Chapter 9 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 401 to 450
Wilson and Blair bismuth sulphite medium is used for the growth of?
- a) Salmonella typhi
- b) Shigella dysenteriae
- c) Vibrio cholerae
- d) E. coli
Explanation:
Wilson and Blair Bismuth Sulphite Agar is a highly selective medium specifically designed for the isolation of Salmonella typhi and other Salmonellae from clinical specimens. S. typhi reduces the bismuth sulphite in the medium to metallic bismuth sulphide, resulting in characteristic black colonies with a metallic sheen.
Why other options are incorrect:
Why other options are incorrect:
- • Shigella dysenteriae: Most strains of Shigella are inhibited by the brilliant green and bismuth sulphite present in this medium.
- • Vibrio cholerae: This organism requires highly alkaline media like TCBS (Thiosulfate-Citrate-Bile Salts-Sucrose) agar for selective growth.
- • E. coli: This is a normal intestinal flora and is generally inhibited on Wilson and Blair medium to allow the pathogens to grow.
Differential staining of bacteria spore is related to?
- a) Albert’s staining
- b) Lugol’ s staining
- c) Moller’s staining
- d) Indian ink preparation
Explanation:
Moller’s staining is a differential staining technique used to detect bacterial spores. Because spores have a highly resistant coat, heat or long exposure to a primary stain (carbol fuchsin) is required. In Moller’s method, spores appear red, while the vegetative part of the cell is stained blue (counterstained with methylene blue).
Why other options are incorrect:
Why other options are incorrect:
- • Albert’s staining: This is used to demonstrate metachromatic granules (Volutin granules) typically found in Corynebacterium diphtheriae.
- • Lugol’s staining: This is an iodine solution used as a mordant in Gram staining or to demonstrate starch; it is also used in parasitology to stain protozoan cysts.
- • Indian ink preparation: This is a negative staining technique used primarily to demonstrate the capsule of bacteria (like Klebsiella) or fungi (like Cryptococcus).
The size of the virus can be determined by?
- a) Micrography
- b) Ultra-centrifugation at high speed
- c) Ultra-filteration
- d) All of these
Explanation:
The size of viruses is extremely small (measured in nanometers) and requires specialized physical methods for measurement. All the listed methods are historically and scientifically valid for determining viral size:
- • Micrography (Electron Microscopy): This is the most direct method, allowing scientists to visualize the virus particles and measure them against a known scale.
- • Ultra-centrifugation: By measuring the sedimentation rate (the speed at which particles sink) in an ultracentrifuge, the size and density of the virus can be calculated using mathematical formulas.
- • Ultra-filtration: By passing viral suspensions through membranes with known pore sizes (like Gradocol membranes), the size can be estimated based on whether the virus passes through or is retained by the filter.
The diagnosis of tuberculosis is carried out by which of the following concentration/processing methods?
- a) Emulator
- b) Antiformin method
- c) Petroff’s method
- d) Concentration method
- e) All of these
Explanation:
Because Mycobacterium tuberculosis may be present in small numbers in clinical specimens like sputum, concentration methods are used to increase the sensitivity of microscopy and culture. All the listed methods (specifically the technical ones) relate to the processing of samples for TB:
- • Petroff’s method: This is a classic technique using 4% Sodium Hydroxide (NaOH) to liquefy sputum and kill contaminating flora, followed by centrifugation to concentrate the bacilli.
- • Antiformin method: An older method using antiformin (a mixture of sodium hypochlorite and caustic soda) to dissolve organic matter and facilitate the concentration of acid-fast bacilli.
- • Concentration method: This is a general term for various techniques (including centrifugation and flotation) used to enrich the sample for better detection.
- • Emulator/Emulsification: While “Emulator” is a less common technical term, the process of emulsifying the sample is a standard initial step in the concentration and diagnosis process.
D. pneumoniae (Streptococcus pneumoniae) can be identified by?
- a) Microscopic exam
- b) Culture of sputum/blood
- c) Animal inoculation
- d) All of these
Explanation:
Diplococcus pneumoniae (now commonly known as Streptococcus pneumoniae) is the primary cause of bacterial pneumonia. All the listed methods are standard laboratory procedures for its identification:
- • Microscopic exam: Gram staining of sputum reveals characteristic Gram-positive, lancet-shaped diplococci. The Quellung reaction (capsular swelling) can also be used for direct identification.
- • Culture: Specimens like sputum or blood are cultured on blood agar, where the organism produces alpha-hemolytic (greenish) colonies. Sensitivity to Optochin and bile solubility are then used to confirm the species.
- • Animal inoculation: Mice are highly susceptible to S. pneumoniae. Intraperitoneal inoculation into a mouse will result in the death of the animal within 1–3 days, and the organism can be easily recovered from the heart’s blood.
D. pneumoniae (Streptococcus pneumoniae) can be cultivated in?
- a) Glucose broth
- b) Serum broth
- c) Agar and blood agar
- d) Chocolate agar
- e) All of these
Explanation:
Streptococcus pneumoniae is a fastidious organism, meaning it has complex nutritional requirements and does not grow on simple ordinary media like nutrient agar. It requires media enriched with blood, serum, or specific sugars.
- • Blood Agar: This is the most common medium used; the organism produces small, translucent colonies with a characteristic zone of alpha-hemolysis (partial greening).
- • Chocolate Agar: Provides the necessary nutrients (released from lysed red blood cells) for robust growth.
- • Serum/Glucose Broth: The addition of serum or glucose to liquid media provides the energy and enrichment factors required for the bacteria to multiply effectively.
For sterilization of fermentation equipment, the method followed is?
