MicroBiology MCQs with Answer and Explanations | Chapter 73

Answer: Bacteriostatic

Bacteriostatic agents halt the growth and reproduction of bacteria without necessarily killing them. Once the bacteriostatic agent is removed, the bacteria can start multiplying again.

The other options are incorrect:

• Bactericidal: These agents kill bacteria. Removing a bactericidal agent wouldn’t affect the already dead bacteria.
• Antibiotic: Antibiotics are a broader category of antimicrobial agents that can be either bacteriostatic (inhibiting growth) or bactericidal (killing bacteria).
• Antiseptic: Antiseptics target microorganisms on living tissue, aiming to kill or inhibit their growth. They aren’t typically used to control bacterial growth in colonies.

Answer: Streptomycin

Streptomycin is one of the primary antibiotics used in combination therapy for tuberculosis (TB). It works by interfering with the protein synthesis of bacteria, hindering their growth and reproduction.

The other options are incorrect:

• Penicillin: Penicillin is ineffective against Mycobacterium tuberculosis, the bacteria that causes TB. It primarily targets bacteria with a cell wall structure different from TB bacteria.
• Chloramphenicol: While chloramphenicol has some broad-spectrum antibiotic properties, it’s not typically used as a first-line treatment for TB due to potential side effects and the availability of more effective medications.
• Cycloserine: This antibiotic can be used in cases of drug-resistant TB but is not a primary choice due to potential neurological side effects.

Answer: Cell wall synthesis

Penicillin belongs to the beta-lactam class of antibiotics. These antibiotics specifically target enzymes called transpeptidases, which are crucial for building the bacterial cell wall. By inhibiting these enzymes, penicillin prevents the bacteria from forming a strong and rigid cell wall. This weakened cell wall can’t withstand the internal pressure of the bacteria, leading to cell death.

The other options are incorrect:

• Cell membrane permeability: While some antibiotics do target the cell membrane, penicillin doesn’t directly affect its permeability.
• DNA synthesis: Penicillin doesn’t directly target DNA replication in bacteria.
• Protein synthesis: Some antibiotics like tetracyclines interfere with protein synthesis, but penicillin’s primary mechanism targets cell wall formation.

Answer: Bactiracin

Bacitracin is a well-known antibiotic produced by some strains of Bacillus subtilis. It’s a cyclic polypeptide antibiotic, meaning it’s a ring-shaped molecule composed of amino acids, effective primarily against Gram-positive bacteria.

The other options are incorrect:

• Vancomycin: Vancomycin is a different type of antibiotic produced by a different strain of bacteria, Streptomyces orientalis. It has a distinct structure and targets cell wall synthesis differently than bacitracin.
• None of these: While Bacillus subtilis can produce various secondary metabolites, not all strains produce antibiotics. However, bacitracin is a confirmed antibiotic produced by some strains.

Answer: Group ‘A’ Streptococci

The bacitracin sensitivity test is a rapid and simple way to differentiate between Group A Streptococci (GAS) and other bacteria, particularly Streptococcus agalactiae (Group B Strep). Group A Strep is sensitive to bacitracin, meaning it won’t grow near a bacitracin disc on an agar plate. Conversely, Group B Strep is resistant and will grow up to the edge of the disc.

The other options are incorrect:

• Pneumococci: While some Streptococcus pneumoniae strains (pneumococci) might be sensitive to bacitracin, the test isn’t routinely used for identifying them due to inconsistent results.
• Gonococci: Neisseria gonorrhoeae (gonococci) are not typically identified using a bacitracin test. They belong to a different bacterial genus and have different antibiotic sensitivities.
• Staphylococci: Staphylococcus species can vary in their bacitracin sensitivity. The test isn’t a reliable sole method for identifying them.

Answer: All of the above

Antibiotics work through various mechanisms to target and inhibit the growth and reproduction of microorganisms. Here’s a breakdown of the listed effects:

• Inhibition of cell-wall synthesis: This is a primary target for many antibiotics, particularly beta-lactams (like penicillin) and glycopeptides (like vancomycin). They disrupt the enzymes or building blocks needed for a strong bacterial cell wall, leading to cell death.
• Damage to the cytoplasmic membrane: Some antibiotics, like polymyxins, target the cytoplasmic membrane, a barrier protecting the bacterial cell’s interior. They can disrupt membrane function, causing leakage of essential cellular components and ultimately cell death.
• Inhibition of nucleic acid and protein synthesis: Antibiotics like tetracyclines and aminoglycosides interfere with the processes of building proteins (essential for bacterial growth) or copying DNA (needed for replication).

