MicroBiology MCQs with Answer and Explnation | Chapter 19

Answer: Penicillin-G

In large-scale submerged fermentations, the primary type of penicillin produced is Penicillin-G. Penicillin-G, also known as benzylpenicillin, is one of the most widely used and effective antibiotics.

The other options are incorrect:

• Penicillin-A: There is no specific designation as “Penicillin-A” in the context of widely recognized penicillins. Penicillin-G is the more common and well-known type.
• Penicillin-D: “Penicillin-D” is not a recognized type of penicillin produced in large-scale submerged fermentations. Penicillin-G is the primary type.

Answer: Penicillium chrysogenum

The strain of fungi used for the large-scale production of penicillin is Penicillium chrysogenum. This fungus is known for its high penicillin-producing capability and has been used in industrial processes for the mass production of the antibiotic.

The other options are incorrect:

• P-notatum: While Penicillium notatum was the original source of penicillin discovered by Alexander Fleming, it is not the primary strain used for large-scale production. Penicillium chrysogenum is the more efficient strain.
• Streptomyces Aurecus: Streptomyces aureus is not a strain used for the large-scale production of penicillin. Penicillium chrysogenum is the more relevant fungus in this context.
• Saccharomyces sps: Saccharomyces species, including Saccharomyces cerevisiae, are yeasts and are not used for the large-scale production of penicillin. Penicillium chrysogenum is the correct fungus for this purpose.

Answer: Acylase

6-amino penicillic acid is prepared from penicillin species by the enzyme acylase. Acylase catalyzes the hydrolysis of the acyl side chain in penicillin, leading to the formation of 6-amino penicillic acid.

The other options are incorrect:

• Punicillin acylase: There is no widely recognized enzyme known as “Punicillin acylase.” The correct term for the enzyme involved is acylase.
• Penicillinone: Penicillinone is not an enzyme but a compound. The conversion of penicillin to 6-amino penicillic acid involves enzymatic hydrolysis by acylase.

Answer: 6.5

The pH to be maintained for the production of penicillin is typically around 6.5. This pH range is optimal for the growth and activity of the penicillin-producing fungus, such as Penicillium chrysogenum, during the fermentation process.

The other options are incorrect:

• 7.5: While a pH of 7.5 is close to neutral, the optimal pH for penicillin production is slightly lower, around 6.5.
• 8.0: A pH of 8.0 is more alkaline and may not be conducive to the optimal production of penicillin. The preferred range is slightly more acidic.
• 5.0: A pH of 5.0 is more acidic than the optimal range for penicillin production. The preferred pH is around 6.5 for efficient fermentation.

Answer: Catalase test

This test is used to differentiate between catalase-positive Staphylococcus and catalase-negative Streptococcus. Catalase is an enzyme produced by some bacteria that catalyzes the breakdown of hydrogen peroxide into water and oxygen. Staphylococcus species are catalase-positive, while Streptococcus species are catalase-negative.

The other options are incorrect:

• Coagulase Test: This test is used to differentiate between pathogenic and non-pathogenic Staphylococcus species. Coagulase-positive Staphylococcus aureus is known for causing more severe infections.
• Phosphatase Test: Phosphatase tests are not typically used to differentiate between Streptococcus and Staphylococcus. These tests are more commonly associated with the identification of bacterial species based on their ability to hydrolyze certain substrates.
• Indole Test: The indole test is used to detect the ability of bacteria to produce indole from tryptophan. It is often used in the identification of Enterobacteriaceae, such as Escherichia coli. This test is not specific for distinguishing between Streptococcus and Staphylococcus.

Answer: Transposon

Also known as a “jumping gene,” a transposon is a DNA sequence that can change its position within a genome, leading to the movement of genes to different locations. This ability to “jump” makes transposons important in genetic diversity and evolution.

The other options are incorrect:

• Episome: An episome is a genetic element that can exist as an independent plasmid or integrate into the bacterial chromosome. It may have the ability to replicate autonomously or integrate into the host genome, but it is not specifically associated with the concept of jumping genes.
• Cosmid: A cosmid is a type of hybrid plasmid containing cos sites (cosmetic sites) that allow it to be packaged into bacteriophage particles for efficient transfer into bacterial cells. While cosmids can carry large DNA fragments, they are not typically associated with the jumping gene phenomenon.
• Plasmid: A plasmid is a small, circular DNA molecule separate from the chromosomal DNA. It can replicate independently in a host cell. While plasmids can carry genes and be transferred between bacteria, they are not inherently associated with the jumping gene phenomenon like transposons.

Answer: Cellulase

Cellulase is an enzyme that breaks down cellulose, a complex carbohydrate found in plant cell walls. Staphylococcus bacteria are not known for secreting cellulase. Cellulase production is more commonly associated with certain bacteria and fungi that are capable of digesting plant material.