- a) Radiation
- b) Chemicals
- c) Heating
- d) All of these
Explanation:
The sterilization of fermentation equipment depends on the type of equipment and the nature of the components. All of these methods are used in different contexts within industrial microbiology:
- • Heating: This is the most common method for large-scale stainless steel fermenters (bioreactors). Steam sterilization (SIP – Sterilization In Place) at 121°C is the standard for vessels and pipelines.
- • Chemicals: Chemical sterilization (using agents like ethylene oxide or liquid disinfectants) is used for heat-sensitive components, probes, or parts of the equipment that cannot withstand high temperatures.
- • Radiation: Gamma radiation is extensively used for the sterilization of modern single-use (disposable) plastic fermenters and related plastic tubing/connectors before they are used in the lab or industry.
Which of the following culture media is specifically used for the growth of fungi?
- a) Sabouraud’s medium
- b) Nutrient agar
- c) Nutrient broth
- d) Minimal agar medium
Explanation:
Sabouraud’s Dextrose Agar (SDA) is the standard medium used for the cultivation of pathogenic and saprophytic fungi (yeasts and molds). It has a low pH (around 5.6) which inhibits the growth of most bacteria while allowing fungi to flourish. It also contains a high concentration of dextrose as an energy source.
Why other options are incorrect:
Why other options are incorrect:
- • Nutrient agar/broth: These are general-purpose media designed primarily for the growth of non-fastidious bacteria. They do not have the acidic pH or specific nutrients required to selectively grow fungi.
- • Minimal agar medium: This contains only the absolute minimum nutrients (salts and a carbon source) required for “wild-type” microorganisms to grow. It is used mostly for genetic studies and is not a primary medium for fungal isolation.
A simple asexual spore which develops by budding is known as?
- a) Chlamydospore
- b) Blastospore
- c) Arthospore
- d) Conidia
Explanation:
A Blastospore is a type of asexual fungal spore produced by budding from a parent cell. This is commonly seen in yeasts like Saccharomyces and Candida, where the daughter cell (bud) eventually pinches off from the mother cell.
Why other options are incorrect:
Why other options are incorrect:
- • Chlamydospore: These are thick-walled, resistant resting spores formed by the rounding up and enlargement of a hyphal segment.
- • Arthospore: Also known as arthroconidia, these are formed by the fragmentation of a septate hypha into individual square or rectangular cells.
- • Conidia: These are asexual spores that are formed at the tip or side of specialized hyphae (conidiophores); while they are asexual, the term specifically for budding spores is “blastospore.”
Which of the following culture media is used for the cultivation of Leishmania?
- a) Sabouraud’s medium
- b) NNN medium
- c) Wilson Blair medium
- d) Czapek–Dox medium
Explanation:
The NNN (Novy-MacNeal-Nicolle) medium is the standard culture medium used for the isolation and cultivation of Leishmania and Trypanosoma cruzi. It is a blood-agar-based medium (usually rabbit blood) that allows the parasites to transform into and multiply as promastigotes.
Why other options are incorrect:
Why other options are incorrect:
- • Sabouraud’s medium: This is a selective medium specifically used for the growth of fungi (yeasts and molds).
- • Wilson Blair medium: This is a selective medium (Bismuth Sulphite Agar) used for the isolation of Salmonella typhi.
- • Czapek–Dox medium: This is a semi-synthetic medium used primarily for the cultivation of fungi (like Aspergillus and Penicillium) and some soil bacteria.
Salt agar is used for the selective isolation of?
- a) Streptococcus
- b) Staphylococcus
- c) Vibrio
- d) Shigella
Explanation:
Salt agar (often used in the form of Mannitol Salt Agar) contains a high concentration of sodium chloride (usually 7.5% to 10%). This makes it highly selective for Staphylococcus species, as they are halotolerant and can grow in high salt environments that inhibit most other human pathogens.
Why other options are incorrect:
Why other options are incorrect:
- • Streptococcus: Most species of Streptococcus are inhibited by high concentrations of salt (with the exception of Enterococci, which can grow in 6.5% NaCl).
- • Vibrio: While Vibrio species are halophilic (salt-loving), they are usually isolated using more specific media like TCBS (Thiosulfate-Citrate-Bile-Sucrose) agar.
- • Shigella: These are enteric Gram-negative rods that are generally sensitive to high salt concentrations and are isolated using media like MacConkey or DCA.
The average incubation period of tetanus is?
- a) 2-3 days
- b) 7-10 days
- c) 14-21 days
- d) 3-4 weeks
Explanation:
The incubation period for tetanus (caused by Clostridium tetani) typically ranges from 3 to 21 days, with an average of about 7 to 10 days. Generally, the further the injury site is from the central nervous system, the longer the incubation period.
Key Points:
Key Points:
- • Short Incubation: A shorter incubation period (less than 7 days) is often associated with more severe disease and a higher risk of mortality.
- • Long Incubation: Cases with longer incubation periods (over 14 days) tend to be milder.
- • Determinants: The length of the incubation period depends on the amount of toxin produced, the distance the toxin must travel to reach the CNS, and the immunity of the individual.
Incubation period of Cl. welchii (Clostridium perfringens) food poisoning is?
- a) 8-12 hours
- b) 7-10 hours
- c) 5-7 hours
- d) 2-4 hours
Explanation:
Clostridium welchii (now commonly called Clostridium perfringens) causes food poisoning with a characteristically short incubation period, typically ranging from 8 to 12 hours (though it can vary from 6 to 24 hours).
Key Facts:
Key Facts:
- • Mechanism: Illness occurs after ingesting a large number of vegetative cells in contaminated food (usually meat dishes). These cells sporulate in the small intestine, releasing a heat-labile enterotoxin.
- • Symptoms: Primarily characterized by abdominal cramps and watery diarrhea; fever and vomiting are usually absent.