Answer: All of the above

Several antibiotics work by targeting the bacterial cell wall. Here’s a quick explanation for each listed option:

• Penicillin: As mentioned previously, penicillin is a classic example of an antibiotic that inhibits cell wall synthesis in bacteria by blocking enzymes crucial for building the wall.
• Bacitracin: This antibiotic also disrupts cell wall formation in Gram-positive bacteria by interfering with the process of building the peptidoglycan layer, a key component of the cell wall.
• Cyclosporin: This medication is not actually an antibiotic. It’s an immunosuppressant drug that acts on the immune system rather than directly targeting bacteria. It doesn’t have any effect on the bacterial cell wall.

Answer: Plasmids

Plasmids carry antibiotic resistance genes and can be transferred between bacteria, contributing to bacterial resistance.

The other options are incorrect:

• Transduction: Transfer of bacterial DNA by viruses (bacteriophages).
• Transformation: Uptake of external DNA by bacteria.
• Mutation: Changes in bacterial DNA, which can lead to resistance.

Answer: Attaching to 50 S unit or ribosome

Erythromycin binds specifically to the 50S subunit of the bacterial ribosome, which is essential for protein assembly. This disrupts the process of adding amino acids to the growing protein chain, ultimately halting protein synthesis.

The other options are incorrect:

• Attaching to 30S ribosome unit: Some antibiotics like tetracycline target the 30S subunit, but erythromycin has a different mechanism.
• By the attachment to t-RNA or m-RNA: These molecules play a role in protein synthesis, but erythromycin directly interferes with the ribosome function, not these individual components.

Answer: Mutation

Mutations in the Mycobacterium tuberculosis (bacteria causing TB) DNA can lead to resistance to anti-TB drugs. These mutations can alter the target site of the drug or create mechanisms for the bacteria to pump the drug out of the cell, rendering it ineffective.

The other options are incorrect:

• Transduction, Transformation, Conjugation: While these mechanisms can transfer genetic material between bacteria, they’re less common for drug resistance in TB compared to mutations. Mycobacterium tuberculosis has a thick cell wall that makes conjugation (direct cell contact) difficult, and while transduction and transformation can occur, mutations are the primary culprit for resistance development.

Answer: Amikacin

Amikacin belongs to a class of antibiotics called aminoglycosides. These antibiotics target the ribosomes of bacteria, hindering protein synthesis essential for bacterial growth and reproduction. They do not affect cell wall synthesis.

The other options are incorrect:

• Penicillin: Penicillin inhibits cell wall synthesis by interfering with the final stages of peptidoglycan cross-linking, leading to weakened cell walls and bacterial cell lysis.
• Carbenicillin: Carbenicillin is a semi-synthetic penicillin derivative that also inhibits cell wall synthesis in bacteria, similar to penicillin.
• Vancomycin: Vancomycin is a glycopeptide antibiotic that inhibits cell wall synthesis by binding to the D-alanyl-D-alanine terminus of peptidoglycan precursors, preventing their incorporation into the growing cell wall.

Answer: The inhibition of DNA synthesis

Nalidixic acid belongs to a class of antibiotics called fluoroquinolones. These antibiotics target an enzyme called DNA gyrase, which is crucial for bacterial DNA replication. By inhibiting DNA gyrase, nalidixic acid prevents bacteria from properly copying their DNA, hindering their growth and reproduction.

The other options are incorrect:

• Inhibition of protein synthesis: Nalidixic acid doesn’t directly target protein synthesis. There are other classes of antibiotics that work through this mechanism.
• Inhibition of cell wall synthesis: While some antibiotics target cell wall formation, nalidixic acid specifically targets DNA replication.
• Both b and c: Neither protein synthesis nor cell wall synthesis are the primary targets of nalidixic acid.

Answer: Both a and b

Both the tube-dilution test and the paper-disc test are commonly used methods for determining the susceptibility of microorganisms to antibiotics and other chemotherapeutic agents. The tube-dilution test involves serial dilutions of the antibiotic in liquid media to determine the minimum inhibitory concentration (MIC), while the paper-disc test (also known as the disk diffusion test) involves placing antibiotic-impregnated paper discs on an agar plate inoculated with the microorganism to assess the zone of inhibition around each disc.

