Chapter 6 with our Microbiology MCQs and explanations! Test your knowledge and understanding of key concepts with our complete set of multiple choice questions with detailed explanations for each answer. Increase your confidence and understanding of the fascinating world of microorganisms!
Microbiology MCQs 251 to 300
The enzymes responsible for decomposition is?
- a) Lipolytic
- b) Proteolytic
- c) Lysozyme
- d) Both Lipolytic and Proteolytic
Explanation:
Decomposition is the process of breaking down complex organic matter into simpler substances. This process primarily requires Proteolytic enzymes (to break down proteins) and Lipolytic enzymes (to break down fats/lipids).
Why other options are incorrect:
Why other options are incorrect:
- • Lipolytic: While correct, it is incomplete as it only refers to the breakdown of lipids.
- • Proteolytic: While correct, it is incomplete as it only refers to the breakdown of proteins.
- • Lysozyme: This is an antimicrobial enzyme found in secretions like tears and saliva that attacks bacterial cell walls; it is not the primary enzyme responsible for the general decomposition of organic matter.
Urea is decomposed by the species?
- a) Micrococcus sps.
- b) Nitrosomonas sps.
- c) Proteus sps.
- d) Both Micrococcus sps. and Proteus sps.
Explanation:
Urea decomposition (ureolysis) is carried out by organisms that produce the enzyme urease, which hydrolyzes urea into ammonia and carbon dioxide. Both Proteus species and many Micrococcus species are well-known for their strong urease activity.
Why other options are incorrect:
Why other options are incorrect:
- • Micrococcus sps.: While these do decompose urea, this option is incomplete because Proteus is also a major decomposer.
- • Nitrosomonas sps.: These are nitrifying bacteria that oxidize ammonia into nitrites; they are not the primary organisms responsible for the initial decomposition of urea.
- • Proteus sps.: While Proteus is famous for rapid urea hydrolysis, this option is incomplete as Micrococcus also possesses this capability.
Phycobiont is?
- a) The algal part in Lichens
- b) The fungal part in Lichens
- c) Laustoria formation
- d) None of these
Explanation:
Lichens are composite organisms consisting of a symbiotic association between a fungus and a photosynthetic partner. The Phycobiont refers specifically to the algal (or cyanobacterial) component, which provides food through photosynthesis.
Why other options are incorrect:
Why other options are incorrect:
- • The fungal part in Lichens: This is known as the Mycobiont, which provides the structural support and absorbs water/minerals.
- • Laustoria formation: This likely refers to Haustoria, which are specialized fungal structures used to penetrate host cells for nutrient absorption, rather than a component name for the lichen partnership.
- • None of these: Incorrect because option ‘a’ accurately defines the term phycobiont.
Parasitic form must contain?
- a) Capsules
- b) Cell-wall
- c) Endospores
- d) Flagella
Explanation:
In microbiology, the capsule is a major virulence factor for many parasitic (pathogenic) bacteria. It protects the organism from the host’s immune system, specifically by preventing phagocytosis by white blood cells.
Why other options are incorrect:
Why other options are incorrect:
- • Cell-wall: While most bacteria have cell walls, this is common to both free-living and parasitic forms; it is not a specific requirement unique to the “parasitic” mode of life.
- • Endospores: These are highly resistant structures formed for survival in harsh external environments (like soil), not necessarily for the parasitic state inside a host.
- • Flagella: These are used for motility. Many parasitic organisms are non-motile and do not require flagella to infect a host.
The total no. of genes in the group of same individuals is?
- a) Genome
- b) Gene map
- c) Gene pool
- d) None of these
Explanation:
The Gene pool is the total sum of all the genes (and their different alleles) present in a breeding population or a group of individuals of the same species at a given time.
Why other options are incorrect:
Why other options are incorrect:
- • Genome: This refers to the complete set of genetic material present in a single organism or cell, rather than the entire group/population.
- • Gene map: This is a graphic representation or physical location of genes on a chromosome; it does not represent the total number of genes in a group.
- • None of these: Incorrect because option ‘c’ is the standard biological term for this concept.
Capsulated forms of bacteria are?
- a) Virulent
- b) A virulent
- c) Useful
- d) Symbiotic
Explanation:
Capsulated forms of bacteria are typically Virulent (disease-causing). The capsule is a smooth, outer polysaccharide layer that prevents the host’s white blood cells from phagocytosing (engulfing) the bacteria, allowing the infection to spread.
Why other options are incorrect:
Why other options are incorrect:
- • A virulent: This refers to bacteria that do not cause disease. Non-capsulated strains are often avirulent because the host immune system can easily destroy them.
- • Useful: While some bacteria are useful (like probiotics), the presence of a capsule is a specific structural feature associated with survival and pathogenicity within a host.
- • Symbiotic: While some symbiotic bacteria might have capsules, the term is most significantly used in microbiology to distinguish between virulent and non-virulent strains of pathogens (e.g., Streptococcus pneumoniae).
The bacterial cells participating in conjugation are?
- a) Conjugants
- b) Fertile cells
- c) Exconjugants
- d) None of these
Explanation:
Bacterial conjugation is the transfer of genetic material between bacterial cells by direct cell-to-cell contact or by a bridge-like connection. The individual cells that take part in this physical union are called Conjugants.