- • Gas Gangrene: Note that if Cl. welchii causes gas gangrene (wound infection), the incubation period is different, usually 1 to 4 days.
Nagler’s reaction is used to detect which of the following enzymes?
- a) Coagulase
- b) Hyaluronidase
- c) Lecithinase
- d) None of these
Explanation:
Nagler’s reaction is a biochemical test used to identify Clostridium perfringens. It detects the presence of Lecithinase (also known as alpha-toxin).
How it works:
How it works:
- • Principle: Cl. perfringens produces lecithinase, which breaks down the lecithin found in egg yolk agar, resulting in an opaque (cloudy) halo around the colonies.
- • Specificity: To confirm the test, one half of the agar plate is smeared with C. perfringens antitoxin. If the opalescence is inhibited by the antitoxin, the reaction is positive.
- • Comparison: Coagulase is used to identify Staphylococcus aureus, while Hyaluronidase is a “spreading factor” produced by various bacteria but not specifically detected by Nagler’s reaction.
Clostridium welchii (C. perfringens) is positive for?
- a) Elek’s gel precipitation test
- b) Nagler’s test
- c) Weil felix test
- d) Bacitracin test
Explanation:
Clostridium welchii (also known as C. perfringens) is positive for Nagler’s test. This test is used to demonstrate the production of lecithinase (alpha-toxin) by the bacteria. When grown on egg yolk agar, the enzyme breaks down lecithin, producing an opaque zone around the colonies which is specifically inhibited by C. perfringens antitoxin.
Why other options are incorrect:
Why other options are incorrect:
- • Elek’s gel precipitation test: This is an in vitro virulence test used to detect toxigenic strains of Corynebacterium diphtheriae.
- • Weil-Felix test: This is a heterophile agglutination test used for the diagnosis of Rickettsial diseases, utilizing Proteus antigens.
- • Bacitracin test: This test is primarily used to differentiate Group A Streptococci (S. pyogenes, which is sensitive) from other beta-hemolytic streptococci.
Which of the following culture media is most suitable for the growth of Clostridia spp?
- a) Lowenstein-Jensen medium
- b) MacConkey’s medium
- c) Robertson’s cooked meat medium
- d) None of these
Explanation:
Robertson’s Cooked Meat (RCM) medium is a classic enrichment medium used for the cultivation of anaerobic bacteria like Clostridia. The cooked meat pieces (usually beef heart) contain unsaturated fatty acids and glutathione, which act as reducing agents to create the anaerobic environment necessary for these organisms to grow.
Why other options are incorrect:
Why other options are incorrect:
- • Lowenstein-Jensen medium: This is an egg-based selective medium used specifically for the cultivation of Mycobacterium tuberculosis.
- • MacConkey’s medium: This is a differential and selective medium used to isolate Gram-negative enteric bacteria (like E. coli) and differentiate them based on lactose fermentation.
- • None of these: Since RCM is a standard medium for Clostridia, this option is incorrect.
Lepra bacillus (Mycobacterium leprae) is best cultured on/in?
- a) Armadillo’s brain
- b) Foot pad of mice
- c) Liver of guinea pig
- d) Any of the above
Explanation:
Mycobacterium leprae is an obligate intracellular parasite that cannot be grown on artificial (non-living) culture media. It is experimentally cultivated in animal models. The foot pad of mice (Shepard’s method) is the standard method for studying the multiplication of the bacilli and testing drug sensitivity.
Why other options are incorrect:
Why other options are incorrect:
- • Armadillo’s brain: While the nine-banded armadillo is a highly susceptible animal model used to produce large quantities of M. leprae, the bacilli primarily multiply in the liver, spleen, and lymph nodes, not specifically the brain.
- • Liver of guinea pig: Guinea pigs are commonly used in the diagnosis of tuberculosis (M. tuberculosis) via animal inoculation, but they are not used for the cultivation of M. leprae.
- • Artificial Media: It is important to remember that unlike M. tuberculosis, M. leprae has never been successfully grown on agar or broth.
Which of the following is the standard culture medium used for Mycobacterium tuberculosis?
- a) LJ medium
- b) Mac Conkey’s medium
- c) Wilson blair medium
- d) None of these
Explanation:
Lowenstein-Jensen (LJ) medium is the most common egg-based solid medium used for the cultivation of Mycobacterium tuberculosis. It contains eggs, glycerol, asparagine, and mineral salts. It also contains malachite green, which acts as a selective agent to inhibit the growth of most other bacteria and fungi.
Why other options are incorrect:
Why other options are incorrect:
- • Mac Conkey’s medium: This is used for the isolation of Gram-negative enteric bacteria (like E. coli and Klebsiella) and differentiates lactose fermenters from non-fermenters.
- • Wilson blair medium: As mentioned previously, this (Bismuth Sulphite Agar) is a highly selective medium used for the isolation of Salmonella typhi.
- • Growth Rate: Unlike common bacteria that grow overnight, M. tuberculosis grows very slowly, typically taking 2 to 8 weeks to form visible colonies on LJ medium.
Which of the following culture media is specifically required for the selective isolation of C. diphtheriae?
- a) LJ medium
- b) Mac Conkey’s medium
- c) Potassium tellurite medium
- d) PDA medium
Explanation:
Potassium tellurite medium (such as Hoyle’s medium or McLeod’s agar) is a selective medium used for Corynebacterium diphtheriae. The potassium tellurite inhibits the growth of most other commensal bacteria of the upper respiratory tract. Furthermore, C. diphtheriae reduces tellurite to metallic tellurium, resulting in characteristic black or grey colonies.
Why other options are incorrect:
Why other options are incorrect:
- • LJ (Lowenstein-Jensen) medium: This is an egg-based medium specifically used for the cultivation of Mycobacterium tuberculosis.