The other options are incorrect:

• Lipase: Staphylococcus bacteria are known to produce lipase, an enzyme that hydrolyzes lipids (fats). Lipase helps Staphylococcus in utilizing lipids as a nutrient source.
• Coagulase: Staphylococcus bacteria are known for producing coagulase, which is an enzyme that causes the clotting of blood plasma. Coagulase is an important virulence factor in pathogenic Staphylococcus species, particularly Staphylococcus aureus.
• Lecithinase: Staphylococcus bacteria are capable of producing lecithinase, also known as phospholipase C. This enzyme hydrolyzes lecithin, a component of cell membranes, and contributes to the pathogenicity of some Staphylococcus strains by disrupting host cell membranes.

Answer: Capsular

The Quellung reaction is a laboratory test used to identify the presence of bacterial capsules, particularly in Streptococcus pneumoniae. Capsules are outer layers composed of polysaccharides that surround some bacteria. In the Quellung reaction, the capsule swells when specific antisera are applied, making it easier to visualize under a microscope.

The other options are incorrect:

• Flagellar Swelling: The Quellung reaction is not related to flagellar swelling. Flagella are the whip-like structures on bacteria used for motility, and they are not involved in the Quellung reaction.
• RBC Swelling: The Quellung reaction does not involve red blood cell (RBC) swelling. It is specifically a test for the swelling of bacterial capsules.
• Ribosomal Swelling: The Quellung reaction is not related to ribosomal swelling. Ribosomes are cellular structures involved in protein synthesis and are not associated with the capsule swelling observed in the Quellung reaction.

Answer: Neisseria

Gram-negative cocci typically include bacteria of the genus Neisseria, such as Neisseria gonorrhoeae and Neisseria meningitidis. These bacteria are characterized by their spherical shape and the ability to retain the red stain during the Gram staining procedure.

The other options are incorrect:

• Staphylococcus: Staphylococcus bacteria are Gram-positive cocci, not Gram-negative. They include species like Staphylococcus aureus.
• Streptococcus: Streptococcus bacteria are also Gram-positive cocci. They form chains and include various species such as Streptococcus pyogenes and Streptococcus pneumoniae.
• Salmonella: Salmonella bacteria are Gram-negative rods, not cocci. They belong to the Enterobacteriaceae family and include species that can cause food poisoning and other infections.

Answer: Bacillus

The Medusa head colony is a characteristic of the bacterium Bacillus anthracis, which is the causative agent of anthrax. The colony appears as a flat, gray disk with irregular edges and projections that resemble Medusa’s hair. This appearance is due to the growth of long, interlacing chains of Bacillus anthracis cells.

The other options are incorrect:

• Clostridium is a genus of bacteria that includes the causative agent of tetanus.
• Pseudomonas is a genus of bacteria that includes the causative agent of pneumonia.
• E. coli is a bacterium that is commonly found in the intestines of animals and humans.

Answer: Mycoplasma

Mycoplasma are bacteria that lack a cell wall. Acid-fast bacteria, on the other hand, have a unique cell wall composition that makes them resistant to decolorization by acid-alcohol during the acid-fast staining procedure. Mycoplasma does not possess this characteristic cell wall structure and, therefore, is not acid-fast.

The other options are incorrect:

• Cryptosporidium: Cryptosporidium is a protozoan parasite, not a bacterium. It is not subjected to acid-fast staining as it lacks the characteristic bacterial cell wall.
• Mycobacterium: Mycobacteria, including species like Mycobacterium tuberculosis, are acid-fast bacteria. They have a unique cell wall structure containing mycolic acids, making them resistant to acid-alcohol decolorization.
• Nocardia: Nocardia is an actinomycete bacterium that is acid-fast. It possesses a cell wall similar to that of mycobacteria, allowing it to retain the stain during acid-fast staining.

Answer: Agglutination

The Widal test is a serological test used for the presumptive diagnosis of enteric fever, including typhoid and paratyphoid fevers. It is based on the principle of agglutination, where specific antibodies in the patient’s serum react with antigens from Salmonella typhi and Salmonella paratyphi, leading to the clumping or agglutination of bacterial cells.

The other options are incorrect:

• Flocculation: Flocculation refers to the formation of small clumps or aggregates in a liquid. While it is a type of agglutination, the Widal test specifically involves macroscopic agglutination reactions and not the fine particles characteristic of flocculation.
• Precipitation: Precipitation is the formation of solid particles from a solution. The Widal test does not involve the precipitation of soluble antigens and antibodies; instead, it focuses on the visible clumping of bacterial cells.
• Both “Flocculation” and “Precipitation”: While flocculation and precipitation are related phenomena, the Widal test primarily involves agglutination rather than fine particle flocculation or precipitation. The correct characterization is “agglutination” in the context of the Widal test.

Answer: dsDNA

Herpes Simplex Virus (HSV) belongs to the family Herpesviridae, and its genome consists of double-stranded DNA. This DNA can be linear or circular, depending on the virus type. The genetic material of HSV is housed within an icosahedral capsid.

