Microbiology MCQs with Answer and Explnation | Chapter 6

Answer: Both Lipolytic and Proteolytic

Enzymes responsible for decomposition break down molecules into smaller components. Lipolytic enzymes break down lipids (fats), while proteolytic enzymes break down proteins. Decomposition involves the breakdown of various organic compounds, and both lipolytic and proteolytic enzymes play crucial roles in this process.

List of incorrect options:

1. Lysozyme: An enzyme that can break down bacterial cell walls by hydrolyzing the peptidoglycan component. However, it’s not the primary enzyme responsible for the wide-ranging decomposition of organic matter.

Each incorrect option targets a specific type of biomolecule (lipids, proteins, or bacterial cell walls) but doesn’t cover the full spectrum of organic matter decomposition.

Answer: Both Micrococcus sps. and Proteus sps.

Urea is decomposed by bacteria through a process called ureolysis. Certain bacterial species possess the enzyme urease, which catalyzes the breakdown of urea into carbon dioxide and ammonia. Both Micrococcus species and Proteus species are known to contain urease enzymes and can decompose urea.

List of incorrect options:

1. Nitrosomonas sps.: Nitrosomonas bacteria are involved in the process of nitrification, oxidizing ammonia to nitrite in the nitrogen cycle, but they don’t typically decompose urea.

Answer: The algal part in Lichens

Phycobiont is the algal component of a lichen, while mycobiont is the fungal component. Lichens are a type of symbiotic organism that is formed by the close association of an alga and a fungus. The alga provides the fungus with food through photosynthesis, while the fungus provides the alga with shelter and protection from the environment.

These Options are incorrect:

• The fungal part in Lichens: This option is incorrect because the fungal part of a lichen is called the mycobiont.
• Laustoria formation: This option is incorrect because laustoria formation is a type of parasitic relationship between a fungus and a plant, not a type of symbiotic relationship like lichenization.

Answer: Capsules

Parasitic forms of bacteria often possess capsules. Capsules are protective structures surrounding some bacterial cells, typically composed of polysaccharides. They serve various functions, including helping the bacteria evade the host’s immune system by inhibiting phagocytosis (the engulfing of bacteria by immune cells). Capsules can also enhance the bacterium’s ability to adhere to host cells and tissues and establish infection within the host organism. This protection and adherence are crucial for the survival and pathogenicity of parasitic bacteria.

Answer: Gene pool

The gene pool is the collection of all the genes that are present in a population of organisms. It is the sum of all the alleles for all the genes in the population.

The gene pool of a population is constantly changing due to mutation, migration, and selection. Mutation is the process by which new alleles are created. Migration is the movement of individuals between populations. Selection is the process by which individuals with certain alleles are more likely to survive and reproduce.

The gene pool is important for the evolution of populations. It is the source of the genetic variation that is necessary for adaptation to new environments.

The other options are not correct:

• Genome is the complete set of genetic instructions for an organism.
• Gene map is a diagram that shows the relative positions of genes on a chromosome.

Answer: Virulent

Virulent bacteria are those that cause disease. Capsules can help virulent bacteria to evade the host’s immune system and cause more severe infections. Examples of virulent encapsulated bacteria include:

Streptococcus pneumoniae
Haemophilus influenzae type B
Neisseria meningitidis
Avirulent bacteria are those that do not cause disease. Some avirulent bacteria, such as Lactobacillus acidophilus, are even beneficial. Capsules can help avirulent bacteria to colonize the body and compete with other bacteria.

Answer: Conjugants

Conjugation is a process by which bacteria exchange genetic material. It is a form of horizontal gene transfer, which is the transfer of genes between cells that are not parent and offspring. Conjugation is mediated by a specialized structure called a pilus. The pilus is a long, thin tube that extends from the donor cell to the recipient cell. Once the pilus has retracted and brought the two cells together, the donor cell transfers a single strand of DNA to the recipient cell. The recipient cell then synthesizes a complementary strand of DNA to complete the double helix.

Conjugation can occur between any two bacterial cells that are compatible. However, it is most common between cells of the same species. Conjugation can be used to transfer a variety of genes, including genes for antibiotic resistance, virulence, and metabolic pathways.

The other options are not correct:

• Fertile cells are cells that are capable of reproduction.
• Exconjugants are cells that have participated in conjugation

Answer: All of these

Phagocytes are a type of white blood cell that engulfs and digests foreign particles, bacteria, and dead or dying cells through a process called phagocytosis. They include various cell types, such as monocytes, basophils, and macrophages, each playing a role in the immune response by actively engulfing and destroying pathogens or debris.