The other options are incorrect:

• Tube-dilution test: This option is actually one of the correct answers. The tube-dilution test is a standard method for determining the MIC of an antibiotic, providing quantitative data on the susceptibility of a microorganism to the antibiotic.
• Paper-disc test: This option is actually one of the correct answers. The paper-disc test is a widely used method for determining the susceptibility of a microorganism to antibiotics, providing qualitative results based on the size of the zone of inhibition around each disc.
• None of these: This option is incorrect because both the tube-dilution test and the paper-disc test are valid methods for testing the susceptibility of microorganisms to antibiotics and other chemotherapeutic agents.

Answer: MIC (minimum inhibitory concentration)

MIC (minimum inhibitory concentration) refers to the lowest concentration of a chemotherapeutic agent (antibiotic, antifungal, etc.) that can inhibit the visible growth of a microorganism in a controlled laboratory setting (in vitro). It’s a crucial parameter used to determine the effectiveness of an antibiotic against a specific organism and to guide appropriate dosing regimens.

The other options are incorrect:

• Thermal death point (TDP): TDP refers to the minimum temperature required to kill a specific microorganism within a certain timeframe. It doesn’t directly measure inhibition of growth but rather the point of cell death due to heat.
• Death rate: Death rate refers to the rate at which microorganisms die under a specific condition. While related to the effectiveness of an agent, it’s not a specific concentration value like MIC.
• None of these: MIC is a well-established term used in antimicrobial susceptibility testing.

Answer: Lysis of the bacterial cells surrounding the disc

The clear zone around an antibiotic disc on an agar plate indicates the area where bacterial growth has been inhibited. This occurs because the antibiotic diffuses through the agar and interferes with the bacteria’s ability to grow and reproduce. In some cases, the antibiotic may even kill the bacteria outright. This zone of inhibition reflects the effectiveness of the antibiotic against the specific bacteria being tested.

The other options are incorrect:

• Growth of the bacterium surrounding of the disc: The presence of a clear zone signifies the opposite – inhibition of bacterial growth.
• The destruction of paper disc (antibiotic): The paper disc itself is not destroyed during the test. The antibiotic diffuses from the disc into the agar, creating the zone of inhibition.
• None of these: While the other options aren’t the primary reason for clear zone formation, this phenomenon is a valuable tool for assessing antibiotic susceptibility.

Answer: B. subtilis

Bacitracin is a polypeptide antibiotic produced by certain strains of the bacteria Bacillus subtilis, specifically the licheniformis group.

The other options are incorrect:

• B. anthracis: This bacterium is responsible for anthrax, a serious infectious disease. It does not produce bacitracin.
• B. cereus: While B. cereus can cause foodborne illness, it is not known to produce bacitracin.
• d. anthracoid: This is not a recognized biological term. It might be a misspelling of “anthracoid,” which can refer to resembling anthrax, but it wouldn’t be a source of bacitracin.

Answer: Streptomyces orientalis

Vancomycin is a glycopeptide antibiotic produced by the fermentation of the soil bacterium Streptomyces orientalis.

The other options are incorrect:

• Streptococcus species: Streptococcus is a genus of bacteria that can cause infections, but it does not produce vancomycin.
• Aspergillus niger: Aspergillus niger is a mold that produces various compounds but not vancomycin.
• Bacillus anthracis: Bacillus anthracis is the bacterium that causes anthrax. It does not produce vancomycin.

Answer: All of these

Healthy human skin has a complex and diverse microbial flora, consisting of a combination of:

• Enterobacteriaceae: These are a group of gram-negative bacteria commonly found in the environment. While some can be pathogenic, some species can exist on the skin without causing harm.
• Aerobic diphtheria bacilli: This refers to specific types of Corynebacterium bacteria, some of which can cause diphtheria (a serious infection). However, other Corynebacterium species are normal residents of the skin.
• Nonhemolytic staphylococci: These are staphylococcus bacteria that do not break down red blood cells (hemolyze). Staphylococcus epidermidis, a nonhemolytic species, is a common resident of healthy skin.

Answer: Lysogenic for ß prophase

The gene encoding diphtheria toxin (tox) is located within a specific type of virus called a bacteriophage, β prophage. When C. diphtheriae is lysogenic for β prophage, the phage integrates its DNA into the bacterial chromosome, allowing the bacteria to produce the toxin.

The other options are incorrect:

• Encapsulated: C. diphtheriae is not typically encapsulated with a polysaccharide capsule.
• Sucrose fermentors: While some C. diphtheriae strains can ferment sucrose, this ability is not directly related to toxin production. Toxigenic and non-toxigenic strains can both ferment sucrose.
• Of the mitis strain: While the mitis strain of C. diphtheriae can be toxigenic (toxin-producing), toxin production is not specific to this strain. All three biotypes (gravis, intermedius, mitis) of C. diphtheriae can harbor the β prophage and produce toxins.