Why other options are incorrect:
Why other options are incorrect:
- • Fertile cells: While the “F-factor” (Fertility factor) determines the donor’s ability to conjugate, the general term for both the donor and recipient during the process is “conjugants.”
- • Exconjugants: This term refers to the cells after they have completed the process of conjugation and separated from each other.
- • None of these: Incorrect because option ‘a’ is the standard biological term for participating cells.
Phagocytes are?
- a) Monocytes
- b) Basophils
- c) Macrophages
- d) All of these
Explanation:
Phagocytes are a type of white blood cell that protects the body by ingesting (phagocytosing) harmful foreign particles, bacteria, and dead or dying cells. Monocytes and Macrophages are professional phagocytes. While Basophils are primarily involved in inflammatory and allergic responses, they are often grouped with other leukocytes in introductory biological contexts when discussing defensive blood cells.
Why other options are incorrect:
Why other options are incorrect:
- • Monocytes: These are phagocytic cells found in the blood, but they are not the only ones.
- • Basophils: While they have very limited phagocytic capability compared to neutrophils or macrophages, they are part of the myeloid white blood cell group.
- • Macrophages: These are the most active phagocytes in the tissues, but they originate from monocytes, making both ‘a’ and ‘c’ correct.
The microorganism engulfed by phagocyte resides in a vacuole is known as?
- a) Phagosome
- b) Lysosome
- c) both Phagosome and Lysosome
- d) None of these
Explanation:
When a phagocyte (like a macrophage or neutrophil) engulfs a microorganism, the cell membrane wraps around the particle to form an internal vesicle. This specific vacuole containing the engulfed microbe is called a Phagosome.
Why other options are incorrect:
Why other options are incorrect:
- • Lysosome: This is a pre-existing organelle in the cytoplasm containing digestive enzymes. It later fuses with the phagosome to destroy the microbe.
- • both Phagosome and Lysosome: Incorrect because they are two distinct structures. The combination of the two after fusion is specifically called a phagolysosome.
- • None of these: Incorrect because option ‘a’ is the scientifically accurate term for the vacuole.
Toxic products in phagolysosome are?
- a) H2 SO4
- b) Singlet O2
- c) Superoxide radicals
- d) All of these
Explanation:
The phagolysosome kills ingested microorganisms using a combination of oxidative and non-oxidative mechanisms. This includes the production of Reactive Oxygen Species (ROS) like Superoxide radicals and Singlet Oxygen (via the respiratory burst), as well as maintaining a highly acidic environment to degrade the pathogen.
Why other options are involved:
Why other options are involved:
- • H2 SO4: While hydrochloric acid or organic acids are more common, this option represents the extreme acidification within the vacuole used to denature microbial proteins.
- • Singlet O2: A highly reactive form of oxygen that causes lipid peroxidation and membrane damage to the microbe.
- • Superoxide radicals: These are the first products of the oxidative burst (produced by NADPH oxidase) and are precursors to other toxic agents like hydrogen peroxide.
The coating of a bacterium with antibody or complement that leads to enhanced phagocytosis of the bacterium by phagocytes is called?
- a) Opsonization
- b) Agglutination
- c) CFT
- d) None of these
Explanation:
Opsonization is the process by which a pathogen is marked for ingestion and destruction by a phagocyte. Opsonins, such as antibodies (IgG) and complement proteins (C3b), coat the surface of the bacteria, acting as “handles” that allow phagocytes to bind more easily.
Why other options are incorrect:
Why other options are incorrect:
- • Agglutination: This is the clumping together of particles (like bacteria or red blood cells) when they react with specific antibodies; it does not specifically refer to the “coating” for phagocytosis.
- • CFT (Complement Fixation Test): This is a laboratory medical test used to detect the presence of specific antibodies or antigens in a patient’s serum using the complement system.
- • None of these: Incorrect because option ‘a’ is the precise term for this immunological process.
Attenuation means?
- a) Killing of the bacteria (microorganism)
- b) Inactivation of bacteria
- c) More activating the bacteria
- d) Both Killing of the bacteria (microorganism) and Inactivation of bacteria
Explanation:
Attenuation is the process of reducing the virulence (harmfulness) of a pathogen while keeping it viable (alive). In this context, “inactivation” refers to rendering the bacteria non-pathogenic or harmless so it can be used in vaccines without causing the disease.
Why other options are incorrect:
Why other options are incorrect:
- • Killing of the bacteria: If the bacteria are killed, it is referred to as a “Killed Vaccine” or “Inactivated Vaccine” in the strict sense. Attenuation specifically implies the organism is still alive but weakened.
- • More activating the bacteria: This is the opposite of attenuation; increasing virulence would make the organism more dangerous.
- • Both Killing and Inactivation: In microbiology, “Killed” and “Attenuated” are two different categories of preparation. Therefore, they cannot both define attenuation.
β-haemolytic bacteria is?
- a) Streptococcus pyogenes
- b) Str. pneumoniae
- c) Str. viridans
- d) Str. faecalis
Explanation:
β-haemolysis (Beta-hemolysis) refers to the complete lysis of red blood cells in the media around and under the colonies on a blood agar plate, appearing as a clear zone. Streptococcus pyogenes (Group A Streptococcus) is the most classic example of a beta-hemolytic bacterium.