- • Mac Conkey’s medium: This is a differential medium used for Gram-negative enteric bacteria; C. diphtheriae (a Gram-positive rod) does not grow well on it.
- • PDA (Potato Dextrose Agar) medium: This is a common mycological medium used for the cultivation of fungi and molds.
On Mac Conkey’s medium, Escherichia coli forms?
- a) Colorless colonies
- b) Greenish pigmentation
- c) Pink coloured colonies
- d) Medusa head appearance
Explanation:
Escherichia coli is a Lactose Fermenter (LF). MacConkey agar contains lactose and a pH indicator called neutral red. When E. coli ferments lactose, it produces organic acids that lower the pH of the medium, causing the neutral red to turn into pink or red coloured colonies.
Why other options are incorrect:
Why other options are incorrect:
- • Colorless colonies: These are formed by Non-Lactose Fermenters (NLF) such as Salmonella, Shigella, and Proteus.
- • Greenish pigmentation: This is often associated with Pseudomonas aeruginosa (on nutrient agar) or the “metallic green sheen” E. coli produces on EMB (Eosin Methylene Blue) agar, but not on MacConkey.
- • Medusa head appearance: This is a classic morphological description for the colonies of Bacillus anthracis when grown on blood agar.
The Kauffmann-White scheme is used for the classification and identification of?
- a) Salmonella spp.
- b) Shigella spp.
- c) E. coli
- d) None of these
Explanation:
The Kauffmann-White scheme is a classification system that differentiates Salmonella species into different serotypes (serovars) based on their surface antigens.
Key Components of the Scheme:
Key Components of the Scheme:
- • O Antigens (Somatic): These are heat-stable polysaccharides located on the outer membrane of the cell wall.
- • H Antigens (Flagellar): These are heat-labile proteins found on the flagella.
- • Vi Antigens (Capsular): A surface polysaccharide found in certain serotypes like S. typhi, related to virulence.
- • Serotypes: Using this scheme, thousands of different serotypes of Salmonella (e.g., S. typhi, S. typhimurium, S. enteritidis) have been identified.
Shigella was first isolated by?
- a) Shiga
- c) Sonnei
- d) Robert Koch
Explanation:
The genus Shigella is named after the Japanese physician and bacteriologist Kiyoshi Shiga, who first isolated Shigella dysenteriae in 1897 during a massive dysentery epidemic in Japan.
Why other options are incorrect:
Why other options are incorrect:
- • Schmitz: Alfred Schmitz described what is now known as Shigella dysenteriae type 2 (Schmitz’s bacillus) in 1917.
- • Sonnei: Carl Olaf Sonne identified Shigella sonnei (Group D) in 1915, which is the most common species causing dysentery in developed countries.
- • Robert Koch: Although he was a pioneer in microbiology and discovered the bacilli causing Anthrax, Tuberculosis, and Cholera, he was not the one who isolated Shigella.
Wilson and Blair medium is used for isolation of?
- a) Staphylococci
- b) Salmonella typhosa
- c) Vibrio cholerae
- d) Shigella shigae
Explanation:
Wilson and Blair Bismuth Sulphite Agar is a highly selective medium specifically designed for the isolation of Salmonella typhosa (now known as Salmonella typhi).
Key Features:
Key Features:
- • Principle: S. typhi reduces the bismuth sulphite in the medium to metallic bismuth sulphide.
- • Appearance: This chemical reaction results in characteristic black colonies often surrounded by a metallic sheen.
- • Selectivity: Brilliant green and bismuth sulphite in the medium inhibit the growth of Gram-positive bacteria and most other members of the Enterobacteriaceae family, including many Shigella species.
Wilson and Blair medium is used for isolation of?
- a) Staphylococci
- b) Salmonella typhosa
- c) Vibrio cholerae
- d) Shigella shigae
Explanation:
Wilson and Blair Bismuth Sulphite Agar is a highly selective medium specifically used for the isolation of Salmonella typhosa (now known as Salmonella typhi) from clinical specimens like stool.
Key Details:
Key Details:
- • Identification: S. typhi reduces bismuth sulphite to metallic bismuth sulphide, producing characteristic black colonies with a metallic sheen.
- • Inhibitory Action: The brilliant green and bismuth sulphite in the medium inhibit the growth of Gram-positive organisms (like Staphylococci) and most other intestinal commensals.
- • Shigella: Most Shigella species (including Shigella shigae) are inhibited on this medium, making it useful for differentiating Salmonella from other enteric pathogens.
The micro-organisms that grow at high salinity are?
- a) Osmophiles
- b) Halophiles
- c) Both Osmophiles and Halophiles
- d) None of these
Explanation:
Halophiles are “salt-loving” organisms that thrive in environments with very high concentrations of salt (salinity). The word comes from the Greek words for “salt-loving.” These organisms have adapted their cellular machinery to prevent water loss (plasmolysis) in hypertonic salty environments.
Why other options are incorrect:
Why other options are incorrect:
- • Osmophiles: These are microorganisms adapted to environments with high osmotic pressure, but this is usually specifically due to high concentrations of sugar rather than salt (e.g., yeasts growing in jam or honey).
- • Both: While high salt creates high osmotic pressure, the specific term for salt-requirement is “Halophile.” An osmophile might not be able to tolerate the specific chemical stress of high sodium chloride.
- • Halotolerant: (Related term) These organisms don’t require high salt to grow but can tolerate it (like Staphylococcus aureus).
Alkaliphiles grow at pH value between?
- a) 1 to 6
- b) 6 to 9
- c) 1 to 11
- d) 7 to 12
Explanation:
Alkaliphiles are a class of extremophilic microbes capable of survival in alkaline environments. They typically grow optimally at pH values ranging from 7 to 12, with many species showing peak growth at a pH of around 9.0 to 10.5.