1. Monocytes: These are a type of white blood cell produced in the bone marrow that can differentiate into macrophages when they move into various tissues, where they act as phagocytes.
2. Basophils: Basophils are a type of white blood cell involved in allergic reactions and inflammation by releasing histamine. While they aren’t primarily phagocytes, they play roles in the immune response through other mechanisms.
3. Macrophages: Macrophages are a type of phagocyte derived from monocytes and are highly effective in engulfing and digesting pathogens and cellular debris as part of the immune response.

Answer: Phagosome

A phagosome is a membrane-bound vesicle that is formed when a phagocyte engulfs a foreign particle. The phagosome then fuses with a lysosome, which contains hydrolytic enzymes that can destroy the foreign particle.

The fusion of the phagosome and lysosome creates a phagolysosome, which is a specialized structure that is dedicated to destroying foreign particles. The hydrolytic enzymes in the phagolysosome break down the foreign particle into smaller molecules, which are then absorbed by the phagocyte.

• The lysosome is also involved in the breakdown of cellular debris and other waste products.

Answer: All of these

The toxic products found in phagolysosomes, generated as a part of the immune response to destroy engulfed pathogens, include:

1. H2SO4 (Sulfuric acid): This strong acid is a product of the breakdown of molecules within the phagolysosome due to the acidic environment created by enzymes.
2. Singlet O2 (Singlet oxygen): Reactive oxygen species (ROS) like singlet oxygen are generated by the action of enzymes in the respiratory burst during phagocytosis. These ROS are highly reactive and contribute to the destruction of engulfed microorganisms.
3. Superoxide radicals: Another type of reactive oxygen species produced during the respiratory burst, these radicals also play a role in damaging and killing pathogens within the phagolysosome.

Answer: Opsonization

The process you’re describing, where a bacterium is coated with antibodies or complement proteins to facilitate its recognition and subsequent enhanced phagocytosis by phagocytes, is called “opsonization.”

Explanation:

• Opsonization: It involves the binding of antibodies or complement proteins (opsonins) to the surface of pathogens, marking them for more efficient recognition and engulfment by phagocytes. Opsonins act as “tags” that label the pathogen for rapid identification and uptake by phagocytic cells.
• Agglutination: This process involves the clumping together of particles, often pathogens, due to the cross-linking by antibodies. While agglutination can occur as part of the immune response, it doesn’t necessarily directly enhance phagocytosis by coating pathogens for ingestion by phagocytes.
• CFT (Complement Fixation Test): CFT is a laboratory technique used to detect the presence of specific antibodies or antigens in a patient’s serum by observing whether complement proteins fix or activate in the presence of these antibodies or antigens. It’s a diagnostic method and not directly related to the process of enhancing phagocytosis.

Answer: Inactivation of bacteria

Attenuation typically refers to the process of weakening or reducing the virulence or disease-causing ability of a microorganism without necessarily killing it.

So, among the options provided:

• Killing of the bacteria (microorganism): Attenuation doesn’t always involve killing the bacteria; instead, it often involves reducing its ability to cause disease while allowing it to survive.
• Inactivation of bacteria: Attenuation might involve inactivating certain aspects of the bacteria’s pathogenicity while keeping it viable.
• More activating the bacteria: Attenuation is the opposite; it decreases the pathogenicity rather than increasing it.

The closest match is “Inactivation of bacteria,” although it’s important to note that attenuation doesn’t always mean complete inactivation. It usually refers to weakening the disease-causing ability of the microorganism while allowing it to survive and potentially induce an immune response without causing severe illness.

Answer: Streptococcus pyogenes

Streptococcus pyogenes is a group A beta-hemolytic Streptococcus (GAS) that is a major human pathogen. It is responsible for a wide range of infections, including strep throat, scarlet fever, rheumatic fever, and impetigo.

β-hemolytic bacteria are characterized by their ability to produce hemolysins, which are enzymes that lyse red blood cells. This results in a clear zone (beta hemolysis) around the bacteria on a blood agar plate.

The other options are not β-hemolytic bacteria:

• Streptococcus pneumoniae is a group B alpha-hemolytic Streptococcus (GBS) that is a major cause of pneumonia, meningitis, and sepsis in infants and young children.
• Streptococcus viridans is a group C viridans Streptococcus that is a normal inhabitant of the human oral cavity and upper respiratory tract. It is also a common cause of endocarditis, especially in patients with prosthetic heart valves.
• Streptococcus faecalis is an enterococcus that is a normal inhabitant of the human gastrointestinal tract. It is also a common cause of urinary tract infections, endocarditis, and intra-abdominal infections.

Answer: Serum component

Opsonin is a “Serum component.” It is a substance, typically found in serum, that enhances phagocytosis by marking pathogens for ingestion by phagocytes. Opsonins include antibodies and complement proteins.