Answer: Salmonella cholerasuis

Salmonella cholerasuis is a serovar of Salmonella bacteria known to cause severe systemic infections, including prolonged septicemia, where the bacteria spread throughout the bloodstream, leading to serious illness.

The other options are incorrect:

• Salmonella anatum: This serovar of Salmonella can cause food poisoning and gastroenteritis but is not typically associated with prolonged septicemia.
• Salmonella typhimurium: Salmonella typhimurium commonly causes gastroenteritis but is not typically associated with prolonged septicemia as much as Salmonella cholerasuis.
• Salmonella enteritidis: Salmonella enteritidis is a common cause of foodborne illness but is not typically associated with prolonged septicemia compared to Salmonella cholerasuis.

Answer: Both Exotoxins and Endotoxins

E. coli can produce two main types of toxins:

• Exotoxins: These are secreted proteins that can directly cause damage to host cells and tissues. Different E. coli strains can produce various exotoxins, with Shiga toxin being a well-known example responsible for severe illness.
• Endotoxins: Lipopolysaccharides (LPS) located in the outer membrane of E. coli act as endotoxins. While not directly damaging cells themselves, endotoxins can trigger a strong inflammatory response in the body when released during bacterial lysis (cell death).

The other options are incorrect:

• Leucocidin: Leucocidins are a specific type of toxin produced by some bacteria that can kill white blood cells (leukocytes). While some E. coli strains might have the genes for leucocidin production, it’s not a common toxin associated with E. coli pathogenesis (disease-causing mechanisms).

Answer: Cl.perfringens

Gas gangrene, also known as clostridial myonecrosis, is primarily caused by Clostridium perfringens bacteria. These bacteria thrive in anaerobic conditions and produce toxins that lead to tissue destruction and the formation of gas within affected tissues.

The other options are incorrect:

• B. anthracis (Bacillus anthracis): Bacillus anthracis is the causative agent of anthrax, a serious infection that primarily affects animals but can also be contracted by humans. Anthrax does not typically cause gas gangrene.
• Clostridium tetani: Clostridium tetani is responsible for tetanus, a neurological illness characterized by muscle stiffness and spasms. While tetanus can involve muscle damage, it does not cause gas production like gas gangrene.
• Cl. difficile (Clostridium difficile): Clostridium difficile is a bacterium that causes antibiotic-associated diarrhea. It is not associated with gas gangrene.

Answer: Bordetella pertussis

Bordetella pertussis is the primary causative organism of whooping cough (also known as pertussis). This highly contagious respiratory illness is characterized by severe coughing spells, often with a characteristic “whooping” sound upon inhalation.

The other options are incorrect:

• Bordetella parapertussis: While Bordetella parapertussis can cause a similar respiratory illness, it is less common than whooping cough caused by B. pertussis. The symptoms of parapertussis infection are generally milder than those of pertussis.
• Bordetella bronchiseptica: This bacterium can cause respiratory infections in animals, but it is not a major cause of whooping cough in humans.

Answer: Vibrio cholerae

The Pfeiffer phenomenon is a test used in microbiology to differentiate between closely related bacterial species. It specifically relies on the immune response generated against a specific bacterium. When observing the Pfeiffer phenomenon, scientists see the lysis (dissolution) of the target bacteria in the presence of specific antibodies.

The other options are incorrect:

• B. anthracis (Bacillus anthracis): The Pfeiffer phenomenon is not typically used for diagnosing Bacillus anthracis infections. Different diagnostic methods are employed for anthrax.
• Rickettsial pox: Rickettsial pox is caused by Rickettsia species, which are obligate intracellular bacteria (they can only live inside host cells). The Pfeiffer phenomenon is not applicable to diagnosing Rickettsial infections because it relies on observing bacterial lysis in an external environment.
• All of these: Only Vibrio cholerae is directly linked to the observation of the Pfeiffer phenomenon.

Answer: Dark ground microscopic examination

Dark-field microscopy is a diagnostic test used to visualize Treponema pallidum, the bacterium that causes syphilis, in early stages of infection. This technique utilizes a specialized microscope that illuminates the sample at an oblique angle, allowing visualization of the motile spirochete bacteria against a dark background.