Why other options are incorrect:
Why other options are incorrect:
- • Str. pneumoniae: These are α-haemolytic (Alpha-hemolytic), meaning they cause partial hemolysis, which produces a greenish discoloration on blood agar.
- • Str. viridans: This group is also primarily α-haemolytic.
- • Str. faecalis: Now classified as Enterococcus faecalis, these are usually γ-haemolytic (Gamma-hemolytic), meaning they produce no hemolysis at all on blood agar.
Opsonin is the?
- a) Cellwall component
- b) Plasma component
- c) Serum component
- d) Cytoplasm component
Explanation:
Opsonins are extracellular proteins that bind to substances or cells to induce phagocytosis. They are primarily found in the blood. In immunology, they are typically described as Serum components because antibodies (IgG) and complement proteins (C3b) are present in the serum.
Why other options are incorrect:
Why other options are incorrect:
- • Cellwall component: Opsonins are produced by the host immune system, not by the bacteria’s own cell wall.
- • Plasma component: While plasma does contain these factors, “Serum” is the more specific immunological term for the fluid containing circulating antibodies and complement proteins.
- • Cytoplasm component: Opsonins act in the extracellular fluid (blood and tissues) to mark pathogens; they are not structural components of the cell’s internal cytoplasm.
Presence of viruses in the blood stream is known as?
- a) Viraemia
- b) Bacteraemia
- c) Septicaemia
- d) Pyemia
Explanation:
Viraemia is the medical term used to describe the presence of viruses in the blood. This allows the virus to spread from the initial site of infection to other organs in the body.
Why other options are incorrect:
Why other options are incorrect:
- • Bacteraemia: This refers specifically to the presence of bacteria in the bloodstream.
- • Septicaemia: Also known as blood poisoning, this is a more severe condition where bacteria are not just present, but are actively multiplying and producing toxins in the blood.
- • Pyemia: This is a form of septicaemia where pus-forming (pyogenic) bacteria spread through the bloodstream, leading to the formation of multiple abscesses in various organs.
Presence of viable bacteria in the blood stream is called?
- a) Viraemia
- b) Septicaemia
- c) Bacteraemia
- d) Bactericidal
Explanation:
Bacteraemia is defined as the simple presence of viable bacteria in the blood. It can occur through small wounds, dental procedures, or vigorous brushing of teeth, and is often transient as the immune system clears the bacteria quickly.
Why other options are incorrect:
Why other options are incorrect:
- • Viraemia: This refers to the presence of viruses in the blood, not bacteria.
- • Septicaemia: This is a more serious condition where bacteria are not only present but are actively multiplying and producing toxins in the blood, leading to a systemic inflammatory response.
- • Bactericidal: This is an adjective describing an agent (like an antibiotic or disinfectant) that kills bacteria. It is not a term for a medical condition of the blood.
Infection that results in pus formation are called?
- a) Focal infection
- b) Acute infection
- c) Pyogenic infection
- d) Chronic infection
Explanation:
An infection that leads to the production of pus is known as a Pyogenic infection. The term “pyogenic” comes from the Greek words ‘pyo’ (pus) and ‘genesis’ (production). This typically occurs when “pyogenic” bacteria, such as Staphylococcus aureus or Streptococcus pyogenes, trigger an intense immune response resulting in dead white blood cells and debris (pus).
Why other options are incorrect:
Why other options are incorrect:
- • Focal infection: This refers to a localized infection (like a tooth abscess) that sends bacteria or toxins to other parts of the body.
- • Acute infection: This describes the timing and severity of an infection (rapid onset, short duration), which may or may not produce pus.
- • Chronic infection: This refers to a long-term infection that persists for weeks, months, or years.
Prophylaxis of cholera is?
- a) Protected water supply
- b) Environmental sanitation
- c) Immunisation with killed vaccines
- d) All of these
Explanation:
Prophylaxis refers to the measures taken to prevent a disease. Since Cholera is a waterborne disease caused by Vibrio cholerae, its prevention requires a multi-faceted approach including clean water, hygiene, and medical intervention.
Why all options are correct:
Why all options are correct:
- • Protected water supply: Cholera is primarily spread through contaminated water. Providing treated or boiled water is the most effective way to break the transmission cycle.
- • Environmental sanitation: Proper disposal of sewage prevents human waste from contaminating soil and water sources, which is critical in controlling outbreaks.
- • Immunisation with killed vaccines: Oral cholera vaccines (containing killed whole cells of V. cholerae) provide significant protection for individuals in endemic areas or during outbreaks.
Cholera vaccine gives protection for?
- a) 1 – 3 months
- b) 3 – 6 months
- c) 6 – 9 months
- d) None of These
Explanation:
The immunity provided by the classical cholera vaccine (particularly the killed parenteral vaccine) is relatively short-lived. It generally provides protection for about 3 to 6 months. Because the protection is temporary and does not provide 100% immunity, booster doses are often required during epidemics.
Why other options are incorrect:
Why other options are incorrect:
- • 1 – 3 months: This duration is too short; even basic cholera vaccines typically cover at least one peak season of the disease (about 6 months).
