helper T cells, are a crucial part of the adaptive immune system. They play a key role in coordinating the immune response by recognizing and interacting with antigen-presenting cells (APCs). These APCs, such as macrophages and dendritic cells, engulf pathogens and display fragments of these invaders, called antigens, on their surface in association with specific major histocompatibility complex (MHC) molecules.

The other options are incorrect:

• MHC I: These molecules are primarily found on all nucleated cells in the body and typically present antigens derived from intracellular pathogens (e.g., viruses) to cytotoxic T cells (CD8 cells) for elimination.
• MHC III: This class of MHC molecules are less well-understood and have limited roles in antigen presentation compared to MHC I and II.
• B-cell receptor: This is a protein molecule expressed on the surface of B cells, another type of immune cell involved in recognizing and responding to specific antigens. It is distinct from the CD4 receptor found on helper T cells.

Answer: Macrophages

Interleukin-1 (IL-1) is primarily produced by macrophages. Macrophages are immune cells that play a key role in the innate immune response. They produce IL-1 in response to infection or inflammation. IL-1 acts as a pro-inflammatory cytokine, promoting the activation of other immune cells and contributing to the inflammatory response.

The other options are incorrect:

• Helper T cells: Helper T cells (CD4+ T cells) are involved in the immune response, but they do not produce IL-1. They release other cytokines to regulate the immune system.
• Helper B cells: Helper B cells are not a recognized cell type. B cells, when activated, can differentiate into plasma cells, which produce antibodies.
• Monocytes: Monocytes are precursors to macrophages, and they can differentiate into macrophages in tissues. While monocytes are involved in immune responses, they are not the primary producers of IL-1.

Answer: Type II

Graves’ disease is an autoimmune disorder characterized by the overproduction of thyroid hormones, leading to hyperthyroidism. This occurs due to the presence of abnormal antibodies, called thyroid-stimulating immunoglobulins (TSIs), which mimic the action of TSH (thyroid-stimulating hormone) on thyroid cells. This results in excessive thyroid hormone production and the associated symptoms of hyperthyroidism.

The other options are incorrect:

• Type I: This type of hypersensitivity involves IgE antibodies and mast cell activation, leading to immediate allergic reactions like anaphylaxis, hay fever, and asthma. Graves’ disease doesn’t involve these typical features.
• Type III: This type involves immune complex formation between antigen and antibody, triggering inflammation and tissue damage in locations where the complexes deposit. Although some features of Graves’ disease, like eye inflammation, might have immune complex involvement, it’s not the primary mechanism.
• Type IV: This type, also known as cell-mediated immunity, involves T cell activation and direct attack on infected cells or foreign tissues. While T cells have roles in Graves’ disease, the antibody-mediated overstimulation of thyroid cells remains the central mechanism.

Answer: Active T cells

Type IV hypersensitivity reactions are classified as cell-mediated immune responses, meaning they are primarily orchestrated by T cells rather than antibodies. These T cells become activated upon recognizing specific antigens presented by antigen-presenting cells (APCs). These activated T cells then trigger various immune responses to eliminate the threat, leading to the characteristic delayed reaction associated with Type IV hypersensitivity.

The other options are incorrect:

• B-cells: These are primarily involved in humoral immunity, generating antibodies to target and neutralize pathogens. They are not directly involved in Type IV reactions.
• NK cells: Natural killer cells are important for eliminating virally infected cells and tumor cells, but their role in Type IV hypersensitivity is limited.
• Plasma cells: These are differentiated B cells that produce antibodies. They are involved in the late stages of humoral immunity and wouldn’t be directly involved in the initial activation and effector phases of Type IV hypersensitivity.

Answer: 17 D

17 D refers to the live attenuated vaccine used for the prevention of yellow fever. Live vaccines contain weakened forms of the infectious agent that are still capable of eliciting an immune response but are attenuated or modified to be less virulent. The yellow fever vaccine (17 D) is an example of a live attenuated vaccine.