The other options are incorrect:

• VDRL test (Venereal Disease Research Laboratory test): While VDRL is a commonly used screening test for syphilis, it detects antibodies produced by the body in response to the infection. A positive VDRL test can indicate syphilis but requires further confirmation with a specific treponemal test like dark-field microscopy.
• Treponema pallidum immobilization test (TPI): This is another specific treponemal test, but it’s less commonly used than dark-field microscopy due to its complexity and lower sensitivity in diagnosing early syphilis.
• Kahn’s test: Similar to the VDRL test, Kahn’s test is a non-specific test for syphilis antibodies. It has been largely replaced by VDRL due to its lower sensitivity and specificity.

Answer: E.coli

Escherichia coli, particularly certain strains, is a well-known culprit behind sporadic summer diarrhea. Some E. coli strains produce toxins that can cause watery diarrhea, abdominal cramps, and nausea. These strains can spread through contaminated food or water, especially during warmer months when improper food handling practices or outdoor activities increase the risk.

The other options are incorrect:

• Enterobacter: While some Enterobacter species can cause opportunistic infections, they are not typically associated with sporadic summer diarrhea.
• Hafnia: Similar to Enterobacter, Hafnia species are not commonly linked to summer diarrhea. They are more frequently associated with healthcare-associated infections.
• Serratia: Serratia species are rarely implicated in causing diarrhea, especially sporadic summer diarrhea. They are more likely to cause hospital-acquired infections.

Answer: Lepra bacilli

The VDRL (Venereal Disease Research Laboratory) test is used to detect antibodies produced by the body in response to the bacterium Treponema pallidum, which causes syphilis. However, sometimes individuals infected with other bacteria, such as Mycobacterium leprae, which causes leprosy, can produce a false-positive result on the VDRL test. This is known as a biological false reaction.

The other options are incorrect:

• Corynebacterium diphtheria: Corynebacterium diphtheriae is the bacterium responsible for causing diphtheria, but it is not associated with causing biological false reactions in the VDRL test.
• Cl. welchii: “Cl. welchii” likely refers to Clostridium welchii, which is now known as Clostridium perfringens. While Clostridium perfringens can cause gas gangrene and food poisoning, it is not associated with causing biological false reactions in the VDRL test.
• None of these: This option is incorrect, as lepra bacilli (Mycobacterium leprae) are indeed related to biological false reactions in the VDRL test.

Answer: Corn steep liquor

Corn steep liquor (CSL) is a by-product of the corn starch industry and is the most commonly used medium for large-scale production of penicillin. It provides essential nutrients like amino acids, vitamins, and minerals that support the growth of Penicillium chrysogenum, the fungus that produces penicillin.

The other options are incorrect:

• Nutrient agar: Nutrient agar is a general-purpose growth medium and doesn’t provide the specific nutrients required for optimal penicillin production by Penicillium chrysogenum.
• Sulfite waste liquor: While research is ongoing to explore alternative sources for penicillin production, sulfite waste liquor is not a commonly used medium due to potential drawbacks like variability in composition and presence of inhibitory substances.
• Whey: Whey, a by-product of cheese production, can be used as a medium for penicillin fermentation.

Answer: Serial dilution method

The serial dilution method involves diluting a sample containing microorganisms serially to obtain progressively diluted samples. These diluted samples are then plated onto agar plates, allowing for the isolation of individual colonies of microorganisms, including antibiotic-producing ones.

The other options are incorrect:

• Disk plate method: This method involves placing antibiotic discs on a plate seeded with microbes. It’s used to assess an organism’s susceptibility to antibiotics, not for isolating antibiotic producers.
• Direct plate method: This involves directly plating the environmental sample on a medium. While it can grow microbes present in the sample, the dense growth often makes it difficult to isolate specific antibiotic producers.
• Crowded plate method: This method involves plating the environmental sample at a high density on a medium.

Answer: Microphilic bacteria

The pyruvate dehydrogenase complex is an enzyme complex involved in the conversion of pyruvate to acetyl-CoA, an important step in aerobic respiration. Microaerophilic bacteria thrive in environments with reduced oxygen levels, but they still require aerobic respiration. However, they may lack the pyruvate dehydrogenase complex or have modified versions due to their specific metabolic adaptations.

The other options are incorrect:

1. Aerobic bacteria: Aerobic bacteria typically possess the pyruvate dehydrogenase complex as they rely on aerobic respiration for energy production.
2. Facultative anaerobic bacteria: Facultative anaerobic bacteria can switch between aerobic and anaerobic metabolism depending on the availability of oxygen.
3. Strictly anaerobic bacteria: Strictly anaerobic bacteria do not require oxygen for growth and metabolism.