The other options are incorrect:

• ssDNA (single-stranded DNA): Herpes Simplex Virus has a double-stranded DNA genome, not a single-stranded one.
• ssRNA (single-stranded RNA): HSV does not have a single-stranded RNA genome. It is classified as a DNA virus.
• dsRNA (double-stranded RNA): Herpes Simplex Virus does not have a double-stranded RNA genome. It is a DNA virus, and its genetic material is in the form of double-stranded DNA.

Answer: PCR

PCR is a molecular biology technique used for the amplification of DNA. It is not a serological method but rather a method that amplifies and detects nucleic acids, making it useful for the detection of genetic material, such as DNA or RNA, from pathogens.

The other options are incorrect:

• CFT (Complement Fixation Test): CFT is a serological test used to detect the presence of antibodies in a patient’s serum by measuring the fixation of complement.
• SRH (Slide Agglutination Test): SRH is a serological method involving the agglutination of particles on a slide. It is commonly used for blood typing and serotyping.
• Western Blot: Western blot is a technique that detects specific proteins in a sample. While it is often used for various diagnostic purposes, it is not a classical serological method primarily focused on the detection of antibodies or antigens in blood serum.

Answer: Rotavirus

Rotavirus primarily infects the gastrointestinal tract, causing gastroenteritis (inflammation of the stomach and intestines). It is a leading cause of severe diarrhea in infants and young children. Unlike the other options listed, rotavirus is not typically associated with respiratory infections.

The other options are incorrect:

• Adenovirus: Adenoviruses can cause respiratory infections, including the common cold, as well as other infections such as conjunctivitis, gastroenteritis, and urinary tract infections.
• Influenza Virus: Influenza viruses, including seasonal influenza and novel influenza strains, are well-known for causing respiratory infections with symptoms such as fever, cough, and sore throat.
• RSV (Respiratory Syncytial Virus): RSV is a common cause of respiratory tract infections, particularly in young children. It can lead to illnesses such as bronchiolitis and pneumonia.

Answer: Flavivirus

Hepatitis C Virus (HCV) is a member of the Flaviviridae family and the genus Flavivirus. Flaviviruses are RNA viruses with a positive-sense, single-stranded RNA genome. Other well-known viruses in the Flavivirus genus include Zika virus, Dengue virus, and West Nile virus.

The other options are incorrect:

• Togavirus: Togaviruses belong to a different virus family called Togaviridae. Examples of Togaviruses include the viruses responsible for diseases such as rubella.
• Filovirus: Filoviruses belong to the Filoviridae family. Notable examples include Ebola virus and Marburg virus, which are associated with severe hemorrhagic fevers.
• Retrovirus: Retroviruses belong to the Retroviridae family. Human Immunodeficiency Virus (HIV) is an example of a retrovirus. Unlike HCV, retroviruses have a reverse transcription step in their life cycle, converting their RNA genome into DNA.

Answer: Aspergillus flavus

Aflatoxins are toxic secondary metabolites produced by fungi, particularly Aspergillus flavus. These mycotoxins can contaminate various crops, especially peanuts, corn, and tree nuts, posing a significant risk to human and animal health when consumed.

The other options are incorrect:

• Candida: Candida is a genus of yeast and is not known to produce aflatoxins. It is more commonly associated with infections in humans.
• Penicillium: While some species of Penicillium can produce mycotoxins, aflatoxins are not typically associated with this genus. Penicillium species are more commonly linked to the production of other mycotoxins, such as patulin.
• Clostridium: Clostridium bacteria are not known for producing aflatoxins. Aflatoxins are primarily associated with certain molds, particularly those in the Aspergillus genus.

Answer: CD4+ cells

HIV primarily targets CD4+ T lymphocytes, which are a type of immune system cell. The virus binds to the CD4 receptor on the surface of these cells, facilitating its entry and replication within the host cell. As HIV replicates, it progressively damages and kills CD4+ T cells, leading to immune system suppression.

The other options are incorrect:

• CD8+ cells: CD8+ T cells, also known as cytotoxic T cells, are not the primary target of HIV. While they play a crucial role in the immune response against infected cells, they are not the main cells infected by the virus.
• B-lymphocytes: B-lymphocytes are not the main target of HIV. These cells are involved in antibody production and are not as commonly infected by the virus compared to CD4+ T cells.
• Basophils: Basophils are a type of white blood cell involved in allergic reactions and inflammatory responses. HIV does not typically infect basophils; its main targets are CD4+ T cells in the immune system.

Answer: Cat

Toxoplasma gondii is an obligate intracellular protozoan parasite, and its life cycle involves sexual reproduction in the intestines of cats. Cats shed oocysts (the infective form of the parasite) in their feces. Other animals, including humans, can become infected by ingesting these oocysts through contaminated food, water, or soil.

The other options are incorrect:

• Dog: While dogs can become infected with Toxoplasma gondii, they are not the primary hosts responsible for the spread of the parasite. Cats play a more significant role in the transmission of the parasite.
• Human: Humans can become intermediate hosts by ingesting oocysts, but they are not the primary source of transmission. Humans are considered accidental hosts in the life cycle of Toxoplasma gondii.
• Sheep: Sheep can become infected with Toxoplasma gondii, but they are not the primary hosts responsible for the spread of the parasite. The main role in transmission is attributed to cats.