Answer: Viraemia

• Viraemia: This term refers specifically to the presence of viruses circulating in the bloodstream. It signifies the systemic dissemination of viruses within the body through the blood.

List of incorrect options:

1. Bacteraemia: This term denotes the presence of bacteria in the bloodstream, not viruses. It describes the transient appearance of bacteria in the blood, often due to infection or invasion but is distinct from viraemia, which involves viruses.
2. Septicaemia: This term refers to a severe systemic illness caused by the spread of bacteria or their toxins in the blood. While it encompasses bacterial infections and their impact on the body, it’s different from viraemia, which specifically relates to viral presence in the bloodstream.
3. Pyemia: Historically, this term described a condition where pus-forming bacteria were present in the blood, leading to the formation of abscesses in various organs. Similar to bacteraemia and septicaemia, pyemia specifically deals with bacterial infections, not viral presence in the blood.

Answer: Bacteraemia

• Bacteraemia: This term denotes the transient or continuous presence of viable bacteria in the bloodstream. It does not necessarily indicate systemic illness but signifies the presence of bacteria in the blood, which could potentially lead to systemic infection if not cleared by the immune system.
• Viraemia: This term refers to the presence of viruses in the bloodstream, not bacteria.
• Septicaemia: This term encompasses a severe systemic illness resulting from the spread of bacteria or their toxins in the blood, leading to a systemic inflammatory response. While it involves the presence of bacteria in the bloodstream, it often indicates a more severe condition than bacteraemia.
• Bactericidal: This term refers to substances or treatments that are capable of killing bacteria, rather than describing the presence of bacteria in the bloodstream.

Answer: Pyogenic infection

• Pyogenic infections: These are infections caused by bacteria that stimulate the production of pus. Pus is a mixture of dead tissue, bacteria, and immune cells that accumulate at the site of infection. Pyogenic infections are characterized by their ability to induce pus formation.
• Focal infection: This term refers to an infection that is confined to a specific area or focal point within the body, often serving as a source for disseminating infections to other parts of the body.
• Acute infection: This term refers to a short-term infection that develops rapidly and resolves relatively quickly, irrespective of pus formation.
• Chronic infection: This refers to an infection that persists over a prolonged period, often for months or years, rather than describing the specific formation of pus.

Answer: All of these

• Protected water supply: Providing clean, safe water is crucial in preventing the spread of cholera. Access to safe water sources helps prevent the ingestion of contaminated water, a common route of cholera transmission.
• Environmental sanitation: Proper sanitation practices, including waste disposal and hygiene measures, are essential in preventing the contamination of water sources and controlling the spread of cholera.
• Immunization with killed vaccines: Cholera vaccines, including killed or inactivated vaccines, are available and can provide protection against cholera. Immunization can be a preventive measure for individuals living in areas with endemic cholera or those at high risk of exposure during outbreaks.

Answer: None of These

Cholera vaccines can offer varying durations of protection based on the specific vaccine used and the individual’s immune response. Generally, the protection provided by cholera vaccines can last for around 2 years or longer in some cases.

None of the options provided (1 – 3 months, 3 – 6 months, 6 – 9 months) accurately represent the typical duration of protection conferred by cholera vaccines.

Answer: Causes less subclinical infections as compared to eltor

• It shares some Inaba, Ogawa subtypes with eltor: Both Vibrio cholerae and Vibrio eltor can share certain serotypes like Inaba and Ogawa. These serotypes are variations in the surface structures (antigens) of the bacteria, allowing for different classifications within the species.
• Resistant to polymyxin: There’s no general resistance of Vibrio cholerae or Vibrio eltor to polymyxin. These bacteria may display varying degrees of sensitivity or resistance to different antibiotics, but resistance to polymyxin isn’t a defining difference between the two.
• Eltor is non-motile: Vibrio eltor is actually motile, just like Vibrio cholerae. Motility is a characteristic shared by both types, as it helps these bacteria move through their environment.
• Causes fewer subclinical infections as compared to eltor: Vibrio cholerae O1 (classical biotype and El Tor biotype) can cause both symptomatic cholera infections and subclinical or asymptomatic infections. There isn’t a substantial difference between Vibrio cholerae and Vibrio eltor regarding their potential to cause subclinical infections.

Answer: Poverty and insanitation

• Poverty and insanitation: Cholera is primarily caused by the consumption of water or food contaminated with the bacterium Vibrio cholerae. Poor sanitation, inadequate access to clean water, and unhygienic living conditions create environments where the bacteria can thrive, leading to cholera outbreaks.