- • 6 – 9 months: This exceeds the standard duration of protection recognized for the traditional killed vaccines in most medical textbooks.
- • None of These: Incorrect because the range of 3–6 months is the standard accepted answer in microbiology examinations.
Vibrio cholerae (Classical) differs from Vibrio eltor by?
- a) It shares some Inaba, Ogawa subtypes with eltor
- b) Resistant to polymyxin
- c) Eltor is non-motile
- d) Causes less subclinical infections as compared to eltor
Explanation:
The Classical biotype of Vibrio cholerae typically produces more severe clinical disease with a higher ratio of symptomatic cases. In contrast, the El Tor biotype is known for causing a much higher number of subclinical (asymptomatic) infections for every one clinical case.
Why other options are incorrect:
Why other options are incorrect:
- • It shares some Inaba, Ogawa subtypes: This is a similarity between the two biotypes, not a difference. Both can belong to these serotypes.
- • Resistant to polymyxin: This is incorrect for the Classical biotype. The Classical biotype is sensitive to polymyxin B (50 units), whereas El Tor is resistant.
- • Eltor is non-motile: Both biotypes are highly motile, exhibiting characteristic “darting motility” due to a single polar flagellum.
Main cause for Cholera is?
- a) Poverty and insanitation
- b) Mosquitoes
- c) Toxin produced by pesticides
- d) None of these
Explanation:
While the biological cause of Cholera is the bacterium Vibrio cholerae, the main environmental and social causes for its spread are poverty and insanitation. The disease is transmitted via the fecal-oral route, which occurs most frequently in areas lacking clean drinking water and proper sewage disposal systems.
Why other options are incorrect:
Why other options are incorrect:
- • Mosquitoes: These are vectors for diseases like Malaria, Dengue, and Zika, but they do not transmit Cholera.
- • Toxin produced by pesticides: Pesticides are chemical agents that may cause chemical poisoning, but Cholera is a biological infection caused by a specific bacterium.
- • None of these: Incorrect because option ‘a’ is widely recognized as the primary socio-economic driver of cholera epidemics.
The natural reservoir of infection for cholera is?
- a) Flies
- b) Horse
- c) Man
- d) None of these
Explanation:
Man (Humans) is considered the only natural reservoir for Vibrio cholerae. The bacteria are maintained in the population through infected individuals and asymptomatic carriers who shed the organism in their stools, which then contaminates the environment and water sources.
Why other options are incorrect:
Why other options are incorrect:
- • Flies: While flies can act as mechanical vectors (carrying the bacteria from feces to food on their feet/bodies), they are not reservoirs where the bacteria naturally live and multiply.
- • Horse: Horses are not involved in the transmission cycle or the biological maintenance of cholera.
- • None of these: Incorrect because ‘Man’ is the scientifically recognized reservoir for this specific pathogen.
Streptococcus forms causes which type of infections?
- a) Fever
- b) Zoonotic
- c) Pyogenic
- d) None of these
Explanation:
Many species of Streptococcus, most notably Streptococcus pyogenes (Group A Strep), are known as Pyogenic bacteria. This means they have a tendency to cause infections that result in the formation of pus, such as strep throat, tonsillitis, and skin infections.
Why other options are incorrect:
Why other options are incorrect:
- • Fever: Fever is a clinical symptom of an infection, not a “type” of infection classification itself.
- • Zoonotic: Zoonotic infections are diseases transmitted from animals to humans. While some streptococci can be found in animals, the primary pathogenic forms in humans (like S. pyogenes or S. pneumoniae) are generally spread human-to-human.
- • None of these: Incorrect because ‘Pyogenic’ is the standard medical classification for these organisms.
Niacin test is positive in case of?
- a) Corynebacterium
- b) M. tuberculosis
- c) M. bovis
- d) M. avium
Explanation:
The Niacin test is a key biochemical test used to identify Mycobacterium tuberculosis. While all Mycobacteria produce niacin, M. tuberculosis lacks the enzyme required to convert free niacin into niacin ribonucleotide, leading to an accumulation of niacin in the culture medium which is then detected by the test.
Why other options are incorrect:
Why other options are incorrect:
- • Corynebacterium: This is a different genus of bacteria entirely; the niacin test is specifically used for the differential identification within the genus Mycobacterium.
- • M. bovis: This species is niacin-negative, which is a major diagnostic feature used to distinguish it from M. tuberculosis.
- • M. avium: As a member of the atypical mycobacteria (MAC), it is generally niacin-negative.
Mycobacteria are stained with?
- a) Gram’s staining
- b) Simple staining
- c) Both Gram’s staining and Simple staining
- d) Ziehl – Neelsen’s staining
Explanation:
Mycobacteria (like M. tuberculosis) have a unique cell wall with a very high lipid and mycolic acid content. This waxy wall makes them resistant to traditional stains. Ziehl-Neelsen staining (also known as Acid-Fast staining) uses heat to drive carbol fuchsin into the cell wall, which then resists decolorization by acid-alcohol.
Why other options are incorrect:
Why other options are incorrect:
- • Gram’s staining: Mycobacteria do not take up Gram stain well because the crystal violet cannot penetrate the thick, waxy cell wall. They often appear as “ghosts” or unstained cells.