Answer: T cells

Cell-mediated immunity involves the activation of T cells, which are a type of lymphocyte. T cells play a central role in recognizing and responding to infected or abnormal cells. They can directly destroy infected cells or coordinate immune responses by releasing signaling molecules (cytokines) that activate other immune cells.

The other options are incorrect:

• B cells: B cells are primarily involved in humoral immunity, where they produce antibodies that circulate in the blood and other bodily fluids to neutralize pathogens.
• Macrophages: Macrophages are phagocytic cells that play a role in both innate and adaptive immunity. While they contribute to the immune response, they are not the main effector cells in cell-mediated immunity.
• Monocytes: Monocytes are precursors to macrophages and dendritic cells. They circulate in the bloodstream and can differentiate into macrophages when they enter tissues. While they are involved in immune responses, they are not the primary effector cells in cell-mediated immunity.

Answer: Immunological memory

Immunological Memory: Vaccination involves exposing the immune system to a harmless form of a pathogen or a component of the pathogen (antigen) to stimulate an immune response. This exposure induces immunological memory, where the immune system “remembers” the pathogen. If the individual is later exposed to the actual pathogen, the immune system can mount a faster and more effective response, providing protection against the disease.

The other options are incorrect:

• Agglutination: Agglutination is a process in which particles or cells clump together. While it is a phenomenon that can be observed in the immune response, vaccination is not based on the principle of agglutination.
• Phagocytosis: Phagocytosis is the process by which certain cells engulf and digest particles or microorganisms. While phagocytosis is a part of the immune response, vaccination is not primarily based on this principle.
• Clonal Deletion: Clonal deletion refers to the elimination of self-reactive immune cells during the development of the immune system to prevent autoimmune reactions. Vaccination does not involve clonal deletion but rather the generation of memory cells for specific pathogens.

Answer: Precipitation

Precipitation refers to the formation of an insoluble complex when a soluble antigen combines with its specific antibody. This complex becomes insoluble and settles out of solution. The reaction between antigen and antibody in the right proportions results in the formation of a visible precipitate.

The other options are incorrect:

• Agglutination: Agglutination is the clumping of cells or particles, not the formation of a precipitate. It is commonly observed in blood typing when antigens on the surface of cells clump together in the presence of specific antibodies.
• Flocculation: Flocculation involves the formation of small clumps or aggregates in a liquid, typically in the form of fine particles. It is a type of agglutination and is not specifically associated with the reaction of soluble antigens with antibodies.
• CFT (Complement Fixation Test): The Complement Fixation Test is a serological test that measures the ability of antibodies to fix complement. It does not directly involve the precipitation of soluble antigens but assesses the activation of the complement system.

Answer: dyes

In the context of various experiments or processes, including biological assays, chemical reactions, or laboratory techniques, dyes are often used for preliminary screening. Dyes can be employed to visualize, stain, or detect specific characteristics or components, aiding in the initial identification or screening of samples.

The other options are incorrect:

• Restriction Enzyme: Restriction enzymes are proteins that cleave DNA at specific recognition sequences. While they are essential tools in molecular biology techniques like DNA analysis, they are not typically used for preliminary screening.
• Antibiotics: Antibiotics are substances that kill or inhibit the growth of bacteria or other microorganisms. They are commonly used in microbiological studies but are not typically used for preliminary screening in a broad context.
• Radiation: Radiation is used in various scientific applications, including medical imaging and cancer treatment, but it is not a standard method for preliminary screening in a general sense. Dyes are often more versatile and applicable in different screening scenarios.

Answer: T cells

T cells are a type of lymphocyte involved in cell-mediated immunity. They play a crucial role in recognizing antigens presented by other cells, particularly antigen-presenting cells (APCs). However, T cells themselves are not typically classified as APCs. Instead, they rely on APCs to present antigens to them.

The other options are incorrect:

• B cells: B cells are antigen-presenting cells. They can capture, process, and present antigens to helper T cells, initiating an immune response.
• Dendritic cells: Dendritic cells are professional APCs that play a key role in initiating immune responses. They are highly effective at capturing and presenting antigens to T cells.
• Langerhans cells: Langerhans cells are a type of dendritic cell found in the skin and mucous membranes. Like other dendritic cells, they are antigen-presenting cells involved in immune responses.

Answer:Both “Specie” and “Environment”

Intrinsic determinants of a disease are factors inherent to the individual and include aspects such as genetics and immune status. Species and environment are extrinsic factors that are external to the individual.

The other options are incorrect:

• Specie: Species refers to the type or class of an organism, and it is an extrinsic factor. In the context of disease determinants, it is not considered intrinsic to an individual.
• Environment: Environment, including external factors such as climate, geography, and exposure to toxins, is an extrinsic determinant. While it influences health and disease, it is not intrinsic to the individual.

Answer: Hapten

Haptens are small molecules that, by themselves, are not immunogenic. However, when they bind to larger carrier molecules (such as proteins), they can induce an immune response. The immune system recognizes the hapten-carrier complex as foreign and generates an immune response against it.