The other options are Incorrect:

1. Mosquitoes: Cholera is not transmitted by mosquitoes. It’s primarily a waterborne disease caused by ingestion of contaminated water or food, not by mosquito bites.
2. Toxin produced by pesticides: Pesticides do not cause cholera. Cholera is caused by a specific bacterium, Vibrio cholerae, and is not linked to toxins produced by pesticides.
3. None of these: This option is incorrect. The primary cause of cholera is related to poor sanitation and contaminated water sources, as explained above.

Answer: None of these

While humans are the primary hosts of cholera, the natural reservoir of infection for cholera is brackish and marine waters. This means that the bacterium Vibrio cholerae can live and reproduce in these environments, and it can be transmitted to humans through contaminated water and food.

Incorrect options with brief explanations:

• Flies: Flies can act as vectors of cholera, meaning that they can carry the bacterium from contaminated sources to humans. However, flies are not the natural reservoir of infection for cholera.
• Horse: Horses are not susceptible to cholera, so they cannot be the natural reservoir of infection for the disease.
• Man: Humans are the primary hosts of cholera, but they are not the natural reservoir of infection. This is because the bacterium can survive and reproduce in brackish and marine waters, and it can be transmitted to humans through contaminated water and food.

Answer: Pyogenic

Streptococcus bacteria are often associated with pyogenic infections, which means they can cause pus-forming infections. These infections can manifest as skin infections, abscesses, pneumonia, and other conditions characterized by the production of pus.

Other incorrect options with brief explanations::

1. Fever: While infections caused by Streptococcus bacteria can induce fever as a symptom, the presence of fever is not a direct classification for the type of infections caused by Streptococcus organisms.
2. Zoonotic: Zoonotic infections are those transmitted from animals to humans. Streptococcus infections are primarily human-to-human transmitted and are not typically classified as zoonotic infections.

Answer: M. tuberculosis

• It’s a biochemical test used to differentiate Mycobacterium tuberculosis from other mycobacteria. M. tuberculosis is capable of producing niacin (nicotinic acid) from niacinamide, leading to a positive reaction in the niacin test. This test is useful in identifying M. tuberculosis strains.

Other incorrect options:

1. Corynebacterium: The niacin test is not typically used to identify Corynebacterium species. Corynebacterium species are not known for their reaction in the niacin test.
2. M. bovis: While related to M. tuberculosis, M. bovis may produce a weakly positive or negative niacin test result, distinguishing it from M. tuberculosis.
3. M. avium: M. avium is not expected to produce a positive niacin test. This bacterium is not typically identified using the niacin test, as it does not convert niacinamide to niacin in the same way as M. tuberculosis does.

Answer: Ziehl – Neelsen’s staining

Ziehl–Neelsen staining: This staining method, also known as acid-fast staining, is specifically used to visualize mycobacteria like Mycobacterium tuberculosis. These bacteria have a unique cell wall composition that resists conventional staining methods like Gram staining. Acid-fast staining employs carbol-fuchsin dye and heat to penetrate the waxy cell wall of mycobacteria, allowing them to retain the stain even after decolorization with acid-alcohol.

Other incorrect options:

1. Gram’s staining: Mycobacteria do not stain well with Gram staining, as their cell walls have a high lipid content that prevents the penetration of the crystal violet dye and the retention of the Gram stain.
2. Simple staining: Simple staining involves the use of a single stain to color bacteria and is not specifically tailored to highlight mycobacteria. Mycobacteria require special staining methods due to their unique cell wall structure.

Answer: Mycobacteria

• Mycobacteria: Acid-fast bacteria are characterized by their ability to retain certain stains, like carbol-fuchsin, even after treatment with acid-alcohol. Mycobacteria, including Mycobacterium tuberculosis, are classic examples of acid-fast bacteria due to their unique cell wall composition, containing high lipid content (mycolic acids) that resists decolorization by acid-alcohol.

Other Incorrect options:

1. Neisseria: Neisseria species, like Neisseria gonorrhoeae and Neisseria meningitidis, are not typically considered acid-fast bacteria. They do not exhibit the characteristic of retaining acid-fast stains.
2. Staphylococci: Staphylococcus bacteria, including Staphylococcus aureus, do not belong to the group of acid-fast bacteria. They are Gram-positive cocci that do not retain acid-fast stains due to their different cell wall composition compared to acid-fast bacteria.

Answer: Sh.shiga

Shigella dysenteriae (Shigella shiga): Shigella dysenteriae is a bacterium responsible for causing severe bacillary dysentery (shigellosis) in humans. It produces a potent toxin called Shiga toxin, which can lead to serious gastrointestinal symptoms.