- • Simple staining: Standard dyes used in simple staining (like methylene blue) cannot penetrate the mycolic acid layer effectively without a specific mordant or heat.
- • Both Gram’s and Simple: Since neither individual method is effective for identifying Mycobacteria, this combination is also incorrect.
Acid fast bacteria are?
- a) Neisseria
- b) Staphylococci
- c) Mycobacteria
- d) All of the above
Explanation:
Mycobacteria (such as Mycobacterium tuberculosis and M. leprae) are termed “acid-fast” because they have a high content of mycolic acids (waxy lipids) in their cell walls. This property allows them to resist decolorization by acids during the staining process (like the Ziehl-Neelsen stain).
Why other options are incorrect:
Why other options are incorrect:
- • Neisseria: These are Gram-negative diplococci and are not acid-fast.
- • Staphylococci: These are Gram-positive cocci and do not contain the mycolic acid layer required for acid-fastness.
- • All of the above: This is incorrect because only the genus Mycobacterium (and a few others like Nocardia to a lesser extent) exhibit acid-fast properties.
Sh.dysenteriae is also known as?
- a) Sh.shiga
- b) Sh.schmitzi
- c) Both Sh.shiga and Sh.schmitzi
- d) Sh.para dysenteriae
Explanation:
Shigella dysenteriae is a species of the genus Shigella. Its important serotypes include Sh. shiga (Serotype 1) and Sh. schmitzi (Serotype 2). Therefore, both names are associated with Shigella dysenteriae.
Why other options are incorrect:
Why other options are incorrect:
- • Sh.shiga: Refers only to Serotype 1 of Shigella dysenteriae.
- • Sh.schmitzi: Refers only to Serotype 2 of Shigella dysenteriae.
- • Sh.para dysenteriae: Historically associated with Shigella flexneri, not Shigella dysenteriae.
Streptococcus pyogenes classification is based on?
- a) Protein M
- b) Protein T
- c) Protein R
- d) Polysaccharide C
Explanation:
The primary classification of Streptococci into groups (Lancefield classification) is based on the antigenic characteristics of the Polysaccharide C (C-carbohydrate) found in the cell wall. Streptococcus pyogenes belongs to Lancefield Group A.
Why other options are incorrect:
Why other options are incorrect:
- • Protein M: While M protein is a major virulence factor and is used for Griffith typing (serotyping within Group A), it is not the basis for the broad classification into groups.
- • Protein T & R: These are surface proteins used for further epidemiological typing of strains but do not determine the primary Lancefield group.
α-haemolytic streptococci are also known as?
- a) Str. pyogenes
- b) Virulence group
- c) Viridans group
- d) None of these
Explanation:
α-haemolytic streptococci are commonly referred to as the Viridans group. The name “Viridans” comes from the Latin word ‘viridis’ (green), because these bacteria cause partial hemolysis on blood agar, resulting in a greenish discoloration around the colonies.
Why other options are incorrect:
Why other options are incorrect:
- • Str. pyogenes: This organism is a β-haemolytic (beta-hemolytic) bacterium, meaning it causes complete lysis of red blood cells on blood agar.
- • Virulence group: This is a general term describing the degree of pathogenicity of a microorganism; it is not a specific taxonomic name for α-haemolytic streptococci.
- • None of these: This is incorrect because “Viridans group” is the standard clinical terminology for these organisms.
Streptolysin O is inactivated by?
- a) CO2
- b) Nitrogen
- c) Oxygen
- d) Serum
Explanation:
Streptolysin O (SLO) is one of the two hemolysins produced by Streptococcus pyogenes. It is characteristically oxygen-labile, meaning it is rapidly inactivated in the presence of oxygen. It is also highly antigenic, which is the basis for the ASO (Antistreptolysin O) titer test.
Why other options are incorrect:
Why other options are incorrect:
- • CO2 & Nitrogen: These gases do not inactivate Streptolysin O; in fact, Streptolysin O is active under anaerobic conditions (lack of oxygen).
- • Serum: Serum does not inactivate Streptolysin O. In contrast, Streptolysin S (the other hemolysin) is oxygen-stable but is often associated with serum proteins for stability.
“Prozone phenomenon” is encountered in?
- a) A typical mycobacteria
- b) Brucella
- c) Streptococcus
- d) Bordetella pertusis
Explanation:
The Prozone phenomenon is a false-negative response in agglutination tests due to antibody excess. It is classically encountered during serological testing for Brucella (Brucellosis). When antibody titers are very high, they saturate all antigen binding sites, preventing the cross-linking required for visible agglutination.
Why other options are incorrect:
Why other options are incorrect:
- • Atypical mycobacteria: Diagnosis is primarily through culture and molecular methods, not standard agglutination tests where prozone is a primary concern.
- • Streptococcus: While serology (like ASO) is used, the prozone effect is not a hallmark diagnostic pitfall for this genus as it is for Brucella.
- • Bordetella pertusis: Diagnosis is usually made via PCR or culture from nasopharyngeal swabs rather than the specific agglutination tests associated with prozone.
Glutamic acid is oxidized by the species except?