The other options are incorrect:

• Antigen: An antigen is a substance that can induce an immune response by itself. It can be a complete molecule, like a protein or a polysaccharide, and does not require binding to another molecule to trigger an immune response.
• Virus: Viruses are complete entities that can induce an immune response without the need to bind to another molecule. The viral components, such as proteins or genetic material, can act as antigens and elicit an immune response.
• Antibody: Antibodies are produced by the immune system in response to the presence of antigens. They are not substances that induce an immune response themselves; rather, they are part of the immune response generated against antigens.

Answer: Case-control

In a case-control study, participants are selected based on their disease or outcome status. Cases (individuals with the disease or outcome of interest) are compared to controls (individuals without the disease or outcome). The presence or absence of a specific risk factor or exposure is then compared between the two groups to assess its association with the disease.

The other options are incorrect:

• Experimental: Experimental studies, such as randomized controlled trials (RCTs), involve the random assignment of participants to different interventions. They are not specifically designed to identify participants based on disease/outcome status and compare the presence of a risk factor; instead, they focus on the impact of interventions.
• Cross-sectional: Cross-sectional studies involve the simultaneous collection of data from participants at a single point in time. While they can assess the prevalence of risk factors and diseases, they do not involve the identification of participants based on disease/outcome status for subsequent comparison.

Answer: Spirochetosis

Spirochetosis refers to diseases caused by spirochetes, which are spiral-shaped bacteria. Some spirochetes are transmitted to humans through arthropod vectors like ticks. Lyme disease, caused by the bacterium Borrelia burgdorferi and transmitted by certain ticks, is an example of a spirochetosis.

The other options are incorrect:

• Avian Influenza: Avian influenza, or bird flu, is caused by influenza viruses and is primarily a respiratory disease in birds. It is not typically transmitted by arthropod vectors.
• Tuberculosis: Tuberculosis is caused by Mycobacterium tuberculosis and is primarily spread through respiratory droplets. It is not an arthropod vector-borne disease.
• CRD (Chronic Respiratory Disease): CRD is a general term for various chronic respiratory conditions, and it is not caused by arthropod vectors. It includes diseases like chronic bronchitis and emphysema.

Answer: Rotavirus

Rotavirus is a double-stranded RNA virus that primarily infects the gastrointestinal tract, causing gastroenteritis. Unlike some other viruses listed, rotavirus infections are generally acute and do not establish a latent phase where the virus remains in a dormant state within the host.

The other options are incorrect:

• HIV (Human Immunodeficiency Virus): HIV is known for establishing latent infections, especially in long-lived cells like CD4+ T cells. The virus can remain dormant for extended periods before becoming actively replicative.
• EBV (Epstein-Barr Virus): EBV, a member of the herpesvirus family, can establish latent infections in B cells. It is known for causing infectious mononucleosis and is associated with various malignancies.
• Cytomegalovirus (CMV): CMV, another herpesvirus, can establish latent infections in various cell types, including monocytes and lymphocytes. Reactivation of latent CMV can occur, especially in individuals with compromised immune systems.

Answer: Lipopolysaccharide

LPS is a major component of the outer membrane of Gram-negative bacteria. It consists of lipid A, a core oligosaccharide, and an O-specific polysaccharide. LPS is considered an endotoxin because its release during bacterial cell death or lysis can trigger strong immune responses and inflammation in the host.

The other options are incorrect:

• Polysaccharide: While polysaccharides are components of bacterial cell walls, the specific endotoxin associated with Gram-negative bacteria is lipopolysaccharide (LPS).
• Glycoprotein: Glycoproteins are molecules that have both protein and carbohydrate components. Endotoxins for Gram-negative bacteria, however, are primarily lipopolysaccharides.
• Lipoprotein: Lipoproteins are components of bacterial cell walls, but they are not specifically considered endotoxins. Lipopolysaccharide, with its lipid A component, is the main endotoxin associated with Gram-negative organisms.

Answer: Adenovirus

Adenoviruses are a group of viruses that can cause respiratory, gastrointestinal, and ocular infections in humans. While they can lead to severe illnesses, adenoviruses are generally not known to be oncogenic, meaning they do not typically cause cancer.

The other options are incorrect:

• HTLV-1 (Human T-cell Lymphotropic Virus-1): HTLV-1 is an oncogenic virus associated with the development of adult T-cell leukemia/lymphoma (ATLL) and other disorders.
• Papillomavirus: Papillomaviruses, including human papillomavirus (HPV), are oncogenic viruses known to be associated with cervical cancer and other malignancies.
• HBV (Hepatitis B Virus): Hepatitis B virus is associated with liver cancer (hepatocellular carcinoma) and is considered an oncogenic virus. Chronic infection with HBV increases the risk of developing liver cancer.

Answer: Clostridium

Clostridium species are obligate anaerobes, meaning they thrive in the absence of oxygen. They are spore-forming bacteria and are commonly found in soil and the gastrointestinal tract. Some Clostridium species can cause infections in wounds or other anaerobic environments.