Answer: Corn steep liquor

Corn steep liquor is a byproduct of the corn wet-milling process and contains essential nutrients like carbohydrates, amino acids, and vitamins required for the growth of Penicillium fungi, which produce penicillin.

The other options are incorrect:

• Corn meal: While corn meal is a source of carbohydrates, it lacks the essential nutrients and complex composition of corn steep liquor needed for optimal penicillin production.
• Cane steep liquor: This byproduct of sugarcane processing might have some similar components to corn steep liquor, but it’s not typically used in penicillin production due to potential differences in nutrient composition and cost-effectiveness.

Answer: Nitrification

Nitrification is a biological process where specific bacteria convert ammonia (NH3) into nitrate (NO3-) through a series of steps. This process is crucial in the nitrogen cycle, making nitrogen usable by plants.

The other options are incorrect:

• Ammonification: This process breaks down organic nitrogen compounds (like dead organisms) into ammonia (NH3), the opposite of nitrification.
• Denitrification: This process converts nitrate (NO3-) back into gaseous forms of nitrogen (like N2), removing it from the nitrogen cycle.
• Nitrogen Fixation: This process converts atmospheric nitrogen (N2) into usable forms like ammonia (NH3) by specific bacteria or through lightning strikes. It doesn’t directly involve nitrate formation.

Answer: Lactobacillus Leichmanni

Lactobacillus leichmannii is a bacterium that requires vitamin B12 for growth. Therefore, its growth can be used as an indicator of the presence and quantity of vitamin B12 in a sample.

The other options are incorrect:

• Lactobacillus spp.: While some Lactobacillus species might be used in vitamin B assays, L. leichmannii is the preferred choice due to its well-established dependence on vitamin B12 for growth.
• Bacillus subtilis: This bacterium doesn’t require vitamin B12 for its growth and wouldn’t be a suitable organism for this specific assay.
• E. coli: E. coli can synthesize its own vitamin B12 and wouldn’t be limited by its presence in the sample, making it unsuitable for this assay.

Answer: Closed system

In batch fermentation, a closed system is used, meaning that all ingredients are added at the beginning of the fermentation process, and there is no addition or removal of materials during fermentation.

The other options are incorrect:

• Open system: An open system allows for the exchange of materials (nutrients or products) with the surrounding environment during the fermentation process. This is not the case in batch fermentation.
• Fed-Batch system: A fed-batch system is a variation of batch fermentation where additional nutrients are added during the process to extend the growth phase or product formation. While it starts similar to a batch system, the addition of fresh ingredients throughout makes it different.
• Sub-merger system: This term isn’t commonly used in fermentation processes. It’s possible it refers to a submerged fermentation where microorganisms are grown suspended in a liquid medium.

Answer: Mac Conkey’s medium

MacConkey’s medium is a selective and differential agar medium commonly used in microbiology to isolate and differentiate between lactose-fermenting and non-lactose-fermenting Gram-negative bacteria, particularly members of the Enterobacteriaceae family.

The other options are incorrect:

• Stuart’s medium: Stuart’s medium is a rich, non-selective medium used for general bacterial growth and doesn’t contain lactose for differentiation.
• Sugar medium: This is a broad term and doesn’t specify the type of sugar. Different sugar mediums can be used for various purposes, but they might not be designed for lactose fermentation specifically.
• Citrate medium: Citrate medium is used to test a bacterium’s ability to utilize citrate as an energy source. It doesn’t involve lactose fermentation.

Answer: All of the above

All three options – Bacteria, Yeast, and Fungi – can be used in fermentation processes.

• Bacteria: Various bacterial species are used in fermenting foods like yogurt (Lactobacillus), cheese (various bacteria), and sauerkraut (Lactobacillus). They can also be used for industrial-scale fermentation processes.
• Yeast: Yeast, particularly Saccharomyces cerevisiae, is a crucial microorganism in fermenting alcoholic beverages like beer and wine. It converts sugars into alcohol and carbon dioxide.
• Fungi: Some fungi, like molds (Aspergillus niger) are used in specific fermentations like citric acid production. They can also play a role in some traditional fermented foods.

Answer: Str. pyogenes

Streptococcus pyogenes, also known as group A Streptococcus, is the primary producer of streptokinase. This enzyme is known for its clot-busting properties and has been used historically to treat blood clots.