Other incorrect options:

1. Shigella shiga and Shigella schmitzi: Shigella dysenteriae is commonly referred to as Shigella shiga due to its association with producing the Shiga toxin. Shigella schmitzi is not a known or recognized species within the Shigella genus.
2. Shigella para dysenteriae: Shigella para dysenteriae is not a scientifically recognized term. Shigella dysenteriae is commonly known as Shigella shiga due to the production of the Shiga toxin.

Answer: Protein M

Protein M: Streptococcus pyogenes, also known as Group A Streptococcus (GAS), is classified based on the presence of surface protein M. This protein is a major virulence factor and plays a role in immune evasion and adherence to host cells.

Other incorrect options:

1. Protein T: There isn’t a specific classification of Streptococcus pyogenes based on Protein T. While Streptococcus pyogenes may have various surface proteins, the primary classification is based on Protein M.
2. Protein R: Protein R is not the basis for the classification of Streptococcus pyogenes. The major classification factor for this bacterium is Protein M.
3. Polysaccharide C: The classification of Streptococcus pyogenes is not primarily based on Polysaccharide C. The presence of surface Protein M is the key factor used for classification and identification of this bacterium.

Answer: Viridans group

Viridans group: α-haemolytic streptococci are a subgroup of streptococci that cause partial or incomplete hemolysis (greenish discoloration) on blood agar plates. They are known as the Viridans group and consist of multiple species of streptococci that are often part of the normal flora in the oral cavity, upper respiratory tract, and other body sites.

Other incorrect options:

1. Str. pyogenes: Streptococcus pyogenes is classified as β-haemolytic and is not considered part of the α-haemolytic or Viridans group. It causes complete hemolysis (clearing around the colonies) on blood agar plates.
2. Virulence group: While α-haemolytic streptococci can possess virulence factors, they are not specifically termed as the “Virulence group.” The term “Viridans group” refers to their characteristic greenish hemolysis on blood agar.
3. None of these: The correct term for α-haemolytic streptococci with greenish hemolysis on blood agar plates is the “Viridans group.”

Answer: Oxygen

Oxygen: Streptolysin O is a hemolysin produced by certain strains of Streptococcus pyogenes (Group A Streptococcus). It is oxygen labile, meaning it gets inactivated or degraded in the presence of oxygen. When exposed to atmospheric oxygen, Streptolysin O loses its activity and becomes non-functional.

Other incorrect options:

1. CO2: Carbon dioxide (CO2) is not known for inactivating Streptolysin O. The inactivation of Streptolysin O primarily occurs in the presence of atmospheric oxygen.
2. Nitrogen: Nitrogen is not involved in the inactivation of Streptolysin O. Oxygen plays the primary role in rendering Streptolysin O inactive.
3. Serum: Serum doesn’t play a direct role in the inactivation of Streptolysin O. Oxygen is the critical factor involved in the inactivation of this hemolysin.

Answer: Brucella

Brucella: The Prozone phenomenon, also known as the “hook effect,” can occur during serological testing for Brucella infection. In this phenomenon, extremely high levels of antibodies can saturate the antigen-antibody complexes, leading to an apparent decrease or absence of agglutination or precipitation reactions in diagnostic tests.

Other incorrect options:

1. A typical mycobacteria: The Prozone phenomenon is not typically associated with mycobacteria. It is more commonly observed in Brucella infections during serological testing.
2. Streptococcus: The Prozone phenomenon is not a characteristic feature encountered in Streptococcus infections. It is specifically associated with certain serological reactions seen in Brucella testing.
3. Bordetella pertussis: The Prozone phenomenon is not commonly observed in Bordetella pertussis infections. It’s specifically related to Brucella and the way certain serological tests react to high levels of antibodies.

Answer: B.canis

B. abortus: Among the options listed, Brucella abortus is the species that does not oxidize glutamic acid. This differentiation is often used in microbiological tests to identify different species of Brucella based on their metabolic characteristics.

Other incorrect options:

1. B. melitensis: This species oxidizes glutamic acid. The question seeks to identify the species that do not oxidize glutamic acid, and B. melitensis is not the correct choice for that distinction.
2. B. suis: This species oxidizes glutamic acid. It is not the species that fails to oxidize this acid.
3. B. canis: B. canis oxidizes glutamic acid. Similar to B. suis and B. melitensis, it is not the species that does not oxidize glutamic acid.

Answer: Cytopathic effects

Cytopathic effects: These are observable morphological or structural changes that occur in cells infected by a virus. In the case of influenza virus infection, cytopathic effects might include cell rounding, detachment, formation of syncytia (fusion of infected cells), and cell death, among other alterations.