The other options are incorrect:

• Bacillus: Bacillus species are generally aerobic or facultative anaerobes, meaning they can grow in the presence or absence of oxygen.
• Staphylococcus: Staphylococcus species are facultative anaerobes, capable of growing both in the presence and absence of oxygen.
• Klebsiella: Klebsiella species are facultative anaerobes, meaning they can grow in both aerobic and anaerobic conditions. They are commonly found in the environment and in the human respiratory and intestinal tracts.

Answer: Incidence

Incidence is a measure that quantifies the rate at which new cases of a specific disease occur in a population during a defined time period. It focuses on newly diagnosed cases and provides information about the risk of developing the disease.

The other options are incorrect:

• % Positivity: % Positivity typically refers to the percentage of positive results in a diagnostic test or the proportion of positive cases among the tested population. It is not a measure of new cases over time.
• Prevalence: Prevalence encompasses both new and existing cases of a disease in a population at a specific point or over a specific period. It includes both old and new cases, making it different from incidence.
• Hyperendemic: Hyperendemic refers to a situation where the prevalence of a particular disease remains consistently high within a specific geographic area or population group. It does not specifically address the number of new cases over time.

Answer: Cryptococcus

• Cryptococcus is a genus of fungi, and some species within this genus, particularly Cryptococcus neoformans, are known to possess a capsule. The capsule is a protective structure around the fungal cell that contributes to its virulence.

The other options are incorrect:

• Candida: Candida is a genus of fungi that includes various species, but it is not typically associated with the presence of a capsule.
• Aspergillus: Aspergillus is a genus of fungi known for producing conidia (asexual spores) and does not possess a capsule.
• Mucor: Mucor is a genus of fungi that belongs to the group known as zygomycetes. It does not typically possess a capsule.

Answer: LD50

LD50 is a standard measure used in toxicology to express the dose of a substance (such as a drug or toxin) that is lethal to 50% of a population (usually laboratory animals) under standardized experimental conditions. It helps assess the toxicity of a substance and is expressed in terms of the amount of substance administered per unit of body weight.

The other options are incorrect:

• ID50 (Infectious Dose 50): ID50 is used in microbiology and refers to the dose of a microorganism (such as a bacterium or virus) required to infect 50% of the test population.
• MLD50 (Minimum Lethal Dose 50): MLD50 is not a standard term commonly used in toxicology or experimental biology.
• TCIC50 (Total Concentration for Inhibition of Cell Growth 50): TCIC50 is not a standard term and is not commonly used in toxicology or experimental biology.

Answer: Safranin

Gram’s staining is a differential staining technique used to classify bacteria into two main groups: Gram-positive and Gram-negative. The procedure involves several steps, including the application of crystal violet (primary stain), iodine (mordant), alcohol or acetone (decolorization), and a counterstain. Safranin is the counterstain used to color the Gram-negative bacteria.

The other options are incorrect:

• Methylene Blue: Methylene blue is a basic dye that can be used in various staining procedures, but it is not a component of Gram’s staining.
• Iodine: Iodine serves as a mordant in Gram’s staining, forming a complex with crystal violet that enhances its retention in Gram-positive bacteria.
• Crystal Violet: Crystal violet is the primary stain used in the initial step of Gram’s staining. It imparts a violet color to all cells.

Answer: Cell wall

Viruses lack cellular structures, including a cell wall. Unlike bacteria and plant cells, which have cell walls, viruses are composed of genetic material (either DNA or RNA) surrounded by a protein coat called a capsid. Some viruses may also have an outer lipid envelope derived from the host cell membrane, but they do not possess a cell wall.

The other options are incorrect:

• DNA: Many viruses can contain DNA as their genetic material. Examples include herpesviruses and adenoviruses.
• RNA: Many viruses contain RNA as their genetic material. Examples include influenza viruses and retroviruses like HIV.
• Enzyme: Some viruses may encode enzymes as part of their genetic material to facilitate their replication within host cells. Examples include viral polymerases.

Answer: Streptococcus

Streptococcus bacteria are characterized by their round shape and the ability to form chains. They are Gram-positive cocci and are often classified based on their hemolytic properties on blood agar. Streptococci play various roles in infections, including causing strep throat, pneumonia, and other diseases.

The other options are incorrect:

• Pneumococcus: Pneumococcus, or Streptococcus pneumoniae, is a specific species of Streptococcus. While it is round-shaped, it is typically not chain-forming but appears in pairs (diplococci) or short chains.
• Staphylococcus: Staphylococcus bacteria are also round-shaped cocci, but they form grape-like clusters rather than chains.
• Diplococcus: Diplococcus refers to bacteria that typically occur in pairs. Neisseria species are examples of diplococci. They are not chain-forming like

Answer: Poliomyelitis

Polio is primarily a human disease caused by the poliovirus. While there are animal viruses related to poliovirus, the natural reservoir for the human poliovirus is humans. Polio is not considered a zoonotic disease.