- a) B. abortus
- b) B. melitensis
- c) B. suis
- d) B. canis
Explanation:
Brucella species are differentiated based on their oxidative metabolic profiles (their ability to oxidize specific amino acids and carbohydrates). B. canis is the exception that does not oxidize glutamic acid, whereas the other three major species do.
Oxidative Patterns:
Oxidative Patterns:
- • B. abortus, B. melitensis, & B. suis: These species characteristically oxidize Glutamic acid, Ornithine, and Ribose.
- • B. canis: This species shows a distinct pattern and does not oxidize glutamic acid or ribose.
Growth of influenza virus is identified by?
- a) Cytopathic effects
- b) Hela cells
- c) Both Cytopathic effects and Hela cells
- d) None of these
Explanation:
The growth of the Influenza virus in cell culture or embryonated eggs is primarily identified by Hemadsorption or Hemagglutination (using guinea pig or human ‘O’ group erythrocytes).
Why other options are incorrect:
Why other options are incorrect:
- • Cytopathic effects: Influenza viruses typically do not produce distinct or rapid Cytopathic Effects (CPE) in most primary cell cultures. Therefore, CPE is not a reliable method for identifying its growth.
- • HeLa cells: Influenza virus does not grow well in HeLa cells. It prefers MDCK (Madin-Darby Canine Kidney) cell lines or the amniotic/allantoic cavities of embryonated chicken eggs.
- • None of these: Since the standard identification methods (Hemagglutination/Hemadsorption) are not listed, this is the correct choice.
Influenza virus is identified by using?
- a) Haemaggulutinin inhibition test
- b) Tissue culture method
- c) Embryonated eggs
- d) Plaque formation
Explanation:
The Haemaggulutinin (Hemagglutination) Inhibition (HI) test is the standard serological method used to identify and sub-type the influenza virus. It works by detecting antibodies that prevent the virus from agglutinating red blood cells, or by using known antibodies to identify an unknown virus isolate.
Why other options are incorrect:
Why other options are incorrect:
- • Tissue culture method & Embryonated eggs: These are methods used for the isolation and cultivation (growth) of the virus, but they do not specifically identify the virus strain on their own.
- • Plaque formation: This technique is primarily used to quantify (titrate) infectious virus particles by counting “plaques” or areas of cell death, rather than for primary identification.
Streptolysin ‘S’ is?
- a) Oxygen unstable
- b) Thermostable
- c) Oxygen stable
- d) None of these
Explanation:
Streptolysin S (SLS) is one of the two hemolysins produced by Streptococcus pyogenes. Unlike Streptolysin O, it is oxygen-stable, meaning it maintains its hemolytic activity in the presence of atmospheric oxygen. It is responsible for the surface hemolysis seen on blood agar plates.
Why other options are incorrect:
Why other options are incorrect:
- • Oxygen unstable: This refers to Streptolysin O (SLO), which is inactivated by oxygen (oxygen-labile).
- • Thermostable: Streptolysin S is heat-labile (destroyed by heat), not thermostable.
- • None of these: This is incorrect as “Oxygen stable” is a fundamental characteristic of Streptolysin S.
Coagulase test is used for?
- a) Salmonella
- b) Staphylococcus
- c) Bordetella
- d) Pneumococcus
Explanation:
The Coagulase test is a key laboratory test used to identify Staphylococcus aureus. This bacterium produces the enzyme coagulase, which converts soluble fibrinogen in plasma into insoluble fibrin, resulting in a visible clot. It is the primary method used to differentiate S. aureus (coagulase-positive) from other species like S. epidermidis (coagulase-negative).
Why other options are incorrect:
Why other options are incorrect:
- • Salmonella: Identified through biochemical tests (like the TSI test) and serotyping (Widal test).
- • Bordetella: Identified via specialized culture media (Bordet-Gengou) and molecular methods; it does not produce coagulase.
- • Pneumococcus: Streptococcus pneumoniae is identified by its sensitivity to Optochin and its solubility in bile.
Gasgangarene bacillus is?
- a) Facultative anaerobe
- b) Obligate anaerobe
- c) Facultative aerobe
- d) Obligate aerobe
Explanation:
The primary “gas gangrene bacillus” is Clostridium perfringens. Members of the genus Clostridium are obligate anaerobes, meaning they can only grow in the absence of oxygen and lack the enzymes (like catalase or superoxide dismutase) to neutralize oxygen’s toxic byproducts.
Why other options are incorrect:
Why other options are incorrect:
- • Facultative anaerobe: These organisms (like E. coli) can grow in both aerobic and anaerobic conditions. Clostridium cannot survive in oxygenated environments.
- • Facultative aerobe: This term is rarely used in standard microbiology but would imply an organism that prefers anaerobic conditions but can live in oxygen; Clostridium is strictly anaerobic.
- • Obligate aerobe: These organisms (like Mycobacterium tuberculosis) require oxygen to survive and cannot grow under anaerobic conditions.
Mc Fadyean’s reaction is used to detect?
- a) Bacillus anthracis
- b) Brucella
- c) Corynaebacterium
- d) None of these
Explanation:
McFadyean’s reaction is a specific staining technique used for the presumptive identification of Bacillus anthracis (the causative agent of Anthrax). When a blood smear is stained with polychrome methylene blue, the bacilli appear blue while the surrounding capsular material appears pinkish or purple and ragged.