The other options are incorrect:

• Staphylococcus aureus: While Staphylococcus aureus produces various enzymes, streptokinase is not one of them.
• Streptococcus pneumoniae: Streptococcus pneumoniae, also known as pneumococcus, doesn’t produce streptokinase.
• Str. faecalis (Streptococcus faecalis): Although some strains of Str. faecalis might exhibit weak plasminogen activation (similar to streptokinase’s function), they are not considered significant producers of true streptokinase.

Answer: All of these

All three options listed are methods of strain improvement used to enhance the characteristics of microorganisms or plants.

• Protoplast fusion: This technique involves fusing together the protoplasts (cells without cell walls) of different strains to create a hybrid with a combination of their traits.
• Recombinant DNA technique: This method allows scientists to insert specific genes from another organism into the target strain, granting it new functionalities.
• Genetic recombination: This is a broader term encompassing natural processes like sexual reproduction (crossing over) or conjugation in bacteria, which lead to offspring with a mix of parental genes.

Answer: Both a & b

Protoplasts, plant or bacterial cells without their cell walls, can be prepared from both Gram-positive and Gram-negative bacteria. The process involves using specific enzymes that break down the cell wall components.

• Gram-positive bacteria: Enzymes like lysozyme are used to digest the peptidoglycan layer, the primary cell wall component in Gram-positive bacteria.
• Gram-negative bacteria: A combination of enzymes might be needed for Gram-negative bacteria. Enzymes like lysozyme can target the inner peptidoglycan layer, while enzymes like cellulase or lipase might be needed to break down the outer membrane components.

The other options are incorrect:

• None of these: This is incorrect because both Gram-positive and Gram-negative bacteria can have their cell walls removed to form protoplasts, although the specific enzymes used might differ.

Answer: Submerged fermentation

Submerged fermentation is a type of fermentation where microorganisms are completely immersed and evenly distributed throughout a liquid nutrient medium. This is achieved by using agitation or aeration to keep the microorganisms suspended and ensure they have optimal access to nutrients and oxygen (if needed).

The other options are incorrect:

• Surface fermentation: This type of fermentation occurs at the air-liquid interface of the culture medium. Microorganisms grow on the surface or form a pellicle (film) on top.
• Dual fermentation: This term isn’t a standard term used in fermentation processes. It’s possible it’s a misunderstanding of submerged and surface fermentation co-existing, but they are typically considered separate approaches.
• All of these: Not all options are correct. Submerged fermentation specifically refers to complete immersion, while surface fermentation involves growth at the surface.

Answer: Coryne bacterium glutamicum

Corynebacterium glutamicum is the primary industrial producer of L-lysine through a fermentation process. This bacterium has been genetically modified to efficiently convert sugars into L-lysine, an essential amino acid often supplemented in animal feed.

The other options are incorrect:

• Corynebacterium sps.: While the genus Corynebacterium includes various species, C. glutamicum is the specific strain optimized for L-lysine production.
• Mycobacterium sps.: Mycobacteria are a different genus of bacteria and are not typically used for L-lysine production.

Answer: Saccharomyces sereviceae

Saccharomyces cerevisiae, commonly known as baker’s yeast or brewer’s yeast, is the primary microorganism used for large-scale alcohol production. It excels at converting sugars like glucose into ethanol (alcohol) and carbon dioxide through a process called alcoholic fermentation. This process is crucial for the production of various alcoholic beverages like beer, wine, and some distilled spirits.

The other options are incorrect:

• Bacillus subtilis: This bacterium doesn’t ferment sugars into alcohol. It’s commonly used for other purposes like producing enzymes or certain food products.
• Penicillium chrysogenum: This mold is known for producing penicillin, an antibiotic. It’s not involved in alcohol fermentation.

Answer: Streptomyces griseus

Streptomyces griseus is the primary microorganism used for industrial production of the antibiotic streptomycin. This bacterium naturally produces streptomycin through a fermentation process.

The other options are incorrect:

• Streptomyces niger: While some Streptomyces species like S. venezuelae can also produce streptomycin, S. griseus is the preferred choice due to its well-established production efficiency.
• Saccharomyces cerevisiae: This yeast, commonly used for alcohol production, is not involved in streptomycin production. It belongs to a different taxonomic class and doesn’t have the genetic machinery to produce this antibiotic.
• All of these: Not all options are correct. While some Streptomyces species can produce streptomycin, S. griseus is the primary industrial producer.

Answer: B. subtilis

Bacillus subtilis is a bacterium known for its ability to produce various enzymes, including amylase. Amylase is an enzyme that catalyzes the breakdown of starch into simpler sugars such as maltose and glucose.