The other options are incorrect:

• Influenza A H5N1: Influenza A H5N1, also known as avian influenza or bird flu, can be zoonotic, with birds (especially poultry) serving as a reservoir. Transmission to humans can occur, and certain strains have caused outbreaks in humans.
• Hantaviruses: Hantaviruses are zoonotic viruses that are transmitted to humans through contact with infected rodents. They can cause diseases such as hantavirus pulmonary syndrome (HPS) and hemorrhagic fever with renal syndrome (HFRS).
• Rabies: Rabies is a zoonotic viral infection transmitted to humans through the saliva of infected animals, typically through bites. Dogs, bats, raccoons, and other mammals can serve as reservoirs for the rabies virus.

Answer: Antagonize

Maternal antibodies transferred to an infant from the mother, either through placental transfer during pregnancy or through breast milk, can provide passive immunity to the infant. However, these maternal antibodies may also interfere with the effectiveness of certain vaccines, especially live attenuated vaccines, by neutralizing the vaccine antigens.

The other options are incorrect:

• Enhance: Maternal antibodies are more likely to interfere with the effectiveness of a vaccine rather than enhance it. This interference is known as maternal antibody interference.
• Synergize: Maternal antibodies do not typically synergize with vaccines. Instead, they may reduce the efficacy of the vaccine by neutralizing the vaccine antigens.
• Complement: While maternal antibodies can complement the infant’s immune system and provide protection against certain infections, the term “complement” in this context refers to a different aspect of immunology and is not directly related to the interference observed with certain vaccines.

Answer: Specificity

Specificity in a diagnostic test refers to its ability to correctly identify individuals without the condition (true negatives). A lack of specificity means that the test may produce false positives, incorrectly indicating the presence of the condition in individuals who do not have it.

The other options are incorrect:

• Predictive Value: Predictive value is a measure that combines sensitivity and specificity. However, the lack of specificity specifically leads to false positives, affecting the positive predictive value.
• Sensitivity: Sensitivity relates to a test’s ability to correctly identify individuals with the condition (true positives). It is not directly associated with false positives; however, a lack of specificity can affect the overall accuracy of a test.
• Reproducibility: Reproducibility pertains to the consistency of results when a test is repeated. While it is essential for the reliability of a diagnostic test, a lack of specificity is specifically associated with false positive results rather than issues of reproducibility.

Answer: antibodies production

The innate immune response is the immediate, non-specific defense mechanism that the body employs against pathogens. It includes physical barriers (such as the skin), phagocytosis (engulfing and destruction of pathogens by cells like macrophages), complement activation (a system of proteins that enhance immune functions), and natural killer (NK) cells activation (a type of lymphocyte that can recognize and destroy infected cells). Antibodies are part of the adaptive immune response, which is more specific and takes time to develop.

The other options are incorrect:

• Phagocytosis: Phagocytosis is a key component of innate immunity, involving the ingestion and digestion of pathogens by phagocytic cells.
• Complement Activation: The complement system, which includes a series of proteins, is part of the innate immune response. It enhances various immune functions, such as phagocytosis and inflammation.
• NK Cells Activation: Natural killer (NK) cells are part of the innate immune response and play a role in the early defense against virus-infected and cancer cells. They do not require prior exposure to specific antigens.

Answer: Obligate intracellular parasites

Viruses are unable to carry out metabolic processes or replicate independently. They lack the cellular machinery necessary for energy production and protein synthesis. Instead, viruses rely on host cells to replicate and complete their life cycle.

The other options are incorrect:

• Have Their Own Metabolism: Viruses do not have their own metabolism. They lack the cellular structures needed for metabolic processes and energy production.
• Divide by Binary Fission: Binary fission is a method of cell division seen in bacteria and some other unicellular organisms. Viruses replicate by infecting host cells and hijacking their cellular machinery for replication.
• Have Both DNA and RNA: While some viruses have DNA (DNA viruses) and others have RNA (RNA viruses), they do not typically have both types of genetic material simultaneously. The genetic material can be single-stranded or double-stranded and can be composed of DNA or RNA, depending on the virus.

Answer: Fleas

Plague is a bacterial infection caused by Yersinia pestis. Fleas, especially those that infest rodents, serve as the vectors for transmitting the bacteria from rodents to humans. The most common vector is the Oriental rat flea (Xenopsylla cheopis), which infests rats.

The other options are incorrect:

• Flies: Flies are not vectors for the transmission of Yersinia pestis, the bacterium that causes plague.
• Mosquitoes: Mosquitoes are not the primary vectors for plague transmission. Fleas are the main vectors associated with the spread of the disease.
• Ticks: While ticks can transmit other diseases, they are not the primary vectors for the transmission of Yersinia pestis, which causes plague. Fleas are the primary vectors in the case of plague.

Answer: Hypersensitivity type-IV

This type of hypersensitivity involves a delayed immune response mediated by T cells. The tuberculin skin test, used for diagnosing tuberculosis (TB), is an example of type-IV hypersensitivity. In this test, exposure to Mycobacterium tuberculosis antigens elicits a delayed response involving sensitized T cells, resulting in the characteristic skin reaction.