Why other options are incorrect:
Why other options are incorrect:
- • Brucella: These are identified using culture methods and serological tests (like the milk ring test or Rose Bengal plate test), not McFadyean’s stain.
- • Corynebacterium: C. diphtheriae is traditionally identified using Albert’s stain or Neisser’s stain to demonstrate metachromatic (volutin) granules.
- • None of these: This is incorrect because Bacillus anthracis is the classic organism associated with this reaction.
Anthrax is a?
- a) Vector borne
- b) Zoonotic infection
- c) Wound borne
- d) Soil borne
Explanation:
Anthrax is a classic Zoonotic infection, meaning it is a disease that is primarily a disease of animals (such as cattle, sheep, and goats) but can be transmitted to humans through contact with infected animals or contaminated animal products like wool, hides, and meat.
Why other options are incorrect:
Why other options are incorrect:
- • Vector borne: Anthrax does not require an arthropod vector (like a mosquito or tick) for transmission to humans.
- • Wound borne: While “Cutaneous Anthrax” enters through skin abrasions, the disease as a whole is classified by its animal origin (Zoonosis).
- • Soil borne: While Bacillus anthracis spores can persist in the soil for decades and infect grazing animals, the term “Zoonotic” more accurately describes the clinical and epidemiological nature of human infection.
Of the following, this is a capsulated organism?
- a) Bacillus anthracis
- b) Escherichia-coli
- c) Corynebacterium
- d) Brucella
Explanation:
Bacillus anthracis is a well-known capsulated organism. Its capsule is unique because it is composed of poly-D-glutamic acid (a polypeptide), unlike most bacterial capsules which are made of polysaccharides. The capsule is essential for its virulence as it protects the bacteria from phagocytosis.
Why other options are incorrect:
Why other options are incorrect:
- • Escherichia coli: While some specific strains of E. coli (like K1) can possess a capsule, the genus as a whole is not typically defined by a capsule in the same way B. anthracis is.
- • Corynebacterium: Most species, including C. diphtheriae, are non-capsulated, non-motile, Gram-positive rods.
- • Brucella: These are small, Gram-negative coccobacilli that are characteristically non-capsulated and non-motile.
Seroconversion in HIV infection takes place in?
- a) 3 weeks
- b) 6 weeks
- c) 9 weeks
- d) 12 weeks
Explanation:
Seroconversion is the period during which HIV antibodies develop and become detectable in the blood. While modern tests can detect HIV earlier, the classic “window period” is generally cited as 6 to 12 weeks. By 12 weeks, the vast majority of infected individuals (over 95-99%) will have developed enough antibodies to produce a positive result on an ELISA test.
Key Points:
Key Points:
- • Window Period: The time between initial infection and the point when a test can reliably detect the virus or antibodies.
- • 3-6 Weeks: Some individuals may seroconvert early (often associated with acute retroviral syndrome symptoms), but a negative test at this stage is not conclusive.
- • 12 Weeks: This is the standard timeframe used in clinical guidelines to confirm a negative status after a potential exposure.
AIDS is caused by?
- a) HTLV – I
- b) Bunya virus
- c) HTLV – III
- d) All
Explanation:
Before the virus was officially named HIV (Human Immunodeficiency Virus) in 1986, it was known by different names. The team led by Robert Gallo at the National Cancer Institute (USA) referred to the virus as HTLV-III (Human T-lymphotropic Virus type III).
Why other options are incorrect:
Why other options are incorrect:
- • HTLV-I: This virus is associated with adult T-cell leukemia/lymphoma (ATL) and a neurological disorder called HAM/TSP, but it does not cause AIDS.
- • Bunya virus: This refers to a large family of viruses (Bunyaviridae) that cause diseases like Hantavirus pulmonary syndrome or Rift Valley fever, not AIDS.
- • All: Since only HTLV-III is an old name for HIV, “All” is incorrect.
AIDS virus is?
- a) RNA virus
- b) DNA virus
- c) Retro virus
- d) Entero virus
Explanation:
The virus that causes AIDS (HIV) is a Retro virus. It belongs to the family Retroviridae and the genus Lentivirus. It is characterized by the use of an enzyme called reverse transcriptase to convert its RNA genome into DNA once it enters a host cell.
Why other options are incorrect:
Why other options are incorrect:
- • RNA virus: While HIV is technically an RNA virus, “Retro virus” is the more specific and accurate taxonomic classification provided in the options.
- • DNA virus: HIV does not store its genetic information as DNA; it only creates a DNA copy (provirus) during its replication cycle inside the host.
- • Entero virus: Enteroviruses are a genus of viruses (like Poliovirus) transmitted via the fecal-oral route and belong to the Picornaviridae family.
Special feature of Retro viruses?
- a) Reverse transcriptase
- b) RNA directed DNA polymerases
- c) Both Reverse transcriptase & RNA directed DNA polymerases
- d) Boils
Explanation:
The defining characteristic of Retroviruses is the presence of the enzyme Reverse transcriptase. This enzyme is biochemically classified as an RNA-directed DNA polymerase because it uses the viral RNA as a template to synthesize a complementary strand of DNA.