Other incorrect options:

1. HeLa cells: HeLa cells are a specific type of human cell line derived from cervical cancer cells. While they are commonly used in scientific research, their use isn’t the primary method for identifying influenza virus growth. Cytopathic effects are the more direct indicator of viral growth.
2. Both Cytopathic effects and HeLa cells: While HeLa cells can be used in influenza virus research, the direct identification of influenza virus growth is most commonly confirmed by observing cytopathic effects caused by the virus in infected cells.

Answer: Haemaggulutinin inhibition test

Haemagglutinin Inhibition Test: This test detects specific antibodies against the haemagglutinin (HA) protein present on the surface of the influenza virus. By observing the inhibition of haemagglutination caused by the interaction between the virus and red blood cells, the presence of antibodies against the virus can be identified, aiding in its diagnosis.

Other Incorrect options:

1. Tissue culture method: While tissue culture methods can be used to propagate and study viruses, they are not the primary method for identifying the Influenza virus. Instead, specific serological tests like the haemagglutinin inhibition test are used for identification.
2. Embryonated eggs: Influenza virus propagation can occur in embryonated eggs, which is a method used for viral cultivation and vaccine production. However, it’s not the primary method for identifying the virus but rather for growing and propagating it.
3. Plaque formation: Plaque formation assay is a technique used to quantify viral particles or infectious units within a sample. It’s not primarily used for the identification of the Influenza virus but rather for estimating viral titer or quantifying the virus.

Answer: Oxygen stable

Oxygen stable: Streptolysin ‘S’ is a hemolysin produced by certain strains of Streptococcus pyogenes (Group A Streptococcus). Unlike Streptolysin ‘O,’ which is oxygen-labile and inactivated by oxygen, Streptolysin ‘S’ remains stable and active even in the presence of oxygen.

List of incorrect options:

1. Oxygen unstable: This statement doesn’t correctly describe Streptolysin ‘S.’ It is stable in the presence of oxygen.
2. Thermostable: Streptolysin ‘S’ stability is primarily associated with its resistance to oxygen, not heat. It’s not commonly referred to as thermostable.

Answer: Staphylococcus

Staphylococcus: The coagulase test is used to differentiate between different species of Staphylococcus bacteria, primarily Staphylococcus aureus and coagulase-negative staphylococci (CoNS). Staphylococcus aureus produces coagulase enzymes that can cause the coagulation of blood plasma, leading to the formation of a clot. This test helps identify Staphylococcus aureus from other species that do not produce coagulase.

Other incorrect options:

1. Salmonella: The coagulase test is not used for the identification of Salmonella. Salmonella is typically identified using other biochemical tests and specific culture methods.
2. Bordetella: The coagulase test is not used for the identification of Bordetella. Bordetella species, such as Bordetella pertussis, are primarily identified through specific culture and molecular methods.
3. Pneumococcus: The coagulase test is not used for the identification of Pneumococcus (Streptococcus pneumoniae). Identification of Streptococcus pneumoniae is based on specific biochemical tests different from the coagulase test used for Staphylococcus aureus.

Answer: Obligate anaerobe

Obligate anaerobe: Clostridium perfringens, responsible for gas gangrene, is a bacterium that thrives in environments devoid of oxygen. It does not require oxygen for growth and metabolism and, in fact, can be inhibited or killed by exposure to oxygen.

Other incorrect options:

1. Facultative anaerobe: Clostridium perfringens is not a facultative anaerobe. Facultative anaerobes can switch between aerobic and anaerobic metabolism depending on the availability of oxygen, but Clostridium perfringens cannot survive in the presence of oxygen.
2. Facultative aerobe: This term refers to organisms that can grow in the presence or absence of oxygen, utilizing oxygen when available but also capable of surviving in its absence. Clostridium perfringens is not a facultative aerobe.
3. Obligate aerobe: Obligate aerobes require oxygen for their growth and metabolism, which is not the case for Clostridium perfringens. This bacterium cannot survive and grow in the presence of oxygen.

Answer: Bacillus anthracis

Bacillus anthracis: McFadyean’s reaction, also known as the McFadyean’s method, is a diagnostic test used specifically for the identification of Bacillus anthracis, the bacterium that causes anthrax. This method involves staining bacterial smears with certain dyes, such as methylene blue or polychrome methylene blue, to visualize the characteristic features of Bacillus anthracis under a microscope.

Other incorrect options:

1. Brucella: McFadyean’s reaction is not primarily used for the detection of Brucella. Brucella species are usually identified using different culture methods and serological tests, not McFadyean’s reaction.
2. Corynaebacterium: McFadyean’s reaction is not typically used to detect Corynebacterium. Corynebacterium species, like Corynebacterium diphtheriae, are usually identified using other laboratory techniques specific to the organism.