Microbial Classification by pH:
Microbial Classification by pH:
- • Acidophiles: Organisms that thrive under highly acidic conditions, usually at pH 5.5 or below.
- • Neutrophiles: Organisms that grow best in a narrow range around neutral pH (5.5 to 8.0). Most human pathogens are neutrophiles.
- • Alkaliphiles: Organisms like Vibrio cholerae or Bacillus alcalophilus that prefer or require high pH levels for growth.
A common laboratory method of cultivating anaerobic micro-organisms is?
- a) Gas pack system
- b) Brewer jar system
- c) Pyrogallic acid over the cotton
- d) None of these
Explanation:
The Gas pack system (GasPak) is the most common and convenient modern laboratory method for creating an anaerobic environment. It utilizes a chemical sachet that releases hydrogen and carbon dioxide; the hydrogen reacts with oxygen in the presence of a palladium catalyst to form water, effectively removing oxygen from the jar.
Methods of Anaerobic Culture:
Methods of Anaerobic Culture:
- • GasPak System: Disposable envelopes containing chemicals are activated with water to generate an oxygen-free atmosphere.
- • Brewer Anaerobic Jar: A specialized jar with a modified lid to facilitate the removal of oxygen, historically used before GasPak became standard.
- • Pyrogallic Acid Method: A chemical method where alkaline pyrogallol is used to absorb oxygen within a sealed container or tube.
- • Robertson’s Cooked Meat (RCM) Media: A liquid medium containing chopped meat that creates a reducing environment for anaerobes.
The term that is used for the bacteria which can withstand pasteurization but does not grow at higher temperatures?
- a) Thermophiles
- b) Extreme thermophiles
- c) Thermoduric
- d) Facultative thermophiles
Explanation:
Thermoduric bacteria are organisms that can survive (withstand) exposure to high temperatures, such as those used during pasteurization, but they do not grow optimally at those temperatures. Their optimal growth usually occurs in the mesophilic range.
Key Definitions:
Key Definitions:
- • Thermoduric: Bacteria like Micrococcus or Bacillus spores that survive heat treatment but prefer moderate temperatures for growth.
- • Thermophiles: Organisms that actually “love” heat and grow best at temperatures between 50°C and 70°C.
- • Extreme Thermophiles: Organisms (often Archaea) that thrive in environments above 80°C, such as hydrothermal vents.
- • Facultative Thermophiles: Organisms that can grow at high temperatures but are also capable of growing at lower temperatures.
Spores of actinomycetes are very sensitive, killed at temperature of?
- a) 52°C for 30 min.
- b) 65°C for 30 min.
- c) 70°C for 30 min.
- d) 43°C for 30 min
Explanation:
Unlike the highly heat-resistant endospores produced by Bacillus or Clostridium, the spores of actinomycetes (often called conidiospores or exospores) are relatively sensitive to heat. They are generally killed at a temperature of 52°C for 30 minutes.
Important Comparisons:
Important Comparisons:
- • Actinomycete Spores: These are asexual spores used for dispersal. While they can survive long periods of dryness (desiccation), they cannot withstand the high temperatures that bacterial endospores can.
- • Bacterial Endospores: These are highly resistant resting structures that can survive boiling (100°C) for several hours and require autoclaving (121°C) to be destroyed.
- • Actinomycetes: A group of Gram-positive bacteria (like Streptomyces) that form branching filaments and are famous for producing many antibiotics.
Culture media for fungi are?
- a) Potato dextrose agar (PDA)
- b) Sabouraud’s agar
- c) Czapekdox agar
- d) All of the above
Explanation:
The correct answer is All of the above. Fungi require specific media that often have a higher carbohydrate content and a slightly acidic pH to inhibit bacterial growth.
Common Fungal Media:
Common Fungal Media:
- • Potato Dextrose Agar (PDA): One of the most widely used media for growing a variety of fungi and molds; it is excellent for observing morphological characteristics.
- • Sabouraud’s Dextrose Agar (SDA): A standard medium used for the cultivation of pathogenic and non-pathogenic fungi, particularly dermatophytes.
- • Czapek-Dox Agar: A semi-synthetic medium used primarily for the cultivation of saprophytic fungi and soil microbes like Aspergillus and Penicillium.
The principle involved in the streak plate method is?
- a) Separation
- b) Streaking
- c) Isolation
- d) Dilution
Explanation:
The fundamental principle of the streak plate method is dilution. By spreading a small amount of inoculum over the surface of an agar plate in a specific pattern, the bacterial cells are mechanically diluted to the point where individual cells are deposited far apart from each other.
Key Concepts of the Streak Plate:
Key Concepts of the Streak Plate:
- • Purpose: To obtain isolated colonies from a mixed culture or a concentrated sample.
- • Mechanical Dilution: Each successive “sector” of streaks contains fewer and fewer bacteria because the loop is sterilized (or not recharged) between sectors.
- • Colony Formation: Each isolated colony is theoretically derived from a single “Colony Forming Unit” (CFU), representing a pure culture.
- • Comparison: While the goal is isolation, the mechanism/principle used to achieve it is the spatial dilution of the sample across the agar surface.
When a bacterial cell and mitochondria are treated with cyanide and carbon monoxide what happens initially?
- a) Respiration inhibits
- b) Photosynthesis inhibits
- c) Protein synthesis inhibits
- d) No effect occurs
Explanation:
The correct answer is Respiration inhibits. Both cyanide and carbon monoxide act as potent inhibitors of the Electron Transport Chain (ETC) in both aerobic bacteria and eukaryotic mitochondria.