Why other options are incorrect:
Why other options are incorrect:
- • Reverse transcriptase: While correct, it is the same thing as option (b), making (c) the most complete answer.
- • RNA directed DNA polymerases: This is the technical biochemical name for Reverse transcriptase.
- • Boils: This refers to a skin infection (furuncle) typically caused by Staphylococcus aureus and has no relation to the biological features of Retroviruses.
HIV is belonging to?
- a) Retro Viridae
- b) Rhabdo Viridae
- c) Toga Viridae
- d) Paramyxo Viridae
Explanation:
The Human Immunodeficiency Virus (HIV) belongs to the family Retroviridae (specifically the genus Lentivirus). These viruses are characterized by having an RNA genome and using the enzyme reverse transcriptase to integrate their genetic material into the host cell’s DNA.
Why other options are incorrect:
Why other options are incorrect:
- • Rhabdo Viridae: This family includes bullet-shaped viruses such as the Rabies virus.
- • Toga Viridae: This family includes viruses like Rubella (German measles) and Chikungunya.
- • Paramyxo Viridae: This family includes common respiratory and systemic viruses like Measles, Mumps, and Parainfluenza.
Confirmatory test for AIDS is?
- a) Western blot test
- c) Karpas test
- d) Fujerbio test
Explanation:
The Western blot test is traditionally considered the gold standard confirmatory test for HIV/AIDS. It is used to verify the results of a positive screening test by detecting antibodies against specific viral proteins (such as p24, gp41, and gp120/160).
Why other options are incorrect:
Why other options are incorrect:
- • ELISA test: This is a highly sensitive screening test. While excellent for initial detection, it can produce false positives, requiring a Western blot for confirmation.
- • Karpas test: This is an immunoperoxidase slide test used for detecting HIV antibodies, but it is not the standard global confirmatory method.
- • Fujerbio test: This refers to a manufacturer (Fujirebio) of various diagnostic assays (like the Particle Agglutination test), not a specific type of confirmatory procedure.
Screening test for AIDS is?
- a) Western blot test
- b) ELISA test
- c) Both Western blot test and ELISA test
- d) VDRL test
Explanation:
The ELISA (Enzyme-Linked Immunosorbent Assay) is the primary screening test for HIV/AIDS. It is used for mass screening because it is highly sensitive, relatively inexpensive, and can detect HIV antibodies (and in newer generations, the p24 antigen) in the blood.
Why other options are incorrect:
Why other options are incorrect:
- • Western blot test: This is a confirmatory test, used only after a screening test (ELISA) has come back positive. It is too complex and expensive for initial screening.
- • Both: This is incorrect because screening and confirmation are two distinct steps in the diagnostic protocol.
- • VDRL test: This stands for Venereal Disease Research Laboratory test, which is a screening test for Syphilis (caused by Treponema pallidum), not HIV.
The interval period between HIV infection and appearance of antibodies in serum is called?
- a) Intrinsic period
- b) Incubation period
- c) Window period
- d) None of these
Explanation:
The Window period is the time between the initial HIV infection and the point when antibodies become detectable by standard serological tests. During this period, an infected person will test negative for antibodies but can still transmit the virus to others.
Why other options are incorrect:
Why other options are incorrect:
- • Intrinsic period: This term is generally used in parasitology to describe the time required for a parasite to complete its development within a host.
- • Incubation period: This is the time interval between the initial infection and the first appearance of clinical symptoms (which in HIV can range from a few weeks to many years).
- • None of these: This is incorrect because “Window period” is the scientifically accurate term for this diagnostic gap.
Which of the following is the most specific in diagnosis of AIDS?
- a) IHA
- b) Western blot
- c) ELISA
- d) Immuno electrophoresis
Explanation:
The Western blot is the most specific test for the diagnosis of HIV/AIDS. High specificity means the test has a very low rate of false positives because it identifies antibodies against specific viral proteins (like gp120, gp41, and p24) separately.
Why other options are incorrect:
Why other options are incorrect:
- • ELISA: While highly sensitive (good for catching all possible cases), it is less specific than Western blot and can occasionally yield false positives.
- • IHA (Indirect Hemagglutination Assay): This is an older technique used for various infectious diseases but is not the standard or most specific method for confirming HIV.
- • Immuno electrophoresis: This is a general technique used to separate and identify proteins based on their electrophoresis and reaction with antibodies; it is not a specific diagnostic test for HIV.
Following is the marker of HIV infection in blood?
- a) Reverse transcriptase
- b) DNA polymerase
- c) RNA polymerase
- d) None of these
Explanation:
Reverse transcriptase is a unique enzyme and a primary biochemical marker of HIV (a retrovirus). It is responsible for translating the viral RNA into DNA. Detecting the activity or presence of this enzyme is a hallmark of retroviral infection. Note: In clinical settings, other common markers include the p24 antigen and HIV antibodies.
Why other options are incorrect:
Why other options are incorrect:
- • DNA polymerase: This is a common enzyme found in all living cells (including humans) for DNA replication; it is not a specific marker for HIV.
- • RNA polymerase: This enzyme is used by all cells to transcribe DNA into RNA and is not specific to the HIV virus.
- • None of these: This is incorrect because Reverse transcriptase is the characteristic enzyme that defines the replication of HIV.
One Comment