The other options are incorrect:

• Hypersensitivity Type-I (Immediate Hypersensitivity): Type-I hypersensitivity involves an immediate IgE-mediated response, leading to the release of histamines and other mediators. Allergic reactions like hay fever and anaphylaxis are examples of type-I hypersensitivity.
• Hypersensitivity Type-II (Cytotoxic Hypersensitivity): Type-II hypersensitivity involves antibodies (IgM or IgG) targeting antigens on the surface of cells, leading to cell destruction. Hemolytic transfusion reactions and some autoimmune diseases are examples of type-II hypersensitivity.
• Hypersensitivity Type-III (Immune Complex-Mediated Hypersensitivity): Type-III hypersensitivity involves the formation of immune complexes that deposit in tissues, leading to inflammation and tissue damage. Conditions like systemic lupus erythematosus (SLE) involve type-III hypersensitivity reactions.

Answer: Annealing

In the polymerase chain reaction (PCR) or DNA sequencing, annealing is a step where the temperature is lowered to allow a primer (a short single-stranded DNA sequence) to bind to its complementary sequence on the DNA template. This step provides a starting point for DNA synthesis by DNA polymerase.

The other options are incorrect:

• Denaturation: Denaturation involves the separation of the DNA double strands by heating, breaking the hydrogen bonds between complementary bases.
• Extension: Extension, also known as elongation, is the step in PCR where DNA polymerase synthesizes a new DNA strand complementary to the DNA template.
• Bounding: “Bounding” is not a term commonly used in the context of PCR or DNA replication. The correct term for the binding of a primer to a DNA template is “annealing.”

Answer: Isopropanol

Isopropanol is commonly used in molecular biology to precipitate DNA from a solution. This process involves adding isopropanol to a DNA-containing solution, which causes the DNA to come out of the solution and form a visible pellet upon centrifugation.

The other options are incorrect:

• SDS (Sodium Dodecyl Sulfate): SDS is a detergent used to solubilize and denature proteins but is not typically used for DNA precipitation.
• Phenol: Phenol is often used for DNA extraction and purification but not for DNA precipitation. It is used in the phenol-chloroform extraction method.
• Chloroform: Chloroform is used in DNA extraction procedures, such as the phenol-chloroform extraction method, but is not the reagent typically used for DNA precipitation.

Answer: Reverse transcriptase

Reverse transcriptase is an enzyme that catalyzes the synthesis of DNA from an RNA template. This process is known as reverse transcription. Reverse transcriptase is commonly used in molecular biology techniques, such as reverse transcription-polymerase chain reaction (RT-PCR), to convert RNA into complementary DNA (cDNA).

The other options are incorrect:

• Taq Polymerase: Taq polymerase is a DNA polymerase used in PCR reactions to amplify DNA but does not have the ability to synthesize DNA from an RNA template.
• Alkaline Phosphatase: Alkaline phosphatase is an enzyme used in molecular biology to remove phosphate groups from DNA or RNA, but it is not involved in the synthesis of DNA from an mRNA template.
• Nuclease: Nucleases are enzymes that cleave the phosphodiester bonds in nucleic acids, and they are not directly involved in the synthesis of DNA from an mRNA template.

Answer: Monitoring

Monitoring is the systematic or continuous collection of data or information about a particular process, condition, or event. It is often used to assess the health, productivity, and environment of a given population or area.

The other options are incorrect:

• GIS (Geographic Information Systems): GIS is a tool that can be used to collect, store, analyze, and visualize geographic data. However, it is not the same as monitoring. GIS can be used to support monitoring activities, but it is not the only tool that can be used for this purpose.
• Surveillance: Surveillance is the systematic collection of data or information about a specific disease or condition. It is often used to track the spread of disease and to identify outbreaks. However, surveillance is a more narrow concept than monitoring. Monitoring can be used to collect data on a wide range of topics, while surveillance is limited to data on disease or condition.
• Cohort studies: Cohort studies are longitudinal studies that follow a group of people over time to investigate the relationship between a particular exposure and a particular outcome. Cohort studies are not typically used to collect routine observations on health, productivity, or environment. Instead, they are used to investigate specific hypotheses about health and disease.

Answer: Psittacosis

Psittacosis, also known as parrot fever, is a zoonotic disease that can be transmitted from parrots to humans. It is caused by the bacterium Chlamydia psittaci. Humans can become infected with Chlamydia psittaci by inhaling the dried droppings, feathers, or dust of infected birds. The disease can also be transmitted through direct contact with the bird’s saliva, blood, or urine.

The other options are incorrect:

• Typhoid is a bacterial infection that is caused by Salmonella typhi. It is not typically transmitted from parrots to humans.
• Bird flu, also known as avian influenza, is a viral infection that is caused by influenza viruses. It can be transmitted from birds to humans, but it is not typically transmitted from parrots to humans.
• Cholera is an bacterial infection that is caused by Vibrio cholerae. It is not typically transmitted from parrots to humans.