Mechanism of Inhibition:
Mechanism of Inhibition:
- • Complex IV Binding: Cyanide ($CN^-$) and Carbon monoxide ($CO$) bind specifically to Cytochrome c oxidase (Complex IV), the final enzyme in the respiratory chain.
- • Blocking Oxygen: By binding to the iron in the heme group of the enzyme, they prevent the transfer of electrons to oxygen (the final electron acceptor).
- • Consequence: Since the flow of electrons is halted, the proton gradient cannot be maintained, ATP production stops, and aerobic respiration is immediately inhibited.
- • Bacteria vs. Mitochondria: Because mitochondria are evolutionarily derived from bacteria (Endosymbiotic theory), they share similar respiratory enzymes that are susceptible to these toxins.
Which virus was first observed?
- a) Hepatitis Virus
- b) TMV
- c) Cauliflower mosaic virus
- d) None of these
Explanation:
TMV (Tobacco Mosaic Virus) was the first virus to be discovered and the first to be observed. While its existence as a “filterable agent” was proven in the late 19th century, it was the first virus ever visualized following the invention of the electron microscope.
Milestones in TMV History:
Milestones in TMV History:
- • 1892 (Discovery): Dmitri Ivanovsky showed that extracts from infected tobacco plants remained infectious after passing through Chamberland filters (which trap bacteria).
- • 1898 (Naming): Martinus Beijerinck called it a contagium vivum fluidum (contagious living fluid) and coined the term ‘virus’.
- • 1935 (Crystallization): Wendell Stanley crystallized the virus, showing it had properties of both living and non-living matter.
- • 1939 (Observation): TMV was the first virus to be “seen” using an electron microscope by Kausche, Pfankuch, and Ruska.
A cell becomes flaccid when placed in a?
- a) Isotonic solution
- b) Hypertonic solution
- c) Hypotonic solution
- d) Normal solution
Explanation:
In plant biology, a cell becomes flaccid when it is placed in an isotonic solution. In this state, the water concentration inside and outside the cell is equal, so there is no net movement of water into or out of the cell.
Effects of Tonicity on Plant Cells:
Effects of Tonicity on Plant Cells:
- • Hypotonic Solution: Water enters the cell. The cell becomes turgid (swollen/firm). This is the ideal state for most plants.
- • Isotonic Solution: There is no net movement of water. The cell becomes flaccid (limp) because there is no turgor pressure against the cell wall.
- • Hypertonic Solution: Water leaves the cell. The cell membrane shrinks away from the cell wall, a process called plasmolysis.
The proteinaceous compound are converted to ammonia by?
- a) Putrification bacteria
- b) Ammonification bacteria
- c) Nitrification bacteria
- d) Denitrifying bacteria
Explanation:
The process of converting organic nitrogen (from proteinaceous compounds in dead organic matter or waste) into ammonia ($NH_3$) or ammonium ions ($NH_4^+$) is known as Ammonification. This is carried out by Ammonifying bacteria (and some fungi).
Steps in the Nitrogen Cycle:
Steps in the Nitrogen Cycle:
- • Ammonification: Breakdown of proteins/amino acids into ammonia. Common bacteria include Bacillus and Clostridium species.
- • Nitrification: The two-step biological oxidation of ammonia into nitrite ($NO_2^-$) and then into nitrate ($NO_3^-$). Performed by bacteria like Nitrosomonas and Nitrobacter.
- • Denitrification: The reduction of nitrates back into nitrogen gas ($N_2$), completing the cycle. Performed by bacteria like Pseudomonas.
- • Putrefaction: A general term for the anaerobic decomposition of organic matter (specifically proteins) by bacteria, which results in foul-smelling products, including ammonia.
Cell cycle is regulated by?
- a) Cyclins
- b) Cyclins and Cdks
- c) Cdks
- d) None of these
Explanation:
The cell cycle is primarily regulated by the interaction of two classes of proteins: Cyclins and Cyclin-dependent kinases (Cdks). Neither can function effectively without the other to drive the cell through various checkpoints.
Key Regulatory Components:
Key Regulatory Components:
- • Cyclins: Regulatory proteins whose concentration fluctuates (cycles) throughout the cell cycle. They “sign” the Cdk to perform its job.
- • Cdks (Cyclin-dependent kinases): Enzymes that are constant in concentration but remain inactive until they bind with a specific cyclin. Once activated, they phosphorylate target proteins to trigger the next phase of the cycle.
- • Checkpoints: The Cyclin-Cdk complexes act at specific checkpoints (G1/S, G2/M, and Spindle checkpoints) to ensure the cell is ready for division and that DNA is undamaged.
A disease that can be transmitted by an infectious agent from one individual to another was called?
- a) Epidemic
- b) Pandemic
- c) Communicable
- d) Comma
Explanation:
A Communicable disease is an illness that can be spread from one person, animal, or the environment to another individual via an infectious agent (like bacteria, viruses, or parasites).
Terminology Overview:
Terminology Overview:
- • Communicable Disease: Also known as infectious or transmissible diseases. Examples include Tuberculosis, Influenza, and Malaria.
- • Epidemic: A sudden increase in the number of cases of a disease above what is normally expected in a specific population or area.
- • Pandemic: An epidemic that has spread over several countries or continents, usually affecting a large number of people (e.g., COVID-19).
- • Non-communicable Disease: Diseases that cannot be transmitted between people, such as Heart Disease or Diabetes.
The most important energy-yielding reaction for an aerobic organism is?
- a) Glycosis
- b) EMP
- c) KDPG
- d) Both EMP and KDPG
Explanation:
The EMP (Embden-Meyerhof-Parnas) pathway, commonly known as classic glycolysis, is the most universal and important energy-yielding respiratory pathway used by the majority of aerobic and anaerobic organisms to break down glucose.