The other options are incorrect:

• Salk: This is an inactivated polio vaccine, meaning the poliovirus has been killed and can no longer replicate. While it provides effective protection against polio, it’s not considered a live vaccine.
• Hepatitis: This can refer to several different vaccines for various hepatitis viruses. Some, like the hepatitis B vaccine, are inactivated and not live vaccines. Others, like the hepatitis A vaccine, are live attenuated vaccines. Therefore, without specifying the specific type of hepatitis vaccine, it’s impossible to determine if it’s live or not.
• HDCV: This stands for Human Diploid Cell Vaccine, which is a specific type of rabies vaccine. Rabies vaccines can be either live attenuated (like the rabies vaccine used for animals) or inactivated (like the HDCV). Without further information, it’s impossible to say definitively whether HDCV is a live vaccine.

Answer: Cell wall of Gram positive organisms

Teichoic acid is a component found in the cell wall of Gram-positive bacteria. It is a polymer that contributes to the structure and function of the cell wall. Teichoic acids are involved in various biological processes, including cell shape maintenance and interactions with the host immune system.

The other options are incorrect:

• Cell wall of Gram-negative organisms: Gram-negative bacteria have a more complex cell wall structure with an outer membrane. While they do contain lipopolysaccharides, these are distinct molecules from teichoic acids and have different functions.
• Cytoplasm of Gram positive organisms: Teichoic acids are predominantly found in the cell wall, not the cytoplasm, which is the inner part of the cell.
• Cytoplasm of Gram negative organisms: Similarly, teichoic acids are not present in the cytoplasm of Gram-negative bacteria.

Answer: All of the above

Each statement accurately describes a different type of immunity:

• Transfer of antibody from mother to child through colostrum: This is an example of natural acquired passive immunity. Antibodies transferred from the mother provide temporary protection against certain infections for the infant.
• Injection of antibodies (Hepatitis): This is an example of artificial acquired passive immunity. Immune globulin or specific antibodies are directly injected to provide immediate protection against specific pathogens.
• Antigenic stimulus given by vaccine (polio): This is an example of artificial active immunity. Weakened or inactivated pathogens in a vaccine trigger the body’s own immune system to develop its own long-lasting immunity against the disease.

Answer: Lowenstein Jensen medium

Lowenstein Jensen (LJ) medium is the most widely used selective media for culturing Mycobacterium species, including Mycobacterium tuberculosis (TB). It’s a solid egg-based medium that contains glycerol and asparagine, favoring the growth of Mycobacterium while inhibiting the growth of other bacteria.

The other options are incorrect:

• Sabourauds medium: This medium is primarily used for culturing fungi, not Mycobacterium.
• Agar – agar: This simple medium lacks the necessary nutrients and selective agents to support the growth of Mycobacterium.
• Loefflers serum slope: This medium is used for culturing Corynebacterium diphtheriae, not Mycobacterium.

Answer: Using a bacterial spore test

The best guarantee for sterilization in a heat sterilizer is provided by using a bacterial spore test. Bacterial spores, especially those of Geobacillus stearothermophilus, are highly resistant to heat. The spore test involves placing spore-containing strips or ampules inside the sterilizer along with items to be sterilized. After the sterilization cycle, these spores are cultured to check for viability, ensuring that the sterilization process effectively killed the highly resistant spores.

The other options are incorrect:

• Using chemical indicator strip or pouch: Chemical indicators, such as strips or pouches, provide a visual signal that the sterilization conditions have been met but do not directly confirm the destruction of bacterial spores.
• Recording temperature/pressure readings from sterilizer gauge: Monitoring temperature and pressure during sterilization is important for process control, but it does not guarantee the destruction of bacterial spores.
• Determining the ability of a sterilizer to kill the hepatitis B virus: While it is important to use effective sterilization methods for preventing the transmission of infectious agents, the ability to kill the hepatitis B virus alone does not guarantee the destruction of all bacterial spores.