Answer: Zoonotic infection

Zoonotic infection: Anthrax is primarily a zoonotic disease, meaning it is naturally transmitted from animals to humans. It commonly affects herbivorous animals, especially cattle, sheep, and goats. Humans can contract anthrax through direct contact with infected animals or their products (such as hides, wool, or meat) or by exposure to contaminated soil.

Other incorrect options:

1. Vector-borne: Anthrax is not typically transmitted through vectors like mosquitoes or ticks. Its primary mode of transmission is direct contact with infected animals or their products.
2. Wound-borne: While anthrax can infect individuals through open wounds, it’s not the primary mode of transmission. Most cases occur through contact with infected animals or contaminated animal products.
3. Soil-borne: Anthrax spores can persist in soil for long periods, but the disease is not transmitted directly from soil to humans. Humans usually acquire anthrax through contact with infected animals or their products.

Answer: Bacillus anthracis

Brucella: Brucella species are encapsulated bacteria. The presence of a capsule helps these bacteria evade the host’s immune response, contributing to their ability to cause chronic infections in various mammals, including humans.

Other incorrect options:

1. Bacillus anthracis: Bacillus anthracis, the causative agent of anthrax, does not typically produce a capsule. Instead, it possesses other virulence factors that contribute to its pathogenicity.
2. Escherichia coli: Escherichia coli is a Gram-negative bacterium, but it is not typically encapsulated.
3. Corynebacterium: While some strains of Corynebacterium can produce capsules, not all Corynebacterium species are encapsulated. The presence of a capsule varies among different strains within this genus.

Answer: 12 Weeks

12 weeks: Seroconversion refers to the period when an individual’s immune system begins producing detectable antibodies against HIV. This process usually occurs within 3 to 12 weeks after initial infection, but in most cases, it can take up to 12 weeks for antibodies to reach levels detectable by standard HIV tests.

List of incorrect options:

1. 3 weeks: This is too early for most individuals to develop detectable antibodies against HIV. It often takes longer for antibodies to reach detectable levels in the bloodstream.
2. 6 weeks: While some individuals may start producing detectable antibodies by 6 weeks after exposure, it is not the typical timeframe for seroconversion for everyone.
3. 9 weeks: Similar to 6 weeks, while some individuals might seroconvert by 9 weeks, it’s not the definitive or average time frame for seroconversion for everyone.

Answer: HTLV – III

HTLV-III (HIV-1): HIV-1, a retrovirus belonging to the family of Lentiviridae, is the causative agent of AIDS. It attacks the immune system, primarily targeting CD4+ T cells, progressively weakening the body’s ability to fight infections and certain cancers, ultimately leading to AIDS.

Other incorrect options:

1. HTLV-I: Human T-cell lymphotropic virus type I (HTLV-I) is associated with a different condition called Adult T-cell Leukemia/Lymphoma (ATLL) and HTLV-I-associated myelopathy/tropical spastic paraparesis (HAM/TSP), but it is not the cause of AIDS.
2. Bunya virus: The Bunyaviridae family includes various viruses, some of which can cause diseases in humans and animals, but they are not associated with causing AIDS.

Answer: Retro virus

Retrovirus: HIV belongs to the retrovirus family. Retroviruses are RNA viruses that use the enzyme reverse transcriptase to convert their RNA genome into DNA, which is then integrated into the host cell’s genome. HIV specifically targets immune cells, primarily CD4+ T cells, leading to progressive immune system deterioration.

Other incorrect options:

1. RNA virus: This is partially accurate for HIV. While it is an RNA virus, the specific classification for HIV is as a retrovirus due to its replication method involving reverse transcription from RNA to DNA.
2. DNA virus: HIV is not a DNA virus. It is an RNA virus that converts its RNA genome into DNA through the action of reverse transcriptase.
3. Entero virus: Entero viruses primarily infect the gastrointestinal tract and cause illnesses like enteroviral infections, but they are not related to HIV or AIDS.

Answer: Both Reverse transcriptase & RNA directed DNA polymerases

Retroviruses are a unique group of viruses that use the enzyme reverse transcriptase to convert their RNA genome into DNA, which is then integrated into the host cell’s genome. This process, known as reverse transcription, is a key feature of retroviruses and allows them to replicate and persist within the host cell.

RNA-directed DNA polymerases are a group of enzymes that can synthesize DNA from an RNA template. This process is essential for the replication of retroviruses and other RNA viruses. Reverse transcriptase is a type of RNA-directed DNA polymerase that is specifically found in retroviruses.

Here is a table summarizing the special features of retroviruses:

Answer: Retro Viridae

Retroviridae: HIV (Human Immunodeficiency Virus) is classified within the Retroviridae family. This family of viruses includes retroviruses, characterized by their RNA genome and the enzyme reverse transcriptase, which converts their RNA into DNA once inside a host cell.