Comparison of Pathways:
Comparison of Pathways:
- • EMP (Embden-Meyerhof-Parnas): The standard glycolytic pathway found in animals, plants, and most bacteria. It yields 2 ATP and 2 NADH per glucose molecule.
- • KDPG (Entner-Doudoroff Pathway): An alternative pathway (utilizing the intermediate 2-keto-3-deoxy-6-phosphogluconate) used by some bacteria, such as Pseudomonas. It is less energy-efficient, yielding only 1 ATP per glucose.
- • Significance: While both pathways breakdown glucose, the EMP pathway is the primary metabolic engine for most aerobic life forms to provide precursors for the TCA cycle.
Genetic constitution of the cell is?
- a) Phenotype
- b) Genotype
- c) Cryptotype
- d) Histotype
Explanation:
The Genotype refers to the complete set of genes or the specific genetic makeup of an organism or cell. It represents the “blueprint” stored in the DNA.
Key Genetic Terms:
Key Genetic Terms:
- • Genotype: The internal genetic information (e.g., having the gene for blue eyes).
- • Phenotype: The observable physical characteristics or traits of an organism (e.g., actually having blue eyes), which result from the interaction of the genotype with the environment.
- • Histotype: Refers to the specific microscopic pattern or “type” of a tissue.
- • Genome: The entire set of genetic material (all the DNA) present in a cell or organism.
The primary mode of transmission of poliomyelitis virus is?
- a) Flies
- b) Milk
- c) Person to person
- d) Food and water
Explanation:
The primary mode of transmission for the Poliomyelitis virus is the fecal-oral route, which occurs most commonly through contaminated food and water.
Key Transmission Facts:
Key Transmission Facts:
- • Fecal-Oral Route: The virus enters the body through the mouth, usually from hands contaminated with the stool of an infected person or by consuming contaminated water/food.
- • Multiplication: The virus multiplies in the throat and intestines before sometimes entering the bloodstream and central nervous system.
- • Environmental Persistence: The virus can survive for long periods in sewage and water, which is why poor sanitation is a major factor in its spread.
- • Other Modes: While less common, it can also spread through respiratory droplets (person-to-person) during the early stages of infection.
Important class of respiratory enzymes?
- a) NAD
- b) Cytochromes
- c) ATPase
- d) Hydrolases
Explanation:
Cytochromes are the most important class of respiratory enzymes. They are heme-containing proteins that function as electron carriers in the Electron Transport Chain (ETC), facilitating the transfer of electrons to oxygen during aerobic respiration.
Roles of the Components:
Roles of the Components:
- • Cytochromes: Essential for oxidative phosphorylation. They undergo reversible oxidation and reduction (Fe²⁺ ⇌ Fe³⁺) to move electrons.
- • NAD: This is a coenzyme (Nicotinamide Adenine Dinucleotide), not an enzyme itself. It carries hydrogen/electrons to the respiratory chain.
- • ATPase: An enzyme that synthesizes ATP using the proton gradient, but it is generally classified as a “synthase” rather than a primary respiratory electron-transfer enzyme.
- • Hydrolases: A class of enzymes that catalyze the cleavage of chemical bonds by the addition of water (e.g., digestive enzymes like amylase).
The formation of spindle fibres in the process of cell division is prevented by?
- a) Colchicine
- b) ATP
- c) Hydrazine
- d) All of these
Explanation:
Colchicine is an alkaloid (derived from the plant Colchicum autumnale) that specifically interferes with the formation of spindle fibers by binding to tubulin subunits, preventing them from polymerizing into microtubules.
Effects on Cell Division:
Effects on Cell Division:
- • Mitotic Poison: Since spindle fibers are required to pull chromosomes apart, colchicine halts cell division at the metaphase stage.
- • Polyploidy: In plant breeding, colchicine is often used to induce polyploidy (doubling the number of chromosomes) because the DNA replicates, but the cell cannot divide without a spindle.
- • Karyotyping: In genetics, it is used to stop cells in metaphase so that chromosomes can be clearly visualized and counted under a microscope.
- • ATP vs. Spindle: Unlike colchicine, ATP is actually required for the energy-demanding process of spindle assembly and chromosome movement.
A mutation causing a substitution of one amino acid is called?
- a) Point mutation
- b) Silent mutation
- c) Missense mutation
- d) None of these
Explanation:
A Missense mutation is a type of point mutation in which a single nucleotide change results in a codon that codes for a different amino acid. This can alter the function of the resulting protein.
Types of Point Mutations:
Types of Point Mutations:
- • Silent Mutation: A change in the DNA sequence that does not change the amino acid produced (due to the redundancy of the genetic code).
- • Missense Mutation: A change that results in the substitution of one amino acid for another (e.g., Sickle Cell Anemia).
- • Nonsense Mutation: A change that converts an amino acid codon into a stop codon, leading to a prematurely shortened, usually non-functional protein.
- • Point Mutation: This is a general term for any mutation that affects only a single base pair in the DNA. While a missense mutation is a point mutation, “missense” specifically describes the effect on the amino acid.
Which of these is a trace element for bacteria?
- a) Mg+2
- b) Na+
- c) Ca+2
- d) Mn+2
Explanation:
Manganese (Mn+2) is considered a trace element (or micronutrient) for bacteria. Trace elements are required in extremely small quantities, usually acting as cofactors for specific enzymes.
Bacterial Nutrients:
Bacterial Nutrients:
- • Macronutrients: Required in relatively large amounts. These include Carbon, Hydrogen, Oxygen, Nitrogen, Phosphorus, Sulfur, Potassium, Magnesium (Mg+2), and Calcium (Ca+2).
- • Micronutrients (Trace Elements): Required in very small amounts. Examples include Manganese (Mn+2), Zinc (Zn+2), Cobalt (Co+2), Molybdenum (Mo+2), Nickel (Ni+2), and Copper (Cu+2).