The other options are incorrect:

• S. cerevisiae: Saccharomyces cerevisiae is a species of yeast commonly used in baking and brewing, but it is not typically used for amylase production. Therefore, “S. cerevisiae” is an incorrect option.
• A. niger: Aspergillus niger is a fungus known for its production of enzymes and organic acids, but it is not commonly used for amylase production. Therefore, “A. niger” is an incorrect option.
• None of these: This option is incorrect because Bacillus subtilis is indeed used for amylase production.

Answer: Trichoderma Koningi

Cellulases are a group of enzymes that degrade cellulose, a complex carbohydrate found in plant cell walls. Trichoderma koningi is a fungus known for its ability to produce cellulases, making it suitable for industrial processes such as biofuel production and textile processing.

The other options are incorrect:

• S. cerevisiae: Saccharomyces cerevisiae is a species of yeast commonly used in baking and brewing but is not typically used for the industrial production of cellulases. Therefore, “S. cerevisiae” is an incorrect option.
• A. niger: Aspergillus niger is a fungus known for its production of enzymes and organic acids, but it is not commonly used for the industrial production of cellulases. Therefore, “A. niger” is an incorrect option.

Answer: Both a and b

Vitamin B12 is a complex molecule and its industrial production can be achieved using several microorganisms. Two commonly used options are:

• Propionibacterium spp.: This group of bacteria, particularly Propionibacterium freudenreichii subspecies shermanii, is a major industrial producer of vitamin B12. It’s known for its efficient fermentation process and good yields.
• Pseudomonas spp.: Certain Pseudomonas species, like Pseudomonas denitrificans, can also be used for vitamin B12 production. Some strains of Pseudomonas might offer advantages like even higher yields compared to Propionibacterium under optimized conditions.

The other options are incorrect:

• None of these: This is incorrect. Both Propionibacterium and Pseudomonas species are established methods for industrial vitamin B12 production.

Answer: Acetone – Butanol

Clostridium acetobutylicum is a bacterium historically used for the large-scale industrial production of a mixture of solvents including acetone, butanol, and ethanol through a process called ABE fermentation. This process involves fermentation of sugars or starches by C. acetobutylicum, resulting in the formation of these solvents.

The other options are incorrect:

• Ethanol: While ethanol is also produced during ABE fermentation, it’s a minor product compared to acetone and butanol. The primary focus of this process is on acetone and butanol production.
• Vitamin-B12: Clostridium acetobutylicum is not known for vitamin B12 production. It lacks the necessary metabolic pathways for vitamin B12 synthesis.

Answer: Both b and c

While Saccharomyces cerevisiae (baker’s yeast) is the dominant microorganism used for industrial ethanol production, another yeast species, Kluyveromyces fragilis, can also be used in some cases.

• Saccharomyces cerevisiae: This yeast is highly efficient at converting sugars into ethanol and is the preferred choice for most large-scale ethanol production due to its well-established fermentation process, high tolerance to ethanol, and overall robustness.
• Kluyveromyces fragilis: This yeast can also ferment various sugars into ethanol and offers some advantages over S. cerevisiae in specific situations.

The other options are incorrect:

• Klebsiella pneumoniae: This bacterium is not typically used for industrial ethanol production. While it can ferment sugars, its efficiency and ethanol tolerance are lower compared to dedicated yeast strains like S. cerevisiae or K. fragilis.

Answer: Citric acid

Aspergillus niger is a well-known fungus used in the industrial production of citric acid. It efficiently converts sugars into citric acid under aerobic conditions.

The other options are incorrect:

• Ethanol: While some Aspergillus species can produce ethanol, A. niger is not commonly used for this purpose.
• Penicillin: Penicillin is an antibiotic produced by the Penicillium fungus, not Aspergillus niger.
• Lactic Acid: Lactic acid is often produced by bacteria, not fungi. While some fungal species can produce lactic acid, A. niger is not a primary choice for this purpose.

Answer: Penicillin-G

Penicillin-G (also known as benzylpenicillin) is the primary form of penicillin produced in large-scale submerged fermentations. It’s the most common and effective natural penicillin for treating various bacterial infections.

The other options are incorrect:

• Penicillin-A: Penicillin-A is a minor component naturally produced by Penicillium mold. It’s not the primary form obtained in large-scale fermentations.
• Penicillin-D: Similar to Penicillin-A, Penicillin-D is a minor component with limited medical use. Submerged fermentations are optimized for Penicillin-G production.