Other Incorrect options:

1. Rhabdo Viridae: Rhabdoviridae is a different family of viruses that includes the rabies virus. It’s not related to HIV, which is a retrovirus.
2. Toga Viridae: Togaviridae is a family of viruses that includes viruses like the rubella virus and alphaviruses. HIV does not belong to this family.
3. Paramyxo Viridae: Paramyxoviridae is a family of viruses that includes the measles virus and mumps virus. HIV is not a member of this family; it belongs to Retroviridae.

Answer: Western blot test

• Western blot test: This test is used as a confirmatory test for HIV/AIDS. It detects specific antibodies against various proteins of the HIV virus in a person’s blood sample. It is performed after a positive result on an initial screening test, such as an ELISA (Enzyme-Linked Immunosorbent Assay), to confirm the presence of HIV antibodies.

Other incorrect options:

1. ELISA test: ELISA is an initial screening test used to detect antibodies or antigens to HIV in blood samples. While it’s sensitive, a positive ELISA test result requires confirmation by a more specific test like the Western blot to confirm HIV infection.
2. Karpas test: Karpas test is not a standard or recognized test for confirming HIV/AIDS. It’s not commonly used for diagnosing HIV infection.
3. Fujerbio test: There isn’t a widely recognized HIV/AIDS test named Fujerbio. This test is not known as a confirmatory test for HIV/AIDS.

Answer: ELISA test

ELISA test: The ELISA test is commonly used as a screening test for HIV/AIDS. It detects antibodies or antigens to HIV in a person’s blood sample. It’s highly sensitive and used as the initial test to identify potential HIV infection. A positive result from an ELISA test requires confirmation with a more specific test like the Western blot.

Other incorrect options:

1. Western blot test: While the Western blot is an important confirmatory test for HIV/AIDS, it is not a screening test. It is used to confirm the presence of HIV antibodies after a positive result on an initial screening test like ELISA.
2. Both Western blot test and ELISA test: While both tests are used in the diagnosis of HIV/AIDS, they serve different purposes. ELISA is the primary screening test, and the Western blot is used for confirmation if the ELISA is positive.
3. VDRL test: The VDRL (Venereal Disease Research Laboratory) test is used for the diagnosis of syphilis, a different sexually transmitted infection. It is not used as a screening test for AIDS/HIV.

Answer: Window period

Window Period: This refers to the period after HIV infection when the virus is present in the body but antibodies to HIV are not yet detectable by standard tests. It can last from a few weeks to several months after infection, during which a person may be infectious but still test negative for HIV antibodies.

Other incorrect options:

1. Intrinsic period: There isn’t a medical term called the “intrinsic period” related to HIV infection. It doesn’t describe the specific phase between infection and antibody appearance.
2. Incubation period: The incubation period refers to the time between exposure to a pathogen and the appearance of symptoms. In the context of HIV, it includes the time from infection to the onset of symptoms of AIDS, not specifically the period before antibodies are detectable.
3. None of these: The term “window period” accurately describes the phase between HIV infection and the detectability of antibodies.

Answer: Western blot

Western blot: This test is highly specific and is used as a confirmatory test for HIV/AIDS. It detects specific antibodies against various proteins of the HIV virus in a person’s blood sample, providing a high degree of specificity in identifying HIV infection.

Other incorrect options:

1. IHA (Indirect Hemagglutination Assay): While IHA is a serological test used in the detection of antibodies, it is not as specific as the Western blot for confirming HIV/AIDS.
2. ELISA (Enzyme-Linked Immunosorbent Assay): ELISA is a sensitive screening test for HIV antibodies but may produce false-positive results. It requires confirmation by a more specific test like the Western blot to confirm HIV infection.
3. Immuno electrophoresis: This technique is not used specifically for diagnosing HIV/AIDS. It is a laboratory technique used for separating and analyzing proteins based on their charge and size, not a standard test for HIV diagnosis.

Answer: Reverse transcriptase

Reverse transcriptase: HIV is a retrovirus that carries the enzyme reverse transcriptase. This enzyme allows the virus to convert its RNA genome into DNA once inside a host cell. Detection of reverse transcriptase activity is a characteristic feature of retroviruses like HIV, indicating their presence in blood samples.

Other Incorrect options:

1. DNA polymerase: DNA polymerase is not a specific marker for HIV infection. While it’s an essential enzyme involved in DNA replication, it’s not unique to HIV.
2. RNA polymerase: RNA polymerase is involved in the transcription of RNA from DNA, but it’s not a specific marker for HIV infection. HIV’s marker is its reverse transcriptase, which converts its RNA into DNA.