- • Role of Mn+2: Manganese acts as an activator for many enzymes, including those involved in phosphate transfer and the protection of the cell against superoxide radicals (Manganese-Superoxide Dismutase).
Most bacteria require vitamins as?
- a) Growth Factors
- b) Sources of energy
- c) Sources of carbon
- d) Sources of electron donors
Explanation:
Bacteria require vitamins as Growth Factors. Growth factors are organic compounds that a cell must have to grow but cannot synthesize on its own from its main carbon and energy sources.
Categories of Growth Factors:
Categories of Growth Factors:
- • Vitamins: Most commonly function as coenzymes or functional groups of enzymes (e.g., B-vitamins like Biotin, Thiamine, and Riboflavin).
- • Amino Acids: Required for protein synthesis in organisms that cannot manufacture all 20 amino acids.
- • Purines and Pyrimidines: Essential for the synthesis of nucleic acids (DNA and RNA).
- • Essentiality: While some bacteria like E. coli can synthesize all their vitamins, others (like many lactic acid bacteria) are “fastidious” and require many vitamins to be added to their culture media.
Ergot disease is caused by?
- a) Puccinia
- b) Rhizopus
- c) Claveceps
- d) Penicillium
Explanation:
Ergot disease (particularly of rye and other cereals) is caused by the fungus Claviceps purpurea. The fungus replaces the grain with a dark, hard mass called a sclerotium (the ergot).
Key Facts about Ergot:
Key Facts about Ergot:
- • Alkaloids: The ergot sclerotia contain potent alkaloids (like ergotamine) that can cause ergotism in humans and livestock if consumed.
- • Ergotism: Also known historically as “St. Anthony’s Fire,” symptoms include hallucinations, gangrene (due to vasoconstriction), and convulsions.
- • Other Fungi: Puccinia causes rust diseases, Rhizopus is a common bread mold, and Penicillium is primarily known for antibiotic production and food spoilage.
- • LSD: Lysergic acid, a precursor to the hallucinogen LSD, was originally derived from the alkaloids found in Claviceps.
Cerebral malaria is caused by?
- a) Plasmodium vivax
- b) P. ovale
- c) P. falciparum
- d) P. malariae
Explanation:
Cerebral malaria is the most severe neurological complication of infection with Plasmodium falciparum. It is characterized by clinical manifestations of abnormal consciousness, coma, or seizures.
Malaria Species Comparison:
Malaria Species Comparison:
- • P. falciparum: Responsible for nearly all severe malaria and deaths. It causes “sequestration,” where infected red blood cells stick to the walls of small blood vessels in the brain, leading to blockages.
- • P. vivax and P. ovale: Cause “benign tertian” malaria. They can persist in the liver (hypnozoites) and cause relapses but rarely lead to cerebral complications.
- • P. malariae: Causes “quartan” malaria with fever spikes every 72 hours; generally considered a milder form.
- • Key Feature: P. falciparum can infect red blood cells of all ages, leading to very high levels of parasitemia in the blood.
The primary mode of transmission of poliomyelitis is?
- a) Oral route
- b) Blood
- c) Milk
- d) Person to person
Explanation:
The primary mode of transmission for poliomyelitis is the fecal-oral route (often simply referred to as the oral route). The virus enters the body through the mouth, typically via contaminated hands, food, or water.
Path of Infection:
Path of Infection:
- • Entry: Ingestion of the virus.
- • Multiplication: The virus first multiplies in the pharynx (throat) and the intestinal mucosa.
- • Excretion: Infected individuals shed the virus in their feces for several weeks, which can then contaminate the environment in areas with poor sanitation.
- • Secondary Route: While the oral route is primary, the virus can also be spread through respiratory secretions (droplets) during the early stages of the illness, though this is less common.
Virulent factor in pneumococcus is?
- a) Cell wall
- b) Capsule
- c) Mesosomes
- d) Endotoxins
Explanation:
The primary virulence factor of Pneumococcus (Streptococcus pneumoniae) is its polysaccharide capsule. Strains without a capsule are typically non-pathogenic (avirulent).
Function of the Capsule:
Function of the Capsule:
- • Antiphagocytic: The capsule prevents host immune cells (phagocytes) from engulfing and destroying the bacteria.
- • Griffith’s Experiment: This was famously demonstrated in Fred Griffith’s 1928 experiment where “Smooth” (encapsulated) strains killed mice, while “Rough” (non-encapsulated) strains did not.
- • Serotypes: There are over 90 different capsule types, which is why individuals can be infected with S. pneumoniae multiple times.
- • Other Factors: While Pneumococcus also produces Pneumolysin (a toxin), the capsule remains the most essential factor for its survival within the host.
The Bacteria that move in response to a magnetic field is?
- a) Spirochetes
- b) Treponema
- c) Aquaspirillum magnetotacticum
- d) None of these
Explanation:
Aquaspirillum magnetotacticum (now often classified as Magnetospirillum) is a well-known example of a magnetotactic bacterium. These bacteria possess the unique ability to sense and align themselves with the Earth’s magnetic field.
How it Works:
How it Works:
- • Magnetosomes: These bacteria contain specialized intracellular structures called magnetosomes, which are membrane-bound crystals of magnetite (iron oxide) or greigite.
- • Magnetotaxis: The chain of magnetosomes acts like a compass needle, allowing the bacteria to swim along magnetic field lines.
- • Biological Purpose: This helps the bacteria migrate vertically to reach anaerobic or microaerophilic (low oxygen) environments in aquatic sediments, which are optimal for their survival.
- • Other Options: Spirochetes and Treponema move using axial filaments (endoflagella) but do not respond to magnetic fields.
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